Nathan Smith

Interests

Teaching

Stars, Stellar Evolution, Supernovae, General Introductory Astrophysics, Interstellar Medium, Spectroscopy

Research

Massive stars (evolution and death, mass loss, binary systems), Explosive and Eruptive Transients, Spectroscopy, Circumstellar Material, Feedback

Courses

Scholarly Contributions

Journals/Publications

• Adhikari}, P., Ajaj, R., Alp{'izar-Venegas}, M., Auty, D., Benmansour, H., Bina, C., Bonivento, W., Boulay, M., Cadeddu, M., Cai, B., C{'ardenas-Montes}, M., Cavuoti, S., Chen, Y., Cleveland, B., Corning, J., Daugherty, S., DelGobbo, P., Di Stefano, P., Doria, L., , Dunford, M., et al. (2022). "First Direct Detection Constraints on Planck-Scale Mass Dark Matter with Multiple-Scatter Signatures Using the DEAP-3600 Detector". prl, 128(1), 011801.
• Corgan, A., Smith, N., Andrews, J., Filippenko, A. V., & Van, D. (2022). "Massive stars dying alone: the remote environment of supernova 2010jp and its associated late-time source". mnras, 510(1), 1-10.
• Creaner, O., Nolan, K., Hickey, E., & Smith, N. (2022). "The Locus Algorithm: A novel technique for identifying optimised pointings for differential photometry". Astronomy and Computing, 38, 100537.
• Ni, Y. Q., Moon, D., Drout, M. R., Polin, A., Sand, D. J., Gonz{'alez-Gait'an}, S., Kim, S. C., Lee, Y., Park, H. S., Howell, D. A., Nugent, P. E., Piro, A. L., Brown, P. J., Galbany, L., Burke, J., Hiramatsu, D., Hosseinzadeh, G., Valenti, S., Afsariardchi, N., , Andrews, J. E., et al. (2022). "Infant-phase reddening by surface Fe-peak elements in a normal type Ia supernova". Nature Astronomy.
• Reach, W. T., Ruaud, M., Wiesemeyer, H., Riquelme, D., Tram, L. N., Cernicharo, J., Smith, N., & Chambers, E. T. (2022). "Ionized Carbon around IRC+10216". apj, 926(1), 69.
• Soraisam, M., Matheson, T., Lee, C., Saha, A., Narayan, G., Wolf, N., Scott, A., Figuereo, S., Nu{~nez}, R., McKinnon, K., Guhathakurta, P., Brink, T. G., Filippenko, A. V., & Smith, N. (2022). "Optical Rebrightening of Extragalactic Transients from the Zwicky Transient Facility". apjl, 926(2), L11.
• Andrews, J. E., Jencson, J. E., Van, D., Smith, N., Neustadt, J. M., Sand, D. J., Kreckel, K., Kochanek, C., Valenti, S., Strader, J., Bersten, M., Blanc, G. A., Bostroem, K. A., Brink, T. G., Emsellem, E., Filippenko, A. V., Folatelli, G., Kasliwal, M. M., Masci, F. J., , McElroy, R., et al. (2021). "The Blue Supergiant Progenitor of the Supernova Imposter AT 2019krl". apj, 917(2), 63.
• Armstrong, P., Tucker, B., Rest, A., Ridden-Harper, R. .., Zenati, Y., Piro, A., Hinton, S., Lidman, C., Margheim, S., Narayan, G., Shaya, E., Garnavich, P., Kasen, D., Villar, V., Zenteno, A., Arcavi, I., Drout, M., Foley, R., Wheeler, J., , Anais, J., et al. (2021). "SN2017jgh: a high-cadence complete shock cooling light curve of a SN IIb with the Kepler telescope". mnras, 507(3), 3125-3138.
• Beasor, E. R., Davies, B., & Smith, N. (2021). "The Impact of Realistic Red Supergiant Mass Loss on Stellar Evolution". apj, 922(1), 55.
• Beasor, E. R., Davies, B., Smith, N., Gehrz, R. D., & Figer, D. F. (2021). "The Age of Westerlund 1 Revisited". apj, 912(1), 16.
• Burke, J., Howell, D., Sarbadhicary, S., Sand, D., Amaro, R., Hiramatsu, D., McCully, C., Pellegrino, C., Andrews, J., Brown, P., Itagaki, K., Shahbandeh, M., Bostroem, K., Chomiuk, L., Hsiao, E., Smith, N., & Valenti, S. (2021). "A Bright Ultraviolet Excess in the Transitional 02es-like Type Ia Supernova 2019yvq". apj, 919(2), 142.
• Dong, Y., Valenti, S., Bostroem, K., Sand, D., Andrews, J. E., Galbany, L., Jha, S. W., Eweis, Y., Kwok, L., Hsiao, E., Davis, S., Brown, P. J., Kuncarayakti, H., Maeda, K., Rho, J., Amaro, R., Anderson, J., Arcavi, I., Burke, J., , Dastidar, R., et al. (2021). "Supernova 2018cuf: A Type IIP Supernova with a Slow Fall from Plateau". apj, 906(1), 56.
• Edwards, C. S., Christensen, P. R., Mehall, G. L., Anwar, S., Tunaiji, E. A., Badri, K., Bowles, H., Chase, S., Farkas, Z., Fisher, T., Janiczek, J., Kubik, I., Harris-Laurila, K., Holmes, A., Lazbin, I., Madril, E., McAdam, M., Miner, M., O'Donnell, W., , Ortiz, C., et al. (2021). "The Emirates Mars Mission (EMM) Emirates Mars InfraRed Spectrometer (EMIRS) Instrument". ssr, 217(7), 77.
• Hirai, R., Podsiadlowski, P., Owocki, S. P., Schneider, F. R., & Smith, N. (2021). "Simulating the formation of {ensuremath{eta} Carinae's surrounding nebula through unstable triple evolution and stellar merger-induced eruption}". mnras, 503(3), 4276-4296.
• Hiramatsu, D., Howell, D. A., Van, D., Goldberg, J. A., Maeda, K., Moriya, T. J., Tominaga, N., Nomoto, K., Hosseinzadeh, G., Arcavi, I., McCully, C., Burke, J., Bostroem, K. A., Valenti, S., Dong, Y., Brown, P. J., Andrews, J. E., Bilinski, C., Williams, G. G., , Smith, P. S., et al. (2021). "The electron-capture origin of supernova 2018zd". Nature Astronomy, 5, 903-910.
• Jencson, J. E., Andrews, J. E., Bond, H. E., Karambelkar, V., Sand, D. J., Dyk, S. D., Blagorodnova, N., Boyer, M. L., Kasliwal, M. M., Lau, R. M., Mohamed, S., Williams, R., Whitelock, P. A., Amaro, R. C., Bostroem, K. A., Dong, Y., Lundquist, M. J., Valenti, S., Wyatt, S. D., , Burke, J., et al. (2021). "AT 2019qyl in NGC 300: Internal Collisions in the Early Outflow from a Very Fast Nova in a Symbiotic Binary". apj, 920(2), 127.
• Lau, R. M., Hankins, M. J., Kasliwal, M. M., Bond, H. E., De, K., Jencson, J. E., Moffat, A. F., Smith, N., & Williams, P. M. (2021). "Revealing Efficient Dust Formation at Low Metallicity in Extragalactic Carbon-rich Wolf-Rayet Binaries". apj, 909(2), 113.
• Lau, R. M., Tinyanont, S., Hankins, M. J., Ashley, M. C., De, K., Filippenko, A. V., Hillenbrand, L. A., Kasliwal, M. M., Mauerhan, J. C., Moffat, A. F., Moore, A. M., Smith, N., Soon, J., Soria, R., Travouillon, T., Hucht, K. A., Williams, P. M., & Zheng, W. (2021). "Discovery of a 310 Day Period from the Enshrouded Massive System NaSt1 (WR 122)". apj, 922(1), 5.
• Leonard, D. C., Dessart, L., Hillier, D. J., Pignata, G., Williams, G. G., Hoffman, J. L., Milne, P., Smith, N., Smith, P. S., & Khandrika, H. G. (2021). "A High-velocity Scatterer Revealed in the Thinning Ejecta of a Type II Supernova". apjl, 921(2), L35.
• Paterson, K., Lundquist, M., Rastinejad, J., Fong, W., Sand, D., Andrews, J., Amaro, R., Eskandari, O., Wyatt, S., Daly, P., Bradley, H., Zhou-Wright, S. .., Valenti, S., Yang, S., Christensen, E., Gibbs, A., Shelly, F., Bilinski, C., Chomiuk, L., , Corsi, A., et al. (2021). "Searches after Gravitational Waves Using ARizona Observatories (SAGUARO): Observations and Analysis from Advanced LIGO/Virgo's Third Observing Run". apj, 912(2), 128.
• Rastinejad, J., Fong, W., Kilpatrick, C., Paterson, K., Tanvir, N., Levan, A., Metzger, B., Berger, E., Chornock, R., Cobb, B., Laskar, T., Milne, P., Nugent, A., & Smith, N. (2021). "Probing Kilonova Ejecta Properties Using a Catalog of Short Gamma-Ray Burst Observations". apj, 916(2), 89.
• Rouco Escorial, A., Fong, W., Veres, P., Laskar, T., Lien, A., Paterson, K., Lally, M., Blanchard, P., Nugent, A., Tanvir, N., Cornish, D., Berger, E., Burns, E., Cenko, S., Cobb, B., Cucchiara, A., Goldstein, A., Margutti, R., Metzger, B., , Milne, P., et al. (2021). "GRB 180418A: A Possibly Short Gamma-Ray Burst with a Wide-angle Outflow in a Faint Host Galaxy". apj, 912(2), 95.
• Sand, D., Sarbadhicary, S., Pellegrino, C., Misra, K., Dastidar, R., Brown, P., Itagaki, K., Valenti, S., Swift, J. J., Andrews, J., Bostroem, K., Burke, J., Chomiuk, L., Dong, Y., Galbany, L., Graham, M., Hiramatsu, D., Howell, D., Hsiao, E., , Janzen, D., et al. (2021). "Circumstellar Medium Constraints on the Environment of Two Nearby Type Ia Supernovae: SN 2017cbv and SN 2020nlb". apj, 922(1), 21.
• Utrobin, V. P., Chugai, N. N., Andrews, J. E., Smith, N., Jencson, J., Howell, D. A., Burke, J., Hiramatsu, D., McCully, C., & Bostroem, K. A. (2021). "Enormous explosion energy of Type IIP SN 2017gmr with bipolar $^{56$Ni ejecta}". mnras, 505(1), 116-125.
• Zapartas, E., Mink, S., Justham, S., Smith, N., Renzo, M., & Koter, A. (2021). "Effect of binary evolution on the inferred initial and final core masses of hydrogen-rich, Type II supernova progenitors". aap, 645, A6.
• Aghakhanloo, M., Murphy, J. W., Smith, N., Parejko, J., D{'iaz-Rodr'iguez}, M., Drout, M. R., Groh, J. H., Guzman, J., & Stassun, K. G. (2020). "Erratum: Inferring the parallax of Westerlund 1 from Gaia DR2". mnras, 495(1), 1372-1373.
• Aghakhanloo, M., Murphy, J. W., Smith, N., Parejko, J., D{'iaz-Rodr'iguez}, M., Drout, M. R., Groh, J. H., Guzman, J., & Stassun, K. G. (2020). Inferring the parallax of Westerlund 1 from Gaia DR2. mnras, 492(2), 2497-2509.
• Allan, A. P., Groh, J. H., Mehner, A., Smith, N., Boian, I., Farrell, E. J., & Andrews, J. E. (2020). "The possible disappearance of a massive star in the low-metallicity galaxy PHL 293B". mnras, 496(2), 1902-1908.
• Beasor, E. R., Davies, B., Smith, N., Loon, J. T., Gehrz, R. D., & Figer, D. F. (2020). A new mass-loss rate prescription for red supergiants. mnras, 492(4), 5994-6006.
• Bilinski, C., Smith, N., Williams, G. G., Smith, P., Andrews, J., Clubb, K. I., Zheng, W., Filippenko, A. V., Fox, O. D., Hosseinzadeh, G., Howell, D. A., Kelly, P. L., Milne, P., Sand, D., Hoffman, J. L., Leonard, D. C., Cargill, S., Casper, C., Halevy, G., , Kim, H., et al. (2020). "SN 2014ab: an aspherical Type IIn supernova with low polarization". mnras, 498(3), 3835-3851.
• Bostroem, K., Valenti, S., Sand, D., Andrews, J., Van, D. S., Galbany, L., Pooley, D., Amaro, R., Smith, N., Yang, S., Anupama, G., Arcavi, I., Baron, E., Brown, P., Burke, J., Cartier, R., Hiramatsu, D., Dastidar, R., DerKacy, J., , Dong, Y., et al. (2020). "Discovery and Rapid Follow-up Observations of the Unusual Type II SN 2018ivc in NGC 1068". apj, 895(1), 31.
• Fox, O. D., Fransson, C., Smith, N., Andrews, J., Azalee Bostroem, K., Brink, T. G., Bradley Cenko, S., Clayton, G. C., Filippenko, A. V., Fong, W., Gallagher, J. S., Kelly, P. L., Kilpatrick, C. D., Mauerhan, J. C., Miller, A. M., Montiel, E., Stritzinger, M. D., Szalai, T., & Van, D. (2020). "The slow demise of the long-lived SN 2005ip". mnras, 498(1), 517-531.
• Groh, J. H., Farrell, E. J., Meynet, G., Smith, N., Murphy, L., Allan, A. P., Georgy, C., & Ekstroem, S. (2020). "Massive Black Holes Regulated by Luminous Blue Variable Mass Loss and Magnetic Fields". apj, 900(2), 98.
• Kareta, T., Andrews, J., Noonan, J. W., Harris, W. M., Smith, N., O'Brien, P., Sharkey, B. N., Reddy, V., Springmann, A., Lejoly, C., Volk, K., Conrad, A., & Veillet, C. (2020). Carbon Chain Depletion of 2I/Borisov. apjl, 889(2), L38.
• Pellegrino, C., Howell, D., Sarbadhicary, S., Burke, J., Hiramatsu, D., McCully, C., Milne, P., Andrews, J., Brown, P., Chomiuk, L., Hsiao, E., Sand, D., Shahbandeh, M., Smith, N., Valenti, S., Vink{'o}, J., Wheeler, J., Wyatt, S., & Yang, Y. (2020). "Constraining the Source of the High-velocity Ejecta in Type Ia SN 2019ein". apj, 897(2), 159.
• Renzo, M., Farmer, R., Justham, S., G{"otberg}, Y., Mink, S., Zapartas, E., Marchant, P., & Smith, N. (2020). "Predictions for the hydrogen-free ejecta of pulsational pair-instability supernovae". aap, 640, A56.
• Smith, N., & Andrews, J. E. (2020). "High-resolution spectroscopy of SN 2017hcc and its blueshifted line profiles from post-shock dust formation". mnras, 499(3), 3544-3562.
• Smith, N., E, A. J., Moe, M., Milne, P., Bilinski, C., Kilpatrick, C. D., Fong, W., Badenes, C., Filippenko, A. V., Kasliwal, M., & Silverman, J. M. (2020). A new and unusual LBV-like outburst from a Wolf-Rayet star in the outskirts of M33. mnras, 492(4), 5897-5915.
• Andrews, J. E., Sand, D., Valenti, S., Smith, N., Dastidar, R., Sahu, D., Misra, K., Singh, A., Hiramatsu, D., Brown, P., Hosseinzadeh, G., Wyatt, S., Vinko, J., Anupama, G., Arcavi, I., Ashall, C., Benetti, S., Berton, M., Bostroem, K., , Bulla, M., et al. (2019). SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries. apj, 885(1), 43.
• Beasor, E. R., Davies, B., Smith, N., & Bastian, N. (2019). Discrepancies in the ages of young star clusters; evidence for mergers?. mnras, 486(1), 266-273.
• Bhirombhakdi, K., Chornock, R., Miller, A. A., Filippenko, A. V., Cenko, S. B., & Smith, N. (2019). The Type II superluminous SN 2008es at late times: near-infrared excess and circumstellar interaction. mnras, 488(3), 3783-3793.
• Chen, W., Kelly, P. L., Diego, J. M., Oguri, M., Williams, L. L., Zitrin, A., Treu, T. L., Smith, N., Broadhurst, T. J., Kaiser, N., Foley, R. J., Filippenko, A. V., Salo, L., Hjorth, J., & Selsing, J. (2019). Searching for Highly Magnified Stars at Cosmological Distances: Discovery of a Redshift 0.94 Blue Supergiant in Archival Images of the Galaxy Cluster MACS J0416.1-2403. apj, 881(1), 8.
• Dimitriadis, G., Foley, R., Rest, A., Kasen, D., Piro, A., Polin, A., Jones, D., Villar, A., Narayan, G., Coulter, D., Kilpatrick, C., Pan, Y., Rojas-Bravo, C. .., Fox, O., Jha, S., Nugent, P., Riess, A., Scolnic, D., Drout, M., , Team, K. M., et al. (2019). K2 Observations of SN 2018oh Reveal a Two-component Rising Light Curve for a Type Ia Supernova. apjl, 870, L1.
• Doctor}, Z., Kessler, R., Herner, K., Palmese, A., Soares-Santos, M. .., Annis, J., Brout, D., Holz, D., Sako, M., Rest, A., Cowperthwaite, P., Berger, E., Foley, R., Conselice, C., Gill, M., Allam, S., Balbinot, E., Butler, R., Chen, H., , Chornock, R., et al. (2019). A Search for Optical Emission from Binary Black Hole Merger GW170814 with the Dark Energy Camera. apjl, 873, L24.
• Fox, O. D., & Smith, N. (2019). Signatures of circumstellar interaction in the unusual transient AT 2018cow. mnras, 488(3), 3772-3782.
• Jencson, J. E., Adams, S. M., Bond, H. E., Dyk, S. D., Kasliwal, M. M., Bally, J., Blagorodnova, N., De, K., Fremling, C., Yao, Y., Fruchter, A., Rubin, D., Barbarino, C., Sollerman, J., Miller, A. A., Hicks, E. K., Malkan, M. A., Andreoni, I., Bellm, E. C., , Buchheim, R., et al. (2019). Discovery of an Intermediate-luminosity Red Transient in M51 and Its Likely Dust-obscured, Infrared-variable Progenitor. apjl, 880(2), L20.
• Jencson, J. E., Kasliwal, M. M., Adams, S. M., Bond, H. E., De, K., Johansson, J., Karambelkar, V., Lau, R. M., Tinyanont, S., Ryder, S. D., Cody, A. M., Masci, F. J., Bally, J., Blagorodnova, N., Castell{'on}, S., Fremling, C., Gehrz, R. D., Helou, G., Kilpatrick, C. D., , Milne, P. A., et al. (2019). The SPIRITS Sample of Luminous Infrared Transients: Uncovering Hidden Supernovae and Dusty Stellar Outbursts in Nearby Galaxies. apj, 886(1), 40.
• Li, W., Wang, X., Vink{'o}, J., Mo, J., Hosseinzadeh, G., Sand, D., Zhang, J., Lin, H., PTSS/TNTS, ., Zhang, T., Wang, L., Zhang, J., Chen, Z., Xiang, D., Rui, L., Huang, F., Li, X., Zhang, X., Li, L., , Baron, E., et al. (2019). Photometric and Spectroscopic Properties of Type Ia Supernova 2018oh with Early Excess Emission from the Kepler 2 Observations. apj, 870, 12.
• Lundquist, M., Paterson, K., Fong, W., Sand, D., Andrews, J., Shivaei, I., Daly, P., Valenti, S., Yang, S., Christensen, E., Gibbs, A., Shelly, F., Wyatt, S., Eskandari, O., Kuhn, O., Amaro, R., Arcavi, I., Behroozi, P., Butler, N., , Chomiuk, L., et al. (2019). Searches after Gravitational Waves Using ARizona Observatories (SAGUARO): System Overview and First Results from Advanced LIGO/Virgotextquoterights Third Observing Run. apjl, 881(2), L26.
• Sand, D., Amaro, R., Moe, M., Graham, M., Andrews, J., Burke, J., Cartier, R., Eweis, Y., Galbany, L., Hiramatsu, D., Howell, D., Jha, S., Lundquist, M., Matheson, T., McCully, C., Milne, P., Smith, N., Valenti, S., & Wyatt, S. (2019). Nebular Hensuremath{alpha} Limits for Fast Declining SNe Ia. apjl, 877(1), L4.
• Singh, A., Kumar, B., Moriya, T. J., Anupama, G., Sahu, D., Brown, P. J., Andrews, J. E., & Smith, N. (2019). Observational Signature of Circumstellar Interaction and $^56$Ni-mixing in the Type II Supernova 2016gfy. apj, 882(1), 68.
• Smith, N. (2019). The isolation of luminous blue variables resembles aging B-type supergiants, not the most massive unevolved stars. mnras, 489(3), 4378-4388.
• Smith, N., & Morse, J. A. (2019). Ultraviolet Mg II emission from fast neutral ejecta around Eta Carinae. mnras, 489(1), 268-281.
• Smith, N., Aghakhanloo, M., Murphy, J. W., Drout, M. R., Stassun, K. G., & Groh, J. H. (2019). On the Gaia DR2 distances for Galactic luminous blue variables. mnras, 488(2), 1760-1778.
• Tinyanont, S., Lau, R. M., Kasliwal, M. M., Maeda, K., Smith, N., Fox, O. D., Gehrz, R. D., De, K., Jencson, J., Bally, J., & Masci, F. (2019). Supernova 2014C: Ongoing Interaction with Extended Circumstellar Material with Silicate Dust. apj, 887(1), 75.
• Van, D., Zheng, W., Maund, J. R., Brink, T. G., Srinivasan, S., Andrews, J. E., Smith, N., Leonard, D. C., Morozova, V., Filippenko, A. V., Conner, B., Milisavljevic, D., Jaeger, T., Long, K. S., Isaacson, H., Crossfield, I. J., Kosiarek, M. R., Howard, A. W., Fox, O. D., , Kelly, P. L., et al. (2019). The Type II-plateau Supernova 2017eaw in NGC 6946 and Its Red Supergiant Progenitor. apj, 875(2), 136.
• Zapartas, E., Mink, S. E., Justham, S., Smith, N., Koter, A., Renzo, M., Arcavi, I., Farmer, R., G{"otberg}, Y., & Toonen, S. (2019). The diverse lives of progenitors of hydrogen-rich core-collapse supernovae: the role of binary interaction. aap, 631, A5.
• Andrews, J., & Smith, N. (2018). "Strong late-time circumstellar interaction in the peculiar supernova iPTF14hls". mnras.
• Arneson, R., Shenoy, D., Smith, N., & Gehrz, R. (2018). SOFIA/FORCAST Observations of the Luminous Blue Variable Candidates MN 90 and HD 168625. apj, 864, 31.
• Bersten, M., Folatelli, G., Garc{'{i}a}, F., Dyk, S., Benvenuto, O., Orellana, M., Buso, V., S{'anchez}, J., Tanaka, M., Maeda, K., Filippenko, A., Zheng, W., Brink, T., Cenko, S., Jaeger, T., Kumar, S., Moriya, T., Nomoto, K., Perley, D., , Shivvers, I., et al. (2018). "A surge of light at the birth of a supernova". nat, 554, 497-499.
• Bilinski, C., Smith, N., Williams, G., Smith, P., Zheng, W., Graham, M., Mauerhan, J., Andrews, J., Filippenko, A., Akerlof, C., Chatzopoulos, E., Hoffman, J., Huk, L., Leonard, D., Marion, G., Milne, P., Quimby, R., Silverman, J., Vink{'o}, J., , Wheeler, J., et al. (2018). "SN2012ab: a peculiar Type IIn supernova with aspherical circumstellar material". mnras, 475, 1104-1120.
• Bochenek, C., Dwarkadas, V., Silverman, J., Fox, O., Chevalier, R., Smith, N., & Filippenko, A. (2018). "X-ray emission from SN 2012ca: A Type Ia-CSM supernova explosion in a dense surrounding medium". mnras, 473, 336-344.
• Bose, S., Dong, S., Kochanek, C., Pastorello, A., Katz, B., Bersier, D., Andrews, J., Prieto, J., Stanek, K., Shappee, B., Smith, N., Kollmeier, J., Benetti, S., Cappellaro, E., Chen, P., Elias-Rosa, N. .., Milne, P., Morales-Garoffolo, A. .., Tartaglia, L., , Tomasella, L., et al. (2018). ASASSN-15nx: A Luminous Type II Supernova with a ldquoPerfectrdquo Linear Decline. apj, 862, 107.
• Bullivant, C., Smith, N., Williams, G., Mauerhan, J., Andrews, J., Fong, W., Bilinski, C., Kilpatrick, C., Milne, P., Fox, O., Cenko, S., Filippenko, A., Zheng, W., Kelly, P., & Clubb, K. (2018). "SN 2013fs and SN 2013fr: exploring the circumstellar-material diversity in Type II supernovae". mnras, 476, 1497-1518.
• Elias-Rosa, N. .., Van, D. S., Benetti, S., Cappellaro, E., Smith, N., Kotak, R., Turatto, M., Filippenko, A., Pignata, G., Fox, O., Galbany, L., Gonz{'alez-Gait'an}, S., Miluzio, M., Monard, L., & Ergon, M. (2018). The Type IIn Supernova SN 2010bt: The Explosion of a Star in Outburst. apj, 860, 68.
• Jencson, J., Kasliwal, M., Adams, S., Bond, H., Lau, R., Johansson, J., Horesh, A., Mooley, K., Fender, R., De, K., O'Sullivan, D., Masci, F., Cody, A., Blagorodnova, N., Fox, O., Gehrz, R., Milne, P., Perley, D., Smith, N., & Van, D. S. (2018). SPIRITS 16tn in NGC 3556: A Heavily Obscured and Low-luminosity Supernova at 8.8 Mpc. apj, 863, 20.
• Kelly, P., Diego, J., Rodney, S., Kaiser, N., Broadhurst, T., Zitrin, A., Treu, T., P{'erez-Gonz'alez}, P., Morishita, T., Jauzac, M., Selsing, J., Oguri, M., Pueyo, L., Ross, T., Filippenko, A., Smith, N., Hjorth, J., Cenko, S., Wang, X., , Howell, D., et al. (2018). Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens. Nature Astronomy, 2, 334-342.
• Kiminki, M., & Smith, N. (2018). A radial velocity survey of the Carina Nebula's O-type stars. mnras, 477, 2068-2086.
• Ryder, S., Van, D. S., Fox, O., Zapartas, E., Mink, S., Smith, N., Brunsden, E., Azalee Bostroem, K., Filippenko, A., Shivvers, I., & Zheng, W. (2018). Ultraviolet Detection of the Binary Companion to the Type IIb SN 2001ig. apj, 856, 83.
• Shen, K., Boubert, D., G{"ansicke}, B., Jha, S., Andrews, J., Chomiuk, L., Foley, R., Fraser, M., Gromadzki, M., Guillochon, J., Kotze, M., Maguire, K., Siebert, M., Smith, N., Strader, J., Badenes, C., Kerzendorf, W., Koester, D., Kromer, M., , Miles, B., et al. (2018). Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-degenerate Double-detonation Type Ia Supernovae. apj, 865, 15.
• Smith, N., Andrews, J., Rest, A., Bianco, F., Prieto, J., Matheson, T., James, D., Smith, R., Strampelli, G., & Zenteno, A. (2018). Light echoes from the plateau in Eta Carinae's Great Eruption reveal a two-stage shock-powered event. mnras, 480, 1466-1498.
• Smith, N., Ginsburg, A., & Bally, J. (2018). "A disrupted molecular torus around Eta Carinae as seen in $^{12$CO with ALMA}". mnras, 474, 4988-4996.
• Smith, N., G{"otberg}, Y., & Mink, S. (2018). "Extreme isolation of WN3/O3 stars and implications for their evolutionary origin as the elusive stripped binaries". mnras, 475, 772-782.
• Smith, N., Rest, A., Andrews, J., Matheson, T., Bianco, F., Prieto, J., James, D., Smith, R., Strampelli, G., & Zenteno, A. (2018). Exceptionally fast ejecta seen in light echoes of Eta Carinae's Great Eruption. mnras, 480, 1457-1465.
• Van, D. S., Zheng, W., Brink, T., Filippenko, A., Milisavljevic, D., Andrews, J., Smith, N., Cignoni, M., Fox, O., Kelly, P., Adamo, A., Yunus, S., Zhang, K., & Kumar, S. (2018). Erratum: ldquoSN 2017ein and the Possible First Identification of a Type Ic Supernova Progenitorrdquo (2018, ApJ, 860, 90). apj, 868, 77.
• Van, D. S., Zheng, W., Brink, T., Filippenko, A., Milisavljevic, D., Andrews, J., Smith, N., Cignoni, M., Fox, O., Kelly, P., Adamo, A., Yunus, S., Zhang, K., & Kumar, S. (2018). SN 2017ein and the Possible First Identification of a Type Ic Supernova Progenitor. apj, 860, 90.
• Abbott, B., Abbott, R., Abbott, T., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R., Adya, V., & al., e. (2017). "A gravitational-wave standard siren measurement of the Hubble constant". nat, 551, 85-88.
• Abbott, B., Abbott, R., Abbott, T., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R., Adya, V., & al., e. (2017). "Multi-messenger Observations of a Binary Neutron Star Merger". apjl, 848, L12.
• Aghakhanloo, M., Murphy, J., Smith, N., & Hlo{v, z. R. (2017). "Modelling luminous-blue-variable isolation". mnras, 472, 591-603.
• Andrews, J., Smith, N., McCully, C., Fox, O., Valenti, S., & Howell, D. (2017). "Optical and IR observations of SN 2013L, a Type IIn Supernova surrounded by asymmetric CSM". mnras, 471, 4047-4059.
• Chornock, R., Berger, E., Kasen, D., Cowperthwaite, P., Nicholl, M., Villar, V., Alexander, K., Blanchard, P., Eftekhari, T., Fong, W., Margutti, R., Williams, P., Annis, J., Brout, D., Brown, D., Chen, H., Drout, M., Farr, B., Foley, R., , Frieman, J., et al. (2017). "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South". apjl, 848, L19.
• Cowperthwaite, P., Berger, E., Villar, V., Metzger, B., Nicholl, M., Chornock, R., Blanchard, P., Fong, W., Margutti, R., Soares-Santos, M. .., Alexander, K., Allam, S., Annis, J., Brout, D., Brown, D., Butler, R., Chen, H., Diehl, H., Doctor, Z., , Drout, M., et al. (2017). "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models". apjl, 848, L17.
• Dwek, E., Arendt, R., Fox, O., Kelly, P., Smith, N., Van, D. S., Filippenko, A., Andrews, J., & Shivvers, I. (2017). "Constraints on the Progenitor of SN 2010jl and Pre-existing Hot Dust in its Surrounding Medium". apj, 847, 91.
• Fox, O., Van, D. S., Dwek, E., Smith, N., Filippenko, A., Andrews, J., Arendt, R., Foley, R., Kelly, P., Miller, A., & Shivvers, I. (2017). "The Candidate Progenitor of the Type IIn SN 2010jl Is Not an Optically Luminous Star". apj, 836, 222.
• Graur, O., Bianco, F., Modjaz, M., Shivvers, I., Filippenko, A., Li, W., & Smith, N. (2017). "LOSS Revisited. II. The Relative Rates of Different Types of Supernovae Vary between Low- and High-mass Galaxies". apj, 837, 121.
• Jencson, J., Kasliwal, M., Johansson, J., Contreras, C., Castell{'on}, S., Bond, H., Monson, A., Masci, F., Cody, A., Andrews, J., Bally, J., Cao, Y., Fox, O., Gburek, T., Gehrz, R., Green, W., Helou, G., Hsiao, E., Morrell, N., , Phillips, M., et al. (2017). "SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-forming Galaxy IC 2163". apj, 837, 167.
• Kasliwal, M., Bally, J., Masci, F., Cody, A., Bond, H., Jencson, J., Tinyanont, S., Cao, Y., Contreras, C., Dykhoff, D., Amodeo, S., Armus, L., Boyer, M., Cantiello, M., Carlon, R., Cass, A., Cook, D., Corgan, D., Faella, J., , Fox, O., et al. (2017). "SPIRITS: Uncovering Unusual Infrared Transients with Spitzer". apj, 839, 88.
• Kiminki, M., Smith, N., Reiter, M., & Bally, J. (2017). "Proper motions of five OB stars with candidate dusty bow shocks in the Carina Nebula". mnras, 468, 2469-2481.
• Milne, P., Williams, G., Porter, A., Smith, P., Smith, N., Leising, M., Jannuzi, B., & Green, E. (2017). "Multiepoch Spectropolarimetry of SN 2011fe". apj, 835, 100.
• Reiter, M., Kiminki, M., Smith, N., & Bally, J. (2017). "Proper motions of collimated jets from intermediate-mass protostars in the Carina Nebula". mnras, 470, 4671-4697.
• Reiter, M., Kiminki, M., Smith, N., & Bally, J. (2017). "The dusty silhouette jet HH 1019 in the Carina Nebula". mnras, 467, 4441-4446.
• Shivvers, I., Modjaz, M., Zheng, W., Liu, Y., Filippenko, A., Silverman, J., Matheson, T., Pastorello, A., Graur, O., Foley, R., Chornock, R., Smith, N., Leaman, J., & Benetti, S. (2017). "Revisiting the Lick Observatory Supernova Search Volume-limited Sample: Updated Classifications and Revised Stripped-envelope Supernova Fractions". pasp, 129(5), 054201.
• Shivvers, I., Zheng, W., Van, D. S., Mauerhan, J., Filippenko, A., Smith, N., Foley, R., Mazzali, P., Kamble, A., Kilpatrick, C., Margutti, R., Yuk, H., Graham, M., Kelly, P., Andrews, J., Matheson, T., Wood-Vasey, W., Ponder, K., Brown, P., , Chevalier, R., et al. (2017). "The nearby Type Ibn supernova 2015G: signatures of asymmetry and progenitor constraints". mnras, 471, 4381-4397.
