Steve Ertel

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• Andrych, K., Kamath, D., Van Winckel, H., Corporaal, A., De Prins, T., Price, D., Ertel, S., & Kluska, J. (2025). SPHERE/ZIMPOL insights into discs around evolved stars: arcs, asymmetries and dust properties. Publications of the Astronomical Society of Australia, 42(Issue). doi:10.1017/pasa.2025.10079
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  Second-generation circumbinary discs around evolved binary stars, such as post-Asymptotic Giant Branch (post-AGB) binaries, provide insights into poorly understood mechanisms of dust processing and disc evolution across diverse stellar environments. We present a multi-wavelength polarimetric survey of five evolved binary systems - ARPup, HR4049, HR4226, UMon, and V709 Car - using the Very Large Telescope SPHERE/ZIMPOL instrument. Post-AGB discs show significant polarimetric brightness at optical and near-IR wavelengths, often exceeding 1% of the system's total intensity. We also measured a maximum fractional polarisation of the scattered light for ARPup of a 1/40.7 in the V-band and a 1/40.55 in the I-band. To investigate wavelength-dependent polarisation, we combine the SPHERE/ZIMPOL dataset with results from previous SPHERE/IRDIS studies. This analysis reveals that post-AGB discs exhibit a grey to blue polarimetric colour in the optical and near-IR. Along with high fractional polarisation of the scattered light and polarised intensity distribution, these findings are consistent with a surface dust composition dominated by porous aggregates, reinforcing independent observational evidence for such grains in post-AGB circumbinary discs. We also find evidence of diverse disc geometries within the post-AGB sample, including arcs, asymmetries and significant variations in disc size across optical and near-IR wavelengths for some systems (UMon, V709 Car). Combining our findings with existing multi-technique studies, we question the classification of two systems in our sample, HR 4226 and V709 Car, which were originally identified as post-AGB binaries based on their near-IR excess. On comparing post-AGB discs to circumstellar environments around AGB stars and YSOs, we found that post-AGB systems exhibit a higher degree of polarisation than single AGB stars and are comparable to the brightest protoplanetary discs around YSOs. Overall, our results reinforce the importance of polarimetric observations in probing dust properties and complex circumbinary structures. We also highlight the importance of combining multi-wavelength and multi-technique observations with advanced radiative-transfer modelling to differentiate between the various evolutionary pathways of circumbinary discs.
• Barbato, D., Mesa, D., D'Orazi, V., Desidera, S., Ruggieri, A., Farinato, J., Marafatto, L., Carolo, E., Vassallo, D., Ertel, S., Hom, J., Anche, R. M., Battaini, F., Becker, A., Bergomi, M., Biondi, F., Cardwell, A., Cerpelloni, P., Chauvin, G., , Chinellato, S., et al. (2025). A multi-technique detection of an eccentric giant planet around the accelerating star HD 57625. Astronomy and Astrophysics, 693(Issue). doi:10.1051/0004-6361/202452832
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  Context. The synergy between different detection methods is a key asset in exoplanetology that allows the precise characterization of detected exoplanets and robust constraints even in the case of a non-detection. The interplay between imaging, radial velocities and astrometry has recently produced significant advancements in exoplanetary science. Aims. We report a first result of an ongoing survey performed with SHARK-NIR, the new high-contrast near-infrared imaging camera at the Large Binocular Telescope, in parallel with LBTI/LMIRCam in order to detect planetary companions around stars with a significant proper motion anomaly. We focus on HD 57625, a F8 star for which we determine a 4.8-2.9+3.7 Ga age, exhibiting significant astrometric acceleration and for which archival radial velocities indicate a previously undetected massive long-period companion. Methods. We analysed the imaging data we collected with SHARK-NIR and LMIRCam in synergy with the available public SOPHIE radial velocity time series and HIPPARCOS-Gaia proper motion anomaly. With this joint multi-technique analysis, we characterised the companion causing the astrometric and radial velocity signals. Results. The imaging observations result in a non-detection, indicating the companion to be in the substellar regime. This is confirmed by the synergic analysis of archival radial velocity and astrometric measurements resulting in the detection of HD 57625 b, a 8.43-0.91+1.1 MJup planetary companion with an orbital separation of 5.70-0.13+0.14 au and an eccentricity of 0.52-0.03+0.04. Conclusions. HD 57625 b joins the small but growing population of giant planets on outer orbits with a true mass determination provided by the synergic usage of multiple detection methods. This again proves the importance of a multi-technique analysis in providing a robust characterization of planetary companions.
• Close, L. M., van Capelleveen, R. F., Weible, G., Wagner, K., Haffert, S. Y., Males, J. R., Ilyin, I., Kenworthy, M. A., Li, J., Long, J. D., Ertel, S., Ginski, C., Weinberger, A. J., Follette, K., Liberman, J., Twitchell, K., Johnson, P., Kueny, J., Apai, D., , Doyon, R., et al. (2025). Wide Separation Planets in Time (WISPIT): Discovery of a Gap Hα Protoplanet WISPIT 2b with MagAO-X. Astrophysical Journal Letters, 990(Issue 1). doi:10.3847/2041-8213/adf7a5
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• Crepp, J. R., Crass, J., Bechter, A. J., Sands, B. L., Ketterer, R., King, D., Kopon, D., Hamper, R., Engstrom, M., Smous, J. E., Bechter, E. B., Harris, R., Johnson, M. C., Baggett, N., Dulz, S., Vansickle, M., Conrad, A., Ertel, S., Gaudi, B. S., , Hinz, P., et al. (2025). Resolving the Young 2 Cygni Runaway Star into a Binary Using iLocater. Astronomical Journal, 169(Issue 1). doi:10.3847/1538-3881/ad9b1d
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  Precision radial velocity spectrographs that use adaptive optics (AO) show promise to advance telescope observing capabilities beyond those of seeing-limited designs. We are building a spectrograph for the Large Binocular Telescope (LBT) named iLocater that uses AO to inject starlight directly into single mode fibers. iLocater's first acquisition camera system (the SX camera), which receives light from one of the 8.4 m diameter primary mirrors of the LBT, was initially installed in summer 2019 and has since been used for several commissioning runs. We present results from first-light observations that include on-sky measurements as part of commissioning activities. Imaging measurements of the bright B3IV star 2 Cygni (V = 4.98) resulted in the direct detection of a candidate companion star at an angular separation of only θ = 70 mas. Follow-up AO measurements using Keck/NIRC2 recover the candidate companion in multiple filters. An R ≈ 1500 miniature spectrograph recently installed at the LBT named Lili provides spatially resolved spectra of each binary component, indicating similar spectral types and strengthening the case for companionship. Studying the multiplicity of young runaway star systems like 2 Cygni (36.6 ± 0.5 Myr) can help to understand formation mechanisms for stars that exhibit anomalous velocities through the Galaxy. This on-sky demonstration illustrates the spatial resolution of the iLocater SX acquisition camera working in tandem with the LBT AO system; it further derisks a number of technical hurdles involved in combining AO with Doppler spectroscopy.