• Smith, N. (2017). "A moderately precise dynamical age for the Homunculus of Eta Carinae based on 13 years of HST imaging". mnras, 471, 4465-4475.
• Smith, N. (2017). "Luminous blue variables and the fates of very massive stars". Philosophical Transactions of the Royal Society of London Series A, 375, 20160268.
• Smith, N., & Stassun, K. (2017). "The Canonical Luminous Blue Variable AG Car and Its Neighbor Hen 3-519 are Much Closer than Previously Assumed". aj, 153, 125.
• Smith, N., Groh, J., France, K., & McCray, R. (2017). "Ultraviolet spectroscopy of the blue supergiant SBW1: the remarkably weak wind of a SN 1987A analogue". mnras, 468, 2333-2344.
• Smith, N., Kilpatrick, C., Mauerhan, J., Andrews, J., Margutti, R., Fong, W., Graham, M., Zheng, W., Kelly, P., Filippenko, A., & Fox, O. (2017). "Endurance of SN 2005ip after a decade: X-rays, radio and H{$alpha$ like SN 1988Z require long-lived pre-supernova mass-loss}". mnras, 466, 3021-3034.
• Wu, Y., Smith, N., Close, L., Males, J., & Morzinski, K. (2017). "Resolving the H{$alpha$-emitting Region in the Wind of $eta$ Carinae}". apjl, 841, L7.
• Zapartas, E., Mink, S., Van, D. S., Fox, O., Smith, N., Bostroem, K., Koter, A., Filippenko, A., Izzard, R., Kelly, P., Neijssel, C., Renzo, M., & Ryder, S. (2017). "Predicting the Presence of Companions for Stripped-envelope Supernovae: The Case of the Broad-lined Type Ic SN 2002ap". apj, 842, 125.
• Annis}, J., Soares-Santos, M. .., Berger, E., Brout, D., Chen, H., Chornock, R., Cowperthwaite, P., Diehl, H., Doctor, Z., Drlica-Wagner, A. .., Drout, M., Farr, B., Finley, D., Flaugher, B., Foley, R., Frieman, J., Gruendl, R., Herner, K., Holz, D., , Kessler, R., et al. (2016). "A Dark Energy Camera Search for Missing Supergiants in the LMC after the Advanced LIGO Gravitational-wave Event GW150914". apjl, 823, L34.
• Cowperthwaite, P., Berger, E., Soares-Santos, M. .., Annis, J., Brout, D., Brown, D., Buckley-Geer, E. .., Cenko, S., Chen, H., Chornock, R., Diehl, H., Doctor, Z., Drlica-Wagner, A. .., Drout, M., Farr, B., Finley, D., Foley, R., Fong, W., Fox, D., , Frieman, J., et al. (2016). "A DECam Search for an Optical Counterpart to the LIGO Gravitational-wave Event GW151226". apjl, 826, L29.
• Decin, L., Richards, A., Millar, T., Baudry, A., De Beck, E., Homan, W., Smith, N., Sande, M., & Walsh, C. (2016). "ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris". aap, 592, A76.
• Farihi, J., Koester, D., Zuckerman, B., Vican, L., G{"ansicke}, B., Smith, N., Walth, G., & Breedt, E. (2016). "Solar abundances of rock-forming elements, extreme oxygen and hydrogen in a young polluted white dwarf". mnras, 463, 3186-3192.
• Folatelli, G., Van, D. S., Kuncarayakti, H., Maeda, K., Bersten, M., Nomoto, K., Pignata, G., Hamuy, M., Quimby, R., Zheng, W., Filippenko, A., Clubb, K., Smith, N., Elias-Rosa, N. .., Foley, R., & Miller, A. (2016). "Disappearance of the Progenitor of Supernova iPTF13bvn". apjl, 825, L22.
• Fong, W., Margutti, R., Chornock, R., Berger, E., Shappee, B., Levan, A., Tanvir, N., Smith, N., Milne, P., Laskar, T., Fox, D., Lunnan, R., Blanchard, P., Hjorth, J., Wiersema, K., Horst, A., & Zaritsky, D. (2016). "The Afterglow and Early-type Host Galaxy of the Short GRB 150101B at z = 0.1343". apj, 833, 151.
• Kilpatrick, C., Andrews, J., Smith, N., Milne, P., Rieke, G., Zheng, W., & Filippenko, A. (2016). "An optical and near-infrared study of the Type Ia/IIn Supernova PS15si". mnras, 463, 1088-1098.
• Kiminki, M., Reiter, M., & Smith, N. (2016). "Ancient eruptions of {$eta$ Carinae: a tale written in proper motions}". mnras, 463, 845-857.
• Larsson, J., Fransson, C., Spyromilio, J., Leibundgut, B., Challis, P., Chevalier, R., France, K., Jerkstrand, A., Kirshner, R., Lundqvist, P., Matsuura, M., McCray, R., Smith, N., Sollerman, J., Garnavich, P., Heng, K., Lawrence, S., Mattila, S., Migotto, K., , Sonneborn, G., et al. (2016). "Three-dimensional Distribution of Ejecta in Supernova 1987A at 10,000 Days". apj, 833, 147.
• Lau, R., Kasliwal, M., Bond, H., Smith, N., Fox, O., Carlon, R., Cody, A., Contreras, C., Dykhoff, D., Gehrz, R., Hsiao, E., Jencson, J., Khan, R., Masci, F., Monard, L., Monson, A., Morrell, N., Phillips, M., & Ressler, M. (2016). "Rising from the Ashes: Mid-infrared Re-brightening of the Impostor SN 2010da in NGC 300". apj, 830, 142.
• Porter, A., Leising, M., Williams, G., Milne, P., Smith, P., Smith, N., Bilinski, C., Hoffman, J., Huk, L., & Leonard, D. (2016). "Asymmetries in SN 2014J near Maximum Light Revealed through Spectropolarimetry". apj, 828, 24.
• Reiter, M., Smith, N., & Bally, J. (2016). "[Fe II] jets from intermediate-mass protostars in Carina". mnras, 463, 4344-4365.
• Smith, N. (2016). "The isolation of luminous blue variables: on subdividing the sample". mnras, 461, 3353-3360.
• Smith, N. (2016). Massive star mergers and the recent transient in NGC 4490: a more massive cousin of V838 Mon and V1309 Sco. MNRAS.
• Smith, N. (2016). The Persistent Eruption of UGC 2773-OT: finally, a decade-long extragalactic Eta Carinae analogue. MNRAS.
• Smith, N., & Fox, O. (2016). An Excess of Mid-infrared Emission from the Type Iax SN 2014dt. ApJ Letters.
• Smith, N., Andrews, J., & Mauerhan, J. (2016). "Massive stars dying alone: the extremely remote environment of SN 2009ip". mnras, 463, 2904-2911.
• Soares-Santos, M. .., Kessler, R., Berger, E., Annis, J., Brout, D., Buckley-Geer, E. .., Chen, H., Cowperthwaite, P., Diehl, H., Doctor, Z., Drlica-Wagner, A. .., Farr, B., Finley, D., Flaugher, B., Foley, R., Frieman, J., Gruendl, R., Herner, K., Holz, D., , Lin, H., et al. (2016). "A Dark Energy Camera Search for an Optical Counterpart to the First Advanced LIGO Gravitational Wave Event GW150914". apjl, 823, L33.
• Tinyanont, S., Kasliwal, M., Fox, O., Lau, R., Smith, N., Williams, R., Jencson, J., Perley, D., Dykhoff, D., Gehrz, R., Johansson, J., Van, D. S., Masci, F., Cody, A., & Prince, T. (2016). "A Systematic Study of Mid-infrared Emission from Core-collapse Supernovae with SPIRITS". apj, 833, 231.
• Adams, J., Herter, T., Hora, J., Schneider, N., Lau, R., Staguhn, J., Simon, R., Smith, N., Gehrz, R., Allen, L., Bontemps, S., Carey, S., Fazio, G., Gutermuth, R., Guzman Fernandez, A., Hankins, M., Hill, T., Keto, E., Koenig, X., , Kraemer, K., et al. (2015). "SOFIA/FORCAST Observations of Warm Dust in S106: A Fragmented Environment". apj, 814, 54.
• Hartigan, P., Reiter, M., Smith, N., & Bally, J. (2015). "A Survey of Irradiated Pillars, Globules, and Jets in the Carina Nebula". aj, 149, 101.
• Miller, A., Bloom, J., Richards, J., Lee, Y., Starr, D., Butler, N., Tokarz, S., Smith, N., & Eisner, J. (2015). "A Machine-learning Method to Infer Fundamental Stellar Parameters from Photometric Light Curves". apj, 798, 122.
• Smith, N. (2015). Extended red objects and stellar-wind bow shocks in the Carina Nebula. MNRAS.
• Smith, N. (2015). On the Progenitor System of the Type Iax Supernova 2014dt in M6. ApJ Letters.
• Smith, N. (2015). PTF11iqb: cool supergiant mass-loss that bridges the gap between Type IIn and normal supernovae. MNRAS.
• Smith, N., & Andrews, J. (2015). Late-time spectroscopy of SN 2002hh: a continued visible light echo with no shock interaction yet. MNRAS.
• Smith, N., & Ben-Ami, S. (2015). Ultraviolet Spectroscopy of Type IIb Supernovae: Diversity and the Impact of Circumstellar Material. ApJ.
• Smith, N., & Bilinski, C. (2015). Constraints on Type IIn supernova progenitor outbursts from the Lick Observatory Supernova Sea. MNRAS.
• Smith, N., & Fox, O. (2015). What powers the 3000-day light curve of SN 2006gy?. MNRAS.
• Smith, N., & France, K. (2015). Mapping High-velocity Hα and Lyα Emission from Supernova 1987A. ApJ Letters.
• Smith, N., & Fransson, C. (2015). The Destruction of the Circumstellar Ring of SN 1987A. ApJ Letters.
• Smith, N., & Mauerhan, J. (2015). Multiwavelength observations of NaSt1 (WR 122): equatorial mass loss and X-rays from an interacting Wolf-Rayet binary. MNRAS.
• Smith, N., & Mauerhan, J. (2015). SN Hunt 248: a super-Eddington outburst from a massive cool hypergiant. MNRAS.
• Smith, N., & Mauerhan, J. (2015). Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion. MNRAS.
• Smith, N., & Ori, F. (2015). On the nature of Type IIn/Ia-CSM supernovae: optical and near-infrared spectra of SN 2012ca and SN 2013dn. MNRAS.
• Smith, N., & Reiter, M. (2015). Disentangling the outflow and protostars in HH 900 in the Carina Nebula. MNRAS.
• Smith, N., & Reiter, M. (2015). HH 666: different kinematics from H α and [Fe II] emission provide a missing link between jets and outflows. MNRAS.
• Smith, N., & Tombleson, R. (2015). Luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution. MNRAS.
• Smith, N., & Vacca, W. (2015). Observations of Type Ia Supernova 2014J with FLITECAM/SOFIA. ApJ.
• Chesneau, O., & Smith, N. (2014). The yellow hyper giant HR 5171A: Resolving a massive interacting binary in the common envelope phase. Astronomy & Astrophysics, 563, 23.
• D., S., Zheng, W., Fox, O. D., Cenko, S. B., Clubb, K. I., Filippenko, A. V., Foley, R. J., Miller, A. A., Smith, N., Kelly, P. L., Lee, W. H., Ben-Ami, S., & Gal-Yam, A. (2014). The type IIb supernova 2013df and its cool supergiant progenitor. Astronomical Journal, 147(2).
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  Abstract: We have obtained early-time photometry and spectroscopy of supernova (SN) 2013df in NGC 4414. The SN is clearly of Type IIb, with notable similarities to SN 1993J. From its luminosity at secondary maximum light, it appears that less 56Ni (≲ 0.06 M ·) was synthesized in the SN 2013df explosion than was the case for the SNe IIb 1993J, 2008ax, and 2011dh. Based on a comparison of the light curves, the SN 2013df progenitor must have been more extended in radius prior to explosion than the progenitor of SN 1993J. The total extinction for SN 2013df is estimated to be AV = 0.30 mag. The metallicity at the SN location is likely to be solar. We have conducted Hubble Space Telescope (HST) Target of Opportunity observations of the SN with the Wide Field Camera 3, and from a precise comparison of these new observations to archival HST observations of the host galaxy obtained 14 yr prior to explosion, we have identified the progenitor of SN 2013df to be a yellow supergiant, somewhat hotter than a red supergiant progenitor for a normal Type II-Plateau SN. From its observed spectral energy distribution, assuming that the light is dominated by one star, the progenitor had effective temperature T eff = 4250 ± 100 K and a bolometric luminosity L bol = 104.94 ± 0.06 L ·. This leads to an effective radius R eff = 545 ± 65 R . The star likely had an initial mass in the range of 13-17 M ·; however, if it was a member of an interacting binary system, detailed modeling of the system is required to estimate this mass more accurately. The progenitor star of SN 2013df appears to have been relatively similar to the progenitor of SN 1993J. © 2014. The American Astronomical Society. All rights reserved.
• Fox, O. D., & Smith, N. (2014). Uncovering the putative B-star binary companion of theSN 1993J progenitor. Astrophysical Journal, 790, 13.
• Koss, M., & Smith, N. (2014). SDSS1133: an unusually persistent transient in a nearby dwarf galaxy. MNRAS.
• Marion, G. H., Vinko, J., Kirshner, R. P., Foley, R. J., Berlind, P., Bieryla, A., Bloom, J. S., Calkins, M. L., Challis, P., Chevalier, R. A., Chornock, R., Culliton, C., Curtis, J. L., Esquerdo, G. A., Everett, M. E., Falco, E. E., France, K., Fransson, C., Friedman, A. S., , Garnavich, P., et al. (2014). Type IIb supernova SN 2011dh: Spectra and photometry from the ultraviolet to the near-infrared. Astrophysical Journal, 781(2).
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  Abstract: We report spectroscopic and photometric observations of the Type IIb SN 2011dh obtained between 4 and 34 days after the estimated date of explosion (May 31.5 UT). The data cover a wide wavelength range from 2000 Å in the ultraviolet (UV) to 2.4 μm in the near-infrared (NIR). Optical spectra provide line profiles and velocity measurements of H I, He I, Ca II, and Fe II that trace the composition and kinematics of the supernova (SN). NIR spectra show that helium is present in the atmosphere as early as 11 days after the explosion. A UV spectrum obtained with the Space Telescope Imaging Spectrograph reveals that the UV flux for SN 2011dh is low compared to other SN IIb. Modeling the spectrum with SYNOW suggests that the UV deficit is due to line blanketing from Ti II and Co II. The H I and He I velocities in SN 2011dh are separated by about 4000 km s-1 at all phases. A velocity gap is consistent with models for a preexplosion structure in which a hydrogen-rich shell surrounds the progenitor. We estimate that the H shell of SN 2011dh is 8 times less massive than the shell of SN 1993J and3 times more massive than the shell of SN 2008ax. Light curves (LCs) for 12 passbands are presented: UVW2, UVM2, UVW1, U, u′, B, V, r′, i′, J, H, and Ks . In the B band, SN 2011dh reached peak brightness of 13.17 mag at 20.0 ± 0.5 after the explosion. The maximum bolometric luminosity of 1.8 ± 0.2 × 10 42 erg s-1 occurred22 days after the explosion. NIR emission provides more than 30% of the total bolometric flux at the beginning of our observations, and the NIR contribution increases to nearly 50% of the total by day 34. The UV produces 16% of the total flux on day 4, 5% on day 9, and 1% on day 34. We compare the bolometric LCs of SN 2011dh, SN 2008ax, and SN 1993J. The LC are very different for the first 12 days after the explosions, but all three SN IIb display similar peak luminosities, times of peak, decline rates, and colors after maximum. This suggests that the progenitors of these SN IIb may have had similar compositions and masses, but they exploded inside hydrogen shells that have a wide range of masses. SN 2011dh was well observed, and a likely progenitor star has been identified in preexplosion images. The detailed observations presented here will help evaluate theoretical models for this SN and lead to a better understanding of SN IIb. © 2014. The American Astronomical Society. All rights reserved.
• Mauerhan, J., & Smith, N. (2014). Multi-epoch spectropolarimetry of SN 2009ip: direct evidence for aspherical circumstellar material. MNRAS, 442, 15.
• Priet, J. L., & Smith, N. (2014). Light Echoes from Eta Carinae's Great Eruption: Spectrophotometric evolution and the rapid formation of nitrogen-rich molecules. Astrophysical Journal, Letters, 787, 6.
• Reiter, M., & Smith, N. (2014). Kinematics of powerful jets from intermediate-mass protostars in the Carina Nebula. MNRAS, 445, 12.
• Sexton, R. O., & Smith, N. (2014). Extended red objects and stellar-wind bow shocks in the Carina Nebula. MNRAS, 446, 13.
• Smith, N. (2014). Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars. Annual Review of Astronomy and Astrophysics, 52, 45.
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  Major Review Article
• Smith, N., & Arnett, W. D. (2014). Preparing for an Explosion:Hydrodynamic instabilities and turbulence in presupernovae. Astrophysical Journal, 785, 12.
• Smith, N., Mauerhan, J. C., & Prieto, J. L. (2014). SN 2009ip and SN 2010mc: Core-collapse type IIn supernovae arising from blue supergiants. Monthly Notices of the Royal Astronomical Society, 438(2), 1191-1207.
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  Abstract: The recent supernova (SN) known as SN 2009ip had dramatic precursor eruptions followed by an even brighter explosion in 2012. Its pre-2012 observations make it the best documented SN progenitor in history, but have fuelled debate about the nature of its 2012 explosion - whether it was a true SN or some type of violent non-terminal event. Both could power shock interaction with circumstellar material (CSM), but only a core-collapse SN provides a self-consistent explanation. The persistent broad emission lines in the spectrum require a relatively large ejecta mass, and a corresponding kinetic energy of at least 1051 erg, while the faint 2012a event is consistent with published models of core-collapse SNe from compact (̃60 R⊙) blue supergiants. The light curves of SN 2009ip and another Type IIn, SN 2010mc, were nearly identical; we demonstrate that their spectra match as well, and that both are standard SNe IIn. Our observations contradict the recent claim that the late-time spectrum of SN 2009ip is returning to its progenitor's luminous blue variable-like state, and we show the that late-time spectra of SN 2009ip closely resemble the spectra of SN 1987A. Moreover, SN 2009ip's changing Hα equivalent width after explosion matches behaviour typically seen in core-collapse SNe IIn. Several key facts about SN 2009ip and SN 2010mc argue strongly in favour of a core-collapse interpretation, and make a non-terminal 1050 erg event implausible. The most straightforward and self-consistent interpretation is that SN 2009ip was an initially faint core-collapse explosion of a blue supergiant that produced about half as much 56Ni as SN 1987A, with most of the peak luminosity from CSM interaction. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Taylor, W. D., & Smith, N. (2014). Sher 25: Pulsating but apparently alone. MNRAS, 442, 8.
• D., S., Zheng, W., Clubb, K. I., Filippenko, A. V., Cenko, S. B., Smith, N., Fox, O. D., Kelly, P. L., Shivvers, I., & Ganeshalingam, M. (2013). The progenitor of supernova 2011dh has vanished. Astrophysical Journal Letters, 772(2).
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  Abstract: We conducted Hubble Space Telescope (HST) Snapshot observations of the Type IIb supernova (SN) 2011dh in M51 at an age of 641 days with the Wide Field Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN HST images, has disappeared, implying that this star was almost certainly the progenitor of the SN. Interpretation of the early time SN data which led to the inference of a compact nature for the progenitor, and to the expected survival of this yellow supergiant, is now clearly incorrect. We also present ground-based UBVRI light curves obtained with the Katzman Automatic Imaging Telescope at Lick Observatory up to SN age 70 days. From the light-curve shape including the very late time HST data, and from recent interacting binary models for SN 2011dh, we estimate that a putative surviving companion star to the now deceased yellow supergiant could be detectable by late 2013, especially in the ultraviolet. No obvious light echoes are detectable yet in the SN environment. © 2013. The American Astronomical Society. All rights reserved.
• Mauerhan, J. C., Smith, N., Filippenko, A. V., Blanchard, K. B., Blanchard, P. K., Casper, C. F., Cenko, S. B., Clubb, K. I., Cohen, D. P., Fuller, K. L., Li, G. Z., & Silverman, J. M. (2013). The unprecedented 2012 outburst of SN 2009ip: A luminous blue variable star becomes a true supernova. Monthly Notices of the Royal Astronomical Society, 430(3), 1801-1810.
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  Abstract: Some reports of supernova (SN) discoveries turn out not to be true core-collapse explosions. One such case was SN 2009ip, which was recognized to be the eruption of a luminous blue variable (LBV) star. This source had a massive (50-80M⊙), hot progenitor star identified in pre-explosion data; it had documented evidence of pre-outburst variability and it was subsequently discovered to have a second outburst in 2010. In 2012, the source entered its third known outburst. Initial spectra showed the same narrow-line profiles as before, suggesting another LBV-like eruption. We present new photometry and spectroscopy of SN 2009ip, indicating that the 2012 outburst transitioned into a genuine SN explosion. The most striking aspect of these data is that unlike any previous episodes, the spectrum developed Balmer lines with very broad P-Cygni profiles characteristic of normal Type II supernovae (SNe II), in addition to overlying narrow emission components. The emission lines exhibit unprecedented (for any known non-terminal LBV-like eruption) full width at half-maximum intensity values of ~8000 km s-1, while the absorption components seen just before the main brightening had blue wings extending out to -13 000 km s-1. These velocities are typical of core-collapse SN explosions, but have never been associated with emission lines from a non-terminal LBV-like eruption. SN 2009ip is the first object to have both a known massive blue progenitor star and LBV-like eruptions with accompanying spectra observed a few years prior to becoming a SN. Immediately after the broad lines first appeared, the peak absolute magnitude of MV ~-14.5 was fainter than that of normal SNe II. However, after a brief period of fading, the source quickly brightened again to MR = -17.5 mag in ~2 d, suggesting a causal link to the prior emergence of the broad-line spectrum. Once the bright phase began, the broad lines mostly disappeared, and the spectrum resembled the early optically thick phases of luminous SNe IIn. The source reached a peak brightness of -18 mag about 2 weeks later, after which broad emission lines again developed in the spectrum as the source faded. We conclude that the most recent 2012 outburst of SN 2009ip was the result of a true core-collapse SN IIn that occurred when the progenitor star was in an LBV-like outburst phase, and where the SN was initially faint and then rapidly brightened due to interaction with circumstellar material. The pulsational pair instability, LBV-like eruptions or other instabilities due to interaction with circumstellar material. The pulsational pair instability, LBV-like eruptions or other instabilities due to late nuclear burning phases in massive stars may have caused the multiple pre-SN eruptions. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Mauerhan, J. C., Smith, N., Silverman, J. M., Filippenko, A. V., Morgan, A. N., Cenko, S. B., Ganeshalingam, M., Clubb, K. I., Bloom, J. S., Matheson, T., & Milne, P. (2013). SN 2011ht: Confirming a class of interacting supernovae with plateau light curves (type IIn-P). Monthly Notices of the Royal Astronomical Society, 431(3), 2599-2611.
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  Abstract: We present photometry and spectroscopy of the Type IIn supernova (SN) 2011ht, identified previously as a possible SN impostor. The light curve exhibits an abrupt transition from a well-defined ~120 d plateau to a steep bolometric decline, plummeting 4-5 mag in the optical and 2-3 mag in the infrared in only ~10 d. Leading up to peak brightness (MV =-17.4 mag), a hot emission-line spectrum exhibits strong signs of interaction with circumstellar material (CSM), in the form of relatively narrowP-Cygni features ofHI and He I superimposed on broad Lorentzian wings. For the latter half of the plateau phase, the spectrum exhibits strengthening P-Cygni profiles of Fe II, Ca II and Hα. By day 147, after the plateau has ended, the SN entered the nebular phase, heralded by the appearance of forbidden transitions of [O I], [O II] and [Ca II] over a weak continuum. At this stage, the light curve exhibits a low optical luminosity that is comparable to that of the most subluminous Type II-P supernovae, and a relatively fast visual wavelength decline that appeared to be significantly steeper than the 56Co decay rate. However, the total pseudo-bolometric decline, including the infrared luminosity, is consistent with 56Co decay, and implies a low 56Ni mass in the range 0.006-0.01M⊙, near the lower end of the range exhibited by SNe II-P. We therefore characterize SN 2011ht as a core-collapse SN very similar to the peculiar SNe IIn 1994W and 2009kn. These three SNe appear to define a subclass, which are Type IIn based on their spectrum, but that also exhibit well-defined plateaus and produce low 56Ni yields. We therefore suggest Type IIn-P as a name for this subclass. The absence of observational signatures of high-velocity material from SNe IIn- P could be the result of an opaque shell at the shocked SN-CSM interface, which remains optically thick longer than the time-scale for the inner ejecta to cool and become transparent. Possible progenitors of SNe IIn-P, consistent with the available data, include 8-10M⊙ stars, which undergo core collapse as a result of electron capture after a brief phase of enhanced mass loss, or more massive (M< 25M⊙) progenitors, which experience substantial fallback of the metal-rich radioactive ejecta. In either case, the energy radiated by these three SNe during their plateau (2-3 × 1049 erg for SN 2011ht) must be dominated by CSM interaction, and the subluminous tail is the result of low 56Ni yield. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Smith, N. (2013). A model for the 19th century eruption of Eta Carinae: CSM interaction like a scaled-down type IIn supernova. Monthly Notices of the Royal Astronomical Society, 429(3), 2366-2379.
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  Abstract: This paper proposes a simple model for the 19th century eruption of Eta Carinae that consists of two components: (1) a strong wind ( Ṁ = 0.33M· yr-1; v∞ = 200 km s-1), blowing for 30 yr, followed by (2) a 1050 erg explosion (10M·; 750-1000 km s-1) occurring in 1844. The ensuing collision between the fast ejecta and the dense circumstellar material (CSM) causes an increase in brightness observed at the end of 1844, followed by a sustained high-luminosity phase lasting for 10-15 yr that provides a close match to the observed historical light curve. The emergent luminosity is powered by converting kinetic energy to radiation through CSM interaction, analogous to the process occurring in more luminous Type IIn supernovae, except with ~10 times lower explosion energy and at slower speeds (causing a longer duration and lower emergent luminosity). We demonstrate that such an explosive event not only provides a natural explanation for the light-curve evolution, but also accounts for a number of puzzling attributes of the highly scrutinized Homunculus, including: (1) rough equipartition of total radiated and kinetic energy in the event, (2) the double-shell structure of the Homunculus, with a thin massive outer shell (corresponding to the coasting cold dense shell) and a thicker inner layer (between the cold dense shell and the reverse shock), (3) the apparent single age and Hubble-like flow of the Homunculus resulting from the thin swept-up shell, (4) the complex mottled appearance of the polar lobes in Hubble Space Telescope images, arising naturally from Raleigh-Taylor orVishniac instabilities at the contact discontinuity of the shock, (5) efficient and rapid dust formation, which has been observed in the post-shock zones of Type IIn supernovae, and (6) the fast (3000-5000 km s-1) material outside the Homunculus, arising from the acceleration of the forward shock upon exiting the dense CSM. In principle, the bipolar shape could be explained borrowing from earlier studies of interacting winds, except that here the requisite pre-existing 'torus' may be provided by periastron collisions occurring around the same time, and the CSM interaction occurs over only 10 yr, producing a thin shell with the resulting structures then frozen-in to a homologously expanding bipolar nebula. This self-consistent picture has a number of implications for other eruptive transients, many of which may also be powered by CSM interaction. A key remaining unknown is the ultimate source of the 1050 erg of energy required in the explosion. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Smith, N. (2013). The crab nebula and the class of type iin-p supernovae caused by sub-energetic electron-capture explosions. Monthly Notices of the Royal Astronomical Society, 434(1), 102-113.
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  Abstract: What sort of supernova (SN) gave rise to the Crab nebula? While there are several indications that the Crab arose from a sub-energetic explosion of an 8-10M⊙ progenitor star, this would appear to conflict with the high luminosity indicated by historical observations. This paper shows that several well-known observed properties of the Crab and SN 1054 are well matched by a particular breed of Type IIn SN. The Crab's properties are best suited to the Type IIn-P subclass (Type IIn spectra with plateau light curves), exemplified by SNe 1994W, 2009kn and 2011ht. These events probably arise from relatively low energy (1050 erg) explosions with low 56Ni yield that may result from electron-capture SN (ecSN) explosions, but their high visual-wavelength luminosity and Type IIn spectra are dominated by shock interaction with dense circumstellar material (CSM) rather than the usual recombination photosphere. In this interaction, a large fraction of the 101050 erg of the total kinetic energy can be converted to visual-wavelength luminosity. After about 120 d, nearly all of the mass outside the neutron star in the CSM and ejecta ends up in a slowly expanding (1000-1500 km s-1) thin dense shell, which is then accelerated and fragmented by the growing pulsar wind nebula in the subsequent 1000 yr, producing the complex network of filaments seen today. There is no need to invoke the extended, invisible fast SN envelope hypothesized to reside outside the Crab. As differentiated from a normal SN II-P, SNe IIn-P provide a much better explanation for several observed features of the Crab: (1) no blast wave outside the Crab nebula filaments, (2) no rapidly expanding SN envelope outside the filaments, (3) a total mass of ~5M⊙ swept up in a thin slow shell, (4) a low kinetic energy of the Crab at least an order of magnitude below a normal core-collapse SN, (5) a high peak luminosity (-18 mag) despite the low kinetic energy, (6) chemical abundances consistent with an 8-10M⊙ star and (7) a low 56Ni yield. A number of other implications are discussed, concerning other Crab-like remnants, the origin of dust in the Crab filaments, diversity in the initial masses of SNe IIn, and the putative association between ecSNe and SN impostors. This model predicts that if/when light echoes from SN 1054 are discovered, they will exhibit a Type IIn spectrum, probably similar to SNe 1994W and 2011ht ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Smith, N., Mauerhan, J. C., Kasliwal, M. M., & Burgasser, A. J. (2013). Near-infrared spectroscopy of SN 2009ip's 2012 brightening reveals a dusty pre-supernova environment. Monthly Notices of the Royal Astronomical Society, 434(4), 2721-2726.
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  Abstract: We present low-resolution near-infrared (IR) 0.8-2.5 μm spectra of Supernova (SN) 2009ip, taken immediately before, during and just after its rapid brightening in late September/October 2012. The first epoch shows the same general spectral characteristics as the later epochs (smooth continuum, narrow H and He I emission lines), but the IR continuum shape is substantially redder than the later epochs. The epoch 1 continuum can be approximated by reddening the peak-luminosity (epoch 3) spectrum by E(B - V) = 1.0 mag, but the blue colour seen in visual-wavelength spectra at the same time indicates that strong wavelength-dependent extinction by circumstellar dust is not the correct explanation. Instead, we favour the hypothesis that the redder colour before the brightening arises from excess emission from hot~2000K circumstellar dust. The minimum radius ({greater-than or approximate}120 au) deduced from the dust temperature and observed luminosity of the transient, combined with the observed expansion speed in the precursor outbursts of SN 2009ip, is consistent with an ejection at least 1.1 yr earlier. The mass of hot dust indicated by the IR excess is ~4 × 10-7M⊙, although this is only a lower limit since the near-IR data do not constrain the mass of cooler dust. Thus, the observed pre-SN outbursts of this object were able to efficiently form dust into which the SN ejecta and radiation now propagate. This is consistent with the notion that the same pre-SN eruptions that generally give rise to SNe IIn also give rise to the dust needed for their commonly observed IR echoes. We also discuss some aspects of the IR line profiles, including He I λ10 830. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Ben-Ami, S., Gal-Yam, A., Filippenko, A. V., Mazzali, P. A., Modjaz, M., Yaron, O., Arcavi, I., Cenko, S. B., Horesh, A., Howell, D. A., Graham, M. L., Horst, J. C., Myunshin, I. m., Jeon, Y., Kulkarni, S. R., Leonard, D. C., Perley, D., Pian, E., Sand, D. J., , Sullivan, M., et al. (2012). Discovery and early multi-wavelength measurements of the energetic type IC supernova ptf12gzk: A massive-star explosion in a dwarf host galaxy. Astrophysical Journal Letters, 760(2).
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  Abstract: We present the discovery and extensive early-time observations of the Type Ic supernova (SN) PTF12gzk. Our light curves show a rise of 0.8mag within 2.5hr. Power-law fits (f(t) (t - t 0)n) to these data constrain the explosion date to within one day. We cannot rule out a quadratic fireball model, but higher values of n are possible as well for larger areas in the fit parameter space. Our bolometric light curve and a dense spectral sequence are used to estimate the physical parameters of the exploding star and of the explosion. We show that the photometric evolution of PTF12gzk is slower than that of most SNe Ic. The high ejecta expansion velocities we measure (∼30, 000kms-1 derived from line minima fourdays after explosion) are similar to the observed velocities of broad-lined SNe Ic associated with gamma-ray bursts (GRBs) rather than to normal SN Ic velocities. Yet, this SN does not show the persistent broad lines that are typical of broad-lined SNe Ic. The host-galaxy characteristics are also consistent with GRB-SN hosts, and not with normal SN Ic hosts. By comparison with the spectroscopically similar SN 2004aw, we suggest that the observed properties of PTF12gzk indicate an initial progenitor mass of 25-35M ⊙ and a large ((5-10) × 10 51erg) kinetic energy, the later being close to the regime of GRB-SN properties. © 2012. The American Astronomical Society. All rights reserved.
• Mauerhan, J., & Smith, N. (2012). Supernova 1998S at 14 years postmortem: Continuing circumstellar interaction and dust formation. Monthly Notices of the Royal Astronomical Society, 424(4), 2659-2666.
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  Abstract: We report late-time spectroscopic observations of the Type IIn supernova (SN) 1998S, taken 14 years after explosion using the Large Binocular Telescope. The optical spectrum exhibits strong, broad emission features of [Oi], [Oii] and Hα, in addition to weaker features of [Oiii], Hβ and [Feii]. The last decade of evolution has exhibited a strengthening of the oxygen transitions relative to Hα, evidence that the late-time emission is powered by increasingly metal-rich SN ejecta crossing the reverse shock. The Hα luminosity of ≈8000 L ⊙ requires that SN 1998S is still interacting with relatively dense circumstellar material (CSM), probably produced by the strong wind of a red supergiant progenitor at least ~10 3 years before explosion. The emission lines exhibit asymmetric blueshifted profiles, which implies that the receding hemisphere of the SN is obscured by dust. The [Oiii] λ5007 line, in particular, exhibits a complete suppression of its red wing. This could be the result of the expected wavelength dependence for dust extinction or a smaller radial distribution for [Oiii]. In the latter case, the red wing of [Oiii] could be absorbed by core dust, while both the blue and red wings are absorbed by dust within the cool dense shell between the forward and reverse shocks; this interpretation could explain why late-time [Oiii] emission from SNe is often weaker than models predict. The [Oi] line exhibits double-peaked structure on top of the broader underlying profile, possibly due to emission from individual clumps of ejecta or ring-like structures of metal-rich debris. The centroids of the peaks are blueshifted and lack a red counterpart. However, an archival spectrum obtained on day 1093 exhibits a third, redshifted peak, which we suspect has become extinguished by dust that formed over the last decade, after day 1093. This implies that the 'missing' red components of multi-peaked oxygen profiles observed in other SNe might be obscured by varying degrees of dust extinction. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
• Mauerhan, J., & Smith, N. (2012). Supernova 1998S at 14 years postmortem: Continuing circumstellar interaction and dust formation. Monthly Notices of the Royal Astronomical Society.
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  Abstract: We report late-time spectroscopic observations of the Type IIn supernova (SN) 1998S, taken 14 years after explosion using the Large Binocular Telescope. The optical spectrum exhibits strong, broad emission features of [Oi], [Oii] and Hα, in addition to weaker features of [Oiii], Hβ and [Feii]. The last decade of evolution has exhibited a strengthening of the oxygen transitions relative to Hα, evidence that the late-time emission is powered by increasingly metal-rich SN ejecta crossing the reverse shock. The Hα luminosity of ≈8000 L ⊙ requires that SN 1998S is still interacting with relatively dense circumstellar material (CSM), probably produced by the strong wind of a red supergiant progenitor at least ∼10 3 years before explosion. The emission lines exhibit asymmetric blueshifted profiles, which implies that the receding hemisphere of the SN is obscured by dust. The [Oiii] λ5007 line, in particular, exhibits a complete suppression of its red wing. This could be the result of the expected wavelength dependence for dust extinction or a smaller radial distribution for [Oiii]. In the latter case, the red wing of [Oiii] could be absorbed by core dust, while both the blue and red wings are absorbed by dust within the cool dense shell between the forward and reverse shocks; this interpretation could explain why late-time [Oiii] emission from SNe is often weaker than models predict. The [Oi] line exhibits double-peaked structure on top of the broader underlying profile, possibly due to emission from individual clumps of ejecta or ring-like structures of metal-rich debris. The centroids of the peaks are blueshifted and lack a red counterpart. However, an archival spectrum obtained on day 1093 exhibits a third, redshifted peak, which we suspect has become extinguished by dust that formed over the last decade, after day 1093. This implies that the 'missing' red components of multi-peaked oxygen profiles observed in other SNe might be obscured by varying degrees of dust extinction. Monthly Notices of the Royal Astronomical Society © 2012 RAS.
• Rest, A., Prieto, J. L., Walborn, N. R., Smith, N., Bianco, F. B., Chornock, R., Welch, D. L., Howell, D. A., Huber, M. E., Foley, R. J., Fong, W., Sinnott, B., Bond, H. E., Smith, R. C., Toledo, I., Minniti, D., & Mandel, K. (2012). Light echoes reveal an unexpectedly cool σ Carinae during its nineteenth-century Great Eruption. Nature, 482(7385), 375-378.
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  PMID: 22337057;Abstract: σCarinae is one of the most massive binary stars in the Milky Way. It became the second-brightest star in our sky during its mid-nineteenth-century Great Eruption, but then faded from view (with only naked-eye estimates of brightness). Its eruption is unique in that it exceeded the Eddington luminosity limit for ten years. Because it is only 2.3 kiloparsecs away, spatially resolved studies of the nebula have constrained the ejected mass and velocity, indicating that during its nineteenth-century eruption, σCar ejected more than ten solar masses in an event that released ten per cent of the energy of a typical core-collapse supernova, without destroying the star. Here we report observations of light echoes of σCarinae from the 1838-1858 Great Eruption. Spectra of these light echoes show only absorption lines, which are blueshifted by-210-km-s-1, in good agreement with predicted expansion speeds. The light-echo spectra correlate best with those of G2-to-G5 supergiants, which have effective temperatures of around 5,000-kelvin. In contrast to the class of extragalactic outbursts assumed to be analogues of the Great Eruption of σCarinae, the effective temperature of its outburst is significantly lower than that allowed by standard opaque wind models. This indicates that other physical mechanisms such as an energetic blast wave may have triggered and influenced the eruption. © 2012 Macmillan Publishers Limited. All rights reserved.
• Rest, A., Prieto, J. L., Walborn, N. R., Smith, N., Bianco, F. B., Chornock, R., Welch, D. L., Howell, D. A., Huber, M. E., Foley, R. J., Fong, W., Sinnott, B., Bond, H. E., Smith, R. C., Toledo, I., Minniti, D., & Mandel, K. (2012). Rest et al. reply. Nature, 486(7403), E1-E2.
• Smith, N., Cenko, S. B., Butler, N., Bloom, J. S., Kasliwal, M. M., Horesh, A., Kulkarni, S. R., Law, N. M., Nugent, P. E., Ofek, E. O., Poznanski, D., Quimby, R. M., Sesar, B., Ben-Ami, S., Arcavi, I., Gal-Yam, A., Polishook, D., Dong, X. u., Yaron, O., , Frail, D. A., et al. (2012). SN 2010jp (PTF10aaxi): A jet in a Type II supernova. Monthly Notices of the Royal Astronomical Society, 420(2), 1135-1144.
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  Abstract: We present photometry and spectroscopy of the peculiar Type II supernova (SN) SN 2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a relatively low peak absolute magnitude of only -15.9 (unfiltered), and a low radioactive decay luminosity at late times, which suggests a low synthesized nickel mass of M ( 56 Ni) ≲ 0.003 M ⊙. Spectra of SN 2010jp display an unprecedented triple-peaked Hα line profile, showing (1) a narrow (full width at half-maximum >rsim800kms -1) central component that suggests shock interaction with dense circumstellar material (CSM); (2) high-velocity blue and red emission features centred at -12600 and +15400kms -1, respectively; and (3) very broad wings extending from -22000 to +25000kms -1. These features persist over multiple epochs during the ~100 d after explosion. We propose that this line profile indicates a bipolar jet-driven explosion, with the central component produced by normal SN ejecta and CSM interaction at mid and low latitudes, while the high-velocity bumps and broad-line wings arise in a non-relativistic bipolar jet. Two variations of the jet interpretation seem plausible: (1) a fast jet mixes 56Ni to high velocities in polar zones of the H-rich envelope; or (2) the reverse shock in the jet produces blue and red bumps in Balmer lines when a jet interacts with dense CSM. Jet-driven Type II SNe are predicted for collapsars resulting from a wide range of initial masses above 25M ⊙, especially at subsolar metallicity. This seems consistent with the SN host environment, which is either an extremely low-luminosity dwarf galaxy or the very remote parts of an interacting pair of star-forming galaxies. It also seems consistent with the apparently low 56Ni mass that may accompany black hole formation. We speculate that the jet survives to produce observable signatures because the star's H envelope was very low mass, having been mostly stripped away by the previous eruptive mass-loss indicated by the Type IIn features in the spectrum. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
• Smith, N., Mauerhan, J. C., Silverman, J. M., Ganeshalingam, M., Filippenko, A. V., Cenko, S. B., Clubb, K. I., & Kandrashoff, M. T. (2012). SN 2011hw: Helium-rich circumstellar gas and the luminous blue variable to Wolf-Rayet transition in supernova progenitors. Monthly Notices of the Royal Astronomical Society, 426(3), 1905-1915.
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  Abstract: We present optical photometry and spectroscopy of the peculiar Type IIn/Ibn supernova (SN) 2011hw. Its optical light curve exhibits a slower decline rate than that of normal SNe Ibc, with a peak absolute magnitude of -19.5 (unfiltered) and a secondary rise 20-30 d later of -18.3mag (R). Spectra of SN 2011hw are highly unusual compared to those of normal SN types, most closely resembling the spectra of SNe Ibn. We centre our analysis on comparing SN 2011hw to the well-studied Type Ibn SN 2006jc. While the two SNe have many important similarities, the differences are quite telling: compared to SN 2006jc, SN 2011hw has weaker He I and Ca II lines and relatively stronger H lines, its light curve exhibits a higher visual-wavelength luminosity and slower decline rate, and emission lines associated with the progenitor's circumstellar material (CSM) are narrower. One can reproduce the unusual continuum shape of SN 2011hw with roughly equal contributions from a 6000-K blackbody and a spectrum of SN 2006jc. We attribute this blackbody-like emission component and many other differences between the two SNe to a small amount of additional H in SN 2011hw, analogous to the small H mass that makes SNe IIb differ from SNe Ib. Slower speeds in the CSM and somewhat elevated H content suggest a connection between SN 2011hw's progenitor and Ofpe/WN9 stars, which have been associated with luminous blue variables (LBVs) in their hot quiescent phases, and are H poor - but not H free like classical Wolf-Rayet (WR) stars. Comparisons between SN 2011hw and SN 2006jc can be largely understood if their progenitors exploded at different points in the transitional evolution from an LBV to a WR star. © 2012 The Authors Monthly Notices of the Royal Astronomical Society.
• Smith, N., Silverman, J. M., Filippenko, A. V., Cooper, M. C., Matheson, T., Bian, F., Weiner, B. J., & Comerford, J. M. (2012). Systematic blueshift of line profiles in the type IIn supernova 2010jl: Evidence for post-shock dust formation?. Astronomical Journal, 143(1).
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  Abstract: Type IIn supernovae (SNe) show spectral evidence for strong interaction between their blast wave and dense circumstellar material (CSM) around the progenitor star. SN 2010jl was the brightest core-collapse supernova in 2010, and it was a Type IIn explosion with strong CSM interaction. Andrews etal. recently reported evidence for an infrared (IR) excess in SN 2010jl, indicating either new dust formation or the heating of CSM dust in an IR echo. Here we report multi-epoch spectra of SN 2010jl that reveal the tell-tale signature of new dust formation: emission-line profiles becoming systematically more blueshifted as the red side of the line is blocked by increasing extinction. The effect is seen clearly in the intermediate-width (400-4000kms-1) component of Hα beginning roughly 30 days after explosion. Moreover, we present near-IR spectra demonstrating that the asymmetry in the hydrogen-line profiles is wavelength dependent, appearing more pronounced at shorter wavelengths. This evidence suggests that new dust grains had formed quickly in the post-shock shell of SN 2010jl arising from CSM interaction. Since the observed dust temperature has been attributed to an IR echo and not to new dust, either (1) IR excess emission at λ < 5 μm is not a particularly sensitive tracer of new dust formation in SNe, or (2) some assumptions about expected dust temperatures might require further study. Lastly, we discuss one possible mechanism other than dust that might lead to increasingly blueshifted line profiles in SNe IIn, although the wavelength dependence of the asymmetry argues against this hypothesis in the case of SN 2010jl.
• Artigau, É., Martin, J. C., Humphreys, R. M., Davidson, K., Chesneau, O., & Smith, N. (2011). Penetrating the homunculus-near-infrared adaptive optics images of Eta Carinae. Astronomical Journal, 141(6).
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  Abstract: Near-infrared adaptive optics imaging with the Near-Infrared Coronagraphic Imager (NICI) and NaCO reveal what appears to be a three-winged or lobed pattern, the "butterfly nebula," outlined by bright Brγ and H2 emission and light scattered by dust. In contrast, the [Fe II] emission does not follow the outline of the wings, but shows an extended bipolar distribution which is tracing the Little Homunculus ejected in η Car's second or lesser eruption in the 1890s. Proper motions measured from the combined NICI and NaCO images together with radial velocities show that the knots and filaments that define the bright rims of the butterfly were ejected at two different epochs corresponding approximately to the great eruption and the second eruption. Most of the material is spatially distributed 10°-20° above and below the equatorial plane apparently behind the Little Homunculus and the larger SE lobe. The equatorial debris either has a wide opening angle or the clumps were ejected at different latitudes relative to the plane. The butterfly is not a coherent physical structure or equatorial torus but spatially separate clumps and filaments ejected at different times, and now 2000-4000AU from the star. © 2011. The American Astronomical Society. All rights reserved.
• Bally, J., Cunningham, N. J., Moeckel, N., Burton, M. G., Smith, N., Frank, A., & Nordlund, A. (2011). Explosive outflows powered by the decay of non-hierarchical multiple systems of massive stars: Orion BN/KL. Astrophysical Journal, 727(2).
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  Abstract: The explosive Becklin-Neugebauer (BN)/Kleinman-Low (KL) outflow emerging from OMC1 behind the Orion Nebula may have been powered by the dynamical decay of a non-hierarchical multiple system ∼500 years ago that ejected the massive stars I, BN, and source n, with velocities of about 10-30 km s -1. New proper-motion measurements of H2 features show that within the errors of measurement, the outflow originated from the site of stellar ejection. Combined with published data, these measurements indicate an outflow age of ∼500 years, similar to the time since stellar ejection. The total kinetic energy of the ejected stars and the outflow is about 2 to 6 × 1047 erg. It is proposed that the gravitational potential energy released by the formation of a short-period binary, most likely source I, resulted in stellar ejection and powered the outflow. A scenario is presented for the formation of a compact, non-hierarchical multiple star system, its decay into an ejected binary and two high-velocity stars, and launch of the outflow. Three mechanisms may have contributed to the explosion in the gas: (1) unbinding of the circumcluster envelope following stellar ejection, (2) disruption of circumstellar disks and high-speed expulsion of the resulting debris during the final stellar encounter, and (3) the release of stored magnetic energy. Plausible protostellar disk end envelope properties can produce the observed outflow mass, velocity, and kinetic energy distributions. The ejected stars may have acquired new disks by fall-back or Bondi-Hoyle accretion with axes roughly orthogonal to their velocities. The expulsion of gas and stars from OMC1 may have been driven by stellar interactions. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
• Broos, P. S., Townsley, L. K., Feigelson, E. D., Getman, K. V., Garmire, G. P., Preibisch, T., Smith, N., Babler, B. L., Hodgkin, S., Indebetouw, R., Irwin, M., King, R., Lewis, J., Majewski, S. R., McCaughrean, M. J., Meade, M. R., & Zinnecker, H. (2011). A catalog of Chandra X-ray sources in the Carina Nebula. Astrophysical Journal, Supplement Series, 194(1).
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  Abstract: We present a catalog of 14,000 X-ray sources observed by the ACIS instrument on the Chandra X-ray Observatory within a 1.42deg2 survey of the Great Nebula in Carina, known as the Chandra Carina Complex Project (CCCP). This study appears in a special issue devoted to the CCCP. Here, we describe the data reduction and analysis procedures performed on the X-ray observations, including calibration and cleaning of the X-ray event data, point-source detection, and source extraction. The catalog appears to be complete across most of the field to an absorption-corrected total-band luminosity of 1030.7ergs-1 for a typical low-mass pre-main-sequence star. Counterparts to the X-ray sources are identified in a variety of visual, near-infrared, and mid-infrared surveys. The X-ray and infrared source properties presented here form the basis of many CCCP studies of the young stellar populations in Carina. © 2011. The American Astronomical Society. All rights reserved.
• Elias-Rosa, N., D., S., Weidong, L. i., Silverman, J. M., Foley, R. J., Ganeshalingam, M., Mauerhan, J. C., Kankare, E., Jha, S., Filippenko, A. V., Beckman, J. E., Berger, E., Cuillandre, J., & Smith, N. (2011). The massive progenitor of the possible type II-Linear supernova 2009hd in Messier 66. Astrophysical Journal, 742(1).
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  Abstract: We present early- and late-time photometric and spectroscopic observations of supernova (SN) 2009hd in the nearby spiral galaxy NGC 3627 (M66). This SN is one of the closest to us in recent years and provides an uncommon opportunity to observe and study the nature of SNe. However, the object was heavily obscured by dust, rendering it unusually faint in the optical given its proximity. We find that the observed properties of SN 2009hd support its classification as a possible Type II-Linear SN (SN II-L), a relatively rare subclass of core-collapse SNe. High-precision relative astrometry has been employed to attempt to identify an SN progenitor candidate, based on a pixel-by-pixel comparison between Hubble Space Telescope (HST) F555W and F814W images of the SN site prior to explosion and at late times. A progenitor candidate is identified in the F814W images only; this object is undetected in F555W. Significant uncertainty exists in the astrometry, such that we cannot definitively identify this object as the SN progenitor. Via insertion of artificial stars into the pre-SN HST images, we are able to constrain the progenitor's properties to those of a possible supergiant, with intrinsic absolute magnitude M 0F555W ≳ -7.6mag and intrinsic color (V - I)0 ≳ 0.99mag. The magnitude and color limits are consistent with a luminous red supergiant (RSG); however, they also allow for the possibility that the star could have been more yellow than red. From a comparison with theoretical massive-star evolutionary tracks which include rotation and pulsationally enhanced mass loss, we can place a conservative upper limit on the initial mass for the progenitor of M ini ≲ 20 M ⊙. If the actual mass of the progenitor is near the upper range allowed by our derived mass limit, then it would be consistent with that for the identified progenitors of the SN II-L 2009kr and the high-luminosity SN II-Plateau (II-P) 2008cn. The progenitors of these three SNe may possibly bridge the gap between lower-mass RSGs that explode as SNe II-P and luminous blue variables, or more extreme RSGs, from which the more exotic SNe II-narrow may arise. Very late time imaging of the SN 2009hd site may provide us with more clues regarding the true nature of its progenitor. © 2011. The American Astronomical Society. All rights reserved.
• Feigelson, E. D., Getman, K. V., Townsley, L. K., Broos, P. S., Povich, M. S., Garmire, G. P., King, R. R., Montmerle, T., Preibisch, T., Smith, N., Stassun, K. G., Wang, J., Wolk, S., & Zinnecker, H. (2011). X-ray star clusters in the Carina Complex. Astrophysical Journal, Supplement Series, 194(1).
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  Abstract: The distribution of young stars found in the Chandra Carina Complex Project (CCCP) is examined for clustering structure. X-ray surveys are advantageous for identifying young stellar populations compared to optical and infrared surveys in suffering less contamination from nebular emission and Galactic field stars. The analysis is based on smoothed maps of a spatially complete subsample of 3000 brighter X-ray sources classified as Carina members and 10,000 stars from the full CCCP sample. The principal known clusters are recovered, and some additional smaller groups are identified. No rich embedded clusters are present, although a number of sparse groups are found. The CCCP reveals considerable complexity in clustering properties. The Trumpler 14 and 15 clusters have rich stellar populations in unimodal, centrally concentrated structures several parsecs across. Non-spherical internal structure is seen, and large-scale low surface density distributions surround these rich clusters. Trumpler 16, in contrast, is comprised of several smaller clusters within a circular boundary. Collinder 228 is a third type of cluster which extends over tens of parsecs with many sparse compact groups likely arising from triggered star formation processes. A widely dispersed, but highly populous, distribution of X-ray stars across the 50 pc CCCP mosaic supports a model of past generations of star formation in the region. Collinder 234, a group of massive stars without an associated cluster of pre-main-sequence stars, may be part of this dispersed population. © 2011. The American Astronomical Society. All rights reserved.
• Fox, O. D., Chevalier, R. A., Skrutskie, M. F., Soderberg, A. M., Filippenko, A. V., Ganeshalingam, M., Silverman, J. M., Smith, N., & Steele, T. N. (2011). A Spitzer survey for dust in type IIn supernovae. Astrophysical Journal, 741(1).
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  Abstract: Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit late-time (>100days) infrared (IR) emission from warm dust more than other types of core-collapse SNe. Mid-IR observations, which span the peak of the thermal spectral energy distribution, provide useful constraints on the properties of the dust and, ultimately, the circumstellar environment, explosion mechanism, and progenitor system. Due to the low SN IIn rate (
• France, K., McCray, R., Penton, S. V., Kirshner, R. P., Challis, P., Laming, J. M., Bouchet, P., Chevalier, R., Garnavich, P. M., Fransson, C., Heng, K., Larsson, J., Lawrence, S., Lundqvist, P., Panagia, N., S., C., Smith, N., Sollerman, J., Sonneborn, G., , Sugerman, B., et al. (2011). HST-COS observations of hydrogen, helium, carbon, and nitrogen emission from the SN 1987A reverse shock. Astrophysical Journal, 743(2).
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  Abstract: We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (Δv ∼ 300kms-1) emission lines from the circumstellar ring, broad (Δv ∼ 10-20 × 10 3kms-1) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise ratio (>40 per resolution element) broad Lyα emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at λ > 1350 can be explained by H I two-photon (2s 2 S 1/2-1s 2 S 1/2) emission from the same region. We confirm our earlier, tentative detection of N V λ1240 emission from the reverse shock and present the first detections of broad He II λ1640, C IV λ1550, and N IV] λ1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 0.06. The N V/Hα line ratio requires partial ion-electron equilibration (Te/Tp ≈ 0.14-0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring. © 2011. The American Astronomical Society. All rights reserved.
• Larsson, J., Fransson, C., Östlin, G., Gröningsson, P., Jerkstrand, A., Kozma, C., Sollerman, J., Challis, P., Kirshner, R. P., Chevalier, R. A., Heng, K., McCray, R., Suntzeff, N. B., Bouchet, P., Crotts, A., Danziger, J., Dwek, E., France, K., Garnavich, P. M., , Lawrence, S. S., et al. (2011). X-ray illumination of the ejecta of supernova 1987A. Nature, 474(7352), 484-486.
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  PMID: 21654749;Abstract: When a massive star explodes as a supernova, substantial amounts of radioactive elements - primarily 56 Ni, 57 Ni and 44 Ti - are produced. After the initial flash of light from shock heating, the fading light emitted by the supernova is due to the decay of these elements. However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium. The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellanic Cloud. From 1994 to 2001, the ejecta faded owing to radioactive decay of 44 Ti as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejecta, enabling us to analyse the structure and chemistry of the vanished star. © 2011 Macmillan Publishers Limited. All rights reserved.
• Lykou, F., Chesneau, O., Zijlstra, A. A., Castro-Carrizo, A., Lagadec, E., Balick, B., & Smith, N. (2011). A disc inside the bipolar planetary nebula M2-9. Astronomy and Astrophysics, 527(13).
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  Abstract: Aims. Bipolarity in proto-planetary and planetary nebulae is associated with events occurring in or around their cores. Past infrared observations have revealed the presence of dusty structures around the cores, many in the form of discs. Characterising those dusty discs provides invaluable constraints on the physical processes that govern the final mass expulsion of intermediate mass stars. We focus this study on the famous M2-9 bipolar nebula, where the moving lighthouse beam pattern indicates the presence of a wide binary. The compact and dense dusty core in the centre of the nebula can be studied by means of optical interferometry. Methods. M2-9 was observed with VLTI/MIDI at 39-47 m baselines with the UT2-UT3 and UT3-UT4 baseline configurations. These observations are interpreted using a dust radiative transfer Monte Carlo code. Results. A disc-like structure is detected perpendicular to the lobes, and a good fit is found with a stratified disc model composed of amorphous silicates. The disc is compact, 25 × 35 mas at 8 μm and 37 × 46 mas at 13 μm. For the adopted distance of 1.2 kpc, the inner rim of the disc is ∼15 AU. The mass represents a few percent of the mass found in the lobes. The compactness of the disc puts strong constraints on the binary content of the system, given an estimated orbital period 90-120 yr. We derive masses of the binary components between 0.6-1.0 M⊙ for a white dwarf and 0.6-1.4 M⊙ for an evolved star. We present different scenarios on the geometric structure of the disc accounting for the interactions of the binary system, which includes an accretion disc as well. © 2011 ESO.
• Povich, M. S., Smith, N., Majewski, S. R., Getman, K. V., Townsley, L. K., Babler, B. L., Broos, P. S., Indebetouw, R., Meade, M. R., Robitaille, T. P., Stassun, K. G., Whitney, B. A., Yonekura, Y., & Fukui, Y. (2011). A pan-carina young stellar object catalog: Intermediate-mass young stellar objects in the Carina Nebula identified via mid-infrared excess emission. Astrophysical Journal, Supplement Series, 194(1).
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  Abstract: We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M Ȯ < m ≲ 10 M Ȯ) objects with disks, including Herbig Ae/Be stars and their less evolved progenitors. The PCYC provides a valuable complementary data set to the CCCP X-ray source catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars. Candidate protostars with X-ray detections tend to be more evolved than those without. In most cases, X-ray emission apparently originating from intermediate-mass, disk-dominated YSOs is consistent with the presence of low-mass companions, but we also find that X-ray emission correlates with cooler stellar photospheres and higher disk masses. We suggest that intermediate-mass YSOs produce X-rays during their early pre-main-sequence evolution, perhaps driven by magnetic dynamo activity during the convective atmosphere phase, but this emission dies off as the stars approach the main sequence. Extrapolating over the stellar initial mass function scaled to the PCYC population, we predict a total population of >2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M Ȯyr-1. The global SFR in the Carina Nebula, averaged over the past 5Myr, has been approximately constant. © 2011. The American Astronomical Society. All rights reserved.
• Smith, N. (2011). Explosions triggered by violent binary-star collisions: Application to Eta Carinae and other eruptive transients. Monthly Notices of the Royal Astronomical Society, 415(3), 2020-2024.
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  Abstract: This paper discusses a scenario where a violent periastron collision of stars in an eccentric binary system induces an eruption or explosion seen as a brief transient source, attributed to luminous blue variables (LBVs), supernova (SN) impostors or other transients. The key ingredient is that an evolved primary increases its photospheric radius on relatively short (year to decade) time-scales, to a point where the radius is comparable to or larger than the periastron separation in an eccentric binary. In such a configuration, a violent and sudden collision would ensue, possibly leading to substantial mass ejection instead of a merger. Sudden energy deposition during the encounter could drive expansion of the optically thick envelope, causing a luminous transient source. Repeated periastral grazings in an eccentric system could quickly escalate to a catastrophic encounter. Outbursts triggered by tidal disturbances or powered by secondary accretion of the primary star's wind have been suggested previously. Instead, this paper proposes a much more violent encounter where the companion star plunges deep inside the photosphere of a bloated primary during periastron, as a result of the primary star increasing its own radius. This is motivated by the case of Eta Carinae, where such a collision must have occurred if conventional estimates of the present-day orbit are correct and where peaks in the light curve coincide with times of periastron. Stellar collisions may explain brief recurring LBV outbursts, such as SN2000ch and SN2009ip, and perhaps outbursts from intermediate-mass progenitor stars (i.e. collisions are not necessarily the exclusive domain of very luminous stars), but they cannot explain all non-SN transients. Finally, mass ejections induced repeatedly at periastron cause orbital evolution; this may explain the origin of eccentric Wolf-Rayet binaries such as WR140. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Smith, N., & Frew, D. J. (2011). A revised historical light curve of Eta Carinae and the timing of close periastron encounters. Monthly Notices of the Royal Astronomical Society, 415(3), 2009-2019.
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  Abstract: The historical light curve of the 19th century 'Great Eruption' of η Carinae provides a striking record of the violent instabilities encountered by massive stars. In this paper, we report and analyse newly uncovered historical estimates of the visual brightness of η Car during its eruption, and we correct some mistakes in the original record. The revised historical light curve looks substantially different from previous accounts; it shows two brief precursor eruptions in 1838 and 1843 that resemble modern supernova impostors, while the final brightening in 1844 December marks the time when η Car reached its peak brightness. We consider the timing of brightening events as they pertain to the binary system in η Car. (1) The brief 1838 and 1843 events rose to peak brightness within weeks of periastron passages if the pre-1845 orbital period was ∼5 per cent shorter than that at present due to the mass-loss of the eruption. Each event lasted only ∼100d. (2) The main brightening at the end of 1844 has no conceivable association with periastron, beginning suddenly more than 1.5yr after periastron. It lasted ∼10yr, with no obvious influence of periastron encounters during that time. (3) The 1890 eruption began to brighten at periastron, but took over 1yr to reach maximum brightness and remained there for almost 10yr. A second periastron passage mid-way through the 1890 eruption had no visible effect. While the evidence for a link between periastron encounters and the two brief precursor events is compelling, the differences between the three cases above make it difficult to explain all three phenomena with the same mechanism. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Smith, N., Cenko, S. B., Butler, N., Bloom, J. S., Kasliwal, M. M., Horesh, A., Kulkarni, S. R., Law, N. M., Nugent, P. E., Ofek, E. O., Poznanski, D., Quimby, R. M., Sesar, B., Ben-Ami, S., Arcavi, I., Gal-Yam, A., Polishook, D., Dong, X. u., Yaron, O., , Frail, D. A., et al. (2011). SN 2010jp (PTF10aaxi): A jet-driven type II supernova. Proceedings of the International Astronomical Union, 7(S279), 159-166.
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  Abstract: We present photometry and spectroscopy of the peculiar Type II supernova SN 2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a relatively low peak absolute magnitude of only-15.9 (unfiltered), and a low radioactive decay luminosity at late times that suggests a low synthesized nickel mass of about 0.003 M · or less. Spectra of SN 2010jp display an unprecedented triple-peaked Hα line profile, showing: (1) a narrow central component that suggests shock interaction with a dense circumstellar medium (CSM); (2) high-velocity blue and red emission features centered at-12,600 and +15,400 km s -1; and (3) very broad wings extending from-22,000 to +25,000 km s -1. We propose that this line profile indicates a bipolar jet-driven explosion, with the central component produced by normal SN ejecta and CSM interaction at mid and low latitudes, while the high-velocity bumps and broad line wings arise in a nonrelativistic bipolar jet. Jet-driven SNe II are predicted for collapsars resulting from a wide range of initial masses above 25 M ·, especially at the sub-solar metallicity consistent with the SN host environment. It also seems consistent with the apparently low 56Ni mass that may accompany black hole formation. We speculate that the jet survives to produce observable signatures because the star's H envelope was very low mass, having been mostly stripped away by the previous eruptive mass loss. © 2012 International Astronomical Union.
• Smith, N., Gehrz, R. D., Campbell, R., Kassis, M., Mignant, D. L., Kuluhiwa, K., & Filippenko, A. V. (2011). Episodic mass loss in binary evolution to the Wolf-Rayet phase: Keck and HST proper motions of RY Scuti's nebula. Monthly Notices of the Royal Astronomical Society, 418(3), 1959-1972.
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  Abstract: Binary mass transfer via -Roche lobe overflow (RLOF) is a key channel for producing stripped-envelope Wolf-Rayet (WR) stars and may be critical to account for Type Ib/c supernova progenitors. RY Scuti is an extremely rare example of a massive binary star caught in this brief but important phase. Its unusual toroidal nebula indicates equatorial mass loss during RLOF, while the mass-gaining star is apparently embedded in an opaque accretion disc. RY Scuti's toroidal nebula has two components: an inner ionized double-ring system, and an outer dust torus that is roughly twice the size of the ionized rings. We present two epochs of L-band Keck natural guide star adaptive optics (NGS-AO) images of the dust torus, plus three epochs of Hubble Space Telescope (HST) images of the ionized gas rings. Proper motions show that the inner ionized rings and the outer dust torus, while having similar geometry, came from two separate ejection events roughly 130 and 250 yr ago. This suggests that WR star formation via RLOF in massive contact binaries can be accompanied by eruptive and episodic bursts of mass loss, reminiscent of luminous blue variables (LBVs). We speculate that the repeating outbursts may arise in the mass gainer from instabilities associated with a high accretion rate. In the case of RY Scuti, we know of no historical evidence that either of its mass-loss events were observed as luminous outbursts, but if discrete mass-loss episodes in other RLOF binaries are accompanied by luminous outbursts, they might contribute to the population of extragalactic optical transients. When RLOF ends for RY Scuti, the overluminous mass gainer, currently surrounded by an accretion disc, will probably become a B[e] supergiant and may outshine the hotter stripped-envelope mass-donor star that should die as a Type Ib/c supernova. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Smith, N., Weidong, L. i., Filippenko, A. V., & Chornock, R. (2011). Observed fractions of core-collapse supernova types and initial masses of their single and binary progenitor stars. Monthly Notices of the Royal Astronomical Society, 412(3), 1522-1538.
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  Abstract: We analyse the observed fractions of core-collapse supernova (SN) types from the Lick Observatory Supernova Search (LOSS), and we discuss the corresponding implications for massive star evolution. For a standard initial mass function, observed fractions of SN types cannot be reconciled with the expectations of single-star evolution. The mass range of Wolf-Rayet (WR) stars that shed their hydrogen envelopes via their own mass-loss accounts for less than half of the observed fraction of Type Ibc supernovae (SNe Ibc). The true progenitors of SNe Ibc must extend to a much lower range of initial masses than classical WR stars, and we argue that most SN Ibc and SN IIb progenitors must arise from binary Roche lobe overflow. In this scenario, SNe Ic would still trace higher initial mass and metallicity, because line-driven winds in the WR stage remove the helium layer and propel the transition from SN Ib to Ic. Less massive progenitors of SNe Ib and IIb may not be classical WR stars; they may be underluminous with weak winds, possibly hidden by overluminous mass-gainer companions that could appear as B[e] supergiants or related objects having aspherical circumstellar material. The remaining SN types (II-P, II-L and IIn) need to be redistributed across the full range of initial masses, so that even some very massive single stars retain H envelopes until explosion. We consider the possibility of direct collapse to black holes without visible SNe, but find this hypothesis difficult to accommodate in most scenarios. Major areas of remaining uncertainty are (1) the detailed influence of binary separation, rotation and metallicity; (2) mass differences in progenitors of SNe IIn compared to SNe II-L and II-P; and (3) the fraction of SNe Ic arising from single stars with the help of eruptive mass-loss, how this depends on metallicity and how it relates to diversity within the SN Ic subclass. Continued studies of progenitor stars and their environments in nearby galaxies, accounting for SN types, may eventually test these ideas. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Smith, N., Weidong, L. i., Miller, A. A., Silverman, J. M., Filippenko, A. V., Cuillandre, J., Cooper, M. C., Matheson, T., & D., S. (2011). A massive progenitor of the luminous type IIn supernova 2010jl. Astrophysical Journal, 732(2).