• Ertel, S., Pearce, T. D., Debes, J. H., Faramaz, V. C., Danchi, W. C., Anche, R. M., Defrère, D., Hasegawa, Y., Hom, J., Kirchschlager, F., Rebollido, I., Rousseau, H., Scott, J., Stapelfeldt, K., & Stuber, T. A. (2025). Review and Prospects of Hot Exozodiacal Dust Research For Future Exo-Earth Direct Imaging Missions. Publications of the Astronomical Society of the Pacific, 137(Issue 3). doi:10.1088/1538-3873/adb6d5
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  Hot exozodiacal dust is dust in the innermost regions of planetary systems, at temperatures around 1000 K-2000 K, and commonly detected by near-infrared interferometry. The phenomenon is poorly understood and has received renewed attention as a potential risk to a planned future space mission to image potentially habitable exoplanets and characterize their atmospheres (exo-Earth imaging) such as the Habitable Worlds Observatory (HWO). In this article, we review the current understanding of hot exozodiacal dust and its implications for HWO. We argue that the observational evidence suggests that the phenomenon is most likely real and indeed caused by hot dust, although conclusive proof in particular of the latter statement is still missing. Furthermore, we find that there exists as of yet no single model that is able to successfully explain the presence of the dust. We find that it is plausible and not unlikely that large amounts of hot exozodiacal dust in a system will critically limit the sensitivity of exo-Earth imaging observations around that star. It is thus crucial to better understood the phenomenon in order to be able to evaluate the actual impact on such a mission, and current and near-future observational opportunities for acquiring the required data exist. At the same time, hot exozodiacal dust (and warm exozodiacal dust closer to a system’s habitable zone) has the potential to provide important context for HWO observations of rocky, HZ planets, constraining the environment in which these planets exist and hence to determine why a detected planet may be capable to sustain life or not.
• Garreau, G., Defrère, D., Ertel, S., Faramaz-Gorka, V., Bryden, G., Sommer, M., Mesa, D., Wagner, K., De Prins, T., Laugier, R., Weinberger, A., Farinato, J., Haniff, C., Hinz, P. M., Isbell, J. W., Kennedy, G. M., Lorenzetto, A., Maier, E. R., Marafatto, L., , Marino, S., et al. (2025). The HOSTS survey: Suspected variable dust emission and constraints on companions around θθ Boo. Astronomy and Astrophysics, 699(Issue). doi:10.1051/0004-6361/202452653
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  Context. During the Hunt for Observable Signatures of Terrestrial Systems (HOSTS) survey by the Large Binocular Telescope Interferometer (LBTI), an excess emission from the main-sequence star, θ Boo (F7V spectral type, 14.5 pc distance) was observed. This excess indicates the presence of exozodiacal dust near the star’s habitable zone (HZ). Previous observations with Spitzer and Herschel show no evidence of outer cold dust within their respective detection limits. Because exozodiacal dust is generally believed to originate from material located farther out in the system, its source around θ Boo remains unclear. Aims. We conducted additional nulling and high-contrast adaptive optics (AO) observations to spatially constrain the dust distribution, search for variability, and directly image potential companions in the system. This study presents the results of these observations and provides an interpretation of the inner system’s architecture. Methods. We observed the star using the LBTI’s N′-band nulling mode during three epochs in 2017, 2018, and 2023. For each epoch, we modeled and constrained the dust distribution using the standard LBTI nulling pipeline, assuming a vertically thin disk with a face-on inclination. We also performed high-contrast AO observations in the L′-band and H-band to constrain the presence of substellar companions around the star. Results. We find several solutions for the dust distribution for each epoch. However, the LBTI nulling observations are unable to discriminate between them. Using upper limits from previous observations, we constrain the representative size of the dust grains to approximately 3–5 µm. We also measured a tentative increase in dust brightness at the Earth-equivalent insolation distance between 2017 and 2023. This increase corresponds to the injection of 4 × 10−8–4 × 10−7 M☉ of new material into the disk. We consider several options to explain the origin of the observed dust and its variability, but no clear sources are identified from the current observations, partly because our high-contrast AO observations could only constrain the presence of companions only down to 11 MJup at 1.3′′ separation.
• Harris, R. J., Crass, J., Johnson, M. C., Bechter, A. J., Power, J., Rosario, A. C., Crepp, J. R., Bechter, E. B., Sands, B. L., Kopon, D., Ertel, S., Barboza, S., & Bianco, A. (2025). Little iLocater: paving the way for iLocater. Monthly Notices of the Royal Astronomical Society, 536(Issue 3). doi:10.1093/mnras/stae2720
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  Diffraction-limited radial-velocity instruments offer a pathway towards improved precision and stability, and the exploration of new parameter spaces at high spatial and spectral resolution. However, achieving the necessary performance requires careful instrument design and considerable on-sky testing. We describe the design and construction of ‘Little iLocater’ (Lili), a compact spectrograph that has been used to validate the performance of the front-end fibre-injection system of the iLocater spectrograph. We present the design, assembly, and performance using on-sky data obtained at the Large Binocular Telescope (LBT), including extraction of spectra from standard stars, testing of the atmospheric dispersion corrector to elevations of 40◦, and spatially resolved spectra from close companion systems. These results show the front-end fibre-injection system is performing as expected and is indicative of iLocater’s capabilities once installed at the LBT.
• Isbell, J. W., Ertel, S., Pott, J. U., Weigelt, G., Stalevski, M., Leftley, J., Jaffe, W., Petrov, R. G., Moszczynski, N., Vermot, P., Hinz, P., Burtscher, L., Gámez Rosas, V., Becker, A., Carlson, J., Faramaz-Gorka, V., Hoffmann, W. F., Leisenring, J., Power, J., & Wagner, K. (2025). Direct imaging of active galactic nucleus outflows and their origin with the 23 m Large Binocular Telescope. Nature Astronomy, 9(Issue 3). doi:10.1038/s41550-024-02461-y
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  Active galactic nuclei (AGNs) are a key component of galaxy evolution owing to feedback on the host from its supermassive black hole. The morphology of warm inflowing and outflowing dusty material can reveal the nature of the onset of feedback, AGN feeding and the unified model of AGN. Here we use the Large Binocular Telescope Interferometer (LBTI) to image the dense, obscuring disk and extended dusty outflow region of NGC 1068. In Fizeau imaging mode, the LBTI synthesizes the equivalent resolution of a 22.8 m telescope. The 8.7 μm Fizeau images of NGC 1068 have an effective resolution of 47 × 90 mas (3.3 × 6.2 pc) in a 5″ field of view after performing point spread function deconvolution techniques described here. This is the only extragalactic source to be Fizeau imaged using the LBTI, and the images bridge the scales measured with the Very Large Telescope Interferometer (0.5–5 pc) and those of single telescopes such as James Webb Space Telescope and Keck (>15 pc). The images detect and spatially resolve the low surface brightness mid-infrared features in the AGN disk/wind region that are overresolved by the Very Large Telescope Interferometer. The images show strong correlation between mid-infrared dust emission and near-infrared emission of highly excited atomic lines observed by SINFONI. Such LBTI imaging is a precursor to infrared imaging using the upcoming generation of extremely large telescopes, with angular resolutions up to six times better than James Webb Space Telescope, the largest space telescope in orbit.