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  Abstract: The bright, nearby, recently discovered supernova (SN) 2010jl is a luminous Type IIn SN. Here, we report archival Hubble Space Telescope (HST) observations of its host galaxy UGC 5189A taken roughly 10yr prior to explosion, as well as early-time optical spectra of the SN. The HST images reveal a luminous, blue point source at the position of the SN, with an absolute magnitude of -12.0 in the F300W filter. If it is not just a chance alignment, the source at the SN position could be (1) a massive young (
• Smith, N., Weidong, L. i., Silverman, J. M., Ganeshalingam, M., & Filippenko, A. V. (2011). Luminous blue variable eruptions and related transients: Diversity of progenitors and outburst properties. Monthly Notices of the Royal Astronomical Society, 415(1), 773-810.
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  Abstract: We present new light curves and optical spectra for a number of extragalactic optical transients or 'supernova impostors' related to giant eruptions of luminous blue variables (LBVs), and we provide a comparative discussion of LBV-like giant eruptions known thus far. New data include photometry and spectroscopy of supernovae (SNe) 1999bw, 2000ch, 2001ac, 2002bu, 2006bv and 2010dn. SN 2010dn appears to be a carbon copy of SN 2008S and NGC 300-OT, whereas SN 2002bu shows spectral evolution from a normal LBV at early times to a twin of these cooler transients at late times. SN 2008S, NGC 300-OT and SN 2010dn appear to be special cases of a broader eruptive phenomenon where the progenitor star was enshrouded by dust, perhaps from a previous unseen eruptive episode. Evidence suggests that their progenitors have initial masses in the range 10-20M⊙, extending the range of masses susceptible to the violent eruptive phenomenon below the canonical LBV mass range. Examining the full sample, SN impostors are characterized by strong photometric variability on a range of time-scales from a day to decades, potentially suffering multiple eruptions of the same source. The upper end of the luminosity distribution overlaps with the least-luminous core-collapse SNe, but in most cases a distinction can be made based on spectra. The low end of the luminosity distribution is far less well defined, and a distinction between LBV giant eruptions, S Doradus phases of LBVs, novae and possible eruptions of intermediate-mass stars is not entirely clear. We discuss observational clues concerning stellar winds or shocks as the relevant mass-loss mechanism, and we evaluate possible ideas for the physical mechanisms of outbursts, but there is still a great need for theoretical work on this problem. Although known examples of these eruptions are sufficient to illustrate their remarkably wide diversity in the peak absolute magnitude, duration, progenitor stars, outburst spectra and other observable properties, their statistical distribution is an area that will benefit greatly from current and upcoming transient surveys. Based on the distribution of these eruptive properties, we propose that the prototypical object SN 1961V was not a member of this class of impostors after all, but was instead a true core-collapse Type IIn SN that was preceded by a giant LBV eruption. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Townsley, L. K., Broos, P. S., Corcoran, M. F., Feigelson, E. D., Gagné, M., Montmerle, T., Oey, M. S., Smith, N., Garmire, G. P., Getman, K. V., Povich, M. S., Evans, N. R., Nazé, Y., Parkin, E. R., Preibisch, T., Wang, J., Wolk, S. J., Chu, Y., Cohen, D. H., , Gruendl, R. A., et al. (2011). An introduction to the Chandra Carina Complex Project. Astrophysical Journal, Supplement Series, 194(1).
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  Abstract: The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of >14,000 X-ray point sources; >9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results. © 2011. The American Astronomical Society. All rights reserved.
• Weidong, L. i., Leaman, J., Chornock, R., Filippenko, A. V., Poznanski, D., Ganeshalingam, M., Wang, X., Modjaz, M., Jha, S., Foley, R. J., & Smith, N. (2011). Nearby supernova rates from the Lick Observatory Supernova Search - II. The observed luminosity functions and fractions of supernovae in a complete sample. Monthly Notices of the Royal Astronomical Society, 412(3), 1441-1472.
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  Abstract: This is the second paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). In this paper, a complete SN sample is constructed, and the observed (uncorrected for host-galaxy extinction) luminosity functions (LFs) of SNe are derived. These LFs solve two issues that have plagued previous rate calculations for nearby SNe: the luminosity distribution of SNe and the host-galaxy extinction. We select a volume-limited sample of 175 SNe, collect photometry for every object and fit a family of light curves to constrain the peak magnitudes and light-curve shapes. The volume-limited LFs show that they are not well represented by a Gaussian distribution. There are notable differences in the LFs for galaxies of different Hubble types (especially for SNe Ia). We derive the observed fractions for the different subclasses in a complete SN sample, and find significant fractions of SNe II-L (10 per cent), IIb (12 per cent) and IIn (9 per cent) in the SN II sample. Furthermore, we derive the LFs and the observed fractions of different SN subclasses in a magnitude-limited survey with different observation intervals, and find that the LFs are enhanced at the high-luminosity end and appear more 'standard' with smaller scatter, and that the LFs and fractions of SNe do not change significantly when the observation interval is shorter than 10d. We also discuss the LFs in different galaxy sizes and inclinations, and for different SN subclasses. Some notable results are that there is not a strong correlation between the SN LFs and the host-galaxy size, but there might be a preference for SNe IIn to occur in small, late-type spiral galaxies. The LFs in different inclination bins do not provide strong evidence for extreme extinction in highly inclined galaxies, though the sample is still small. The LFs of different SN subclasses show significant differences. We also find that SNe Ibc and IIb come from more luminous galaxies than SNe II-P, while SNe IIn come from less luminous galaxies, suggesting a possible metallicity effect. The limitations and applications of our LFs are also discussed. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Elias-Rosa, N., D., S., Weidong, L. i., Morrell, N., Gonzalez, S., Hamuy, M., Filippenko, A. V., Cuillandre, J., Foley, R. J., & Smith, N. (2010). Erratum: On the progenitor of the type II-plateau SN 2008cn in NGC 4603 (ApJ (2009) 706 (1174)). Astrophysical Journal Letters, 711(2), 1343-.
• France, K., McCray, R., Heng, K., Kirshner, R. P., Challis, P., Bouchet, P., Crotts, A., Dwek, E., Fransson, C., Garnavich, P. M., Larsson, J., Lawrence, S. S., Lundqvist, P., Panagia, N., S., C., Smith, N., Sollerman, J., Sonneborn, G., Stocke, J. T., , Wang, L., et al. (2010). Observing supernova 1987A with the refurbished hubble space telescope. Science, 329(5999), 1624-1627.
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  PMID: 20813921;Abstract: Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 with the use of the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Lyα and Hα lines from shock emission continue to brighten, whereas their maximum velocities continue to decrease. We observe broad, blueshifted Lyα, which we attribute to resonant scattering of photons emitted from hot spots on the equatorial ring. We also detect N v λλ1239, 1243 angstrom line emission, but only to the red of Lyα. The profiles of the N v lines differ markedly from that of Hα, suggesting that the N4+ ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock.
• Jan, A., Smith, N., Owocki, S. P., & Veelen, B. v. (2010). Numerical models of collisions between core-collapse supernovae and circumstellar shells. Monthly Notices of the Royal Astronomical Society, 407(4), 2305-2327.
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  Abstract: Recent observations of luminous Type IIn supernovae (SNe) provide compelling evidence that massive circumstellar shells surround their progenitors. In this paper we investigate how the properties of such shells influence the SN light curve by conducting numerical simulations of the interaction between an expanding SN and a circumstellar shell ejected a few years prior to core collapse. Our parameter study explores how the emergent luminosity depends on a range of circumstellar shell masses, velocities, geometries and wind mass-loss rates, as well as variations in the SN mass and energy. We find that the shell mass is the most important parameter, in the sense that higher shell masses (or higher ratios of Mshell/MSN) lead to higher peak luminosities and higher efficiencies in converting shock energy into visual light. Lower mass shells can also cause high peak luminosities if the shell is slow or if the SN ejecta are very fast, but only for a short time. Sustaining a high luminosity for durations of more than 100 d requires massive circumstellar shells of the order of 10 MȮ or more. This reaffirms previous comparisons between pre-SN shells and shells produced by giant eruptions of luminous blue variables (LBVs), although the physical mechanism responsible for these outbursts remains uncertain. The light-curve shape and observed shell velocity can help diagnose the approximate size and density of the circumstellar shell, and it may be possible to distinguish between spherical and bipolar shells with multi-wavelength light curves. These models are merely illustrative. One can, of course, achieve even higher luminosities and longer duration light curves from interaction by increasing the explosion energy and shell mass beyond values adopted here. © 2010 The Authors. Journal compilation. © 2010 RAS.
• Miller, A. A., Silverman, J. M., Butler, N. R., Bloom, J. S., Chornock, R., Filippenko, A. V., Ganeshalingam, M., Klein, C. R., Li, W., Nugent, P. E., Smith, N., & Steele, T. N. (2010). SN 2008iy: An unusual Type IIn Supernova with an enduring 400-d rise time. Monthly Notices of the Royal Astronomical Society, 404(1), 305-317.
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  Abstract: We present spectroscopic and photometric observations of the Type IIn supernova (SN) 2008iy. SN 2008iy showed an unprecedentedly long rise time of ~400 d, making it the first known SN to take significantly longer than 100 d to reach peak optical luminosity. The peak absolute magnitude of SN 2008iy was Mr ≈ -19.1 mag, and the total radiated energy over the first ~700 d was ~2 × 1050 erg. Spectroscopically, SN 2008iy is very similar to the Type IIn SN 1988Z at late times and, like SN 1988Z, it is a luminous X-ray source (both SNe had an X-ray luminosity LX > 1041 erg s-1). SN 2008iy has a growing near-infrared excess at late times similar to several other SNe IIn. The Hα emission-line profile of SN 2008iy shows a narrow P Cygni absorption component, implying a pre-SN wind speed of ~100 km s-1. We argue that the luminosity of SN 2008iy is powered via the interaction of the SN ejecta with a dense, clumpy circumstellar medium. The ~400-d rise time can be understood if the number density of clumps increases with distance over a radius ~1.7 × 1016 cm from the progenitor. This scenario is possible if the progenitor experienced an episodic phase of enhanced mass loss
• Miller, A. A., Smith, N., Li, W., Bloom, J. S., Chornock, R., Filippenko, A. V., & Prochaska, J. X. (2010). New observations of the very luminous supernova 2006gy: Evidence for echoes. Astronomical Journal, 139(6), 2218-2229.
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  Abstract: Supernova (SN) 2006gy was a hydrogen-rich core-collapse SN that remains one of the most luminous optical SNe ever observed. The total energy budget (>2 × 1051erg radiated in the optical alone) poses many challenges for standard SN theory. We present new ground-based near-infrared (NIR) observations of SN 2006gy, as well as a single epoch of Hubble Space Telescope (HST) imaging obtained more than two years after the explosion. Our NIR data taken around peak optical emission show an evolution that is largely consistent with a cooling blackbody, with tentative evidence for a growing NIR excess starting around day ∼130. Our late-time Keck adaptive optics NIR image, taken on day 723, shows little change from previous NIR observations taken around day 400. Furthermore, the optical HST observations show a reduced decline rate after day 400, and the SN is bluer on day 810 than it was at peak. This late-time decline is inconsistent with 56Co decay, and thus is problematic for the various pair-instability SN models used to explain the nature of SN 2006gy. The slow decline of the NIR emission can be explained with a light echo, and we confirm that the late-time NIR excess is the result of a massive (≳10 M ̇) dusty shell heated by the SN peak luminosity. The late-time optical observations require the existence of a scattered light echo, which may be generated by the same dust that contributes to the NIR echo. Both the NIR and optical echoes originate in the proximity of the progenitor, ∼1018cm for the NIR echo and ≲10-40 pc for the optical echo, which provides further evidence that the progenitor of SN 2006gy was a very massive star. © 2010. The American Astronomical Society. All rights reserved.
• Raga, A. C., Lora, V., & Smith, N. (2010). HH jets aligned perpendicular to elephant trunks. Revista Mexicana de Astronomia y Astrofisica, 46(1), 179-184.
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  Abstract: We consider a system of outflows ejected from low mass young stars embedded in the tips of elephant trunks. We assume that these outflows have axes which are intrinsically perpendicular to the axes of the host elephant trunks. We then derive the distribution function expected for the angle between the projections of the outflow and elephant trunk axes on the plane of the sky. These distribution functions are useful for interpreting the alignments (or lack thereof) observed between HH outflow and elephant trunk axes in photoionized regions. © Copyright 2010: Instituto de Astronomía, Universidad Nacional Autónoma de México.
• Scowen, P. A., Jansen, R. H., Beasley, M. N., Calzetti, D., Desch, S., Fullerton, A. W., S., J., Lisman, P. D., Macenka, S. A., Malhotra, S., McCaughrean, M. J., Nikzad, S., O'Connell, R. W., Oey, S., Padgett, D. L., Rhoads, J. E., Roberge, A., H., O., Shaklan, S. B., , Smith, N., et al. (2010). Design and implementation of the NUV/optical widefield Star Formation Camera for the Theia observatory. Proceedings of SPIE - The International Society for Optical Engineering, 7731.
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  Abstract: The Star Formation Camera (SFC) is a wide-field (~19'×15', >280 arcmin2), high-resolution (18 mas pixels) UV/optical dichroic camera designed for the Theia 4-m space-borne space telescope concept. SFC will deliver diffraction-limited images at λ > 300 nm in both a blue (190-517nm) and a red (517-1075nm) channel simultaneously. The goal is to conduct a comprehensive and systematic study of the astrophysical processes and environments relevant for the births and life cycles of stars and their planetary systems, and to investigate the range of environments, feedback mechanisms, and other factors that most affect the outcome of star and planet formation. © 2010 SPIE.
• Smith, N. (2010). Episodic post-shock dust formation in the colliding winds of Eta Carinae. Monthly Notices of the Royal Astronomical Society, 402(1), 145-151.
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  Abstract: Eta Carinae shows broad peaks in near-infrared (IR) JHKL photometry, roughly correlated with times of periastron passage in the eccentric binary system. After correcting for secular changes attributed to reduced extinction from the thinning Homunculus nebula, these peaks have IR spectral energy distributions (SEDs) consistent with emission from hot dust at 1400-1700 K. The excess SEDs are clearly inconsistent, however, with the excess being entirely due to free-free wind or photospheric emission. One must conclude, therefore, that the broad near-IR peaks associated with Eta Carinae's 5.5 yr variability are due to thermal emission from hot dust. I propose that this transient hot dust results from episodic formation of grains within compressed post-shock zones of the colliding winds, analogous to the episodic dust formation in Wolf-Rayet (WR) binary systems like WR 140 or the post-shock dust formation seen in some supernovae like SN 2006jc. This dust formation in Eta Carinae seems to occur preferentially near and after periastron passage; near-IR excess emission then fades as the new dust disperses and cools. With the high grain temperatures and Eta Car's C-poor abundances, the grains are probably composed of corundum or similar species that condense at high temperatures, rather than silicates or graphite. Episodic dust formation in Eta Car's colliding winds significantly impacts our understanding of the system, and several observable consequences are discussed. © 2009 The Author. Journal compilation © 2009 RAS.
• Smith, N. (2010). Eruptive outflow phases of massive stars. Proceedings of the International Astronomical Union, 6(S272), 571-580.
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  Abstract: I review recent progress on understanding eruptions of unstable massive stars, with particular attention to the diversity of observed behavior in extragalatic optical transient sources that are generally associated with giant eruptions of luminous blue variables (LBVs). These eruptions are thought to represent key mass loss episodes in the lives of massive stars. I discuss the possibility of dormant LBVs and implications for the duration of the greater LBV phase and its role in stellar evolution. These eruptive variables show a wide range of peak luminosity, decay time, expansion speeds, and progenitor luminosity, and in some cases they have been observed to suffer multiple eruptions. This broadens our view of massive star eruptions compared to prototypical sources like Eta Carinae, and provides important clues for the nature of the outbursts. I will also review and discuss some implications about the possible physical mechanisms involved, although the cause of the eruptions is not yet understood. © International Astronomical Union 2011.
• Smith, N., Bally, J., & Walborn, N. R. (2010). HST/ACS Hα imaging of the Carina Nebula: Outflow activity traced by irradiated Herbig-Haro Jets. Monthly Notices of the Royal Astronomical Society, 405(2), 1153-1186.
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  Abstract: We report the discovery of new Herbig-Haro (HH) jets in the Carina Nebula, and we discuss the protostellar outflow activity of a young OB association. These are the first results of an Hα imaging survey of Carina conducted with the Hubble Space Telescope (HST)/Advanced Camera for Surveys. Adding to the one previously known example (HH 666), we detect 21 new HH jets, plus 17 new candidate jets, ranging in length from 0.005 to 3 pc. Using the Hα emission measure to estimate jet densities, we derive jet mass-loss rates ranging from 8 × 10-9 to ∼10-6 M⊙ yr-1, but a comparison to the distribution of jet mass-loss rates in Orion suggests that we may be missing a large fraction of the jets below 10-8 M⊙ yr-1. A key qualitative result is that even some of the smallest dark globules with sizes of ≲1 arcsec (0.01 pc) are active sites of ongoing star formation because we see HH jets emerging from them, and that these offer potential analogues to the cradle of our Solar system because of their proximity to dozens of imminent supernovae that will enrich them with radioactive nuclides like 60Fe. Although most proplyd candidates identified from ground-based data are dark cometary globules, HST images now reveal proplyd structures in the core of the Tr 14 cluster, only 0.1-0.2 pc from several extreme O-type stars. Throughout Carina, some HH jets have axes bent away from nearby massive stars, while others show no bend, and still others are bent toward the massive stars. These jet morphologies serve as 'wind socks'; strong photoevaporative flows can shape the jets, competing with the direct winds and radiation from massive stars. We find no clear tendency for jets to be aligned perpendicular to the axes of dust pillars. Finally, even allowing for a large number of jets that may escape detection, we find that HH jets are negligible to the global turbulence of the surrounding region, which is driven by massive star feedback. © 2010 The Authors. Journal compilation © 2010 RAS.
• Smith, N., Miller, A., Weidong, L. i., Filippenko, A. V., Silverman, J. M., Howard, A. W., Nugent, P., Marcy, G. W., Bloom, J. S., Ghez, A. M., Jessica, L. u., Yelda, S., Bernstein, R. A., & Colucci, J. E. (2010). Discovery of precursor luminous blue variable outbursts in two recent optical transients: The fitfully variable missing links UGC 2773-ot and SN 2009ip. Astronomical Journal, 139(4), 1451-1467.
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  Abstract: We present progenitor-star detections, light curves, and optical spectra of supernova (SN) 2009ip and the 2009 optical transient in UGC 2773 (U2773-OT), which were not genuine SNe. Precursor variability in the decade before outburst indicates that both of the progenitor stars were luminous blue variables (LBVs). Their pre-outburst light curves resemble the S Doradus phases that preceded giant eruptions of the prototypical LBVs η Carinae and SN 1954J (V12 in NGC 2403), with intermediate progenitor luminosities. Hubble Space Telescope detections a decade before discovery indicate that the SN 2009ip and U2773-OT progenitors were supergiants with likely initial masses of 50-80 M · and ≳20 M ·, respectively. Both outbursts had spectra befitting known LBVs, although in different physical states. SN 2009ip exhibited a hot LBV spectrum with characteristic speeds of 550 km s-1, plus evidence for faster material up to 5000 km s -1, resembling the slow Homunculus and fast blast wave of η Carinae. In contrast, U2773-OT shows a forest of narrow absorption and emission lines comparable to that of S Dor in its cool state, plus [Ca II] emission and an infrared excess indicative of dust, similar to SN 2008S and the 2008 optical transient in NGC 300 (N300-OT). The [Ca II] emission is probably tied to a dusty pre-outburst environment, and is not a distinguishing property of the outburst mechanism. The LBV nature of SN 2009ip and U2773-OT may provide a critical link between historical LBV eruptions, while U2773-OT may provide a link between LBVs and the unusual dust-obscured transients SN 2008S and N300-OT. Future searches will uncover more examples of precursor LBV variability of this kind, providing key clues that may help unravel the instability driving LBV eruptions in massive stars. © 2010. The American Astronomical Society. All rights reserved.
• Smith, N., Povich, M. S., Whitney, B. A., Churchwell, E., Babler, B. L., Meade, M. R., Bally, J., Gehrz, R. D., Robitaille, T. P., & Stassun, K. G. (2010). Spitzer space telescope observations of the Carina nebula: The steady march of feedback-driven star formation. Monthly Notices of the Royal Astronomical Society, 406(2), 952-974.
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  Abstract: We report the first results of imaging the Carina nebula (NGC 3372) with the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope, providing a photometry catalogue of over 44 000 point sources as well as a catalogue of over 900 candidate young stellar objects (YSOs) based on fits to their spectral energy distributions (SEDs). We discuss several aspects of the extended emission, including the structure of dozens of dust pillars that result when a clumpy molecular cloud is shredded by feedback from massive stars. There are surprisingly few of the 'extended green objects' (EGOs) that are normally taken as signposts of outflow activity in Spitzer data, and not one of the dozens of Herbig-Haro jets detected optically are seen as EGOs. EGOs are apparently poor tracers of outflow activity in strongly irradiated environments, due to the effects of massive star feedback. A population of 'extended red objects' tends to be found around late O-type and early B-type stars, some with clear bow-shock morphology. These are dusty shocks where stellar winds collide with photoevaporative flows off nearby clouds. Finally, the relative distributions of O-type stars, small star clusters and subclusters of YSOs as compared to the dust pillars show that while some YSOs are located within dust pillars, many more stars and YSOs reside just outside pillar heads. We suggest that pillars are transient phenomena, part of a continuous outwardly propagating wave of star formation driven by feedback from massive stars. As the pillars are destroyed, they leave newly formed stars in their wake, and these are then subsumed into the young OB association. The YSOs are found predominantly in the cavity between pillars and massive stars, arguing that their formation was in fact triggered. Altogether, the current generation of YSOs shows no strong deviation from a normal initial mass function (IMF). The number of YSOs is consistent with a roughly constant star-formation rate over the past ∼3 Myr, implying that propagating star formation in pillars constitutes an important mechanism to construct unbound OB associations. These accelerated pillars may give birth to massive O-type stars that, after several million years, could appear to have formed in isolation. © 2010 The Authors. Journal compilation © 2010 RAS.
• Elias-Rosa, N., D., S., Weidong, L. i., Morrell, N., Gonzalez, S., Hamuy, M., Filippenko, A. V., Cuillandre, J., Foley, R. J., & Smith, N. (2009). On the progenitor of the type II-plateau SN 2008cn in NGC 4603. Astrophysical Journal Letters, 706(2), 1174-1183.
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  Abstract: A trend is emerging regarding the progenitor stars that give rise to the most common core-collapse supernovae (SNe), those of Type II-Plateau (II-P): they generally appear to be red supergiants with a limited range of initial masses, ∼8-16 M·. Here, we consider another example, SN 2008cn, in the nearly face-on spiral galaxy NGC4603. Even with limited photometric data, it appears that SN 2008cn is not a normal SN II-P, but is of the high-luminosity subclass. Through comparison of pre- and post-explosion images obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope, we have isolated a supergiant star prior to explosion at nearly the same position as the SN. We provide evidence that this supergiant may well be the progenitor of the SN, although this identification is not entirely unambiguous. This is exacerbated by the distance to the host galaxy, 33.3 Mpc, making SN 2008cn the most distant SN II-P yet for which an attempt has been made to identify a progenitor star in pre-SN images. The progenitor candidate has a more yellow color ([V - I]0 = 0.98 mag and Teff = 5200 300 K) than generally would be expected and, if a single star, would require that it exploded during a "blue loop" evolutionary phase, which is theoretically not expected to occur. Nonetheless, we estimate an initial mass of Mini = 15 ±2 · for this star, which is within the expected mass range for SN II-P progenitors. The yellower color could also arise from the blend of two or more stars, such as a red supergiant and a brighter, blue supergiant. Such a red supergiant hidden in this blend could instead be the progenitor and would also have an initial mass within the expected progenitor mass range. Furthermore, the yellow supergiant could be in a massive, interacting binary system, analogous to the possible yellow supergiant progenitor of the high-luminosity SN II-P 2004et. Finally, if the yellow supergiant is not the progenitor, or is not a stellar blend or binary containing the progenitor, then we constrain any undetected progenitor star to be a red supergiant with Mini ≲ 11 M·, considering a physically more realistic scenario of explosion at the model endpoint luminosity for a rotating star. © 2009. The American Astronomical Society. All rights reserved.
• Harper, G. M., Carpenter, K. G., Ryde, N., Smith, N., Brown, J., Brown, A., & Hinkle, K. H. (2009). UV, IR, and MM studies of CO surrounding the red supergiant α orionis (M2 Iab). AIP Conference Proceedings, 1094, 868-871.
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  Abstract: Carbon monoxide has been detected in Betelgeuse's ultraviolet (electronic), infrared (vibrational), and mm-radio (rotational) spectra, but its spatial distribution has remained elusive. We have obtained new mm-radio interferometry (CARMA), infrared spatially-resolved spectra (Phoenix/Gemini-South), and we have performed non-LTE simulations to help establish the spatial location of the S1 (V = 10km/s) and S2 (V = 17km/s) CO shells. The strong CO Fourth-Positive ultraviolet scattering signature is apparent in the HST GHRS G140L spectrum and the S1 and S2 shells account for much of the UV opacity. Phoenix spectra reveal that the low velocity S1 shell is present at 1.5arcsec West of the star and extends out to ∼4arcsec, and its mm-radio emission appears to originate within an 6 arcsec radius. The interpretation of the S2 shell is less clear. The Phoenix spectra tentatively suggest that the S2 shell extends to ∼7 arcsec. The CARMA channel maps show an additional strong narrow emission component 5 arcsec from the star, but the spectra do not show all the expected S1 and S2 signatures. Future CARMA observations should help to disentangle the signature of the S1 and S2 shells. © 2009 American Institute of Physics.
• Miller, A. A., Chornock, R., Perley, D. A., Ganeshalingam, M., Li, W., Butler, N. R., Bloom, J. S., Smith, N., Modjaz, M., Poznanski, D., Filippenko, A. V., Griffith, C. V., Shiode, J. H., & Silverman, J. M. (2009). The exceptionally luminous type II-linear supernova 2008es. Astrophysical Journal Letters, 690(2), 1303-1312.
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  Abstract: We report on our early photometric and spectroscopic observations of the extremely luminous Type II supernova (SN) 2008es. SN 2008es, with an observed peak optical magnitude of mV = 17.8 and at a redshift z = 0.213, has a peak absolute magnitude of MV = -22.3, making it the second most luminous SN ever observed. The photometric evolution of SN 2008es exhibits a fast decline rate ( 0.042 mag d-1), similar to the extremely luminous Type II-Linear (II-L) SN 2005ap. We show that SN 2008es spectroscopically resembles the luminous Type II-L SN 1979C. Although the spectra of SN 2008es lack the narrow and intermediate-width line emission typically associated with the interaction of an SN with the circumstellar medium of its progenitor star, we argue that the extreme luminosity of SN 2008es is powered via strong interaction with a dense, optically thick circumstellar medium. The integrated bolometric luminosity of SN 2008es yields a total radiated energy at ultraviolet and optical wavelengths of ≳ 1051 erg. Finally, we examine the apparently anomalous rate at which the Texas Supernova Search has discovered rare kinds of SNe, including the five most luminous SNe observed to date, and find that their results are consistent with those of other modern SN searches. © 2009. The American Astronomical Society. All rights reserved.
• Poznanski, D., Butler, N., Filippenko, A. V., Ganeshalingam, M., Weidong, L. i., Bloom, J., Chornock, R., Foley, R. J., Nugent, P. E., Silverman, J. M., Cenko, S. B., Gates, E. L., Leonard, D. C., Miller, A. A., Modjaz, M., J., F., Smith, N., Swift, B. J., & Wong, D. S. (2009). Improved standardization of type II-P supernovae: Application to an expanded sample. Astrophysical Journal Letters, 694(2), 1067-1079.
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  Abstract: In the epoch of precise and accurate cosmology, cross-confirmation using a variety of cosmographic methods is paramount to circumvent systematic uncertainties. Owing to progenitor histories and explosion physics differing from those of Type Ia supernovae (SNeIa), Type II-plateau supernovae (SNeII-P) are unlikely to be affected by evolution in the same way. Based on a new analysis of 17 SNeII-P, and on an improved methodology, we find that SNeII-P are good standardizable candles, almost comparable to SNeIa. We derive a tight Hubble diagram with a dispersion of 10% in distance, using the simple correlation between luminosity and photospheric velocity introduced by Hamuy and Pinto. We show that the descendent method of Nugent etal. can be further simplified and that the correction for dust extinction has low statistical impact. We find that our SN sample favors, on average, a very steep dust law with total to selective extinction RV < 2. Such an extinction law has been recently inferred for many SNeIa. Our results indicate that a distance measurement can be obtained with a single spectrum of a SNII-P during the plateau phase combined with sparse photometric measurements. © 2009. The American Astronomical Society. All rights reserved.
• Smith, N., Ganeshalingam, M., Chornock, R., Filippenko, A. V., Weidong, L. i., Silverman, J. M., Steele, T. N., Griffith, C. V., Joubert, N., Lee, N. Y., Lowe, T. B., Mobberley, M. P., & Winslow, D. M. (2009). SN 2008S: A cool super-eddington wind in a supernova impostor. Astrophysical Journal Letters, 697(1 PART 2), L49-L53.
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  Abstract: We present visual-wavelength photometry and spectroscopy of supernova (SN) 2008S. Based on the low peak luminosity for a SN of MR = -13.9 mag, photometric and spectral evolution unlike that of low-luminosity SNe, a late-time decline rate slower than 56Co decay, and slow outflow speeds of 600-1000 km s-1, we conclude that SN 2008S is not a true core-collapse SN and is probably not an electron-capture SN. Instead, we show that SN 2008S more closely resembles an "SN impostor" event like SN 1997bs, analogous to the giant eruptions of luminous blue variables (LBVs). Its total radiated energy was 1047.8 erg, and it may have ejected 0.05-0.2 M in the event. We discover an uncanny similarity between the spectrum of SN 2008S and that of the Galactic hypergiant IRC+10420, which is dominated by narrow Hα, [Ca II], and Ca II emission lines formed in an opaque wind. We propose a scenario where the vastly super-Eddington (Γ 40) wind of SN 2008S partly fails because of reduced opacity due to recombination, as suggested for IRC+10420. The range of initial masses susceptible to eruptive LBV-like mass loss was known to extend down to 20-25 M, but estimates for the progenitor of SN 2008S (and the similar NGC 300 transient) may extend this range to ≲15 M. As such, SN 2008S may have implications for the progenitor of SN 1987A. © 2009. The American Astronomical Society. All rights reserved.
• Smith, N., Hinkle, K. H., & Ryde, N. (2009). Red supergiants as potential type IIn supernova progenitors: Spatially resolved 4.6 μm CO emission aroung VY CMa and betelgeuse. Astronomical Journal, 137(3), 3558-3573.
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  Abstract: We present high-resolution 4.6 μm CO spectra of the circumstellar environments of two red supergiants (RSGs) that are potential supernova (SN) progenitors: Betelgeuse and VY Canis Majoris (VY CMa). Around Betelgeuse, 12CO emission within 3″ (12 km s-1) follows a mildly clumpy but otherwise spherical shell, smaller than its 55″ shell in K I λ7699. In stark contrast, 4.6 μm CO emission around VY CMa is coincident with bright K I in its clumpy asymmetric reflection nebula, within 5″ (40 km s-1) of the star. Our CO data reveal redshifted features not seen in K I spectra of VY CMa, indicating a more isotropic distribution of gas punctuated by randomly distributed asymmetric clumps. The relative CO and K I distribution in Betelgeuse arises from ionization effects within a steady wind, whereas in VY CMa, K I is emitted from skins of CO cloudlets resulting from episodic mass ejections 500-1000 yr ago. In both cases, CO and K I trace potential pre-SN circumstellar matter: we conclude that an extreme RSG like VY CMa might produce a Type IIn event like SN 1988Z if it were to explode in its current state, but Betelgeuse will not. VY CMa demonstrates that luminous blue variables are not necessarily the only progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer enhanced episodic mass loss shortly before exploding. © 2009. The American Astronomical Society. All rights reserved.
• Smith, N., Whitney, B. A., Conti, P. S., G., C., & Jackson, J. M. (2009). Massive star formation and feedback in W49A: The source of our Galaxy's most luminous water maser outflow. Monthly Notices of the Royal Astronomical Society, 399(2), 952-965.
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  Abstract: We present high spatial resolution mid-infrared (mid-IR) images of the ring of ultracompact H ii regions in W49A obtained at Gemini North, allowing us to identify the driving source of its powerful H2O maser outflow. These data also confirm our previous report that several radio sources in the ring are undetected in the mid-IR because they are embedded deep inside the cloud core. We locate the source of the water maser outflow at the position of the compact mid-IR peak of source G (source G:IRS1) to within 0.07 arcsec. This IR source is not coincident with any identified compact radio continuum source, but is coincident with a hot molecular core, so we propose that G:IRS1 is a hot core driving an outflow analogous to the wide-angle bipolar outflow in OMC-1. G:IRS1 is at the origin of a larger bipolar cavity and CO outflow. The water maser outflow is orthogonal to the bipolar CO cavity, so the masers probably reside near its waist in the thin cavity walls. Models of the IR emission require a massive protostar with M* ≃ 45 M⊙, L * ≃ 3 × 105 L⊙ and an effective envelope accretion rate of ∼10-3 M⊙ yr-1. Feedback from the central star could potentially drive the small-scale H2O maser outflow, but it has insufficient radiative momentum to have driven the large-scale bipolar CO outflow, requiring that this massive star had an active accretion disc over the past 104 yr. Combined with the spatially resolved morphology in IR images, G:IRS1 in W49 provides compelling evidence for a massive protostar that formed by accreting from a disc, accompanied by a bipolar outflow. © 2009 RAS.
• Temim, T., Gehrz, R. D., Woodward, C. E., Roellig, T. L., Smith, N., Rudnick, L. R., Polomski, E. F., Davidson, K. D., Yuen, L., & Onaka, T. (2009). Erratum: "Spitzer space telescope infrared imaging and spectroscopy of the Crab nebula" (The Astronomical Journal (2006) 132, (1610)). Astronomical Journal, 137(6), 5155-.
• Foley, R. J., Bloom, J. S., Weidong, L. i., Filippenko, A. V., Gavazzi, R., Ghez, A., Konopacky, Q., Malkan, M. A., Marshall, P. J., Pooley, D., Treu, T., Woo, J., & Smith, N. (2008). Late-time observations of SN 2006gy: Still going strong. Astrophysical Journal, 686(1), 485-491.
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  Abstract: Owing to its extremely high luminosity and long duration, supernova (SN) 2006gy radiated more energy in visual light than any other known SN. Two hypotheses to explain its high luminosity at early times - that it was powered by shock interaction with circumstellar material (CSM) as implied by its Type IIn spectrum, or that it was fueled by radioactive decay from a large mass of 56Ni synthesized in a pair-instability SN-predicted different late-time properties. Here we present observations of SN 2006gy obtained more than a year after discovery. We were unable to detect it at visual wavelengths, but clear near-infrared (IR) K′ and H-band detections show that it is still at least as luminous as the peak of a normal Type II SN. We also present spectra giving an upper limit to the late-time Ha luminosity of ≲S10 39 erg s-1. Based on the weak late-time Ha, X-ray, and radio emission, combined with the difficulty of explaining the shift to IR wavelengths, we can rule out ongoing CSM interaction as the primary late-time power source of SN 2006gy. Instead, we propose that the evolution of SN 2006gy is consistent with one of two possible scenarios: (1)apairinstability SN plus modest CSM interaction, where the radioactive decay luminosity shifts to the IR because of dust formation; or (2) an IR echo, where radiation emitted during peak luminosity heats a pre-existing dust shell at radii near 1 light year, requiring the progenitor star to have ejected another shell of ∼10 M ⊙ about 1500 yr before the SN. © 2008. The American Astronomical Society. All rights reserved.
• Hrivnak, B. J., Smith, N., Y., K., & Sahai, R. (2008). A study of H₂ emission in three bipolar proto-planetary nebulae: IRAS 16594-4656, Hen 3-401, and Rob 22. Astrophysical Journal, 688(1), 327-343.
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  Abstract: We have carried out a spatial-kinematic study of three proto-planetary nebulae, IRAS 16594-4656, Hen 3-401, and Rob 22. High-resolution H2 images were obtained with NICMOS on the Hubble Space Telescope, and high-resolution spectra were obtained with the Phoenix spectrograph on Gemini-South. IRAS 16594-4656 shows a "peanutshaped" bipolar structure with H2 emission from the walls and from two pairs of more distant, point-symmetric faint blobs. The velocity structure shows the polar axis to be in the plane of the sky, contrary to the impression given by the more complex visual image and the visibility of the central star, with an ellipsoidal velocity structure. Hen 3-401 shows the H2 emission coming from the walls of the very elongated, open-ended lobes seen in visible light, along with a possible small disk around the star. The bipolar lobes appear to be tilted 10°-15° with respect to the plane of the sky, and their kinematics display a Hubble-like flow. In Rob 22, the H2 appears in the form of an "S"-shape, approximately tracing out the similar pattern seen in the visible. H2 is especially seen at the ends of the lobes and at two opposite regions close to the unseen central star. The axis of the lobes is nearly in the plane of the sky. Expansion ages of the lobes are calculated to be ∼1600 yr (IRAS 16594-4656), ∼1100 yr (Hen 3-401), and ∼640 yr (Rob 22), based on approximate distances. © 2008. The American Astronomical Society. All rights reserved.
• Scowen, P. A., Jansen, R., Beasley, M., Cooke, B., Nikzad, S., Siegmund, O., Woodruff, R., Calzetti, D., Desch, S., Fullerton, A., Gallagher, J., Malhotra, S., McCaughrean, M., O'Connell, R., Oey, S., Padgett, D., Rhoads, J., Roberge, A., Smith, N., , Stern, D., et al. (2008). The star formation observatory (SFO) mission to study cosmic origins near and far. Proceedings of SPIE - The International Society for Optical Engineering, 7010.
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  Abstract: The Star Formation Observatory (SFO) is a 1.65m space telescope that addresses pivotal components in the 2007 NASA Science Plan, with a primary focus on Cosmic Origins. The design under consideration provides 100 times greater imaging efficiency and >10 times greater spectroscopic efficiency below 115 nm than existed on previous missions. The mission has a well-defined Origins scientific program at its heart: a statistically significant survey of local, intermediate, and high-redshift sites and indicators of star formation, to investigate and understand the range of environments, feedback mechanisms, and other factors that most affect the outcome of the star and planet formation process. This program relies on focused capabilities unique to space and that no other planned NASA mission will provide: near-UV/visible (200-1100 nm) wide-field, diffraction-limited imaging; and high-efficiency, low- and high-resolution (R ∼40,000) UV (100-175 nm) spectroscopy using far-UV optimized coatings and recent advances in Micro-Channel Plate (MCP) detector technology. The Observatory imager has a field of view in excess of 17′×17′ (>250 arcmin2) and uses a dichroic to create optimized UV/blue and red/near-IR channels for simultaneous observations, employing detectors that offer substantial quantum efficiency gains and that suffer lower losses due to cosmic rays.
• Smith, N. (2008). A blast wave from the 1843 eruption of η Carinae. Nature, 455(7210), 201-203.
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  PMID: 18784719;Abstract: Very massive stars shed much of their mass in violent precursor eruptions as luminous blue variables (LBVs) before reaching their most likely end as supernovae, but the cause of LBV eruptions is unknown. The nineteenth-century eruption of η Carinae, the prototype of these events, ejected about 12 solar masses at speeds of 650 km s-1, with a kinetic energy of almost 1050 erg (ref. 4). Some faster material with speeds up to 1,000-2,000 km s-1 had previously been reported but its full distribution was unknown. Here I report observations of much faster material with speeds up to 3,500-6,000 km s-1, reaching farther from the star than the fastest material in previous reports. This fast material roughly doubles the kinetic energy of the nineteenth-century event and suggests that it released a blast wave now propagating ahead of the massive ejecta. As a result, η Carinae's outer shell now mimics a low-energy supernova remnant. The eruption has usually been discussed in terms of an extreme wind driven by the star's luminosity, but the fast material reported here indicates that it may have been powered by a deep-seated explosion rivalling a supernova, perhaps triggered by the pulsational pair instability. This may alter interpretations of similar events seen in other galaxies. ©2008 Macmillan Publishers Limited. All rights reserved.
• Smith, N. (2008). Galactic twins of the ring nebula around SN1987A and a possible LBV-like phase for SK-69 202. Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias, 33, 154-156.
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  Abstract: Some core-collapse supernovae show clear signs of interaction with dense circumstellar material that often appears to be non-spherical. Circumstellar nebulae around supernova progenitors provide clues to the origin of that asymmetry in immediate pre-supernova evolution. Here I discuss outstanding questions about the formation of the ring nebula around SN1987A and some implications of similar ring nebulae around Galactic B supergiants. Several clues hint that SN1987A's nebula may have been ejected in an LBV-like event, rather than through interacting winds in a transition from a red supergiant to a blue supergiant. © 2008: Instituto de Astronomía.
• Smith, N. (2008). Possible detection of a pair instability supernova in the modern universe, and implications for the first stars. AIP Conference Proceedings, 990, 122-126.
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  Abstract: SN 2006gy radiated far more energy in visual light than any other supernova so far, and potential explanations for its energy demands have implications for galactic chemical evolution and the deaths of the first stars. It remained bright for over 200 days, longer than any normal supernova, and it radiated more than 1051 ergs of luminous energy at visual wavelengths. I argue that this Type IIn supernova was probably the explosion of an extremely massive star like Eta Carinae that retained its hydrogen envelope when it exploded, having suffered relatively little mass loss during its lifetime. That this occurred at roughly Solar metallicity challenges current paradigms for mass loss in massive-star evolution. I explore a few potential explanations for SN2006gy's power source, involving either circumstellar interaction, or instead, the decay of 56Ni to 56Co to 56Fe. If SN 2006gy was powered by the conversion of shock energy into light, then the conditions must be truly extraordinary and traditional interaction models don't work. If SN 2006gy was powered by radioactive decay, then the uncomfortably huge 56Ni mass requires that the star exploded as a pair instability supernova. The mere possibility of this makes SN 2006gy interesting, especially at this meeting, because it is the first good candidate for a genuine pair instability supernova. © 2008 American Institute of Physics.
• Smith, N., & Conti, P. S. (2008). On the role of the WNH phase in the evolution of very massive stars: Enabling the LBV instability with feedback. Astrophysical Journal, 679(2), 1467-1477.
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  Abstract: We propose the new designation "WNH" for luminous Wolf-Rayet (WR) stars of the nitrogen sequence with hydrogen in their spectra. These have been commonly referred to as WNL stars (WN7h, for example), but this new shorthand avoids confusion because there are late-type WN stars without hydrogen and early-type WN stars with hydrogen. Clearly differentiating WNH stars from Ib-poor WN stars is critical when discussing them as potential progenitors of Type Ib/c supernovae and gamma-ray bursts-the massive WNH stars are not likely Type Ib /c supernova progenitors, and are distinct from core He burning WR stars. We show that masses of WNH stars are systematically higher than for bona fide H-poor WR stars (both WN and WC), with little overlap. Also, hydrogen mass fractions of the most luminous WNH stars are higher than those of luminous blue variables (LBVs). While on the main sequence, a star's mass is reduced due to winds and its luminosity slowly rises, so the star increases its Eddington factor, which in turn strongly increases the mass-loss rate, pushing it even closer to the Eddington limit. Accounting for this feedback, observed properties of WNH stars are a natural and expected outcome for very luminous stars approaching the end of core H burning. Feedback from the strong WNH wind itself plays a similar role, enabling the eruptive instability seen subsequently as an LBV. Altogether, for initial masses above 40-60 M⊙, we find a strong and self-consistent case that luminous WNH stars are pre-LBVs rather than post-LBVs (for lower initial mass, the case is less clear). The steady march toward increased mass-loss rates from feedback also provides a natural explanation for the continuity in observed spectral traits from O3 V to O3 If* to WNH noted previously. © 2008. The American Astronomical Society. All rights reserved.
• Smith, N., Chornock, R., Weidong, L. i., Ganeshalingam, M., Silverman, J. M., Foley, R. J., Filippenko, A. V., & Barth, A. J. (2008). SN 2006tf: Precursor eruptions and the optically thick regime of extremely luminous type IIn supernovae. Astrophysical Journal, 686(1), 467-484.
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  Abstract: SN 2006tf is the third most luminous supernova (SN) discovered so far, after SN 2005ap and SN 2006gy. SN 2006tf is valuable because it provides a link between two regimes: (1) luminous Type Un supernovae powered by emission directly from interaction with circumstellar material (CSM), and (2) the most extremely luminous SNe where the CSM interaction is so optically thick that energy must diffuse out from an opaque shocked shell. As SN 2006tf evolves, it slowly transitions from the second to the first regime as the clumpy shell becomes more porous. This link suggests that the range in properties of the most luminous SNe is largely determined by the density and speed of hydrogen-rich material ejected shortly before they explode. The total energy radiated by SN 2006tf was at least 7 × 1050 ergs. If the bulk of this luminosity came from the thermalization of shock kinetic energy, then the star needs to have ejected ∼18 M⊙ in the 4-8 yr before core collapse, and another 2-6 M⊙ in the decades before that. AType Ia explosion is therefore excluded. From the Hα emission-line profile, we derive a blast wave speed of 2000 km s-1 that does not decelerate, and from the narrow P Cygni absorption from preshock gas we deduce that the progenitor's wind speed was ∼190 km s-1. This is reminiscent of the wind speeds of luminous blue variables (LBVs), but not of red supergiants or Wolf-Rayet stars. We propose that like SN 2006gy, SN 2006tf marked the death of a very massive star that retained a hydrogen envelope until the end of its life and suffered extreme LBV-like mass loss in the decades before it exploded. © 2008. The American Astronomical Society. All rights reserved.
• Smith, N., Foley, R. J., & Filippenko, A. V. (2008). Dust formation and He II λ4686 emission in the dense shell of the peculiar type Ib supernova 2006jc. Astrophysical Journal, 680(1), 568-579.
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  Abstract: We present evidence for the formation of dust grains in an unusual Type Ib supernova (SN) based on late-time spectra of SN 2006jc. The progenitor suffered an outburst qualitatively similar to those of luminous blue variables (LBVs) just 2 yr prior to the SN, and we propose that the dust formation is a consequence of the SN blast wave overtaking that .LBV-like shell. The key evidence for dust formation is (1) the appearance of a red/near-infrared continuum emission source that can be fit by T ≈, 1600 K graphite grains, and (2) fading of the redshifted sides of intermediate-width He I emission lines, yielding progressively more asymmetric blueshifted lines as dust obscures receding material. This provides the strongest case yet for dust formation in any SN Ib/c. Both developments occurred between 51 and 75 days after peak brightness, while the few other SNe observed to form dust did so after a few hundred days. Geometric considerations indicate that dust formed in the dense swept-up shell between the forward and reverse shocks, and not in the freely expanding SN ejecta. The rapid cooling leading to dust formation may have been aided by extremely high shell densities of 1010 cm-3, indicated by Heiline ratios. The brief epoch of dust formation is accompanied by He n 24686 emission and enhanced X-ray emission, suggesting a common link. These clues imply that the unusual dust formation in this object was not attributable to properties of the SN itself, but instead-like most peculiarities of SN 2006jc-was a consequence of interaction with the dense environment created by an LBV-like eruption 2 yr before the SN. © 2008. The American Astronomical Society. All rights reserved.
• Walborn, N. R., Stahl, O., Gamen, R. C., Szeifert, T., Morrell, N. I., Smith, N., Howarth, I. D., Humphreys, R. M., Bond, H. E., & Lennon, D. J. (2008). A three-decade outburst of the LMC luminous blue variable R127 draws to a close. Astrophysical Journal, 683(1 PART 2), L33-L36.
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  Abstract: The paradigmatic luminous blue variable R127 in the Large Magellanic Cloud has been found in the intermediate, peculiar early-B state, and substantially fainter in visual light, signaling the final decline from its major outburst that began between 1978 and 1980. This transformation was detected in 2008 January, but archival data show that it began between early 2005 and early 2007. In fact, significant changes from the maximum, peculiar A-type spectrum, which was maintained from 1986 through 1998, had already begun the following year, coinciding with a steep drop in visual light. We show detailed correspondences between the spectrum and light, in which the decline mimics the rise. Moreover, these trends are not monotonic but are characterized by multiple spikes and dips, which may provide constraints on the unknown outburst mechanism. Intensive photometric and spectroscopic monitoring of R127 should now resume, to follow the decline presumably back to the quiescent Ofpe/WN9 state, in order to fully document the remainder of this unique observational opportunity. ©2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Walborn, N. R., Stahl, O., Gamen, R. C., Szeifert, T., Morrell, N. I., Smith, N., Howarth, I. D., Humphreys, R. M., Bond, H. E., & Lennon, D. J. (2008). A three-decade outburst of the lmc luminous blue variable R127 draws to a close. Astrophysical Journal, 684(1 PART 2), L33-L36.
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  Abstract: The paradigmatic luminous blue variable R127 in the Large Magellanic Cloud has been found in the inter-mediate, peculiar early-B state, and substantially fainter in visual light, signaling the final decline from its major outburst that began between 1978 and 1980. This transformation was detected in 2008 January, but archival data show that it began between early 2005 and early 2007. In fact, significant changes from the maximum, peculiar A-type spectrum, which was maintained from 1986 through 1998, had already begun the following year, coinciding with a steep drop in visual light. We show detailed correspondences between the spectrum and light, in which the decline mimics the rise. Moreover, these trends are not monotonic but are characterized by multiple spikes and dips, which may provide constraints on the unknown outburst mechanism. Intensive photometric and spec-troscopic monitoring of R127 should now resume, to follow the decline presumably back to the quiescent Ofpe/WN9 state, in order to fully document the remainder of this unique observational opportunity. ©2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Wang, X., Weidong, L. i., Filippenko, A. V., Foley, R. J., Smith, N., & Wang, L. (2008). The detection of a light echo from the type Ia supernova 2006X in M100. Astrophysical Journal, 677(2), 1060-1068.
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  Abstract: We report the discovery of a light echo (LE) from the Type Ia supernova (SN ) 2006X in the nearby galaxy M100. The presence of the LE is supported by analysis of both the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images and the Keck optical spectrum that we obtained at ~300 days after maximum brightness. In the image procedure, both the radial-profile analysis and the point-spread function (PSF) subtraction method resolve significant excess emission at 2-5 ACS pixels (∼0.05″-0.13″) from the center. In particular, the PSF-subtracted ACS images distinctly appear to have an extended, ringlike echo. Due to limitations of the image resolution, we cannot confirm any structure or flux within 2 ACS pixels from the SN. The late-time spectrum of SN 2006X can be reasonably fit with two components: a nebular spectrum of a normal SN Ia and a synthetic LE spectrum. Both image and spectral analysis show a rather blue color for the emission of the LE, suggestive of a small average grain size for the scattering dust. Using the Cepheid distance to M100 of 15.2 Mpc, we find that the dust illuminated by the resolved LE is ~27-170 pc from the SN. The echo inferred from the nebular spectrum appears to be more luminous than that resolved in the images (at the ∼2 σ level), perhaps suggesting the presence of an inner echo at
• Chesneau, O., Lykou, F., Balick, B., Lagadec, E., Matsuura, M., Smith, N., Spang, A., Wolf, S., & Zijlstra, A. A. (2007). A silicate disk in the heart of the Ant. Astronomy and Astrophysics, 473(3), L29-L32.
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  Abstract: Aims. We aim at getting high spatial resolution information on the dusty core of bipolar planetary nebulae to directly constrain the shaping process. Methods. We present observations of the dusty core of the extreme bipolar planetary nebula Menzel 3 (Mz 3, Hen 2-154, the Ant) taken with the mid-infrared interferometer MIDI/VLTI and the adaptive optics NACO/VLT. Results. The core of Mz 3 is clearly resolved with MIDI in the interferometric mode, whereas it is unresolved from the Ks to the N bands with single dish 8.2 m observations on a scale ranging from 60 to 250 mas. A striking dependence of the dust core size with the PA angle of the baselines is observed, that is highly suggestive of an edge-on disk whose major axis is perpendicular to the axis of the bipolar lobes. The MIDI spectrum and the visibilities of Mz 3 exhibit a clear signature of amorphous silicate, in contrast to the signatures of crystalline silicates detected in binary post-AGB systems, suggesting that the disk might be relatively young. We used radiative-transfer Monte Carlo simulations of a passive disk to constrain its geometrical and physical parameters. Its inclination (74° ± 3°) and position angle (5° ± 5°) are in accordance with the values derived from the study of the lobes. The inner radius is 9 ±1 AU and the disk is relatively flat. The dust mass stored in the disk, estimated as 1 × 10-5 M ⊙, represents only a small fraction of the dust mass found in the lobes and might be a kind of relic of an essentially polar ejection process. © ESO 2007.
• Foley, R. J., Smith, N., Ganeshalingam, M., Weidong, L. i., Chornock, R., & Filippenko, A. V. (2007). SN 2006jc: A Wolf-Rayet star exploding in a dense He-rich circumstellar medium. Astrophysical Journal, 657(2 II), L105-L108.
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  Abstract: We present optical photometry and spectra of the peculiar Type Ib supernova (SN) 2006jc. Strong and relatively narrow He I emission lines indicate the progenitor star exploded inside a dense circumstellar medium (CSM) rich in He. An exceptionally blue apparent continuum persists from our first spectrum obtained 15 days after discovery through our last spectrum ∼1 month later. Based on the presence of isolated Fe II emission lines, we interpret the blue "continuum" as blended, perhaps fluorescent, Fe emission. One or two of the reddest He I line profiles in our spectra are double-peaked, suggesting that the CSM has an aspherical geometry. The He I lines that are superposed on the blue continuum show P Cygni profiles, while the redder He I lines do not, implying that the blue continuum also originates from an asymmetric mass distribution. The He-rich CSM, aspherical geometry, and line velocities indicate that the progenitor star was a WNE Wolf-Rayet (W-R) star. A recent (2 years before the SN), coincident, luminous outburst similar to those seen in luminous blue variables (LBVs) is the leading candidate for the dense CSM. Such an eruption associated with a W-R star has not been seen before, indicating that the progenitor star may have recently transitioned from the LBV phase. We also present unpublished spectral and photometric data on SN 2002ao, which, along with SN 1999cq, is very similar to SN 2006jc. We propose that these three objects may represent a new and distinct class of SNe arising from W-R progenitors surrounded by a dense CSM. © 2007. The American Astronomical Society. All rights reserved.
• Grundstrom, E. D., Gies, D. R., Hillwig, T. C., McSwain, M. V., Smith, N., Gehrz, R. D., Stahl, O., & Kaufer, A. (2007). A spectroscopic study of mass outflows in the interacting binary RY scuti. Astrophysical Journal, 667(1 I), 505-519.
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  Abstract: The massive interacting binary RY Scuti is an important representative of an active mass-transferring system that is changing before our eyes and which may be an example of the formation of a Wolf-Rayet star through tidal stripping. Utilizing new and previously published spectra, we present examples of how a number of illustrative absorption and emission features vary during the binary orbit. We identify spectral features associated with each component, calculate a new, double-lined spectroscopic binary orbit, and find masses of 7.1 ± 1.2 M⊙ for the bright supergiant and 30.0 ± 2.1 M ⊙ for the hidden massive companion. Through tomographic reconstruction of the component spectra from the composite spectra, we confirm the O9.7 Ibpe spectral class of the bright supergiant and discover a B0.5 I spectrum associated with the hidden massive companion; however, we suggest that the latter is actually the spectrum of the photosphere of the accretion torus immediately surrounding the massive companion. We describe the complex nature of the mass-loss flows from the system in the context of recent hydrodynamical models for β Lyr, leading us to conclude RY Scuti has matter leaving the system in two ways: (1) a bipolar outflow from winds generated by the hidden massive companion, and (2) an outflow from the bright O9.7 Ibpe supergiant in the region near the L2 point to fill out a large, dense circumbinary disk. This circumbinary disk (radius ≈1 AU) may feed the surrounding double-toroidal nebula (radius ≈2000 AU). © 2007. The American Astronomical Society. All rights reserved.
• Smith, N. (2007). Discovery of a nearby twin of SN 1987A'S nebula around the luminous blue variable HD 168625: Was SK - 69 202 an LBV?. Astronomical Journal, 133(3), 1037-1040.
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  Abstract: Spitzer Space Telescope images of the luminous blue variable (LBV) candidate HD 168625 reveal the existence of a bipolar nebula several times larger than its previously known equatorial dust torus. The outer nebula of HD 168625 has a full extent of ∼80″ or 0.85 pc, and one of the lobes has a well-defined polar ring. The nebula is a near twin of the triple-ring system around SN 1987A. Because of these polar rings, and accounting for stellar/progenitor luminosity, HD 168625 is an even closer twin of SN 1987A than the B supergiant Sher 25 in NGC 3603. HD 168625's nebula was probably ejected during a giant LBV eruption and not during a red supergiant phase, so its similarity to the nebula around SN 1987A may open new possibilities for the creation of SN 1987A's rings. Namely, the hypothesis that Sk - 69 202 suffered an LBV-like eruption would avert the complete surrender of single-star models for its bipolar nebula by offering an alternative to an unlikely binary merger scenario. It also hints that LBVs are the likely progenitors of some Type II supernovae, and that HP 168625's nebula is a good example of a pre-explosion environment. © 2007. The American Astronomical Society. All rights reserved.
• Smith, N. (2007). Episodic mass loss and pre-SN circumstellar envelopes. Proceedings of the International Astronomical Union, 3(S250), 193-200.
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  Abstract: I discuss observational clues concerning episodic mass-loss properties of massive stars in the time before the final supernova explosion. In particular, I will focus on the mounting evidence that LBVs and related stars are candidates for supernova progenitors, even though current paradigms place them at the end of core-H burning. Namely, conditions in the immediate circumstellar environment within a few 102 AU of Type IIn supernovae require very high progenitor mass-loss rates. Those rates are so high that the only known stars that come close are LBVs during rare giant eruptions. I will highlight evidence from observations of some recent extraordinary supernovae suggesting that explosive or episodic mass loss (a.k.a. LBV eruptions like the 19th century eruption of Eta Car) occur in the 5-10 years immediately preceding the SN. Finally, I will discuss some implications for stellar evolution from these SNe, the most important of which is the observational fact that the most massive stars can indeed make it to the ends of their lives with substantial H envelopes intact, even at Solar metallicity. © 2008 Copyright International Astronomical Union 2008.
• Smith, N. (2007). Galactic twins of the nebula around SN 1987A: Hints that LBVs may be supernova progenitors. AIP Conference Proceedings, 937, 163-170.
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  Abstract: I discuss outstanding questions about the formation of the ring nebula around SN1987A and some implications of similar ring nebulae around Galactic B supergiants. There are notable obstacles for the formation of SN1987A's bipolar nebula through interacting winds in a transition from a red supergiant to a blue supergiant. Instead, several clues hint that the nebula may have been ejected in an LBV-like event. In addition to the previously known example of Sher 25, there are two newly-discovered Galactic analogs of SN1987A's ringed nebula. Of these three Galactic analogs around blue supergiants, two (Sher 25 and SBW1) have chemical abundances indicating that they have not been through a red supergiant phase, and the remaining ringed bipolar nebula surrounds a luminous blue variable (HD168625). Although SK - 69 202's initial mass of ∼20M ⊙ is lower than those atributed to most LBVs, it is not far off and the low-luminosity end of the LBV phenomenon is not well defined. Furthermore, HD168625's luminosity indicates an initial mass of only ∼25M ⊙, that of SBW1 is consistent with ∼20M ⊙, and there is a B[e] star in the SMC with an initial mass of ∼20M ⊙ that experienced an LBV outburst in the 1990s. These similarities may be giving us important clues about Sk - 69 202's pre-SN evolution and the formation mechanism of its nebula. © 2007 American Institute of Physics.
• Smith, N., & Brooks, K. J. (2007). A census of the Carina Nebula - II. Energy budget and global properties of the nebulosity. Monthly Notices of the Royal Astronomical Society, 379(4), 1279-1292.
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  Abstract: The first paper in this series took a direct census of energy input from the known OB stars in the Carina Nebula, and in this paper we study the global properties of the surrounding nebulosity. This detailed comparison may prove useful for interpreting observations of extragalactic giant H ii regions and ultraluminous infrared (IR) galaxies. We find that the total IR luminosity of Carina is about 1.2 × 107 L⊙, accounting for only about 50-60 per cent of the known stellar luminosity from Paper I. Similarly, the ionizing photon luminosity derived from the integrated radio continuum is about 7 × 1050 s-1, accounting for ∼75 per cent of the expected Lyman continuum from known OB stars. The total kinetic energy of the nebula is about 8 × 1051 erg, or ∼30 per cent of the mechanical energy from stellar winds over the lifetime of the nebula, so there is no need to invoke a supernova (SN) explosion based on energetics. Warm dust grains residing in the H ii region interior dominate emission at 10-30 μm, but cooler grains at 30-40 K dominate the IR luminosity and indicate a likely gas mass of ∼106 M⊙. We find an excellent correlation between the radio continuum and 20-25 μm emission, consistent with the idea that the ∼80-K grain population is heated by trapped Lyα photons. Similarly, we find a near perfect correlation between the far-IR optical depth map of cool grains and 8.6-μm hydrocarbon emission, indicating that most of the nebular mass resides as atomic gas in photodissociation regions and not in dense molecular clouds. Synchronized star formation around the periphery of Carina provides a strong case that star formation here was indeed triggered by stellar winds and ultraviolet radiation. This second generation appears to involve a cascade toward preferentially intermediate- and low-mass stars, but this may soon change when η Carinae and its siblings explode. If the current reservoir of atomic and molecular gas can be tapped at that time, massive star formation may be rejuvenated around the periphery of Carina much as if it were a young version of Gould's Belt. Furthermore, when these multiple SNe occur, the triggered second generation will be pelted repeatedly with SN ejecta bearing short-lived radioactive nuclides. Carina may therefore represent the most observable analogue to the cradle of our own Solar system. © 2007 RAS.
• Smith, N., & Ferland, G. J. (2007). The structure of the Homunculus. II. Modeling the physical conditions in η Carinae's molecular shell. Astrophysical Journal, 655(2 I), 911-919.
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  Abstract: We present models that reproduce the observed double-shell structure of the Homunculus Nebula around η Carinae, including the stratification of infrared H2 and [Fe II] emission seen in data obtained with the Phoenix spectrograph on Gemini South, as well as the corresponding stratified grain temperature seen in thermal-infrared data. Tuning the model to match the observed shell thickness allows us to determine the threshold density that permits survival of H2. An average density of nH ≃ (0.5-1) × 107 cm-3 in the outer zone is required to allow H2 to exist at all latitudes in the nebula, and for Fe + to recombine to Fe0. This gives independent confirmation of the very large mass of the Homunculus, indicating a total of roughly 15-35 M⊙ (although we note reasons why the lower end of this range is favored). At the interface between the atomic and molecular zones, we predict a sharp drop in the dust temperature, in agreement with the bimodal dust color temperatures observed in the two zones. In the outer molecular shell, the dust temperature drops to nearly the blackbody temperature, and becomes independent of grain size because of self-shielding at shorter UV wavelengths and increased heating at longer wavelengths. This relaxes constraints on large grain sizes suggested by near-blackbody color temperatures. Finally, from the strength of infrared [Fe II] emission in the inner shell we find that the gas-phase Fe abundance is roughly solar. This is astonishing in such a dusty object, where one normally expects gaseous iron to be depleted by 2 orders of magnitude. © 2007. The American Astronomical Society. All rights reserved.
• Smith, N., & H., R. (2007). The structure of the homunculus. III. Forming a disk and bipolar lobes in a rotating surface explosion. Astrophysical Journal, 666(2 I), 967-975.
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  Abstract: We present a semianalytic model for the shaping of the Homunculus Nebula around η Carinae that accounts for the simultaneous production of bipolar lobes and an equatorial disk through a rotating surface explosion. Material is launched normal to the surface of an oblate rotating star with an initial kick velocity that scales approximately with the local escape speed. Thereafter, ejecta follow ballistic orbital trajectories, feeling only a central force corresponding to a radiatively reduced gravity. Our model is conceptually similar to the wind-compressed disk model of Bjorkman & Cassinelli, but we modify it to an explosion instead of a steady line-driven wind, we include a rotationally distorted star, and we treat the dynamics somewhat differently. A continuum-driven explosion, where the radiation force is independent of velocity, avoids the disk inhibition mechanisms that normally operate in line-driven winds. This allows midlatitude material with appropriate initial specific energy to migrate toward the equator, where it collides with material from the opposite hemisphere to form a disk. Thus, our model provides a simple method by which rotating hot stars can simultaneously produce intrinsically bipolar and equatorial mass ejections, without relying on an aspherical environment or magnetic fields. Although motivated by η Carinae, the model may have generic application to episodic mass ejection where rotation is important, including other luminous blue variables, B[e] stars, the nebula around SN 1987A, or possibly even bipolar supernova explosions themselves. In cases where near-Eddington radiative driving is less influential, our model generalizes to produce bipolar pinched-waist morphologies without disks, as seen in many planetary nebulae. If rotating single stars can produce strongly axisymmetric ejecta by this mechanism, then the presence of aspherical ejecta by itself is insufficient justification to invoke close binary evolution. © 2007. The American Astronomical Society. All rights reserved.
• Smith, N., & McCray, R. (2007). High resolution spectroscopy of SN1987A's rings: He i λ 10830 and Hα from the hotspots. AIP Conference Proceedings, 937, 179-181.
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  Abstract: We present the first high-dispersion spectroscopy of He I λ 10830 from the hotspots in the ring around SN1987A, obtained at Gemini South, spatially resolving the near and far sides of the ring. We compare these line profiles to similar echelle spectra of Hα and [N II] λ6583 obtained at the Magellan Observatory. We find that the He I profiles are much broader than Hα or [N II], but the He I profiles also have different shapes - they have enhanced emission at high speeds, with extra blueshifted emission on the north side of the ring, and extra redshifted emission on the south side. To explain this, we invoke a simple geometric picture where the extra He I emission traces hotter gas from faster shocks that strike the apex of the hotspots directly, while the Hα preferentially traces cooler lower-ionization gas from slower transverse shocks that penetrate into the sides of the ring. © 2007 American Institute of Physics.
• Smith, N., & McCray, R. (2007). Shell-shocked diffusion model for the light curve of sn 2006gy. Astrophysical Journal, 671(1 PART 2), L17-L20.