• Martinod, M. A., Defrère, D., Laugier, R., Ertel, S., Absil, O., Norris, B., & Mennesson, B. (2025). GRIP: a generic data reduction package for nulling interferometry. Journal of Astronomical Telescopes, Instruments, and Systems, 11(Issue 2). doi:10.1117/1.jatis.11.2.028003
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  Nulling interferometry is a powerful observing technique to study exoplanets and circumstellar dust at separations too small for direct imaging with single-dish telescopes. With recent photonic developments and the near-future ground-based instrumental projects, it bears the potential to detect young giant planets near the snow lines of their host stars. The observable quantity of a nulling interferometer is called the null depth, and its precise measurement and calibration remain challenging against instrument and atmospheric noise. Null self-calibration is a method aiming to model the statistical distribution of the nulled signal. It has proven to be more sensitive and accurate than average-based data reduction methods in nulling interferometry. The variety of existing and upcoming nullers raises the issue of consistency of the calibration process, the structure of the data, and the ability to reduce archived data in the long term. It has also led to many different implementations of the null self-calibration method. We introduce GRIP: the first open-source toolbox to reduce nulling data with enhanced statistical self-calibration methods from any nulling interferometric instrument within a single and consistent framework. Astrophysical results show good consistency with two published Guided-Light Interferometric Nulling Technology and Large Binocular Telescope Interferometer datasets and confirm nulling precision down to a few 10−4
• Matrà, L., Marino, S., Wilner, D. J., Kennedy, G. M., Booth, M., Krivov, A. V., Williams, J. P., Hughes, A. M., Del Burgo, C., Carpenter, J., Davies, C. L., Ertel, S., Kral, Q., Lestrade, J. F., Marshall, J. P., Milli, J., Öberg, K. I., Pawellek, N., Sepulveda, A. G., , Wyatt, M. C., et al. (2025). REsolved ALMA and SMA Observations of Nearby Stars (REASONS): A population of 74 resolved planetesimal belts at millimetre wavelengths. Astronomy and Astrophysics, 693(Issue). doi:10.1051/0004-6361/202451397
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  Context. Planetesimal belts are ubiquitous around nearby stars, and their spatial properties hold crucial information for planetesimal and planet formation models. Aims. We present resolved dust observations of 74 planetary systems as part of the REsolved ALMA and SMA Observations of Nearby Stars (REASONS) survey and archival reanalysis. Methods. We uniformly modelled interferometric visibilities for the entire sample to obtain the basic spatial properties of each belt, and combined these with constraints from multi-wavelength photometry. Results. We report key findings from a first exploration of this legacy dataset: (1) Belt dust masses are depleted over time in a radially dependent way, with dust being depleted faster in smaller belts, as predicted by collisional evolution. (2) Most belts are broad discs rather than narrow rings, with much broader fractional widths than rings in protoplanetary discs. We link broad belts to either unresolved substructure or broad planetesimal discs produced if protoplanetary rings migrate. (3) The vertical aspect ratios (h = H/R) of 24 belts indicate orbital inclinations of ∼1-20°, implying relative particle velocities of ∼0.1-4 km/s, and no clear evolution of heights with system age. This could be explained by early stirring within the belt by large bodies (with sizes of at least ∼140 km to the size of the Moon), by inheritance of inclinations from the protoplanetary disc stage, or by a diversity in evolutionary pathways and gravitational stirring mechanisms. We release the REASONS legacy multidimensional sample of millimetre-resolved belts to the community as a valuable tool for follow-up multi-wavelength observations and population modelling studies.
• Mesa, D., Gratton, R., D'orazi, V., Carolo, E., Vassallo, D., Farinato, J., Marafatto, L., Wagner, K., Hom, J., Ertel, S., Henning, T., Desgrange, C., Barbato, D., Bergomi, M., Cerpelloni, P., Desidera, S., Di Filippo, S., Doelman, D., Machado, T. S., , Greggio, D., et al. (2025). Deep imaging of three accelerating stars using SHARK-NIR and LMIRCam at LBT. Monthly Notices of the Royal Astronomical Society, 536(Issue 2). doi:10.1093/mnras/stae2706
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  The combination of detection techniques enhances our ability to identify companions orbiting nearby stars. We employed high-contrast imaging to constrain mass and separation of possible companions responsible for the significant proper motion anomalies of the nearby stars HIP 11696, HIP 47110, and HIP 36277. These targets were observed using the LBT's high-contrast camera, SHARK-NIR, in H band using a Gaussian coronagraph, and with the LMIRCam instrument in the L' band and using a vAPP coronagraph. Both observations were conducted simultaneously. Additionally, constraints at short separations from the host star are derived analysing the renormalized unit weight error values from the Gaia catalogue. We find that the companion responsible for the anomaly signal of HIP 11696 is likely positioned at a distance from 2.5 to 28 astronomical units from its host. Its mass is estimated to be between 4 and 16 Jupiter masses, with the greater mass possible only at the upper end of the separation range. Similar limits were obtained for HIP 47110 where the companion should reside between 3 and 30 au with a mass between 3 and 10 MJup. For HIP 36277, we identified a faint stellar companion at large separation, though it might be substellar depending on the assumed age for the star. Considering the older age, this object accounts for the absolute value of the PMa vector but not for its direction. Additionally, we found a substellar candidate companion at a closer separation that could explain the PMa signal, considering a younger age for the system.
• Ollmann, K., Kirchschlager, F., Stuber, T. A., Tsishchankava, K., Matter, A., Ertel, S., Pearce, T. D., Krivov, A. V., & Wolf, S. (2025). Hot exozodiacal dust around Fomalhaut: The MATISSE perspective. Astronomy and Astrophysics, 699(Issue). doi:10.1051/0004-6361/202451592
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  Context. Excess over the stellar photospheric emission of main-sequence stars has been found in interferometric near-infrared observations, and is attributed to the presence of hot exozodiacal dust (HEZD). As part of our effort to detect and characterize HEZD around the nearby A3 V star Fomalhaut, we carried out the first interferometric observations with the MATISSE instrument at the VLTI in the photometric bands L and M for the Fomalhaut system. Aims. We investigate whether the new MATISSE data indicate the presence of HEZD around Fomalhaut. If detected, we aim to constrain the dust grain size, location, dust species, and total dust mass based on these data. We also investigate if the possibly detected circumstellar radiation could have an alternative explanation. Methods. Assuming a dust distribution either as a narrow ring or spherical shell for modeling the HEZD, we aim to constrain the HEZD parameters by generating visibilities and fitting them to the MATISSE data using different approaches. Results. The MATISSE L band data provide a marginal detection of circumstellar radiation, potentially caused by the presence of HEZD, which is only the second detection of HEZD emission in the L band. An analysis of the data with different fitting approaches showed that the best-fit values for the HEZD parameters are consistent with those of previous Fomalhaut observations, which again underlines the functionality of MATISSE. We derived the following best-fit HEZD parameter values: Assuming a dust ring, it would have an inner ring radius of 0.11 au, an outer ring radius of 0.12 au, a narrow dust grain size distribution around a dust grain radius constrained by 0.53 μm, and a total dust mass of 3.25 ×-10-10 M⊕ . However, even with an additional consideration of previous VINCI (K band) and KIN (N band) measurements, we cannot further tighten the constraints for the HEZD properties than in previous Fomalhaut studies. Because our data cannot directly constrain the morphology of the excess radiation source, even the presence of a stellar companion can reproduce the detected marginal visibility deficit. Moreover, the MATISSE data neither imply nor exclude the existence of a double ring structure close to Fomalhaut. Finally, the results indicate that the choice of the geometric model has a more significant impact on the derived dust-to-star flux ratio than the specific fitting approach applied. Conclusions. Since different dust-to-star flux ratios can result from the applied fitting approaches, this also has an impact on the parameter values of the HEZD around Fomalhaut. This circumstance should also be investigated for HEZD systems analyzed so far only with the fitting approach usually applied. Moreover, further NIR and MIR data are required for a more comprehensive description of the emission originating in the close vicinity of Fomalhaut.
• Wagner, K., Douglas, E., Ertel, S., Grattan, K., Pete Worden, S., Sanghi, A., Quarles, B., & Beichman, C. (2025). Astrometric Methods for Detecting Exomoons Orbiting Imaged Exoplanets: Prospects for Detecting Moons Orbiting a Giant Planet in α Centauri A’s Habitable Zone. Astrophysical Journal Letters, 991(Issue 2). doi:10.3847/2041-8213/ae0741
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  Nearby giant exoplanets offer an opportunity to search for moons (exomoons) orbiting them. Here, we present a simulation framework for investigating the possibilities of detecting exomoons via their astrometric signal in planet-to-star relative astrometry. We focus our simulations on α Centauri A, orbited by a hypothetical giant planet consistent with candidate detections in Very Large Telescope and James Webb Space Telescope observations. We consider a variety of observatory architectures capable of searching for exomoons, including upcoming facilities and also a hypothetical dedicated facility—e.g., a purpose-built space telescope with diameter = 3 m, central observing wavelength of 500 nm, and contrast-limited performance of ∼10−9 in 1 hr observations. We find that such a facility would be capable of detecting ∼Earth-mass moons in a 5 yr campaign, assuming a Saturn-mass planet. More generally, we simulate expected detection limits for a variety of levels of astrometric precision. We find that moons as small as ∼0.2 M⊕ on orbital periods of 4−30 days can be detected with astrometric precision of 0.1 mas and observing cadence of 1 hr over a 5 yr campaign. Additionally, we find that a 39 m ground-based telescope can detect Earth-sized exomoons orbiting the same hypothetical planet with a more modest observing cadence of 1 day. We discuss these results as motivation for a dedicated space observatory as well as a more detailed study of the physical parameters of a greater variety of star-planet-moon systems.
• Weible, G., Wagner, K., Stone, J., Ertel, S., Apai, D., Kratter, K., & Leisenring, J. (2025). Orbital and Atmospheric Modeling of H ii 1348B: An Eccentric Young Substellar Companion in the Pleiades. Astronomical Journal, 169(Issue 4). doi:10.3847/1538-3881/adadf6
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  Brown dwarfs with known physical properties (e.g., age and mass) are essential for constraining models of the formation and evolution of substellar objects. We present new high-contrast imaging observations of the circumbinary brown dwarf H ii 1348B—one of the few known substellar companions in the Pleiades cluster. We observed the system in the infrared L ′ band with the Large Binocular Telescope Interferometer in dual-aperture direct-imaging mode (i.e., with the two telescope apertures used separately) on 2019 September 18. The observations attained a high signal-to-noise ratio (SNR > 150) photometric detection and relative astrometry with uncertainties of ∼5 mas. This work presents the first model of the companion’s orbital motion using relative astrometry from five epochs across a total baseline of 23 yr. Orbital fits to the compiled data show the companion’s semimajor axis to be a = 14 0 − 30 + 130 au with an eccentricity of e = 0.7 8 − 0.29 + 0.12 . We infer that H ii 1348B has a mass of 60-63 ± 2 MJ from comparison to brown dwarf evolutionary models given the well-constrained distance and age of the Pleiades. No other objects were detected in the H ii 1348 system, and through synthetic planet injection and retrievals we establish detection limits at a cluster age of 112 ± 5 Myr down to ∼10-30 MJ for companions with projected separations of 21.5-280 au. With this work, H ii 1348B becomes the second directly imaged substellar companion in the Pleiades with measured orbital motion after HD 23514B.
• Cesario, L., Lichtenberg, T., Alei, E., Carrión-González, Ó., Dannert, F. A., Defrère, D., Ertel, S., Fortier, A., García Muñoz, A., Glauser, A. M., Hansen, J. T., Helled, R., Huber, P. A., Ireland, M. J., Kammerer, J., Laugier, R., Lillo-Box, J., Menti, F., Meyer, M. R., , Noack, L., et al. (2024). Large Interferometer For Exoplanets (LIFE): XIV. Finding terrestrial protoplanets in the galactic neighborhood. Astronomy and Astrophysics, 692(Issue). doi:10.1051/0004-6361/202450764
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  Context. The increased brightness temperature of young rocky protoplanets during their magma ocean epoch makes them potentially amenable to atmospheric characterization at distances from the Solar System far greater than thermally equilibrated terrestrial exoplanets, offering observational opportunities for unique insights into the origin of secondary atmospheres and the near surface conditions of prebiotic environments. Aims. The Large Interferometer For Exoplanets (LIFE) mission will employ a space-based midinfrared nulling interferometer to directly measure the thermal emission of terrestrial exoplanets. In this work, we seek to assess the capabilities of various instrumental design choices of the LIFE mission concept for the detection of cooling protoplanets with transient high-temperature magma ocean atmospheres at the tail end of planetary accretion. In particular, we investigate the minimum integration times necessary to detect transient magma ocean exoplanets in young stellar associations in the Solar neighborhood. Methods. Using the LIFE mission instrument simulator (LIFEsim), we assessed how specific instrumental parameters and design choices, such as wavelength coverage, aperture diameter, and photon throughput, facilitate or disadvantage the detection of protoplan-ets. We focused on the observational sensitivities of distance to the observed planetary system, protoplanet brightness temperature (using a blackbody assumption), and orbital distance of the potential protoplanets around both G- and M-dwarf stars. Results. Our simulations suggest that LIFE will be able to detect (S/N ≥ 7) hot protoplanets in young stellar associations up to distances of 100 pc from the Solar System for reasonable integration times (up to a few hours). Detection of an Earth-sized protoplanet orbiting a Solar-sized host star at 1 AU requires less than 30 minutes of integration time. M-dwarfs generally need shorter integration times. The contribution from wavelength regions smaller than 6 μm is important for decreasing the detection threshold and discriminating emission temperatures. Conclusions. The LIFE mission is capable of detecting cooling terrestrial protoplanets within minutes to hours in several local young stellar associations hosting potential targets. The anticipated compositional range of magma ocean atmospheres motivates further architectural design studies to characterize the crucial transition from primary to secondary atmospheres.
• Conrad, A., Pedichini, F., Li Causi, G., Antoniucci, S., de Pater, I., Davies, A. G., de Kleer, K., Piazzesi, R., Testa, V., Vaccari, P., Vicinanza, M., Power, J., Ertel, S., Shields, J. C., Ragland, S., Giorgi, F., Jefferies, S. M., Hope, D., Perry, J., , Williams, D. A., et al. (2024). Observation of Io's Resurfacing via Plume Deposition Using Ground‐Based Adaptive Optics at Visible Wavelengths With LBT SHARK‐VIS. Geophysical Research Letters, 51(11). doi:10.1029/2024gl108609
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  Since volcanic activity was first discovered on Io from Voyager images in 1979, changes on Io's surface have been monitored from both spacecraft and ground-based telescopes. Here, we present the highest spatial resolution images of Io ever obtained from a ground-based telescope. These images, acquired by the SHARK-VIS instrument on the Large Binocular Telescope, show evidence of a major resurfacing event on Io's trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images show that a plume deposit from a powerful eruption at Pillan Patera has covered part of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io's surface using adaptive optics at visible wavelengths.