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  Abstract: We explore a simple model for the high luminosity of SN 2006gy involving photon diffusion of shock-deposited thermal energy. The distinguishing property of the model is that the large "stellar" radius of ∼160 AU required to prevent adiabatic losses is not the true stellar radius, but rather, it is the radius of an opaque, unbound circumstellar envelope, created when ∼10 M was ejected in the decade before the supernova in an eruption analogous to that of η Carinae. The supernova light is produced primarily by diffusion of thermal energy following the passage of the blast wave through this shell. This model differs from traditional models of supernova debris interacting with an external circumstellar medium (CSM) in that here the shell is optically thick and the escape of radiation is delayed. We show that any model attempting to account for SN 2006gy's huge luminosity with radiation emitted by ongoing CSM interaction fails for the following basic reason: the CSM density required to achieve the observed luminosity makes the same circumstellar envelope opaque (r ≥ 300), forcing a thermal diffusion solution. In our model, the weaker CSM interaction giving rise to SN 2006gy's characteristic Type Hn spectrum and soft X-rays is not linked to the power source of the visual continuum; instead, it arises after the blast wave breaks free from the opaque shell into the surrounding wind. While a simple diffusion model can explain the gross properties of the early light curve of SN 2006gy, it predicts that the light curve must plummet rapidly at late times, unless an additional power source is present. © 2007. The American Astronomical Society, All rights reserved.
• Smith, N., Bally, J., & Walawender, J. (2007). And in the darkness bind them: Equatorial rings, B[e] supergiants, and the waists of Bipolar Nebulae¹. Astronomical Journal, 134(2), 846-859.
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  Abstract: We report the discovery of two new circumstellar ring nebulae in the western Carina Nebula, and we discuss their significance in stellar evolution. The brighter of the two new objects, SBW 1, resembles a lidless staring eye and encircles a B1.5 lab supergiant. Although seen in Carina, its luminosity class and radial velocity imply a larger distance of ∼7 kpc in the far Carina arm. At that distance its size and shape are nearly identical to the equatorial ring around SN 1987A, but SBW 1 's low N abundance indicates that the ring was excreted without its star passing through a red supergiant phase. The fainter object, SBW 2, is a more distorted ring, is N-rich, and is peculiar in that its central star seems to be invisible. We discuss the implications of these two new nebulae in context with other circumstellar rings such as those around SN 1987A, Sher 25, HD 168625, RY Scuti, WeBo 1, SuWt 2, and others. The ring bearers fall into two groups: Five rings surround hot supergiants, and it is striking that all except for the one known binary are carbon copies of the ring around SN 1987A. We propose a link between these B supergiant rings and B[e] supergiants, where the large spatially resolved rings derive from the same material that would have given rise to emission lines during the earlier B[e] phase, when it was much closer to the star. The remaining four rings surround evolved intermediate-mass stars; all members of this ring fellowship are close binaries, hinting that binary interactions govern the forging of such rings. Two-thirds of our sample are found in or near giant H II regions. We estimate that there may be several thousand more dark rings in the Galaxy, but we are scarcely aware of their existence-either because they are only illuminated in precious few circumstances or because of selection effects. For intermediate-mass stars, these rings might be the preexisting equatorial density enhancements invoked to bind the waists of bipolar nebulae. © 2007. The American Astronomical Society. All rights reserved.
• Smith, N., Li, W., Foley, R. J., Wheeler, J. C., Pooley, D., Chornock, R., Filippenko, A. V., Silverman, J. M., Quimby, R., Bloom, J. S., & Hansen, C. (2007). SN 2006gy: Discovery of the most luminous supernova ever recorded, powered by the death of an extremely massive star like η carinae. Astrophysical Journal, 666(2 I), 1116-1128.
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  Abstract: We report the discovery and early observations of the peculiar Type IIn supernova (SN) 2006gy in NGC 1260. With a peak visual magnitude of about -22, it is the most luminous supernova ever recorded. Its very slow rise to maximum took ∼70 days, and it stayed brighter than -21 mag for about 100 days. It is not yet clear what powers the enormous luminosity and the total radiated energy of ∼1051 erg, but we argue that any known mechanism - thermal emission, circumstellar interaction, or 56Ni decay - requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star, which, in the decades before its death, must have experienced a luminous blue variable (LBV) eruption like the 19th century eruption of η Carinae. However, this scenario fails to explain the weak and unabsorbed soft X-rays detected by Chandra. Radioactive decay of 56Ni may be a less objectionable hypothesis, but it would imply a large Ni mass of ∼22 M⊙, requiring SN 2006gy to have been a pair-instability supernova where the star's core was obliterated. While this is still uncertain, SN 2006gy is the first supernova for which we have good reason to suspect a pair-instability explosion. Based on a number of lines of evidence, we eliminate the hypothesis that SN 2006gy was a "Type IIa" event, that is, a white dwarf exploding inside a hydrogen envelope. Instead, we propose that the progenitor was a very massive evolved object like η Carinae that, contrary to expectations, failed to shed its hydrogen envelope. SN 2006gy implies that some of the most massive stars can explode prematurely during the LBV phase, never becoming Wolf-Rayet stars. SN 2006gy also suggests that they can create brilliant supemovae instead of experiencing ignominious deaths through direct collapse to a black hole. If such a fate is common among the most massive stars, then observable supernovae from Population III stars in the early universe will be more numerous than previously believed. © 2007. The American Astronomical Society. All rights reserved.
• Walborn, N. R., Smith, N., Howarth, I. D., Kober, G. V., Gull, T. R., & Morse, J. A. (2007). Interstellar absorption-line evidence for high-velocity expanding structures in the Carina Nebula foreground. Publications of the Astronomical Society of the Pacific, 119(852), 156-169.
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  Abstract: The extreme, high-velocity interstellar absorption-line profiles toward η Carinae and 16 neighboring stars in Trumpler 16 are examined, including several new sight lines observed in the ultraviolet with the Hubble Space Telescope or in the optical from the Magellan and European Southern Observatories. No two sight lines are identical, but many velocity components are in common. When the velocity scale is shifted to a standard of rest defined by the Carina Nebula emission lines, the symmetries between negative and positive velocities are striking; at least 15 distinct "shells" can be recognized. This circumstance suggests that the complex expanding structures are predominantly in front of the ionizing cluster. There may be a relationship to indications of a supernova remnant in this direction, including a recent Chandra X-Ray Observatory image. Interpretations in terms of high-energy phenomena generated by ongoing star formation possibly on the near side of the giant H II region are also discussed. © 2007. The Astronomical Society of the Pacific. All rights reserved.
• Bally, J., Licht, D., Smith, N., & Walawender, J. (2006). Irradiated and bent jets in the Orion Nebula. Astronomical Journal, 131(1), 473-500.
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  Abstract: We present new images and proper-motion measurements of irradiated outflows from young stars in the outskirts of the Orion Nebula obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope. The images reveal many new outflows and new details in previously detected flows. The large-scale bipolar flows such as HH 502, 505, 874, and 876 contain multiple shocks whose velocities systematically decrease with increasing distance from their sources as the flows bend away from the core of the Orion Nebula. We consider several mechanisms for bending jets, including radiation pressure, the rocket effect on a neutral jet, and the impact of a side wind. While mild bends may be explained by either radiation pressure or the rocket effect, the extreme bends of some Orion jets and LL Ori-type bow shocks are best explained by the interaction of these outflows with a large-scale flow from the nebular core. The jet Hα emission measures and geometry are used to estimate their mass-loss rates, which range from about Ṁ ∼ 10 -9 to 10 -6 M ⊙ yr -1. Many of the quasi-parabolic bow shocks that wrap around young stars in Orion (the LL Ori-type objects) exhibit large gaps between the observed jets and the parabolic fronts facing the core of the nebula. These may indicate the additional action of a wide-angle outflow component such as a T Tauri stellar wind, a proplyd photoablation flow, or possibly a photoablation flow from the jet itself. The Hα surface brightness and radii of the LL Ori fronts are used to estimate that the ṀV W products of the wide-angle flow components have values around 10 -6 M ⊙ yr -1 km s -1. The side-wind density and velocity are also constrained. Outside the nebular core, the greatest concentration of bent jets and LL Ori-type parabolic fronts is located south and west of the Trapezium. The nonuniform, clumpy spatial distribution of jets, outflow sources, and proplyds in the outskirts of the Orion Nebula indicate that star formation occurred in small hierarchical clusters. © 2006. The American Astronomical Society. All rights reserved.
• Bautista, M. A., Hartman, H., Gull, T. R., Smith, N., & Lodders, K. (2006). [Ti II] and [Ni II] emission from the strontium filament of η Carinae. Monthly Notices of the Royal Astronomical Society, 370(4), 1991-2003.
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  Abstract: We study the nature of the [Ti II] and [Ni II] emission from the so-called strontium filament found in the ejecta of η Carinae. To this purpose, we employ multilevel models of the Ti II and Ni II systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Tin ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 107 cm-3 and a temperature around 6000 K. In analysing three observations with different slit orientations recorded between 2000 March and 2001 November, we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust-gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of η Carinae. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of Ti is likely the result of selective photoevaporation of Ti-bearing grains. Some mechanisms for such a scenario are proposed. © 2006 RAS.
• Heng, K., McCray, R., Zhekov, S. A., Challis, P. M., Chevalier, R. A., P., A., Fransson, C., Garnavich, P., Kirshner, R. P., Lawrence, S. S., Lundqvist, P., Panagia, N., Pun, C. S., Smith, N., Sollerman, J., & Wang, L. (2006). Evolution of the reverse shock emission from SNR 1987A. Astrophysical Journal, 644(2 II), 959-970.
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  Abstract: We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of the Hα and Lyα emission from supernova remnant (SNR) 1987A. With the aid of earlier data, from 1997 October to 2002 October, we track the local evolution of Lyα emission and both the local and global evolution of Hα emission. The most recent observations allow us to directly compare the Hα and Lyα emission from the same slit position and at the same epoch. Consequently, we find clear evidence that, unlike Hα, Lyα is reflected from the debris by resonant scattering, In addition to emission that we can clearly attribute to the surface of the reverse shock, we also measure comparable emission, in both Hα and Lyα, that appears to emerge from supernova debris interior to the surface. New observations taken through slits positioned slightly eastward and westward of a central slit show a departure from cylindrical symmetry in the Hα surface emission. Using a combination of old and new observations, we construct a light curve of the total Hα flux, F, from the reverse shock, which has increased by a factor of ∼4 over about 8 yr. However, due to large systematic uncertainties, we are unable to discern between the two limiting behaviors of the flux: F ∝ t (self-similar expansion) and F ∝ t 5 (halting of the reverse shock). Such a determination is important for constraining the rate of hydrogen atoms crossing the shock, which is relevant to the question of whether the reverse shock emission will vanish in ≳7 yr. Future deep, low- or moderate-resolution spectra are essential for accomplishing this task. © 2006. The American Astronomical Society. All rights reserved.
• Hrivnak, B. J., Smith, N., Y., K., Kelly, D. M., Kwok, S., & Sahai, R. (2006). Using H₂ emission to study the fast wind in proto-planetary nebulae. Proceedings of the International Astronomical Union, 2(234), 423-424.
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  Abstract: We present the results of a high-resolution H2 imaging and spectroscopic study of four bipolar proto-planetary nebulae: IRAS 16594-4656, Hen 3-401, Rob 22, and IRAS 17150-3224. These reveal the locations and kinematics of the H2 emission and the shaping of the nebulae by their collimated fast winds. © 2006 International Astronomical Union.
• Lynch, D. K., Woodward, C. E., Geballe, T. R., Russell, R. W., Rudy, R. J., Venturini, C. C., Schwarz, G. J., Gehrz, R. D., Smith, N., Lyke, J. E., Bus, S. J., Sitko, M. L., Harrison, T. E., Fisher, S., Eyres, S. P., Evans, A., Shore, S. N., Starrfield, S., Bode, M. F., , Greenhouse, M. A., et al. (2006). Early infrared spectral development of V1187 scorpii (nova scorpii 2004 NO. 2). Astrophysical Journal Letters, 638(2 I), 987-1003.
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  Abstract: We report on an unprecedented infrared time series of spectra of V1187 Sco, a very fast ONeMg nova. The observations covered a 56 day period (2004 August 6-September 30) starting 2 days after the nova's peak brightness. Time evolution of the spectra revealed changing line strengths and profiles on timescales of less than a day to weeks as the nova evolved from early postmaximum to early coronal phases. When our ground-based optical and Spitzer Space Telescope data were combined, the wavelength coverage of 0.38-36 μm allowed an accurate spectral energy distribution to be derived when it was about 6 weeks after outburst. Developing double structure in the He I lines showed them changing from narrow to broad in only a few days. Using the O I lines in combination with the optical spectra, we derived a reddening of E(B - V) = 1.56 ± 0.08 and a distance of 4.9 ± 0.5 kpc. Modeling of the ejected material strongly suggested that it was geometrically thick with ΔR/R = 0.8-0.9 (more of a wind than a shell) and a low filling factor of order a few percent. The line shapes were consistent with a cylindrical jet, bipolar, or spherical Hubble flow expansion with a maximum speed of about -3000 km s-1. The central peak appeared to be more associated with the spherical component, while the two peaks (especially in Hβ) suggested a ring with either a lower velocity component or with its axis inclined to the line of sight. © 2006. The American Astronomical Society. All rights reserved.
• Millier, D. J., Gull, T., Nielsen, K., Sonneborn, G., Iping, R., Smith, N., Corcoran, M., Damineli, A., Hamann, F. W., Martin, J. C., & Weis, K. (2006). The UV scattering halo of the central source associated with η carinae. Astrophysical Journal Letters, 642(2 I), 1098-1116.
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  Abstract: We have made an extensive study of the UV spectrum of 77 Carinae and find that we do not directly observe the star and its wind in the UV. Because of dust along our line of sight, the UV light that we observe arises from bound-bound scattering at large impact parameters. We obtain a reasonable fit to the UV spectrum by using only the flux that originates outside (X'033. This explains why we can still observe the primary star in the UV despite the large optical extinction: it is due to the presence of an intrinsic coronagraph in the 77 Car system and to the extension of the UV-emitting region. It is not due to peculiar dust properties alone. We have computed the spectrum of the purported companion star and show that it could only be directly detected in the UV spectrum, preferentially in the FUSE spectral region (912-1175 A). However, we find no direct evidence for a companion star, with the properties indicated by X-ray studies and studies of the Weigelt blobs, in UV spectra. This might be due to reprocessing of the companion's light by the dense stellar wind of the primary. Broad Fe n and [Fe II] emission lines, which form in the stellar wind, are detected in spectra taken in the southeastern lobe, 0″.2 from the central star. The wind spectrum shows some similarities to the spectra of the B and D Weigelt blobs but also shows some marked differences in that lines pumped by Lyα are not seen. The detection of the broad lines lends support to our interpretation of the UV spectrum and to our model for η Car. © 2006. The American Astronomical Society. All rights reserved.
• Morse, J. A., Smith, N., Blair, W. P., Kirshner, R. P., Winkler, P. F., & Hughes, J. P. (2006). Hubble space telescope observations of oxygen-rich supernova remnants in the magellanic clouds. III. WFPC2 imaging of the young, Crab-like supernova remnant SNR 0540-69.3. Astrophysical Journal Letters, 644(1), 188-197.
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  Abstract: HST images with WFPC2 of the young, oxygen-rich, Crab-like supernova remnant SNR 0540-69.3 in the Large Magellanic Cloud (LMC) reveal details of the emission distribution and the relationship between the expanding ejecta and synchrotron nebula. The emission distributions appear very similar to those seen in the Crab Nebula, with the ejecta located in a thin envelope surrounding the synchrotron nebula. The [O III] emission is more extended than other tracers, forming a faint "skin" around the denser filaments and synchrotron nebula, as also observed in the Crab. The [O III] exhibits somewhat different kinematic structure in long-slit spectra, including a more extended high-velocity emission halo not seen in images. Yet even the fastest expansion speeds in SNR 0540-69.3's halo are slow when compared to most other young supernova remnants, although the Crab Nebula has similar slow expansion speeds. We show a striking correspondence between the morphology of the synchrotron nebula observed in an optical continuum filter with that recently resolved in Chandra X-ray images. We argue that the multicomponent kinematics and filamentary morphology of the optical emission-line features likely result from magnetic Rayleigh-Taylor instabilities that form as the synchrotron nebula expands and sweeps up ejecta, as seen in the Crab Nebula. Our images and spectra help to refine our understanding of SNR 0540-69.3 in several more detailed respects: they confirm the identification of Hα + [N II] in the red spectrum, show that the systemic velocity of SNR 0540-69.3 is not significantly different from that of the LMC, and hint at a lower Ne abundance than the Crab (potentially indicating a more massive progenitor star). © 2006. The American Astronomical Society. All rights reserved.
• Smith, N. (2006). A census of the Carina Nebula - I. Cumulative energy input from massive stars. Monthly Notices of the Royal Astronomical Society, 367(2), 763-772.
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  Abstract: The Carina Nebula (NGC 3372) is our richest nearby laboratory in which to study feedback through ultraviolet radiation and stellar winds from very massive stars during the formation of an OB association, at an early phase in the evolution of the surrounding proto-superbubble before supernova explosions have influenced the environment. This feedback is triggering successive generations of new star formation around the periphery of the nebula, while simultaneously evaporating the gas and dust reservoirs out of which young stars are trying to accrete material. This paper takes inventory of the combined effect from all the known massive stars that power the Carina Nebula through their total ionizing flux and integrated mechanical energy from their stellar winds. Carina is close enough and accessible enough that spectral types for individual stars are available, and many close binary and multiple systems have recently been spatially resolved, so that one can simply add them. Adopting values from the literature for corresponding spectral types, the present-day total ionizing photon luminosity produced by the 65 O stars and three WNL stars in Carina is, the total bolometric luminosity of all stars earlier than B2 is, and the total mechanical luminosity of stellar winds is. The total QH was about 25 per cent higher when η Carinae was on the main sequence, before it and its companion were surrounded by its obscuring dust shell; for the first 3 Myr, the net ionizing flux of the 70 O stars in Carina was about 150 times greater than in the Orion Nebula. About has been contributed to the H ii region by stellar wind mass-loss during the past 3 Myr. Values for QH and L SW are also given for the individual clusters Tr14, 15 and 16, and Bo10 and 11, which are more relevant on smaller spatial scales than the total values for the whole nebula. © 2006 RAS.
• Smith, N. (2006). Erratum: A census of the Carina Nebula - I. Cumulative energy input from massive stars (Monthly Notices of the Royal Atronomical Society (2006) 367 (763-772)). Monthly Notices of the Royal Astronomical Society, 368(4), 1983-1984.
• Smith, N. (2006). The structure of the Homunculus. I. Shape and latitude dependence from H₂ and [Fe II] velocity maps of η Carinae. Astrophysical Journal, 644(2 II), 1151-1163.
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  Abstract: High-resolution long-slit spectra obtained with the Phoenix spectrograph on Gemini South provide our most accurate probe of the three-dimensional structure of the Homunculus Nebula around η Carinae. The new near-infrared spectra dramatically confirm the double-shell structure inferred previously from thermal dust emission, resolving the nebula into a very thin outer shell seen in H 2 and a warmer, thicker inner layer seen in [Fe II]. The remarkably thin and uniform H2 skin hints that the most important mass loss during the 19th century eruption had a very short duration of ≲5 yr. H 2 emission traces the majority of the more than 10 M⊙ of material in the nebula and has an average density of order n H≳106.5 cm-3. This emission, in turn, yields our first definitive picture of the exact shape of the nebula, plus a distance of 2350 ± 50 pc and an inclination angle of ∼41°. The distribution of the H2 emission provides the first measure of the latitude dependence of the speed, mass loss, and kinetic energy associated with η Car's 19th century explosion. Almost 75% of the total mass and more than 90% of the kinetic energy in the ejecta were released at high latitudes between 45° and the polar axis. This rules out a model for the bipolar shape in which an otherwise spherical explosion was pinched at the waist by a circumstellar torus. Instead, most of the mass appears to have been directed poleward by the explosion itself. H2 emission also provides our first reliable picture of the critical innermost waist of the Homunculus, yielding clues to the observed morphology of the core and the more extended equatorial debris. © 2006. The American Astronomical Society. All rights reserved.
• Smith, N., & Hartigan, P. (2006). Infrared [Fe II] emission from P Cygni's nebula: Atomic data, mass, kinematics, and the 1600 AD outburst. Astrophysical Journal Letters, 638(2 I), 1045-1055.
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  Abstract: We present moderate- and high-dispersion 1-2.5 μm spectra of the ∼ 10quot; radius nebula around P Cygni, dominated by bright emission lines of [Fe II]. Observed [Fe II] line ratios disagree with theoretical transition rates in the literature, so we use the spectrum of P Cyg's nebula to constrain the atomic data for low-lying levels of [Fe II]. Of particular interest is the ratio [Fe II] λ12567/λ16435, often used as a reddening indicator, for which we empirically derive an intrinsic value of 1.49, which is 10%-40% higher than previous estimates. High-dispersion spectra of [Fe II] λ16435 constrain the geometry, detailed structure, and kinematics of P Cyg's nebula, which is the major product of P Cyg's outburst in 1600 AD. We use the [N II]/[N I] line ratio to conclude that the nebula is mostly ionized, with a total mass of ∼0.1 M⊙, more than the mass lost by the stellar wind since the eruption. For this mass, we would expect a larger infrared excess than observed. We propose that the dust that obscured the star after the outburst has since been largely destroyed, releasing Fe into the gas phase to produce the bright [Fe II] emission. The kinetic energy of this shell is ∼1046.3 ergs, far less than the kinetic energy released during the giant eruption of η Car in the 1840s, but close to the value for η Car's smaller 1890 outburst. In this respect, it is interesting that the infrared spectrum of P Cyg's nebula resembles that of the "Little Homunculus" around η Car, ejected in that star's 1890 eruption. The mass and kinetic energy in the nebulae of η Car and P Cyg give insight into the range of parameters expected for extragalactic η Car-like eruptions. © 2006. The American Astronomical Society. All rights reserved.
• Smith, N., & Owocki, S. P. (2006). On the role of continuum-driven eruptions in the evolution of very massive stars and population III stars. Astrophysical Journal Letters, 645(1 II), L45-L48.
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  Abstract: We suggest that the mass lost during the evolution of very massive stars may be dominated by optically thick, continuum-driven outbursts or explosions, instead of by steady line-driven winds. In order for a massive star to become a Wolf-Rayet star, it must shed its hydrogen envelope, but new estimates of the effects of clumping in winds from O-type stars indicate that line driving is vastly insufficient. We discuss massive stars above roughly 40-50 M ⊙, which do not become red supergiants and for which the best alternative is mass loss during brief eruptions of luminous blue variables (LBVs). Our clearest example of this phenomenon is the 19th century outburst of η Carinae, when the star shed 12-20 M⊙ or more in less than a decade. Other examples are circumstellar nebulae of LBVs and LBV candidates, extragalactic η Car analogs (the so-called supernova impostors), and massive shells around supernovae and gamma-ray bursters. We do not yet fully understand what triggers LBV outbursts or what supplies their energy, but they occur nonetheless, and they present a fundamental mystery in stellar astrophysics. Since line opacity from metals becomes too saturated, the extreme mass loss probably arises from a continuum-driven wind or a hydrodynamic explosion, both of which are insensitive to metallicity. As such, eruptive mass loss could have played a pivotal role in the evolution and ultimate fate of massive metal-poor stars in the early universe. If they occur in these Population III stars, such eruptions would also profoundly affect the chemical yield and types of remnants from early supernovae and hypernovae thought to be the origin of long gamma-ray bursts. © 2006. The American Astronomical Society. All rights reserved.
• Smith, N., Brooks, K. J., Koribalski, B. S., & Bally, J. (2006). Cleaning up η Carinae: Detection of ammonia in the Homunculus Nebula. Astrophysical Journal Letters, 645(1 II), L41-L44.
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  Abstract: We report the first detection of ammonia in the Homunculus Nebula around η Carinae, which is also the first detection of emission from a polyatomic molecule in this or any other luminous blue variable (LBV) nebula. Observations of the NH3 (J, K) = (3, 3) inversion transition made with the Australia Telescope Compact Array reveal emission at locations where infrared H2 emission had been detected previously, near the strongest dust emission in the core of the Homunculus. We also detect ammonia emission from the so-called strontium filament in the equatorial disk. The presence of NH 3 around η Car hints that molecular shells around some Wolf-Rayet stars could have originated in prior LBV eruptions, rather than in cool red supergiant winds or the ambient interstellar medium. Combined with the lack of any CO detection, NH3 seems to suggest that the Homunculus is nitrogen-rich like the ionized ejecta around η Car. It also indicates that the Homunculus is a unique laboratory in which to study unusual molecule and dust chemistry, as well as their rapid formation in a nitrogen-rich environment around a hot star. We encourage future observations of other transitions like NH3 (1, 1) and (2, 2), related molecules like N2H +, and renewed attempts to detect CO. © 2006. The American Astronomical Society. All rights reserved.
• Temim, T., Gehrz, R. D., Woodward, C. E., Roellio, T. L., Smith, N., Rudnick, L., Polomski, E. F., Davidson, K., Yuen, L., & Onaka, T. (2006). Spitzer space telescope infrared imaging and spectroscqpy of the Crab Nebula. Astronomical Journal, 132(4), 1610-1623.
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  Abstract: We present 3.6, 4.5, 5.8, 8.0, 24, and 70 μm images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, low- and high-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II] 1.644 μm. The 8.0 μm image, made with a bandpass that includes [Ar II] 7.0 μm, resembles the general morphology of visible Hα and near-IR [Fe II] line emission, while the 3.6 and 4.5 μm images are dominated by continuum synchrotron emission. The 24 and 70 μm images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 μm images reveals a spatial variation in the synchrotron power-law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum of the jet and torus with the steeper spectrum of the diffuse nebula. We also see suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and polar jet structures seen in Chandra and Hubble Space Telescope images (Hester et al. 2002), can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high-resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of ≈1264 km s -1. © 2006. The American Astronomical Society. All rights reserved.
• Bally, J., Cunningham, N., Moeckel, N., & Smith, N. (2005). Nearby regions of massive star formation. Proceedings of the International Astronomical Union, 1, 12-22.
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  Abstract: Observations of the nearest regions of massive star formation such as Orion are reviewed. Early-type stars in the local OB associations, as well as their superbubbles and supershells provide a fossil record of massive star birth in the Solar vicinity over about the last 40 Myr. This record shows that most massive stars are born from dense, high-pressure, hot cores which spawn transient clusters that dissipate into the field soon after formation. A large fraction (15 to 30%) of massive stars are high-velocity runaways moving at more than 20 km s-1. High-mass stars have a larger companion fraction than their lower-mass siblings. The Orion star forming complex contains the nearest site of on-going massive star formation. Studies of the Orion Nebula and the dense molecular cloud core located immediately behind the HII region provide our sharpest view of massive star birth. This region has formed a hierarchy of clusters within clusters. The Trapezium, OMC-1S, and OMC-1 regions represent three closely spaced sub-clusters within the more extended Orion Nebula Cluster. The oldest of these sub-clusters, which consists of the Trapezium stars, has completely emerged from its natal core. The OMC-1S and OMC-1 regions, are still highly embedded and forming clusters of additional moderate and high mass stars. Over a dozen YSOs embedded in OMC-1S are driving jets and outflows, many of which are injecting energy and momentum into the Orion Nebula. Recent proper motion measurements indicate that the Becklin-Neugebauer object is a high-velocity star moving away from the OMC1 core with a velocity of 30 km s-1, making it the youngest high-velocity star known. Source I may be moving in the opposite direction with a velocity of about 12 km s-1. The projected separation between source I and BN was less than few hundred AU about 500 years ago. The spectacular bipolar molecular outflow and system of shock-excited H2 fingers emerging from OMC-1 has a dynamical age of about 1100 years. It is possible that a dynamical interaction between three or more stars in OMC-1 led to the formation of this eruptive outflow. © 2005 International Astronomical Union.
• Bally, J., Licht, D., Smith, N., & Walawender, J. (2005). Outflows in the Orion Nebula: HH 540 from the beehive proplyd. Astronomical Journal, 129(1), 355-362.
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  Abstract: We present Hubble Space Telescope Advanced Camera for Surveys images of the giant proplyd 181-826 in the southern Orion Nebula. This object exhibits a variety of known proplyd properties - an optically visible central star, a silhouette disk, a bright proplyd ionization front, and a bipolar microjet emerging along the disk axis that powers a larger Herbig-Haro flow. The proplyd ionization front is remarkable because of its large size (a radius of about 800 AU) and because of its corrugated structure consisting of a set of coaxial rings with the same orientation as the embedded silhouette disk. The rings are centered on the disk/jet axis, and we discuss possible mechanisms for their formation. The silhouette disk has an outer radius of about 160 AU, and its axis is inclined by an angle of about 60° with respect to our line of sight. A prominent reflection nebula protrudes along the disk axis toward the south, marking the base of the approaching outflow, and a faint knot on the north side of the disk indicates that the nebula is bipolar. Fabry-Pérot images reveal a high-velocity blueshifted jet with a mass-loss rate of about 10 -8 M⊙ yr -1 emerging along the disk axis. It has a velocity (corrected for the outflow inclination angle) of about 160 km s -1 and can be traced for about 1′ toward the south. A chain of three lower velocity blueshifted bow shocks, collectively known as HH 540, extend several arcminutes south of 181-826 along the same axis, tracing a large-scale outflow powered by this jet. © 2005. The American Astronomical Society. All rights reserved.
• Brooks, K. J., Garay, G., Nielbock, M., Smith, N., & Cox, P. (2005). Simba observations of the keyhole nebula. Astrophysical Journal Letters, 634(1 I), 436-441.
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  Abstract: We report observations made with the SIMBA bolometer at SEST to measure the 1.2 mm continuum emission toward the Keyhole nebula. We have detected 1.2 mm emission toward the ionized gas filaments of the Car II radio source that is attributed to thermal free-free emission. Several compact 1.2 mm emission sources have also been identified and found to correspond to bright-rimmed molecular globules. Under the assumption that for these sources the 1.2 mm emission corresponds to dust, we find mass estimates in the range 3-19 M ⊙, which are consistent with previous molecular line measurements. The data also yield new 1.2 mm flux measurements at two different epochs during the cyclic brightness variation of η Carinae. No emission was detected toward the trademark dark keyhole of the nebula, consistent with it being cool molecular gas situated at the outskirts of the H II region. © 2005. The American Astronomical Society. All rights reserved.
• Grosso, N., Feigelson, E. D., Getman, K. V., Townsley, L., Broos, P., Flaccomio, E., McCaughrean, M. J., Micela, G., Sciortino, S., Bally, J., Smith, N., Muench, A. A., Garmire, G. P., & Palla, F. (2005). Chandra Orion ultradeep project census of X-ray stars in the BN-KL and OMC-1S regions. Astrophysical Journal, Supplement Series, 160(2), 530-556.
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  Abstract: We present a study of the X-ray sources detected in the vicinity of two density peaks in the Orion Molecular Cloud 1 (OMC-1) behind the Orion Nebula Cluster (ONC), as seen in the exceptionally deep (∼10 days) exposure of the Chandra Orion Ultradeep Project (COUP). We focus on a 40″ × 50″ region around the Becklin-Neugebauer object and Kleinmann-Low nebula (collectively BN-KL) and a 60″ × 75″ region around OMC-1S, a secondary star-forming peak some 90″ south of BN-KL. A total of 43 and 60 X-ray sources were detected in BN-KL and OMC-1S, respectively, of which one-half and one-third, respectively, were found to be foreground members of the ONC, while the remaining sources are identified as obscured X-ray sources with column densities 22 ≲ log (N H/cm -2) ≲ 24. All but 5 and 18 of these sources have near-infrared stellar counterparts, and 22 of these appear to be young stellar objects (YSOs). X-ray sources are found close to four luminous mid-IR sources, namely, BN, IRc3-i2, IRc2-C, and source n; their X-ray variability and spectral properties are typical of coronal activity in low-mass stars rather than wind emission from massive stars, suggesting that the X-ray emission may be arising from companions. The X-ray light curve of the X-ray source close to BN shows a periodicity of ∼8.3 days, and from an X-ray image deconvolution of the region around BN, we conclude that either BN itself or a low-mass companion with a projected separation of ≃200 AU was detected. On the other hand, no emission is seen from the bright radio source I, held by some to be the main source of luminosity in BN-KL. In OMC-1S, Chandra unveils a new subcluster of seven YSOs without infrared counterparts. We compare the hard-band X-ray luminosity functions of obscured X-ray sources in BN-KL and OMC-1S with unobscured X-ray sources in the ONC, and we estimate that the true population of obscured sources in BN-KL and OMC-IS is ≃46 and 57 stars, with 90% confidence intervals of 34-71 and 42-82 stars, respectively. © 2005. The American Astronomical Society. All rights reserved.
• Smith, N. (2005). Doppler tomography of the Little Homunculus: High-resolution spectra of [Fe II] λ16 435 around Eta Carinae. Monthly Notices of the Royal Astronomical Society, 357(4), 1330-1336.
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  Abstract: High-resolution spectra of [Fe II] λ16435 around η Carinae provide powerful diagnostics of the geometry and kinematics of the 'Little Homunculus' (LH) growing inside the larger Homunculus nebula. The LH expansion is not perfectly homologous: while low latitudes are consistent with linear expansion since 1910, the polar caps imply ejection dates around 1920-1930. However, the expansion speed of the LH is much slower than the post-eruption wind, so the star's powerful wind may accelerate the LH. With an initial ejection speed of 200 km s-1 in 1890, the LH would have been accelerated to its present speed if the mass is roughly 0.1 M⊙. This agrees with an independent estimate of the LH mass based on its density and volume. In any case, an ejection after 1930 is ruled out. Using the LH as a probe of the 1890 event then, it is evident that its most basic physical parameters (total mass and kinetic energy, which are 0.1 M⊙ and 1046.9 erg, respectively) are orders of magnitude less than during the giant eruption in the 1840s. Thus, the ultimate energy sources were different for these two events - yet their ejecta have the same bipolar geometry. This clue may point toward a collimation mechanism separate from the underlying causes of the outbursts. © 2005 RAS.