• Romero, C., Milli, J., Lagrange, A., De Rosa, R., Ertel, S., & Del Burgo, C. (2024). Multiple reference star differential imaging with VLT/SPHERE: Influence of the reference frame selection and library. Astronomy and Astrophysics, 691(Issue). doi:10.1051/0004-6361/202346361
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  Context. High-contrast imaging observations mostly rely on angular differential imaging, a successful technique for detecting point-sources, such as planets. However, in the vicinity of the star (typically below 300 mas), this technique suffers from signal self-subtraction when there is not enough field rotation. Building large libraries of reference stars from archival data later used to optimally subtract the stellar halo is a powerful technique known as reference star differential imaging (RSDI) that can overcome this limitation. Aims. We aim at investigating new methods for creating reference libraries composed of multiple stars when applying reference star differential imaging to VLT/SPHERE data. We used for that purpose a data set from the SPHERE High Angular Resolution Debris Disk Survey (SHARDDS), composed of 55 targets observed in broad-band H with the InfraRed Dual-band Imager and Spectrograph (IRDIS) during 2015-2016, with a total of ~20 000 frames. We consider HD 206893, known to host a close-in bound substellar companion HD 206893 B, as a benchmark science target to demonstrate the improved sensitivity provided by this method. Methods. We created libraries of reference frames based on different image similarity metrics: the cosine distance between descriptors created by a convolutional neural network, the Pearson correlation coefficient, the Structural Similarity Index, the Strehl ratio, and raw contrast criteria. We used principal component analysis (PCA) to subtract the stellar halo and tested various normalization options. Results. We obtained the best signal-to-noise ratio (S/N) on HD 206893 B by using the Pearson correlation coefficient (PCC) applied to an annulus between 245 and 612 mas to select reference frames. The ten reference libraries with the highest S/N on the substellar companion HD 206893 B were all based on the PCC method, outperforming other similarity metrics. While the Strehl ratio is the environment variable most correlated to the contrast, it is insufficient to select similar images. We also show that having multiple reference stars in the reference library produces better results than using a single well-chosen reference star. Conclusions. Using the Pearson correlation computed on a specific area of interest to select reference frames is a promising alternative to improve the detectability of faint point-sources when applying reference star differential imaging. In the future, reducing all the data available in the SPHERE archive using this technique might offer interesting results in the search for previously undetected planets.
• Rousseau, H., Ertel, S., Faramaz, V., Wagner, K., & Defrère, D. (2024). Improving mid-infrared thermal background subtraction with principal component analysis. Astronomy and Astrophysics, 687(Issue). doi:10.1051/0004-6361/202348574
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  Context. Ground-based large-aperture telescopes, interferometers, and future extremely large telescopes equipped with adaptive optics (AO) systems provide angular resolution and high-contrast performance superior to space-based telescopes at thermal infrared wavelengths. Their sensitivity, however, is critically limited by the high thermal background inherent to ground-based observations in this wavelength regime. Aims. We aim to improve the subtraction quality of the thermal infrared background from ground-based observations using principal component analysis (PCA). Methods. We used data obtained with the Nulling-Optimized Mid-Infrared Camera on the Large Binocular Telescope Interferometer as a proxy for general high-sensitivity AO-assisted ground-based data. We applied both a classical background subtraction-using the mean of dedicated background observations-and a new background subtraction based on a PCA of the background observations. We compared the performances of these two methods in both high-contrast imaging and aperture photometry. Results. Compared to the classical approach for background subtraction, PCA background subtraction delivers up to two times better contrasts down to the diffraction limit of the LBT's primary aperture (i.e., 350 mas in N-band), that is, in the case of high-contrast imaging. An improvement factor between two and three was obtained over the mean background retrieval within the diffraction limit in the case of aperture photometry. Conclusions. The PCA background subtraction significantly improves the sensitivity of ground-based thermal infrared imaging observations. When apply to LBTI's nulling interferometry data, we expect the method to improve the sensitivity by a similar factor of two to three. This study paves the way to maximizing the potential of future infrared ground-based instruments and facilities, such as the future 30m-class telescopes.
• Sutlieff, B. J., Birkby, J. L., Stone, J. M., Derkink, A., Backs, F., Doelman, D. S., Kenworthy, M. A., Bohn, A. J., Ertel, S., Snik, F., Woodward, C. E., Ilyin, I., Skemer, A. J., Leisenring, J. M., Strassmeier, K. G., Wang, J., Charbonneau, D., & Biller, B. A. (2024). Exploring the directly imaged HD 1160 system through spectroscopic characterization and high-cadence variability monitoring. Monthly Notices of the Royal Astronomical Society, 531(1), 2168-2189. doi:10.1093/mnras/stae1315
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  The time variability and spectra of directly imaged companions provide insight into their physical properties and atmospheric dynamics. We present follow-up R ∼40 spectrophotometric monitoring of red companion HD 1160 B at 2.8-4.2 μm using the double-grating 360° vector Apodizing Phase Plate (dgvAPP360) coronagraph and ALES integral field spectrograph on the Large Binocular Telescope Interferometer. We use the recently developed technique of gvAPP-enabled differential spectrophotometry to produce differential light curves for HD 1160 B. We reproduce the previously reported ∼3.2 h periodic variability in archival data, but detect no periodic variability in new observations taken the following night with a similar 3.5 per cent level precision, suggesting rapid evolution in the variability of HD 1160 B. We also extract complementary spectra of HD 1160 B for each night. The two are mostly consistent, but the companion appears fainter on the second night between 3.0-3.2 μm. Fitting models to these spectra produces different values for physical properties depending on the night considered. We find an effective temperature Teff = K on the first night, consistent with the literature, but a cooler Teff = K on the next. We estimate the mass of HD 1160 B to be 16-81 MJup, depending on its age. We also present R = 50 000 high-resolution optical spectroscopy of host star HD 1160 A obtained simultaneously with the PEPSI spectrograph. We reclassify its spectral type to A1 IV-V and measure its projected rotational velocity = km s-1. We thus highlight that gvAPP-enabled differential spectrophotometry can achieve repeatable few per cent level precision and does not yet reach a systematic noise floor, suggesting greater precision is achievable with additional data or advanced detrending techniques.
• Andrych, K., Kamath, D., Kluska, J., Van Winckel, H., Ertel, S., & Corporaal, A. (2023). Second-generation protoplanetary discs around evolved binaries: a high-resolution polarimetric view with SPHERE/IRDIS. Monthly Notices of the Royal Astronomical Society, 524(3), 4168-4195. doi:10.1093/mnras/stad1968
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  Binary post-asymptotic giant branch (post-AGB) stars are products of a poorly understood binary interaction process that occurs during the AGB phase. These systems comprise a post-AGB primary star, a main-sequence secondary companion and a stable circumbinary disc. Studying the structure and properties of these circumbinary discs is crucial for gaining insight into the binary interaction process that governs post-AGB binaries as well as comprehending the disc's creation, evolution, and its interaction with the post-AGB binary system. We aim to use near-infrared polarimetric imaging to investigate the morphology and potential substructures of circumbinary discs around eight representative post-AGB binary stars. To achieve this, we performed polarimetric differential imaging in H and Y bands using the high-angular resolution capabilities of the European Southern Observatory-Very Large Telescope/SPHERE-Infra-Red Dual-beam Imaging and Spectroscopy instrument. We resolved the extended circumbinary disc structure for a diverse sample of eight post-AGB binary systems. Our analysis provided the first estimates of the disc scale height for two of the systems: IW Car and IRAS 15469-5311. We also investigated the morphological differences between the full discs (with the inner rim at the dust sublimation radius) and transition discs (which are expected to have larger inner cavities), as well as similarities to protoplanetary discs around young stellar objects. We found that the transition discs displayed a more intricate and asymmetric configuration. Surprisingly, no correlation was found between the overresolved flux in near-infrared interferometric data and the polarimetric observations, suggesting that scattering of light on the disc surface may not be the primary cause of the observed overresolved flux component.
• Anugu, N., Kluska, J., Gardner, T., Monnier, J., Van Winckel, H., Schaefer, G., Kraus, S., Le Bouquin, J., Ertel, S., Klement, R., Davies, C., Ennis, J., Labdon, A., Lanthermann, C., Setterholm, B., Brummelaar, T., Corporaal, A., Sabin, L., Rajagopal, J., & Mérand, A. (2023). Three-dimensional Orbit of AC Her Determined: Binary-induced Truncation Cannot Explain the Large Cavity in This Post-AGB Transition Disk. Astrophysical Journal, 950(2). doi:10.3847/1538-4357/acd1e6
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  Some evolved binaries, namely post-asymptotic giant branch (AGB) binaries, are surrounded by stable and massive circumbinary disks similar to protoplanetary disks found around young stars. Around 10% of these disks are transition disks: they have a large inner cavity in the dust. Previous interferometric measurements and modeling have ruled out these cavities being formed by dust sublimation and suggested that they are due to massive circumbinary planets that trap dust in the disk and produce the observed depletion of refractory elements on the surfaces of the post-AGB stars. In this study, we test an alternative scenario in which the large cavities could be due to dynamical truncation from the inner binary. We performed near-infrared interferometric observations with the CHARA Array on the archetype of such a transition disk around a post-AGB binary: AC Her. We detect the companion at ten epochs over 4 yr and determine the three-dimensional orbit using these astrometric measurements in combination with a radial velocity time series. This is the first astrometric orbit constructed for a post-AGB binary system. We derive the best-fit orbit with a semimajor axis of 2.01 ± 0.01 mas (2.83 ± 0.08 au), inclination (142.9 ± 1.1)°, and longitude of the ascending node (155.1 ± 1.8)°. We find that the theoretical dynamical truncation and dust sublimation radii are at least ∼3× smaller than the observed inner disk radius (∼21.5 mas or 30 au). This strengthens the hypothesis that the origin of the cavity is due to the presence of a circumbinary planet.
• Brady, M., Faramaz-Gorka, V., Bryden, G., & Ertel, S. (2023). Long-term Evolution of Warps in Debris Disks - Application to the Gyr-old System HD 202628. Astrophysical Journal, 954(1). doi:10.3847/1538-4357/ace9bb
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  We present the results of N-body simulations meant to reproduce the long-term effects of mutually inclined exoplanets on debris disks, using the HD 202628 system as a proxy. HD 202628 is a Gyr-old solar-type star that possesses a directly observable, narrow debris ring with a clearly defined inner edge and nonzero eccentricity, hinting at the existence of a sculpting exoplanet. The eccentric nature of the disk leads us to examine the effect on it over Gyr timescales from an eccentric and inclined planet, placed on its orbit through scattering processes. We find that, in systems with dynamical timescales akin to that of HD 202628, a planetary companion is capable of completely tilting the debris disk. This tilt is preserved over the Gyr age of the system. Simulated observations of our models show that an exoplanet around HD 202628 with an inclination misalignment ≳10° would cause the disk to be observably diffuse and broad, which is inconsistent with Atacama Large Millimeter Array (ALMA) observations. With these observations, we conclude that, if there is an exoplanet shaping this disk, it likely had a mutual inclination of less than 5° with the primordial disk. The conclusions of this work can be applied either to debris disks appearing as narrow rings (e.g., Fomalhaut and HR 4796) or to disks that are vertically thick at ALMA wavelengths (e.g., HD 110058).
• Marshall, J., Ertel, S., Birtcil, E., Villaver, E., Kemper, F., Boffin, H., Scicluna, P., & Kamath, D. (2023). Evidence for the Disruption of a Planetary System During the Formation of the Helix Nebula. Astronomical Journal, 165(1). doi:10.3847/1538-3881/ac9d90
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  The persistence of planetary systems after their host stars evolve into their post-main-sequence phase is poorly constrained by observations. Many young white dwarf systems exhibit infrared excess emission and/or spectral absorption lines associated with a reservoir of dust (or planetesimals) and its accretion. However, most white dwarfs are too cool to sufficiently heat any circumstellar dust to detectable levels of emission. The Helix Nebula (NGC 7293) is a young, nearby planetary nebula; observations at mid- and far-infrared wavelengths have revealed excess emission associated with its central white dwarf (WD 2226-210). The origin of this excess is ambiguous. It could be a remnant planetesimal belt, a cloud of comets, or the remnants of material shed during the post-asymptotic giant branch (post-AGB) phase. Here we combine infrared (Stratospheric Observatory for Infrared Astronomy, Spitzer, Herschel) and millimeter (Atacama Large Millimeter/submillimeter Array) observations of the system to determine the origin of this excess using multiwavelength imaging and radiative transfer modeling. We find the data are incompatible with a compact remnant planetesimal belt or post-AGB disk, and conclude the dust most likely originates from deposition by a cometary cloud. The measured dust mass, and lifetime of the constituent grains, implies disruption of several thousand Hale-Bopp equivalent comets per year to fuel the observed excess emission around the Helix Nebula’s white dwarf.
• Marshall, J., Ertel, S., Kemper, F., del Burgo, C., Otten, G., Scicluna, P., Zeegers, S., Ribas, Á., & Morata, O. (2023). Sudden Extreme Obscuration of a Sun-like Main-sequence Star: Evolution of the Circumstellar Dust around ASASSN-21qj. Astrophysical Journal, 954(2). doi:10.3847/1538-4357/ace629
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  ASASSN-21qj is a distant Sun-like star that recently began an episode of deep dimming events after no prior recorded variability. Here we examine archival and newly obtained optical and near-infrared data of this star. The deep aperiodic dimming and absence of previous infrared excess are reminiscent of KIC 8462852 (“Boyajian’s Star”). The observed occultations are consistent with a circumstellar cloud of submicron-sized dust grains composed of amorphous pyroxene, with a minimum mass of 1.50 ± 0.04 × 10−9 M ⊕ derived from the deepest occultations, and a minimum grain size of 0.29 − 0.18 + 0.01 μ m assuming a power-law size distribution. We further identify the first evidence of near-infrared excess in this system from NEOWISE 3.4 and 4.6 μm observations. The excess emission implies a total circumstellar dust mass of around 10−6 M ⊕, comparable to the extreme, variable disks associated with terrestrial planet formation around young stars. The quasiperiodic recurrence of deep dips and the inferred dust temperature (ranging from 1800 to 700 K across the span of observations) independently point to an orbital distance of ≃0.2 au for the dust, supporting the occulting material and excess emission being causally linked. The origin of this extended, opaque cloud is surmised to be the breakup of one or more exocometary bodies.
• Martinod, M., Defrère, D., Ireland, M., Kraus, S., Martinache, F., Tuthill, P., Bigioli, A., Bouzerand, E., Bryant, J., Chhabra, S., Courtney-Barrer, B., Crous, F., Cvetojevic, N., Dandumont, C., Ertel, S., Gardner, T., Garreau, G., Glauser, A. M., Labadie, L., , Lagadec, T., et al. (2023). High-angular resolution and high contrast observations from Y to L band at the Very Large Telescope Interferometer with the Asgard Instrumental suite. Journal of Astronomical Telescopes, Instruments, and Systems, 9(02). doi:10.1117/1.jatis.9.2.025007
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  European Southern Observatory (ESO)'s Very Large Telescope Interferometer (VLTI), Paranal, Chile, is one of the most proficient observatories in the world for high angular resolution astronomy. It has hosted several interferometric instruments operating in various bandwidths in the infrared. As a result, the VLTI has yielded countless discoveries and technological breakthroughs. We propose to ESO a new concept for a visitor instrument for the VLTI: Asgard. It is an instrumental suite comprised of four natively collaborating instruments: High-Efficiency Multiaxial Do-it ALL Recombiner (HEIMDALLR), an all-in-one instrument performing both fringe tracking and stellar interferometry with the same optics; Baldr, a Strehl optimizer; Beam-combination Instrument for studying the Formation and fundamental paRameters of Stars and planeTary systems (BIFROST), a combiner whose main science case is studying the formation processes and properties of stellar and planetary systems; and Nulling Observations of dusT and planeTs (NOTT), a nulling interferometer dedicated to imaging young nearby planetary systems in the L band. The overlap between the science cases across different spectral bands yields the idea of making the instruments complementary to deliver sensitivity and accuracy from the J to L bands. Asgard is to be set on the former AMBER optical table. Its control architecture is a hybrid between custom and ESO-compliant developments to benefit from the flexibility offered to a visitor instrument and foresee a deeper long-term integration into VLTI for an opening to the community.