• Smith, N., & Bally, J. (2005). Discovery of a candidate protoplanetary disk around the embedded source IRc9 in Orion. Astrophysical Journal Letters, 622(1 II), L65-L68.
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  Abstract: We report the detection of spatially extended mid-infrared emission around the luminous embedded star IRc9 in OMC-1, as seen in 8.8, 11.7, and 18.3 μm images obtained with the Thermal-Region Camera and Spectrograph on Gemini South. The extended emission is asymmetric, and the morphology is reminiscent of warm dust disks around other young stars. The putative disk has a radius of roughly 1′.5 (700 AU) and a likely dust mass of almost 10 Moplus;. The infrared spectral energy distribution of IRc9 indicates a total luminosity of ∼100 Loplus;, implying that it will become an early A-type star when it reaches the main sequence. Thus, the candidate disk around IRc9 may be a young analog of the planetary debris disks around Vega-like stars and the disks of Herbig Ae stars, and may provide a laboratory in which to study the earliest phases of planet formation. A disk around IRc9 may also add weight to the hypothesis that an enhanced T Tauri-like wind from this star has influenced the molecular outflow from the OMC-1 core. © 2005. The American Astronomical Society. All rights reserved.
• Smith, N., & Gehrz, R. D. (2005). Bipolar symbiotic planetary nebulae in the thermal infrared: M2-9, Mz 3, and He 2-104. Astronomical Journal, 129(2), 969-978.
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  Abstract: We present thermal-infrared images of three extreme bipolar objects, M2-9, Mz 3, and He 2-104. They are bipolar planetary nebulae with bright central stars and are thought to be powered by symbiotic binary systems. The mid-infrared images spatially resolve the spectral energy distributions of the central engines from the surrounding nebulae. A warm dust component of several hundred degrees can account for the core emission, while a cooler component of ∼ 100 K produces the more extended emission from the bipolar lobes. In every case, the dust mass for the unresolved core region is orders of magnitude less than that in the extended lobes, raising doubts that the hypothetical disks in the core could have been responsible for pinching the waists of the nebulae. We find total masses of roughly 0.5-1 M⊙ in the nebulae of M2-9 and Mz 3, requiring that this material was donated by intermediate-mass progenitor stars. The mass of He 2-104's nebula is much lower, and any extended emission is too faint to detect in our images. Extended dust emission is detected around both M2-9 and Mz 3, in both cases resembling the distribution of ionized gas. Our images of Mz 3 have the highest signal-to-noise ratio in the extended polar lobes, and we show that the fairly uniform color temperature derived from our images can explain the 110 K dust component that dominates the far-infrared spectral energy distribution. In the case of Mz 3, most of the mass traced by dust is concentrated at high latitudes, and we note possible evidence for grain destruction in shocks indicated by an anticorrelation between [Fe II] and dust emission. Except for these regions with enhanced [Fe n] emission, the dust continuum closely resembles the distribution of ionized gas. © 2005. The American Astronomical Society. All rights reserved.
• Smith, N., Balick, B., & Gehrz, R. D. (2005). Kinematic structure of H ₂ and [Fe II] in the bipolar planetary nebula M2-9. Astronomical Journal, 130(2), 853-861.
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  Abstract: We present new high-dispersion, long-slit, infrared (IR) spectra of the double-shell bipolar planetary nebula M2-9 in the emission lines [Fe II] λ16435 and H 2 v = 1-0 S(1) λ21218. H 2 spectra reveal for the first time the kinematic structure of the outer shell in M2-9. Kinematics of the inner shell, traced by [Fe II], resemble those of optical forbidden lines like [N II] λ6583, although we note subtle differences. [Fe II] and H 2 shells have expansion speeds roughly proportional to distance from the star ("Hubble" flows) and share the same dynamical age of 1200-2000 yr, depending on the distance to M2-9. Thus, the inner ionized lobes and outer molecular lobes, as well as the molecular torus and "outer loops" measured by other observers, were all formed around the same time. Consequently, their nested structure likely arises from an excitation gradient rather than independent ejections. H 2 and [Fe II] emission is distributed more uniformly than [N II], and IR lines are not dominated by the moving ionization pattern like visual-wavelength lines. We suggest that this is because IR lines of [Fe II] and H 2 are excited by relatively isotropic far-UV radiation (Balmer continuum), whereas optical lines respond to a directed rotating beam of Lyman continuum. Finally, we highlight intriguing similarities between M2-9 and the Homunculus of η Car, despite the different central engines powering the two nebulae. © 2005. The American Astronomical Society. All rights reserved.
• Smith, N., Bally, J., Licht, D., & Walawender, J. (2005). New silhouette disks with reflection nebulae and outflows in the Orion Nebula and M43. Astronomical Journal, 129(1), 382-392.
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  Abstract: We report the detection of several new circumstellar disks seen in silhouette against background nebular light in the outskirts of the Orion Nebula and the neighboring H II region M43. These were detected as part of our Ha survey of Orion with the Advanced Camera for Surveys on board the Hubble Space Telescope. Several of the disks show bipolar reflection nebulae, microjets, or pronounced temporal variability of their central stars. The relatively large fraction of bipolar reflection nebulae and microjets in our sample may be a selection effect caused by the faint nebular background far from the Trapezium. Two disks in our sample are large and particularly noteworthy: A nearly edge-on disk, d216-0939, is located several arcminutes northwest of M43 and resembles the famous HH 30 disk/jet system in Taurus. It drives the 0.15 pc long bipolar outflow HH 667 and exhibits a remarkable asymmetric reflection nebula caused by the tilt of the flared disk. With a diameter of ∼2″6 (1200 AU), d216-0939 is as large as the giant edge-on silhouette disk d114-426 in the core of the Orion Nebula. The large disk d253-1536 is located in a binary system embedded within an externally ionized giant proplyd in M43. The disk exhibits distortions that we attribute to tidal interactions with the companion star. The bipolar jet HH 668 emerges from the proplyd ionization front in a direction orthogonal to the disk and can be traced to the young star embedded within it. A bow shock lies 54″ south of this binary system along the outflow axis. Proper motions over a 1.4 yr baseline confirm that these emission knots are indeed moving away from d253 -1536 with speeds as high as ∼330 km s -1 in the HH 668 microjet and slower motion farther from the star. © 2003. The American Astronomical Society. All rights reserved.
• Smith, N., Bally, J., Shuping, R. Y., Morris, M., & Kassis, M. (2005). Thermal dust emission from proplyds, unresolved disks, and shocks in the Orion Nebula. Astronomical Journal, 130(4), 1763-1777.
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  Abstract: We present a new 11.7 μm mosaic image of the inner Orion Nebula obtained with the T-ReCS instrument on Gemini South. The map covers 2.′7 × 1.′6, with a diffraction-limited spatial resolution of 0.″35; it includes the BN/KL region, the Trapezium, and OMC-1 South. Excluding BN/KL, we detect 91 thermal-IR point sources, with 27 known proplyds and over 30 "naked" stars showing no extended structure in Hubble Space Telescope (HST) images. Within the region we surveyed, ∼80% of known proplyds show detectable thermal-IR emission, almost 40% of naked stars are detected at 11.7 μm, and the fraction of all visible sources with 11.7 μm excess emission (including both proplyds and stars with unresolved disks) is roughly 50%. These fractions exclude embedded sources. Thermal dust emission from stars exhibiting no extended structure in HST images is surprising and means that they have retained circumstellar dust disks comparable to the size of our solar system. Proplyds and stars with IR excess are not distributed randomly in the nebula; instead, they show a clear anticorrelation in their spatial distribution, with proplyds clustered close to θ1 Ori C and other IR sources found preferentially farther away. We suspect that the clustered proplyds trace the youngest ∼0.5 Myr age group associated with the Trapezium, while the more uniformly distributed sources trace the older 1-2 Myr population of the Orion Nebula Cluster. This suggests that small protoplanetary disks persist for a few million years in irradiated environments and hints that hierarchical subclustering has been important on ∼30″ scales around the Trapezium. We detect 11.7 μm emission from the five brightest members of the Trapezium (θ1 Ori A, B, C, D, and E), caused by free-free stellar wind emission and possibly emission from dusty disks around companion stars. Within 30″ of θ1 Ori C, 100% of known proplyds are detected at 11.7 μm, and they exhibit remarkable limb-brightened dust arcs at the collision of the proplyd mass loss and the wind from θ1 Ori C. The star θ1 Ori D is associated with the most prominent mid-IR dust arc of the Ney-Allen Nebula. We propose that this arc is the consequence of θ1 Ori D being the closest member of the Trapezium to the background cloud. Finally, we detect dust emission from Herbig-Haro jets in Orion, including HH 202, 529, 513, and 514. This is the first detection of mid-IR continuum emission from dust in the body of a collimated HH jet or bow shock. The presence of dust implies that some jet material must be lifted from large radii in the accretion disk (outside the dust sublimation radius) or entrained from the circumstellar environment. © 2005. The American Astronomical Society. All rights reserved.
• Smith, N., Morse, J. A., & Bally, J. (2005). The [O III] veil: Astropause of η Carinae's wind?. Astronomical Journal, 130(4), 1778-1783.
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  Abstract: We present narrowband images of η Carinae in the light of [O III] λ5007 obtained with the Hubble Space Telescope (HST) Wide Field Planetary Camera 2, as well as a ground-based image in the same emission line with a larger field of view. These images show a thin veil of [O III] emission around η Car and its ejecta, confirming the existence of an oxygen-bearing "cocoon" inferred from spectra. This [O III] veil may be the remnant of the preoutburst wind of η Car, and its outer edge probably marks the interface where η Car's ejecta meet the stellar wind of the nearby O4 V((f)) star HD 303308 or other ambient material in the Carina Nebula; i.e., it marks the "astropause" in η Car's wind. This veil is part of a more extensive [O III] shell that appears to be shaped and ionized by HD 303308. A pair of HST images with a 10 yr baseline shows no significant proper motion, limiting the expansion speed away from η Car to 12 ± 13 km s -1, or an expansion age of a few times 10 4 yr. Thus, this is probably the decelerated preoutburst luminous blue variable wind of 77 Car. The [O III] morphology is very different from that seen in [N II], which traces younger dense knots of CNO-processed material; this represents a dramatic shift in the chemical makeup of material recently ejected by η Car. This change in the chemical abundances of the ejecta may have resulted from the sudden removal of the star's outer envelope during η Car's 19th century outburst or an earlier but similar event. © 2005. The American Astronomical Society. All rights reserved.
• Smith, N., Stassun, K. G., & Bally, J. (2005). Opening the treasure Chest: A newborn star cluster emerges from its dust pillar in Carina. Astronomical Journal, 129(2), 888-899.
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  Abstract: We present detailed observations of the Treasure Chest, a compact nebula at the head of a dust pillar in the southern Carina Nebula. This object is of interest because it is an example of a dense young cluster containing at least one massive star, the formation of which may have been triggered by feedback from the very massive stars in the Carina Nebula, and possibly 77 Carinae itself. Our observations include narrowband images of Hα, [S II], [0 III], Paß, [Fe II], and H 2, broadband JHK images, and a visual wavelength spectrum of the nebula. We use these data to investigate both the nebular and stellar content of the object. The near-infrared emission-line images reveal a cavity inside the head of the dust pillar, which contains a dense cluster of young stars, whereas the observed spectrum of the nebula is consistent with an H II region ionized by the 09.5 V star CPD -59°2661. The embedded infrared cluster was discovered in Two Micron All Sky Survey data, but our new JHK images have improved spatial resolution and sensitivity, allowing an analysis of the stellar content of the newborn cluster. After subtracting contamination of field stars within the Carina Nebula itself, we compare the cluster's color-magnitude diagram with pre-main-sequence isochrones to derive a likely cluster age of less than about 0.1 Myr. This is in reasonable agreement with the dynamical age of a few times 104 yr for the expanding nebular cavity, indicating extreme youth. Stars in the Treasure Chest cluster are highly reddened, with extinction values as large as A V ∼ 50. Two-thirds of cluster members show strong infrared excess colors indicative of circumstellar disks, which may prove to be among the highest fraction yet seen for a young cluster once I-band photometry is considered. All evidence suggests that the Treasure Chest is an extremely young cluster that is just now breaking out of its natal cloud into the surrounding massive star-forming region and is a good target for more detailed study. ©2005. The American Astronomical Society. All rights reserved.
• Smith, N., Zhekov, S. A., Heng, K., Mccray, R., Morse, J. A., & Gladders, M. (2005). The reverse shock of SNR 1987A at 18 years after outburst. Astrophysical Journal Letters, 635(1 II), L41-L44.
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  Abstract: We use low-dispersion spectra obtained at the Magellan Observatory to study the broad Hα emission from the reverse shock of the infant supernova remnant SNR 1987A. These spectra demonstrate that the spatiokinematic structure of the reverse shock can be distinguished from that of the circumstellar ring and hot spots, even at ground-based spatial resolution. We measure a total dereddened Hα flux of 1.99(±0.22) × 10-13 ergs s-1 cm-2 at an epoch 18.00 yr after outburst. At 50 kpc, the total reverse shock luminosity in Hα is roughly 15 L⊙, which implies a total flux of neutral hydrogen atoms across the reverse shock of 8.9 × 1046 s1, or roughly 2.3 × 10 -3 M⊙ yr-1. This represents an increase by a factor of ∼4 since 1997. Lyman continuum radiation from gas shocked by the forward blast wave can ionize neutral hydrogen atoms in the supernova debris before they reach the reverse shock. If the inward flux of ionizing photons exceeds the flux of hydrogen atoms approaching the reverse shock, this preionization will shut off the broad Lyα and Haα emission. The observed X-ray emission of SNR 1987A implies that the ratio of ionizing flux to hydrogen atom flux across the reverse shock is presently at least 0.04. The X-ray emission is increasing much faster than the flux of atoms, and if these trends continue, we estimate that the broad Lyα and Hα emission will vanish in ≤7 yr. © 2005. The American Astronomical Society. All rights reserved.
• Corcoran, M. F., Hamaguchi, K., Gull, T., Davidson, K., Petre, R., Hillier, D. J., Smith, N., Damineli, A., Morse, J. A., Walborn, N. R., Verner, E., Collins, N., White, S., Pittard, J. M., Weis, K., Bomans, D., & Butt, Y. (2004). Waiting in the wings: Reflected X-ray emission from the Homunculus nebula. Astrophysical Journal Letters, 613(1 I), 381-386.
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  Abstract: We report the first detection of X-ray emission associated with the Homunculus nebula that surrounds the supermassive star η Car. The emission is characterized by a temperature in excess of 100 MK and is consistent with scattering of the time-delayed X-ray flux associated with the star. The nebular emission is bright in the northwestern lobe and near the central regions of the Homunculus, and fainter in the southeastern lobe. We also report the detection of an unusually broad Fe K fluorescent line, which may indicate fluorescent scattering off the wind of a companion star or some other high-velocity outflow. The X-ray Homunculus is the nearest member of the small class of Galactic X-ray reflection nebulae, and the only one in which both the emitting and reflecting sources are distinguishable.
• Hartman, H., Gull, T., Johansson, S., & Smith, N. (2004). Identification of emission lines in the low-ionization strontium filament near Eta Carinae. Astronomy and Astrophysics, 419(1), 215-224.
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  Abstract: We have obtained deep spectra from 1640 to 10100 Å with the Space Telescope Imaging Spectrograph (STIS) of the strontium filament, a largely neutral emission nebulosity lying close to the very luminous star Eta Carinae and showing an uncommon spectrum. Over 600 emission lines, both permitted and forbidden, have been identified. The majority originates from neutral or singly-ionized iron group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the only neutron capture element detected. The presence of Sr II, numerous strong Ti II and V II lines and the dominance of Fe I over Fe II are notable discoveries. While emission lines of hydrogen, helium, and nitrogen are associable with other spatial structures at other velocities within the Homunculus, no emission lines from these elements correspond to the spatial structure or velocity of the Sr filament. Moreover, no identified Sr filament emission line requires an ionization or excitation energy above approximately 8 eV. Ionized gas extends spatially along the aperture, oriented along the polar axis of the Homunculus, and in velocity around the strontium filament. We suggest that the strontium filament is shielded from ultraviolet radiation at energies above 8 eV, but is intensely irradiated by the central star at wavelengths longward of 1500 Å.
• Smith, N. (2004). Spatially extended K I λ7699 emission in the nebula of VY CMa: Kinematics and geometry. Monthly Notices of the Royal Astronomical Society, 349(2), L31-L35.
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  Abstract: Long-slit echelle spectra reveal bright extended emission from the K I λ7699 resonance line in the reflection nebula surrounding the extreme red supergiant VY Canis Majoris. The central star has long been known for its unusually bright K I emission lines, but this is the first report of intrinsic emission from K I in the nebula. The extended emission is not just a reflected spectrum of the star, but is due to resonant scattering by K atoms in the outer nebula itself, and is therefore a valuable probe of the kinematics and geometry of the circumstellar environment of VY CMa. Dramatic velocity structure is seen in the long-slit spectra, and most lines of sight through the nebula intersect multiple distinct velocity components. A faint 'halo' at large distances from the star does appear to show a reflected spectrum, however, and suggests a systemic velocity of +40 km s-1 with respect to the Sun. The most striking feature is blueshifted emission from the filled interior of a large shell seen in images; the kinematic structure is reminiscent of a Hubble flow, and provides strong evidence for asymmetric and episodic mass loss due to localized eruptions on the stellar surface.
• Smith, N. (2004). The systemic velocity of eta Carinae. Monthly Notices of the Royal Astronomical Society, 351(1), L15-L18.
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  Abstract: High-resolution spectra of molecular hydrogen in the Homunculus nebula allow for the first direct measurement of the systemic velocity of η Carinae. Near-infrared long-slit data for H2 1-0 S(1) λ21218 obtained with the Phoenix spectrometer on the Gemini South telescope give V sys = -8.1 ± 1 km s-1 (heliocentric), or V LSR = -19.7 ± 1 km s-1, from the average of the near and far sides of the Homunculus. This measurement considerably improves the precision for the value of -7 ± 10 km s-1 inferred from neighbouring O-type stars in the Carina nebula. New near-infrared spectra also provide a high-resolution line profile of [Fe II] λ16435 emission from gas condensations known as the Weigelt objects without contamination from the central star, revealing a line shape with complex kinematic structure. Previously, uncertainty in the kinematics of the Weigelt knots was dominated by the adopted systemic velocity of η Car.
• Smith, N., & Morse, J. A. (2004). Nitrogen and oxygen abundance variations in the outer ejecta of η Carinae: Evidence for recent chemical enrichment. Astrophysical Journal Letters, 605(2 I), 854-863.
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  Abstract: We present optical spectra of the ionized "outer ejecta" of η Car that reveal differences in chemical composition at various positions. In particular, young condensations just outside the dusty Homunculus nebula show strong nitrogen lines and little or no oxygen, but farther away, nitrogen lines weaken and oxygen lines become stronger. The observed variations in the apparent N/O ratio may signify either that the various blobs were ejected with different abundances or, more likely, that the more distant condensations are interacting with normal composition material. The second hypothesis is supported by various other clues involving kinematics and X-ray emission and would suggest that η Car is enveloped in a "cocoon" deposited by previous stellar wind mass loss. In particular, all emission features in which we detect strong oxygen lines are coincident with or outside the soft X-ray shell. In either case, the observed abundance variations suggest that η Car's ejection of nitrogen-rich material is a recent phenomenon, taking place in just the last few thousand years. Thus, η Car may be at a critical stage of evolution when ashes of the CNO cycle have just appeared at its surface. Finally, these spectra reveal some extremely fast nitrogen-rich material, with Doppler velocities up to 3200 km s-1 and actual space velocities that may be much higher. This is the fastest material yet seen in η Car's nebula, but with unknown projection angles its age is uncertain.
• Smith, N., Bally, J., & Brooks, K. J. (2004). HH 666: The axis of evil in the Carina Nebula. Astronomical Journal, 127(5 1781), 2793-2808.
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  Abstract: We report the discovery of the iniquitous parsec-scale outflow HH 666 - the first protostellar jet in the Carina Nebula - as well as the infrared identification of its embedded driving source. The HH 666 jet emanates from a bright-rimmed molecular globule (G287.57-0.91) at the head of a dust pillar in the southern part of Carina. Optical and near-infrared images reveal structures that resemble bow shocks and internal working surfaces in other Herbig-Haro (HH) jets, and which are especially bright in [Fe II] λ16435. Except for extended bow shock wings, all features lie within a few degrees of a single axis oriented roughly southeast to northwest, with a remarkable highly collimated flow breaking out of the natal globule. Long-slit echelle spectra reveal only redshifted velocities toward the southeast of the globule and blueshifted velocities toward the northwest. The observed features conspire to form a single, coherent bipolar jet with a total projected length of over 4.′5, or more than 3 pc. Doppler shifts as high as ±250 km s -1 are seen, indicating that the jet axis has a significant tilt from the plane of the sky, and the total length of the jet may be closer to 4 or 5 pc. HH 666 is therefore among the longest HH jets known. Condemned to toil in the inferno of the Carina Nebula, scorched by UV radiation from the hot stars that power the H II region, much of the jet is influenced by radiative excitation. Infrared images reveal a reddened star embedded in the molecular globule lying along the jet axis. We identify this evildoer (HH 666 IRS) as the likely driving source of the jet. The infrared spectral energy distribution of HH 666 IRS is consistent with that of a Class I protostellar object, with a luminosity of a few hundred to 10 3 L ⊙, and a probable main-sequence mass of a few to 8 M ⊙. This Class I object associated with a prominent bipolar jet constitutes the first direct evidence of ongoing active star formation by accretion in the Carina Nebula.
• Smith, N., Bally, J., Shuping, R. Y., Morris, M., & Hayward, T. L. (2004). Thermal-infrared detection of optical outflow sources in OMC-1 South. Astrophysical Journal Letters, 610(2 II), L117-L120.
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  Abstract: We present the first thermal-infrared imaging photometry for several embedded sources in the OMC-1 South cloud core in the Orion Nebula, and we propose that some of these drive the optical Herbig-Haro jets emerging from the region. Thermal-infrared images at 8.8 and 11.7 μm obtained at Gemini South show a handful of sources in OMC-1 South with no visual-wavelength counterparts, although a few can be seen in recent near-infrared data. For the three brightest mid-infrared sources, we also present 18.75 μm photometry obtained with the Keck telescope. The most prominent blueshifted outflows in the Orion Nebula at visual wavelengths, such as HH 202, HH 203/204, HH 529, and HH 269, all originate from OMC-1S. The brightest infrared source in OMC-1S at 11.7 μm is located at the base of the prominent jet that powers HH 202 and is likely to be the sought-after driver of this outflow. The second brightest infrared source is located at the base of the HH 529 jet. We consider the possibility that HH 203/204 and HH 269 trace parts of a single bent outflow from the third brightest infrared source. While there may be some lingering ambiguity about which infrared stars drive specific jets, there is now a sufficient number of embedded sources to plausibly account for the multiple outflows from OMC-1S.
• Smith, N., Barbá, R. H., & Walborn, N. R. (2004). Carina's defiant finger: HST observations of a photoevaporating globule in NGC 3372. Monthly Notices of the Royal Astronomical Society, 351(4), 1457-1470.
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  Abstract: We present Hubble Space Telescope Wide Field Planetary Camera 2 images of a prominent externally ionized molecular globule in the Carina Nebula (NGC 3372), supplemented with ground-based infrared images and visual-wavelength spectra. This molecular globule has a shape resembling a human hand, with an extended finger that points toward its likely source of ionizing radiation. Following an analysis of the spatially resolved ionization structure and spectrum of the photoevaporative flow from the Finger, we conclude that the dominant ionizing source is either the WNL star WR25 (HD 93162), the adjacent O4 If-type star Trl6-244, or perhaps both. We estimate a mass-loss rate of ∼2 × 10 -5 M ⊙ yr -1 from the main evaporating surface of the globule, suggesting a remaining lifetime of 10 5.3-10 6 yr. We find a total mass for the entire globule of more than 6 M ⊙ , in agreement with previous estimates. The hydrogen column density through the globule derived from extinction measurements is a few times 10 22 cm -2, so the photodissociation region behind the ionization front should be limited to a thin layer compared to the size of the globule, in agreement with the morphology seen in H 2 images. Although a few reddened stars are seen within the boundary of the globule in near-infrared continuum images, these may be background stars. We do not detect a reddened star at the apex of the finger, for example, down to a limiting magnitude of m k≃ 17. However, considering the physical properties of the globule and the advancing ionization front, it appears that future star formation is likely in the Finger globule, induced by radiation-driven implosion.
• Smith, N., Morse, J. A., Collins, N. R., & Gull, T. R. (2004). The purple haze of ν Carinae: Binary-induced variability?. Astrophysical Journal Letters, 610(2 II), L105-L108.
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  Abstract: Asymmetric variability in ultraviolet images of the Homunculus obtained with the Advanced Camera for Surveys/High Resolution Camera on the Hubble Space Telescope suggests that ν Carinae is indeed a binary system. Images obtained before, during, and after the recent "spectroscopic event" in 2003.5 show alternating patterns of bright spots and shadows on opposite sides of the star before and after the event, providing a strong geometric argument for an azimuthally evolving, asymmetric UV radiation field as one might predict in some binary models. The simplest interpretation of these UV images, where excess UV escapes from the secondary star in the direction away from the primary, places the major axis of the eccentric orbit roughly perpendicular to our line of sight, sharing the same equatorial plane as the Homunculus, and with apastron for the hot secondary star oriented toward the southwest of the primary. However, other orbital orientations may be allowed with more complicated geometries. Selective UV illumination of the wind and ejecta may be partly responsible for line profile variations seen in spectra. The brightness asymmetries cannot be explained plausibly with delays due to light-travel time alone, so a single-star model would require a seriously asymmetric shell ejection.
• Smith, N., Morse, J. A., Gull, T. R., Hillier, D. J., Gehrz, R. D., Walborn, N. R., Bautista, M., Collins, N. R., Corcoran, M. F., Damineli, A., Hamann, F., Hartman, H., Johansson, S., Stahl, O., & Weis, K. (2004). Kinematics and ultraviolet to infrared morphology of the inner Homunculus of η Carinae. Astrophysical Journal Letters, 605(1 I), 405-424.
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  Abstract: We present the first ultraviolet and optical images of η Car and its circumstellar Homunculus nebula, obtained with the Advanced Camera for Surveys/High Resolution Camera (ACS/HRC) on board the Hubble Space Telescope (HST). Compared to those at visual wavelengths, UV images reveal excess emission 0″.1-0.″6 from the central source along the minor axis that may emanate from the outer parts of η Car's nonspherical stellar wind, which dominates the UV flux from η Car. The UV emission fills the cavity inside a dust torus measured from infrared (IR) data; within 0″.2 of the star the UV emission projects a morphology reminiscent of the IR torus, but it is a factor of 10 smaller. This "little torus" seen in the UV may be related to the "Little Homunculus" discovered recently, signifying recurrent mass ejections with the same geometry. Finally, we reexamine the kinematics of nebular condensations near the star (Weigelt objects C and D) in HST images and spectra obtained over the past decade. We measure heliocentric velocities slower than previous estimates, and from proper motions we derive an ejection date of 1908 ± 12 yr, assuming linear motion. However, because of radiative acceleration, these objects may have been ejected earlier - perhaps during the 1890 outburst of η Car.
• Smith, N., Vink, J. S., & Koter, A. D. (2004). The missing luminous blue variables and the bistability jump. Astrophysical Journal Letters, 615(1 I), 475-484.
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  Abstract: We discuss an interesting feature of the distribution of luminous blue variables (LBVs) on the H-R diagram, and we propose a connection with the bistability jump seen in the winds of early-type supergiants. There appears to be a deficiency of quiescent LBVs on the S Doradus instability strip at luminosities between log (L/L≃) ≃ 5.6 and 5.8. The upper boundary, interestingly, is also where the temperature-dependent S Doradus instability strip intersects the bistability jump at about Teff ≃ 21,000 K. Because of increased opacity, winds of early-type supergiants are slower and denser on the cool side of the bistability jump, and we postulate that this may trigger optically thick winds that inhibit quiescent LBVs from residing there. We conduct numerical simulations of radiation-driven winds for a range of temperatures, masses, and velocity laws at log (L/L⊙) = 5.7 to see what effect the bistability jump should have. We find that for relatively low stellar masses, the order-of-magnitude increase in the wind density at the bistability jump leads to the formation of a modest to strong pseudophotosphere that might alter a star's apparent position on the H-R diagram. The effect is strongest for LBVs approaching 10 M⊙, where the pseudophotospheres are sufficiently extended to make an early B-type star appear as a yellow hypergiant. Thus, the proposed mechanism will be most relevant for LBVs that are post-red supergiants [curiously, the upper boundary at log (L/L⊙) ≃ 5.8 coincides with the upper luminosity limit for red supergiants]. Further work is obviously needed, especially with regard to a possible evolutionary connection between the "missing" LBVs and the most luminous red supergiants and yellow hypergiants. Specifically, yellow hypergiants such as IRC +10420 and ρ Cas occupy the same luminosity range as the missing LBVs and show apparent temperature variations at constant luminosity. If these yellow hypergiants do eventually become Wolf-Rayet stars, we speculate that they may skip the normal LBV phase, at least as far as their apparent positions on the H-R diagram are concerned.
• Ishibashi, K., Gull, T. R., Davidson, K., Smith, N., Lanz, T., Lindler, D., Feggans, K., Verner, E., Woodgate, B. E., Kimble, R. A., Bowers, C. W., Kraemer, S., Heap, S. R., Danks, A. C., Maran, S. P., Joseph, C. L., Kaiser, M. E., Linsky, J. L., Roesler, F., & Weistrop, D. (2003). Discovery of a little homunculus within the Homunculus Nebula of η Carinae. Astronomical Journal, 125(6 1770), 3222-3236.
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  Abstract: We report long-slit spectroscopic mapping of the η Carinae nebula obtained using the Space Telescope Imaging Spectrograph. The observations reveal the presence of a previously unknown bipolar emission nebula (roughly ±2″ along its major axis) embedded within the well-known and larger Homunculus Nebula. A preliminary analysis suggests that this embedded nebula may have originated from a minor eruption event circa 1890, 50 years after the formation of the larger Homunculus.
• Smith, N. (2003). Spatial distribution of near-infrared and optical emission properties in the bipolar nebula Menzel 3. Monthly Notices of the Royal Astronomical Society, 342(2), 383-398.
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  Abstract: Visiting Astronomer at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. Ground-based optical spectra combined with near-infrared spectra and images of the young bipolar planetary nebula Menzel 3 (Mz 3) reveal positional variations in extinction, excitation, density and other characteristics. Interstellar extinction is probably less than Av = 2.65, while extinction toward the nucleus is approximately 4.6 mag. The lobes show stratified ionization, with high-excitation emission localized at high latitudes. Quantitative analysis using the CLOUDY spectral synthesis code suggests that the polar lobes 'see' an excitation source similar to a blackbody of roughly 36 000 K and 10 000 L⊙, and chemical abundances reveal that the ejecta have He enhanced by a factor of ∼2, and N enhanced more strongly, with N/O∼1. The lobes are probably radiatively excited, but shocks may heat the 'blisters' at the polar axis. The bright, unresolved nucleus has a crowded emission spectrum distinct from the diffuse bipolar lobes, and it indicates high electron densities of 106-107 cm-3. An equatorial disc-like geometry for dense gas in the nucleus is likely. The nucleus also shows a nearly power-law continuum; when corrected for reddening it may require two stars, one hot star and one cool giant, along with hot ∼900-K dust. A distance up to ∼2.5 kpc is possible. In general, the spectral characteristics of Mz 3 are similar to those of the well-studied nebula M 2-9, and the two objects may share a similar evolutionary history. However, an important difference between them is that Mz 3 appears to be mostly devoid of molecular hydrogen, while infrared H2 lines are conspicuous in M 2-9.
• Smith, N. (2003). The integrated optical spectrum of the Crab nebula and evidence for its fading synchrotron continuum. Monthly Notices of the Royal Astronomical Society, 346(3), 885-889.
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  Abstract: A flux-calibrated optical spectrum integrated over the entire Crab nebula was obtained by making drift scans with a long-slit spectrograph. Compared to observations obtained over the past 40 years, these new data confirm an earlier controversial result that the [O III] λλ4959, 5007 equivalent width is increasing with time, although the rate of ∼0.9 per cent yr -1 is somewhat slower than that measured previously. Additionally, the Hβ equivalent width is increasing at a comparable rate, but the measured fluxes of both Hβ and [O III] have changed less than their respective equivalent widths. The different rates of change in the measured fluxes and equivalent widths of these lines suggest that the optical synchrotron continuum from the Crab nebula is indeed fading rapidly. The apparent decline is consistent with a rate around -0.5 (±0.2) per cent yr -1 at wavelengths near 5000 Å inferred independently from measurements of the optical continuum flux during the same time period.
• Smith, N., Bally, J., & Morse, J. A. (2003). Numerous proplyd candidates in the harsh environment of the Carina Nebula. Astrophysical Journal Letters, 587(2 II), L105-L108.
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  Abstract: We report the discovery of dozens of compact objects in the Carina Nebula (NGC 3372) that closely resemble proplyds (photoablating protoplanetary disks and dark silhouette disks) seen previously in the Orion Nebula. This is the first detection of a large number of such objects outside Orion. They imply that low- and intermediate-mass star formation is proceeding actively in Carina, despite threatening conditions imposed by very hot massive stars. The proplyd candidates that we have detected are larger than those in Orion but more compact than irregular molecular globules within the H II region. Smaller proplyds may still be lurking in Carina, waiting to be discovered. Orion apparently lacks objects of comparable size, and we consider several explanations. Larger proplyds may come from larger and more massive circumstellar disks surrounding young Herbig Ae/Be stars that should be numerous in Carina. Alternatively, far-UV radiation from the massive star η Car may have, in the recent past, enhanced photoablation and expanded proplyd ionization fronts. Some unusual proplyd candidates may also imply that time-dependent effects associated with η Car's current evolutionary state may be critical.
• Smith, N., Davidson, K., Gull, T. R., Ishibashi, K., & Hillier, D. J. (2003). Latitude-dependent effects in the stellar wind of η Carinae. Astrophysical Journal Letters, 586(1 I), 432-450.
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  Abstract: The Homunculus reflection nebula around η Carinae provides a rare opportunity to observe the spectrum of a star from more than one direction. In the case of η Car, the nebula's geometry is known well enough to infer how line profiles vary with latitude. We present Space Telescope Imaging Spectrograph (STIS) spectra of several positions in the Homunculus, showing directly that η Car has an aspherical stellar wind. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the polar axis. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from radiative driving with equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, offering clues to the wind geometry and ionization structure. During η Car's high-excitation state in 2000 March, the wind was fast and dense at the poles, with higher ionization at low latitudes. Older STIS data obtained since 1998 reveal that this global stellar wind geometry changes during η Car's 5.5 yr cycle and may suggest that this star's spectroscopic events are shell ejections. Whether or not a companion star triggers these outbursts remains ambiguous. The most dramatic changes in the wind occur at low latitudes, while the dense polar wind remains relatively undisturbed during an event. The apparent stability of the polar wind also supports the inferred bipolar geometry. The wind geometry and its variability have critical implications for understanding the 5.5 yr cycle and long-term variability but do not provide a clear alternative to the binary hypothesis for generating η Car's X-rays.
• Smith, N., Morse, J. A., Bally, J., & Phelps, R. L. (2003). The mysterious ring in the open cluster NGC 3572: Planetary nebula or photoevaporating globule?. Publications of the Astronomical Society of the Pacific, 115(805), 342-350.
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  Abstract: We discuss optical and infrared emission from the putative planetary nebula in the young open cluster NGC 3572. Velocity images of [N II] λ6583 obtained with the Rutgers/CTIO Fabry-Perot interferometer reveal that most gas in the nebula is expanding at velocities ≲5 km s-1, with marginal evidence for bipolar expansion. A few outer condensations are seen at faster redshifted velocities, but their origin is uncertain. Optical spectra reveal a spatial excitation gradient, with higher excitation in a diffuse outer halo and low excitation in the bright inner nebula, suggesting that the nebula is externally ionized by hot stars in the open cluster and that the nebula and cluster are therefore equidistant. The nebula coincides with an infrared source detected by the MSX and IRAS satellites and has a spectral energy distribution implying a total mass of 5-10 M⊙. MSX also reveals diffuse infrared emission associated with the cluster, and its morphology implies a connection with the ring nebula. We discuss two very different interpretations of this object - it is either a strange planetary nebula or (more probably) a young photoevaporating globule left over from the molecular cloud that formed the cluster.
• Humphreys, R. M., Davidson, K., & Smith, N. (2002). Crossing the yellow void: Spatially resolved spectroscopy of the post-red supergiant IRC +10420 and its circumstellar ejecta. Astronomical Journal, 124(2 1760), 1026-1044.
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  Abstract: IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the "yellow void." We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long-slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double-peaked Hα emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and massloss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently, the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a "rain" model, in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass-loss rate, IRC +10420 may be about to shed its opaque wind, cross the yellow void, and emerge as a hotter star.
• Smith, N. (2002). Dissecting the Homunculus nebula around Eta Carinae with spatially resolved near-infrared spectroscopy. Monthly Notices of the Royal Astronomical Society, 337(4), 1252-1268.
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  Abstract: Near-infrared emission lines are unique diagnostics of the geometry, structure, kinematics, and excitation of the circumstellar ejecta of η Carinae, and give clues to the nature of its wind. The infrared spectrum is a strong function of position in η Car's nebula, with a mix of intrinsic and reflected emission. Molecular hydrogen traces cool gas and dust in the polar lobes, while [Fe II] blankets their inner surfaces. These lines reveal the back wall of the SE polar lobe for the first time, and give the clearest picture yet of the three-dimensional geometry. Additionally collisionally excited [Fe II] reveals the kinematic structure of a recently discovered 'Little Homunculus' expanding inside the larger one. Equatorial gas in the 'Fan', on the other hand, shows a spectrum indicating recombination and fluorescent Lyα pumping. Some equatorial ejecta glow in the He I λ10830 line, showing evidence for material ejected in the 1890 outburst of η Car Closer to the star, the compact 'Weigelt blobs' are marginally resolved, allowing their infrared spectrum to be separated from the star for the first time. In general, infrared spectra reveal a coherent, directional dependence of excitation in the Homunculus: polar ejecta are collisionally excited, whereas equatorial ejecta are dominated by fluorescence and normal photoexcitation. These are important clues to the geometry of the central star's ultraviolet radiation field. Reflected near-infrared emission lines also reveal interesting latitudinal dependence in the stellar wind.
• Smith, N. (2002). Infrared [Fe II] emission in the circumstellar nebulae of luminous blue variables. Monthly Notices of the Royal Astronomical Society, 336(2), L22-L26.
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  Abstract: After a serendipitous discovery of bright [Fe II] λ16435 emission in nebulae around η Carinae and P Cygni, infrared spectra of other luminous blue variables (LBV) and LBV candidates were obtained. Bright infrared [Fe II] emission appears to be a common property among LBVs with prominent nebulae; this is an interesting discovery because strong [Fe II] λ16435 is typically seen in shock-excited objects like supernova remnants and outflows from newly formed massive stars, as well as in active galactic nuclei (AGN), where the excitation mechanism is uncertain. This paper presents spectra in the H-band (1.5 to 1.75 μm) for the central stars and nebulae of η Car, AG Car, P Cyg, Wra 751, HR Car, HD 168625, HD 160529, R 127 and S Doradus. Seven of nine targets show bright [Fe II] λ16435 in their nebulae, while it is absent in all central stars except the LBV candidate Wra 751. The two objects (S Dor and HD 160529) without prominent [Fe II] λ16435 are not yet known to have nebulae detected in optical images, and both lack bright thermal infrared emission from dust. The possible excitation mechanisms for this line and the implications of its discovery in LBV nebulae are discussed; there are good reasons to expect shock excitation in some objects, but other mechanisms cannot be ruled out.
• Smith, N. (2002). Near-infrared and optical emission-line structure of the Keyhole Nebula in NGC 3372. Monthly Notices of the Royal Astronomical Society, 331(1), 7-12.
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  Abstract: Narrow-band infrared and optical images of the Keyhole Nebula in NGC 3372 reveal which structures are caused by extinction, and show the underlying morphology of photoionized and shock-excited gas. Dark clouds conspire with ionized gas to create the apparent keyhole shape which is prominent at blue wavelengths and less apparent in the infrared. The Paβ/Hα line ratio shows the spatial distribution of foreground extinction. The wavelength dependence of this extinction indicates a reddening law with R ≈ 4.8, different from the normal interstellar medium. This confirms previous estimates of reddening toward the Carina Nebula determined from stellar photometry, and reveals that the anomalous extinction is patchy and within the Hn region. The morphology of the ionized gas is different from the extinction clouds; it shows an edge-on ionization front running NE to SW, with a limb-brightened indentation that forms the upper outline of the keyhole shape. A fast polar wind from η Carinae may have punctured the ionization front, since the indentation is directly along a projection of the polar axis of the star. This is supported by the morphology of shock-excited gas revealed by a high [S II]/Hα ratio. High-excitation gas emitting [O III] and He I has a smoother distribution. Molecular clumps in the region are also discussed.
• Smith, N., Gehrz, R. D., Stahl, O., Balick, B., & Kaufer, A. (2002). The WR+OB progenitor RY Scuti: Intensive spectroscopy of its compact double-ring nebula. Astrophysical Journal Letters, 578(1 I), 464-485.
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  Abstract: We present a detailed spectroscopic analysis of the peculiar nebula around RY Scuti using data from the Space Telescope Imaging Spectrograph (STIS) and various ground-based observatories. This massive contact binary may represent a rapid evolutionary phase in transition to a short-period WR+OB system, and it is surrounded by a young nebula with unusual geometry. The ionized nebula is only about 1″ across, so STIS has allowed us to spatially resolve the spectrum of the star from its circumstellar nebula for the first time. Combining STIS data with ground-based spectra at optical and infrared wavelengths solves some geometric ambiguities posed by previous images and reveals the kinematic relationship between the nebular geometry and RY Scuti's complex emission-line profiles. We offer a new determination of the systemic velocity of 20 ± 3 km s-1, and we estimate the distance to RY Scuti as 1.8 ± 0.1 kpc. Nebular lines show subtle phase-dependent variability in addition to expected changes in equivalent width due to eclipses of stellar continuum. These changes in equivalent width yield an updated ephemeris, but a previously suggested period change is still uncertain after considering these new data. The nebula contains roughly 0.003 M ⊙ of material that is He-and N-rich and probably O-deficient compared to solar abundances, indicating that CNO-processed material has reached the surface in at least one component of the binary system. Diagnostic line ratios suggest that the electron density and temperature in the nebula are 2 × 105 cm-3 and ∼9500 K, respectively. There are concentrated regions of higher density as well; emission knots seen around the rings suggest that common envelope mass loss during massive contact binary evolution may be characterized by strong azimuthal asymmetry and sporadic mass ejection events.
• Davidson, K., Smith, N., Gull, T. R., Ishibashi, K., & Hillier, D. J. (2001). The shape and orientation of the Homunculus Nebula based on spectroscopic velocities. Astronomical Journal, 121(3), 1569-1577.
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  Abstract: Doppler velocities give information about the three-dimensional shape and orientation of the bipolar ejecta of η Car. We report slit spectroscopy obtained using the Space Telescope Imaging Spectrograph (HST/STIS), with spatial resolution adequate for good models. These data allow an independent estimate of the distance to this object. Equatorial velocities, not clearly recognized in earlier work, provide the first definite measure of the bipolar inclination angle relative to our line of sight. Equatorial structure is arguably the most significant new spectroscopic result reported here, and some of the equatorial gas has higher and lower velocities which probably represent later and earlier ejection events. A range of bipolar lobe shapes fit the data reasonably well; the worst ambiguities result from the nature of the object more than from instrumental limitations.
• Gehrz, R. D., Smith, N., Jones, B., Puetter, R., & Yahil, A. (2001). Keck LWS images of the compact nebula around RY Scuti in the thermal infrared. Astrophysical Journal Letters, 559(1 PART 1), 395-401.
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  Abstract: We report new 3 to 20 μm Keck Telescope images of the massive eclipsing binary RY Scuti with ∼0″.25 spatial resolution. These images show complex structure near the diffraction limit of the 10 m telescope in a nebula less than 2″ across. The limb-brightened structure is consistent with optically thin emission from a circumstellar torus. At 3 to 5 μm, the extended emission is predominantly scattered photospheric light from the central stars. The 8.9, 11.7, 12.5, and 18.7 μm images are dominated by thermal emission from warm carbon and silicate dust in the outer regions of the torus. The new observations are consistent with the geometric models previously proposed by Gehrz et al. and Smith et al. to explain the structures observed in the circumstellar environment of RY Scuti. For example, the inside of the torus is ionized by the central star and shows strong emission from [Ne II] at 12.8 μm. Double-ring structure similar to that seen in Hubble Space Telescope images is partly resolved at the limb-brightened edges of the torus in the new mid-infrared continuum images, and the new IR images are consistent with two parallel dust rings adjacent to the ionized gas rings and farther from the star. The new mid-infrared images at 8.9, 11.7, and 12.5 μm show faint emission from a thin disk outside the previously detected torus. We estimate a dust mass in the torus of 1.4 × 10-6 M⊙ and a neon abundance in the ionized gas of nNe/nH ≳ 1.77 × 10-4 from the 12.8 μm [Ne II] emission.
• Smith, N., & Davidson, K. (2001). The shocking near-infrared spectrum of the Homunculus Nebula surrounding η Carinae. Astrophysical Journal Letters, 551(1 PART 2), L101-L104.
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  Abstract: Near-infrared long-slit spectra of the Homunculus Nebula surrounding η Carinae reveal emission from molecular hydrogen for the first time in this object, as well as strong intrinsic [Fe II] emission. H2 emission is seen only in the polar lobes of the Homunculus, which show v = 1-0 emission in the K band, but no v = 2-1 emission. The strengths of certain [Fe II] lines are enhanced in the same regions of the polar lobes as the H2 emission, where [Fe II] 1.6435 μm is by far the brightest near-infrared line emitted in the Homunculus Nebula. The intrinsic spectrum of the northwest polar lobe resembles the near-infrared spectra of some supernova remnants, and shock excitation is required to explain the strengths of the [Fe II] and H2 lines. Shock-excited emission in the polar lobes suggests that the central star has a fast bipolar wind and a slower equatorial wind. The H2 lines observed in these spectra represent the first detection of any molecular gas in the Homunculus Nebula, which has important implications for the density structure in the polar lobes and in the stellar wind during and after the Great Eruption.
• Smith, N., Gehrz, R. D., & Goss, W. M. (2001). Proper motion and excitation structure of the expanding ionized rings around RY Scuti. Astronomical Journal, 122(5), 2700-2706.
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  Abstract: Multiepoch HST/WFPC2 images of the massive eclipsing binary RY Scuti reveal that the compact ionized rings in its circumstellar nebula are expanding. Radio images of the free-free continuum at 15 GHz obtained with the Very Large Array confirm the expansion rate and extend the temporal baseline. Combined Hα and radio proper-motion measurements of the nebula's outer edge across the major axis suggest that the nebula is roughly 120 yr old, although complications exist due to nonuniform motion. The linear expansion rate supports a shell ejection hypothesis for the origin of RY Scuti's double-ring nebula and has important implications for the mass-loss history and evolutionary state of the stellar components. Historical observations lead us to speculate that at least one of the components in the binary system is an S Doradus variable or a close relative of this class of stars. [S III] λ9532 emission traces higher excitation than Hα, but it shows only minor intensity variations with position in the nebula. The width of the ionization fronts at the limb-brightened edges of the nebula are nearly unresolved in our WFPC2 images, validating proper-motion measurements that combine both Hα and radio continuum emission.
• Smith, N., Humphreys, R. M., & Gehrz, R. D. (2001). Post-eruption detection of variable 12 in NGC 2403 (SN 1954j): Another η Carinae variable. Publications of the Astronomical Society of the Pacific, 113(784), 692-696.
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  Abstract: We have obtained optical and near-infrared imaging photometry of the irregular variable V12 in NGC 2403 (SN 1954j), roughly 50 years after its giant eruption. The observations confirm that the star survived the event and that it was therefore not a peculiar supernova but instead was an η Carinae-like eruption. Variable 12 is now very faint and red, which could be due to extinction and reddening of a hot star by circumstellar dust that formed in ejecta from the giant eruption in 1954. A clear excess at ∼2 μm probably indicates thermal emission from hot circumstellar dust.
• Smith, N., Humphreys, R. M., Davidson, K., Gehrz, R. D., Schuster, M. T., & Krautter, J. (2001). The asymmetric nebula surrounding the extreme red supergiant VY Canis Majoris. Astronomical Journal, 121(2), 1111-1125.
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  Abstract: We present HST/WFPC2 images plus ground-based infrared images and photometry of the very luminous OH/IR star VY Canis Majoris. Our WFPC2 data show a complex distribution of knots and filamentary arcs in the asymmetric reflection nebula around the obscured central star. The reflection arcs may result from multiple, asymmetric ejection episodes due to localized events on VY CMa's surface. Such events probably involve magnetic fields and convection, by analogy with solar activity. Surface photometry indicates that the star may have experienced enhanced mass loss over the past 1000 yr. We also demonstrate that the apparent asymmetry of the nebula results from a combination of high extinction and backscattering by dust grains. Thermal-infrared images reveal a more symmetric distribution, elongated along a nearly east-west direction. VY CMa probably has a flattened disklike distribution of dust with a northeast-southwest polar axis and may be experiencing activity analogous to solar prominences. The presence of an axis of symmetry raises interesting questions for a star the size of Saturn's orbit. Magnetic fields and surface activity may play an important role in VY CMa's mass-loss history.
• Smith, N., Jones, T. J., Gehrz, R. D., Klebe, D., & Creech-Eakman, M. J. (2001). Thermal infrared imaging of the bipolar H II region S106. Astronomical Journal, 121(2), 984-991.
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  Abstract: The extended infrared emission from Sharpless 106 shows complex structure in ground-based images obtained at wavelengths from 3 to 20 μm. The structure of the ionization fronts and photodissociation regions are resolved in Brα emission at 4.05 μm and emission from polycyclic aromatic hydrocarbons at 3.29 μm, with the H I emission residing interior to the hydrocarbon emission. The mid-infrared observations at 10 to 20 μm reveal the distribution of continuum emission from warm dust in the nebula. These images have a higher spatial resolution than previous mid-infrared maps, but they support earlier findings of a relatively constant dust color temperature of ∼ 135 K in the extended dust, excluding the dust near the self-luminous sources IRS 2 and 4. All infrared images presented here show a dark lane bisecting the nebula, which probably results from shadowing of light from the central engine rather than line-of-sight extinction. If this shadow is caused by a compact disk around IRS 4, its ionized inner edge would be within the radio photosphere of the stellar wind at wavelengths longer than about 1.5 cm. There appears to be a faint point source seen at near-infrared wavelengths that is coincident with the position of a bright far-infrared source. This source is adjacent to some bright near-infrared nebulosity but is not clearly detected in thermal infrared dust emission.
• Davidson, K., & Smith, N. (2000). A massive cool dust torus around η Carinae?. Nature, 405(6786), 532-.
• Davidson, K., Ishibashi, K., Gull, T. R., Humphreys, R. M., & Smith, N. (2000). η Carinae: Testing a binary orbit model with the Hubble Space Telescopei/Space Telescope Imaging Spectrograph. Astrophysical Journal Letters, 530(2 PART 2), L107-L110.
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  Abstract: Ground-based spectroscopy of η Car shows periodic changes in some emission-line wavelengths. These variations have been cited as strong evidence that this object is a 5.5 yr binary system and have been used to produce specific orbit models. High spatial resolution data obtained with the Hubble Space Telescope/Space Telescope Imaging Spectrograph, however, do not confirm the predicted velocity behavior; therefore, the published orbit models are almost certainly invalid. Wavelength fluctuations seen at ground-based spatial resolution most likely result from other effects, which we describe. If this object is a binary system (which has not been proven), then the parameters of the secondary star and of the orbit remain largely unknown.
• Smith, N., & Gehrz, R. D. (2000). Recent changes in the near-infrared structure of η Carinae. Astrophysical Journal Letters, 529(2 PART 2), L99-L102.
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  Abstract: Near-infrared imaging at two phases in the 5 yr spectroscopic cycle of η Carinae reveals changes in the spatial structure of the inner core that may be related to recently reported near-infrared photometric variability. The central source changed from a pointlike object to a more extended, bipolar or shell structure. This behavior is reminiscent of changes observed in the radio continuum. NICMOS images show a toroidal distribution of dust and gas around the central star and confirm the morphology of several other structures observed in ground-based images of the Homunculus. The morphological variations appear to be confined to the central core of the nebula.
• Smith, N., Egan, M. P., Carey, S., Price, S. D., Morse, J. A., & Price, P. A. (2000). Large-scale structure of the Carina Nebula. Astrophysical Journal Letters, 532(2 PART 2), L145-L148.
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  Abstract: Observations obtained with the Midcourse Space Experiment (MSX) satellite reveal for the first time the complex mid-infrared morphology of the entire Carina Nebula (NGC 3372). On the largest size scale of ∼100 pc, the thermal infrared emission from the giant H II region delineates one coherent structure: a (somewhat distorted) bipolar nebula with the major axis perpendicular to the Galactic plane. The Carina Nebula is usually described as an evolved H II region that is no longer actively forming stars, clearing away the last vestiges of its natal molecular cloud. However, the MSX observations presented here reveal numerous embedded infrared sources that are good candidates for sites of current star formation. Several compact infrared sources are located at the heads of dust pillars or in dark globules behind ionization fronts. Because their morphology suggests a strong interaction with the peculiar collection of massive stars in the nebula, we speculate that these new infrared sources may be sites of triggered star formation in NGC 3372.
• Smith, N., Jackson, J. M., Kraemer, K. E., Deutsch, L. K., Bolatto, A., Hora, J. L., Fazio, G., Hoffmann, W. F., & Dayal, A. (2000). Thermal infrared imaging of ultracompact H II regions in W49A. Astrophysical Journal Letters, 540(1 PART 1), 316-331.
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  Abstract: Several compact radio continuum sources in W49A show detectable 8-20 μm emission in MIRAC2 images obtained at the IRTF. In general, the infrared morphologies of these sources closely resemble the radio continuum emission. Spectral energy distributions indicate an infrared continuum excess above the level expected from free-free emission, consistent with thermal emission from dust grains heated to a few hundred K. The bright radio continuum sources concentrated at the western end of the ring of ultracompact H II regions are not detected in the mid-infrared, while those at other positions in the ring are detected. This could be due to a localized region of high extinction along the line of sight. In addition, there are a few new infrared sources with no radio continuum counterparts. Finally, several infrared sources show strong 12.8 μm [Ne II] emission, yielding neon abundances that are typically a few percent of the cosmic abundance of neon but are high considering the expected Ne+ +/Ne+ ratios for the range of spectral types of the ionizing sources. We conclude that the [Ne II] emission must come from shells around the ultracompact H II regions, where the neon is able to survive as Ne+ rather than Ne+ + because the radiation field has been softened by absorption of hard UV photons within the H II regions.
• Smith, N., Morse, J. A., Davidson, K., & Humphreys, R. M. (2000). Recent changes in the near-ultraviolet and optical structure of η carinae. Astronomical Journal, 120(2), 920-934.
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  Abstract: Multiepoch HST/WFPC2 images of η Carinae are used to investigate the relationship between the photometric variability of the circumstellar nebula and the variability of the central star. In the past few years, the central star has brightened considerably, and the response of the reflection nebula to this brightening has been surprisingly complex. While the central star has brightened by a factor of 2 at near-ultraviolet and optical wavelengths, bright dust condensations in the bipolar lobes have increased by only a factor of ∼ 1.3, and dark lanes between these dust condensations have brightened by factors of 1.5-2. Certain regions of the nebula have brightened much more than the star itself (as much as a factor of 8), and others have actually faded, despite the brightening of the star. Some of the anomalous fading can be attributed to contributions of intrinsic [S III] and [N II] line emission. The variations of the equivalent width of [S III] λ6312 and [N II] λ6583 as measured in the WFPC2 F631N and F658N filters follow the same trend of other high-excitation lines observed in ground-based spectra during η Car's 5.5 yr spectroscopic cycle, and the amplitude of the change accounts for the total change measured in ground-based spectra for these same lines. The WFPC2 images indicate, however, that these high-excitation lines are emitted by circumstellar gas at distances of a few hundred to a few thousand AU from the star, probably located in the equatorial plane. Thus, periodic ionization of gas at large distances from the central star appears to dominate the spectroscopic changes that define the 5.5 yr cycle. The fact that the variable high-excitation emission is extended places important constraints on models for η Car's 5.5 yr spectroscopic variability.
• Gehrz, R. D., Smith, N., Low, F. J., Krautter, J., Nollenberg, J. G., & Jones, T. J. (1999). Thermal infrared images of the remarkable young nearby multiple star HD 98800. Astrophysical Journal Letters, 512(1 PART 2), L55-L58.
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  Abstract: We present thermal infrared images of the unusual multiple stellar system HD 98800, which contains two double-star systems (A and B) separated by ≈0″.8 in the north/south direction. This system may have formed in a recent burst of star formation in a very low mass cloud in the local solar neighborhood. Our images resolve the A and B components. Both A and B emit roughly equal fluxes at 4.71 μm, where radiation is primarily photospheric. The northern component (B) is about 3.7 times brighter than the southern component (A) at 9.78 μm where the radiation is due to thermal emission from dust, showing that 78% of the circumstellar dust in the system resides around component B. The two primary components are nearly identical K5 V pre-main-sequence stars, both with very significant amounts of dust emission. The dust system around the B component may have size, temperature, and possible structure analogous to those of a primitive zodiacal cloud.
• Humphreys, R. M., Davidson, K., & Smith, N. (1999). η Carinae's second eruption and the light curves of the η Carinae variables. Publications of the Astronomical Society of the Pacific, 111(763), 1124-1131.
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  Abstract: Within the general class of highly unstable massive stars called luminous blue variables (LBVs), four stars have experienced "giant eruptions" during which the total luminosities of the stars actually increase. This rare group includes η Carinae, P Cygni, SN 1961v, and V12 in NGC 2403. Several different observations now suggest that some of the material in η Car's equatorial region was probably ejected during its lesser or second eruption around 1890. When the old visual observations are corrected for the probable circumstellar extinction at that time, we find that its 1890 eruption is much more significant in terms of its luminosity, energy, and mass loss than previously assumed and resembles the second peak seen in the historical light curve for P Cyg. The light curves of all four η Carinae variables share a very distinctive appearance with a postmaximum plateau; a second, lesser eruption; and obscuration by circumstellar dust after the giant eruption.
• Smith, N., Gehrz, R. D., Humphreys, R. M., Davidson, K., Jones, T. J., & Krautter, J. (1999). Hubble Space Telescope images of the compact nebula around RY Scuti. Astronomical Journal, 118(2), 960-971.
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  Abstract: We present HST Wide Field Planetary Camera 2 images of the very massive eclipsing binary RY Scuti. The HST Hα image shows a very complex ionized nebula roughly 1″ in size. Several interesting structures are revealed, including what appears to be a pair of concentric ionized rings above and below the equatorial plane of the system, located at the inner edge of a more extended dust torus. We reexamine some essential physical characteristics of the nebula, such as a possible magnetic field and the complicated mass-loss geometry of this near-Eddington limit contact binary. The effects of a rotating illumination source are considered to explain the brightness distribution in the rings. We suggest a model for the origin of the mass and detailed structure in the nebula. This model invokes a previous mass ejection that is shaped by nonspherical interacting winds and possibly magnetic fields.
• Smith, N., & Gehrz, R. D. (1998). Proper motions in the ejecta of η Carinae with a 50 year baseline. Astronomical Journal, 116(2), 823-828.
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  Abstract: Observations of η Carinae from three separate epochs spanning a total of 50 years are used to measure the proper motions of several easily identifiable features in the Homunculus Nebula. Our principal conclusion is that the equatorial features were ejected significantly after the "Great Eruption," very likely in the outburst that occurred around 1890. The rest of the inner nebula was ejected during the bright phase of 1822 to 1856 that climaxed with the eruption of 1843. The expansion of the bipolar lobes appears to be primarily linear, with a scatter in ejection dates during the period of the Great Eruption. We find a mean ejection date for the southeast polar lobe of 1843.8 ± 7.3 yr, and an ejection date of 1885.8 ± 6.5 yr for the equatorial ejecta.
• Smith, N., Gehrz, R. D., & Krautter, J. (1998). The infrared morphology of nη Carinae. Astronomical Journal, 116(3), 1332-1345.
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  Abstract: We present results of a recent 2-12 μm ground-based infrared (IR) imaging study of Eta Carinae. We discuss the comparative spatial morphology of the bipolar lobes, the "skirt" defined by the equatorial ejecta, and the bright features in the core. We derive separate color temperature values of 200, 240, and 420 K for the bipolar lobes, skirt, and core, respectively. The mass of the Homunculus Nebula estimated from thermal dust emission and a standard gas-to-dust ratio is 2.5 M⊙. Roughly one-fifth of the total mass is contained in the fast-moving equatorial ejecta. These mass estimates, combined with expansion velocities in the lobes and the skirt, lead us to conclude that the 1890 outburst and the Great Eruption of 1843 were almost comparable in terms of total kinetic energy output. We argue that it is unlikely that these eruptions were caused by tidal interactions with a companion star.
• Humphreys, R. M., Smith, N., Davidson, K., Jones, T. J., Gehrz, R. D., Mason, C. G., Hayward, T. L., Houck, J. R., & Krautter, J. (1997). HST and infrared images of the circumstellar environment of the cool hypergiant IRC+10420. Astronomical Journal, 114(6), 2778-2788.
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  Abstract: We present HST WFPC2 and ground-based infrared images of the very evolved, luminous OH/IR star IRC+10420. The HST optical images reveal an amazingly complex environment, with one or more distant reflection shells probably ejected during the star's previous red supergiant stage plus numerous features within two arcseconds of the star including condensations arrayed in jet-like structures, rays, and an intriguing group of small, nearly spherical shell or arcs apparently at ends of some of the jet-like features. In contrast, the lower resolution infrared images show two lobes of emission coincident with some of the optical structures. We propose a nearly pole-on model for IRC+10420 with some bipolar symmetry and with the jet-like features, condensations, and arcs produced primarily in the equatorial region. We also present evidence that the mass loss rate has varied during the past few thousand years with a probable high mass loss event during the last 600 years. © 1997 The American Astronomical Society.

Proceedings Publications

• Bilinski, C., Williams, G. G., Smith, P. S., Smith, N., Milne, P., Hoffman, J. L., Huk, L. N., Leonard, D. C., & Dessart, L. (2014, jan). The Supernova Spectropolarimetry Project: Results from Multi-Epoch Observations of the Type IIb SN 2011dh. In American Astronomical Society Meeting Abstracts, 223, #354.23.
• Hoffman, J. L., Smith, N., Bilinski, C., Dessart, L., Huk, L. N., Leonard, D. C., Milne, P., Smith, P. S., & Williams, G. (2014, jan). The Supernova Spectropolarimetry Project: Evolution of Asymmetries in the Very Luminous Type Ib SN 2012au. In American Astronomical Society Meeting Abstracts, 223, #354.21.
• Khandrika, H. G., Leonard, D. C., Horst, C., Rachubo, A., Duong, N., Williams, G. G., Smith, P. S., Smith, N., Milne, P., Hoffman, J. L., Huk, L. N., & Dessart, L. (2014, jun). The Supernova Spectropolarimetry Project: Photometric Followup in the Optical and Near- Infrared by the Mount Laguna Supernova Survey. In American Astronomical Society Meeting Abstracts, 224, #121.16.
• Milne, P., Williams, G., Smith, P. S., & Smith, N. (2014, jan). Spectropolarimetry of SN 2011fe. In American Astronomical Society Meeting Abstracts, 223, #354.39.
• Reiter, M., & Smith, N. (2014, jan). Powerful jets driven by intermediate-mass protostars in the Carina Nebula. In American Astronomical Society Meeting Abstracts, 223, #436.04.
• Smith, N., Mauerhan, J., & Prieto, J. (2014, jan). The remarkably similar explosions of SN2009ip and SN2010mc, and the late fading of Type IIn supernovae. In American Astronomical Society Meeting Abstracts, 223, #354.30.
• Williams, G. G., Dessart, L., Hoffman, J. L., Huk, L. N., Leonard, D. C., Milne, P., Smith, N., & Smith, P. S. (2014, jan). The Supernova Spectropolarimetry Project: Results from Multi-Epoch Observations of the Type IIn SN 2010jl. In American Astronomical Society Meeting Abstracts, 223, #354.22.
• Mauerhan, J., Smith, N., Filippenko, A. V., Silverman, J., Cenko, B., & Clubb, K. (2013, jan). The Unprecedented Third Outburst of SN 2009ip: A Luminous Blue Variable Becomes a Supernova. In American Astronomical Society Meeting Abstracts, 221, #233.03.
• Reiter, M., & Smith, N. (2013, jan). [Fe II] Emission Tracing Dense Jets from Intermediate-mass Protostars in Carina. In American Astronomical Society Meeting Abstracts, 221, #251.21.
• Reiter, M., & Smith, N. (2013, jul). [Fe II] Emission Tracing Massive, Irradiated Jets from Intermediate-Mass Protostars in the Carina Nebula. In Protostars and Planets VI Posters, 49.
• Rest, A., Prieto, J. L., Bianco, F., Matheson, T., Smith, N., Smith, C., Chornock, R., Sinnott, B., Welch, D., & Walborn, N. (2013, jun). Spectrophotometric Evolution of Eta Carinae's Great Eruption. In Massive Stars: From alpha to Omega.
• Sexton, R., Povich, M. S., Smith, N., & Rudolph, A. L. (2013, jan). Extended Red Objects and Stellar Wind Bow Shocks in the Carina Nebula. In American Astronomical Society Meeting Abstracts, 221, #349.22.
• Smith, N. (2013, jun). The Nature of LBVs. In Massive Stars: From alpha to Omega.
• Rest, A., Sinnott, B., Welch, D. L., Bianco, F., Prieto, J. L., Smith, N., Foley, R. J., Huber, M., & Challis, P. (2012, jan). Spectroscopic Time-Series of Transients with Light Echoes. In American Astronomical Society Meeting Abstracts #219, 219, #242.35.
• Smith, N. (2012). All Things Homunculus. In Astrophysics and Space Science Library, 384, 145.
• Smith, N. (2012, jan). SN2010jp: A Jet-Driven Type II Supernova. In American Astronomical Society Meeting Abstracts #219, 219, #242.36.
• Williams, G. G., Smith, P., Smith, N., Milne, P., Hoffman, J., Huk, L., Leonard, D., & Dessart, L. (2012, may). The Supernova Spectropolarimetry Project; A Study of the Evolution of Aspherical Stellar Explosions. In American Astronomical Society Meeting Abstracts #220, 220, #523.24.

Poster Presentations

• Williams, G. G., Smith, P. S., Smith, N., Milne, P. A., Bilinski, C., Dessart, L., Hoffman, J., Leonard, D., Huk, L., Mauerhan, J., & Porter, A. (2016, 2016-05-16). The Supernova Spectropolarimetry Project. The Transient Sky. Cambridge, MA: Harvard-Smithsonian Center for Astrophysics.