• Stuber, T., Kirchschlager, F., Pearce, T., Ertel, S., Krivov, A., & Wolf, S. (2023). How much large dust could be present in hot exozodiacal dust systems?. Astronomy and Astrophysics, 678(Issue). doi:10.1051/0004-6361/202346109
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  Context. An infrared excess over the stellar photospheric emission of main-sequence stars has been found in interferometric surveys, commonly attributed to the presence of hot exozodiacal dust (HEZD). While submicrometer-sized grains in close vicinity to their host star have been inferred to be responsible for the found near-infrared excesses, the presence and amount of larger grains as part of the dust distributions are weakly constrained. Aims. We quantify how many larger grains (above-micrometer-sized) could be present in addition to submicrometer-sized grains, while being consistent with observational constraints. This is important in order to distinguish between various scenarios for the origin of HEZD and to better estimate its observational appearance when observed with future instruments. Methods. We extended a model suitable to reproduce current observations of HEZD to investigate a bimodal size distribution. By deriving the characteristics of dust distributions whose observables are consistent with observational limits from interferometric measurements in the K and N bands we constrained the radii of sub- and above-micrometer-sized grains as well as their mass, number, and flux density ratios. Results. In the most extreme cases of some of the investigated systems, large grains ∼10 μm might dominate the mass budget of HEZD while contributing up to 25 % of the total flux density originating from the dust at a wavelength of 2.13 μm and up to 50 % at a wavelength of 4.1 μm; at a wavelength of 11.1 μm their emission might clearly dominate over the emission of small grains. While it is not possible to detect such hot-dust distributions using ALMA, the ngVLA might allow us to detect HEZD at millimeter wavelengths. Conclusions. Large dust grains (above-micrometer-sized) might have a more important impact on the observational appearance of HEZD than previously assumed, especially at longer wavelengths.
• Sutlieff, B. J., Birkby, J. L., Stone, J. M., Doelman, D. S., Kenworthy, M. A., Panwar, V., Bohn, A. J., Ertel, S., Snik, F., Woodward, C. E., Skemer, A. J., Leisenring, J. M., Strassmeier, K. G., & Charbonneau, D. (2023). Measuring the variability of directly imaged exoplanets using vector Apodizing Phase Plates combined with ground-based differential spectrophotometry. Monthly Notices of the Royal Astronomical Society, 520(Issue 3). doi:10.1093/mnras/stad249
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  Clouds and other features in exoplanet and brown dwarf atmospheres cause variations in brightness as they rotate in and out of view. Ground-based instruments reach the high contrasts and small inner working angles needed to monitor these faint companions, but their small fields of view lack simultaneous photometric references to correct for non-astrophysical variations. We present a novel approach for making ground-based light curves of directly imaged companions using high-cadence differential spectrophotometric monitoring, where the simultaneous reference is provided by a double-grating 360◦ vector Apodizing Phase Plate (dgvAPP360) coronagraph. The dgvAPP360 enables high-contrast companion detections without blocking the host star, allowing it to be used as a simultaneous reference. To further reduce systematic noise, we emulate exoplanet transmission spectroscopy, where the light is spectrally dispersed and then recombined into white-light flux. We do this by combining the dgvAPP360 with the infrared Arizona Lenslets for Exoplanet Spectroscopy integral field spectrograph on the Large Binocular Telescope Interferometer. To demonstrate, we observed the red companion HD 1160 B (separation ∼780 mas) for one night, and detect 8.8 per cent semi-amplitude sinusoidal variability with an ∼3.24 h period in its detrended white-light curve. We achieve the greatest precision in ground-based high-contrast imaging light curves of sub-arcsecond companions to date, reaching 3.7 per cent precision per 18-min bin. Individual wavelength channels spanning 3.59–3.99 μm further show tentative evidence of increasing variability with wavelength. We find no evidence yet of a systematic noise floor; hence, additional observations can further improve the precision. This is therefore a promising avenue for future work aiming to map storms or find transiting exomoons around giant exoplanets.
• Wagner, K., Stone, J., Skemer, A., Ertel, S., Dong, R., Apai, D., Spalding, E., Leisenring, J., Sitko, M., Kratter, K., Barman, T., Marley, M., Miles, B., Boccaletti, A., Assani, K., Bayyari, A., Uyama, T., Woodward, C., Hinz, P., , Briesemeister, Z., et al. (2023). Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758. Nature Astronomy, 7(10). doi:10.1038/s41550-023-02028-3
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  Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present observations in the thermal infrared that are uniquely sensitive to redder (that is, colder, or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of roughly 100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with T eff = 500 ± 100 K for a low level of extinction (A V ≤ 30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk.
• Antoniucci, S., Boccaletti, A., Bonavita, M., Bonnefoy, M., Cantalloube, F., Chauvin, G., Claudi, R., Defrere, D., Desidera, S., Ertel, S., Fedele, D., Feldt, M., Garufi, A., Ginski, C., Gratton, R., Hagelberg, J., Henning, T., Hugot, E., Janson, M., , Lagrange, A. M., et al. (2022). Signs of late infall and possible planet formation around DR Tau using VLT/SPHERE and LBTI/LMIRCam. Astronomy & Astrophysics, 658(Issue), A63. doi:10.1051/0004-6361/202142219
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  Context. Protoplanetary disks around young stars often contain substructures like rings, gaps, and spirals that could be caused by interactions between the disk and forming planets. Aims. We aim to study the young (1–3 Myr) star DR Tau in the near-infrared and characterize its disk, which was previously resolved through submillimeter interferometry with ALMA, and to search for possible substellar companions embedded into it. Methods. We observed DR Tau with VLT/SPHERE both in polarized light (H broad band) and total intensity (in Y, J, H, and K spectral bands). We also performed L′ band observations with LBTI/LMIRCam on the Large Binocular Telescope (LBT). We applied differential imaging techniques to analyze both the polarized data, using dual beam polarization imaging, and the total intensity data, using angular and spectral differential imaging. Results. We found two previously undetected spirals extending north-east and south of the star, respectively. We further detected an arc-like structure north of the star. Finally a bright, compact and elongated structure was detected at a separation of 303 ± 10 mas and a position angle 21.2 ± 3.7 degrees, just at the root of the north-east spiral arm. Since this feature is visible both in polarized light and total intensity and has a blue spectrum, itis likely caused by stellar light scattered by dust. Conclusions. The two spiral arms are at different separations from the star, have very different pitch angles, and are separated by an apparent discontinuity, suggesting they might have a different origin. The very open southern spiral arm might be caused by infalling material from late encounters with cloudlets into the formation environment of the star itself. The compact feature could be caused by interaction with a planet in formation still embedded in its dust envelope and it could be responsible for launching the north–east spiral. We estimate a mass of the putative embedded object of the order of few MJup.
• Augereau, J., Bensberg, A., Booth, M., Ertel, S., Kirchschlager, F., Krivov, A. V., Pearce, T. D., Rouillé, G., & Wolf, S. (2022). Hot exozodis: cometary supply without trapping is unlikely to be the mechanism. Monthly Notices of the Royal Astronomical Society, 517(1), 1436-1451. doi:10.1093/mnras/stac2773
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  Excess near-infrared emission is detected around one fifth of main-sequence stars, but its nature is a mystery. These excesses are interpreted as thermal emission from populations of small, hot dust very close to their stars ('hot exozodis'), but such grains should rapidly sublimate or be blown out of the system. To date, no model has fully explained this phenomenon. One mechanism commonly suggested in the literature is cometary supply, where star-grazing comets deposit dust close to the star, replenishing losses from grain sublimation and blowout. However, we show that this mechanism alone is very unlikely to be responsible for hot exozodis. We model the trajectory and size evolution of dust grains released by star-grazing comets, to establish the dust and comet properties required to reproduce hot-exozodi observations. We find that cometary supply alone can only reproduce observations if dust ejecta has an extremely steep size distribution upon release, and the dust-deposition rate is extraordinarily high. These requirements strongly contradict our current understanding of cometary dust and planetary systems. Cometary supply is therefore unlikely to be solely responsible for hot exozodis, so may need to be combined with some dust-trapping mechanism (such as gas or magnetic trapping) if it is to reproduce observations.
• Dahlqvist, C., Milli, J., Absil, O., Cantalloube, F., Matra, L., Choquet, E., Del Burgo, C., Marshall, J., Wyatt, M., & Ertel, S. (2022). The SHARDDS survey: limits on planet occurrence rates based on point sources analysis via the Auto-RSM framework. Astronomy and Astrophysics, 666(Issue). doi:10.1051/0004-6361/202244145
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  Context. In the past decade, high contrast imaging allowed the detection and characterisation of exoplanets, brown dwarfs, and circumstellar disks. Large surveys provided new insights about the frequency and properties of massive sub-stellar companions with separations from 5 to 300 au. Aims. In this context, our study aims to detect and characterise potential exoplanets and brown dwarfs within debris disks, considering a diverse population of stars with respect to stellar age and spectral type. We present in this paper the analysis of a set of H-band images taken by the VLT/SPHERE instrument in the context of the SHARDDS survey. This survey gathers 55 main-sequence stars within 100 pc, known to host a high-infrared-excess debris disk, allowing us to potentially better understand the complex interactions between substellar companions and disks. Methods. We rely on the Auto-RSM framework to perform an in-depth analysis of the considered targets, via the computation of detection maps and contrast curves. A clustering approach is used to divide the set of targets into multiple subsets, in order to reduce the computation time by estimating a single optimal parametrisation for each considered subset. Detection maps generated with different approaches are used along with contrast curves to identify potential planetary companions. Planet detection and planet occurrence frequencies are derived from the generated contrast curves, relying on two well-known evolutionary models, namely AMES-DUSTY and AMES-COND. Finally, we study the influence of the observing conditions and observing sequence characteristics on the performance measured in terms of contrast. Results. The use of Auto-RSM allows us to reach high contrast at short separations, with a median contrast of 105 at 300 mas, for a completeness level of 95%. A new planetary characterisation algorithm, based on the RSM framework, is developed and tested successfully, showing a higher astrometric and photometric precision for faint sources compared to standard approaches. Apart from the already known companion of HD 206893 and two point-like sources around HD 114082 which are most likely background stars, we did not detect any new companion around other stars. A correlation study between achievable contrasts and parameters characterising high contrast imaging sequences highlights the importance of the Strehl ratio, wind speed at a height of 30 meters, and presence of wind-driven halo to define the quality of high contrast images. Finally, planet detection and occurrence rate maps are generated and show, for the SHARDDS survey, a high sensitivity between 10 and 100 au for substellar companions with masses >10 MJ.
• Doelman, D., Stone, J., Briesemeister, Z., Skemer, A., Barman, T., Brock, L., Hinz, P., Bohn, A., Kenworthy, M., Haffert, S., Snik, F., Ertel, S., Leisenring, J., Woodward, C., & Skrutskie, M. (2022). L-band Integral Field Spectroscopy of the HR 8799 Planetary System. Astronomical Journal, 163(5). doi:10.3847/1538-3881/ac5d52
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  Understanding the physical processes sculpting the appearance of young gas-giant planets is complicated by degeneracies confounding effective temperature, surface gravity, cloudiness, and chemistry. To enable more detailed studies, spectroscopic observations covering a wide range of wavelengths are required. Here we present the first L-band spectroscopic observations of HR 8799 d and e and the first low-resolution wide-bandwidth L-band spectroscopic measurements of HR 8799 c. These measurements were facilitated by an upgraded LMIRCam/ALES instrument at the Large Binocular Telescope, together with a new apodizing phase plate coronagraph. Our data are generally consistent with previous photometric observations covering similar wavelengths, yet there exists some tension with narrowband photometry for HR 8799 c. With the addition of our spectra, each of the three innermost observed planets in the HR 8799 system has had its spectral energy distribution measured with integral field spectroscopy covering ∼0.9-4.1 μm. We combine these spectra with measurements from the literature and fit synthetic model atmospheres. We demonstrate that the bolometric luminosity of the planets is not sensitive to the choice of model atmosphere used to interpolate between measurements and extrapolate beyond them. Combining luminosity with age and mass constraints, we show that the predictions of evolutionary models are narrowly peaked for effective temperature, surface gravity, and planetary radius. By holding these parameters at their predicted values, we show that more flexible cloud models can provide good fits to the data while being consistent with the expectations of evolutionary models.
• Quanz, S., Ottiger, M., Fontanet, E., Kammerer, J., Menti, F., Dannert, F., Gheorghe, A., Absil, O., Airapetian, V., Alei, E., Allart, R., Angerhausen, D., Blumenthal, S., Buchhave, L., Cabrera, J., Chauvin, G., Danchi, W., Dandumont, C., Dorn, C., , Ehrenreich, D., et al. (2022). Large Interferometer For Exoplanets (LIFE): I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission. Astronomy and Astrophysics, 664(Issue). doi:10.1051/0004-6361/202140366
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  Context. One of the long-term goals of exoplanet science is the atmospheric characterization of dozens of small exoplanets in order to understand their diversity and search for habitable worlds and potential biosignatures. Achieving this goal requires a space mission of sufficient scale that can spatially separate the signals from exoplanets and their host stars and thus directly scrutinize the exoplanets and their atmospheres. Aims. We seek to quantify the exoplanet detection performance of a space-based mid-infrared (MIR) nulling interferometer that measures the thermal emission of exoplanets. We study the impact of various parameters and compare the performance with that of large single-aperture mission concepts that detect exoplanets in reflected light. Methods. We have developed an instrument simulator that considers all major astrophysical noise sources and coupled it with Monte Carlo simulations of a synthetic exoplanet population around main-sequence stars within 20 pc of the Sun. This allows us to quantify the number (and types) of exoplanets that our mission concept could detect. Considering single visits only, we discuss two different scenarios for distributing 2.5 yr of an initial search phase among the stellar targets. Different apertures sizes and wavelength ranges are investigated. Results. An interferometer consisting of four 2 m apertures working in the 4'18.5 m wavelength range with a total instrument throughput of 5% could detect up to 550 exoplanets with radii between 0.5 and 6 R-with an integrated S=N 7. At least-160 of the detected exoplanets have radii 1.5 R-. Depending on the observing scenario 25'45 rocky exoplanets (objects with radii between 0.5 and 1.5 R-) orbiting within the empirical habitable zone (eHZ) of their host stars are among the detections. With four 3.5 m apertures, the total number of detections can increase to up to 770, including-60'80 rocky eHZ planets. With four times 1 m apertures, the maximum detection yield is-315 exoplanets, including-20 rocky eHZ planets. The vast majority of small, temperate exoplanets are detected around M dwarfs. The impact of changing the wavelength range to 3'20-m or 6'17-m on the detection yield is negligible. Conclusions. A large space-based MIR nulling interferometer will be able to directly detect hundreds of small, nearby exoplanets, tens of which would be habitable world candidates. This shows that such a mission can compete with large single-aperture reflected light missions. Further increasing the number of habitable world candidates, in particular around solar-type stars, appears possible via the implementation of a multi-visit strategy during the search phase. The high median S/N of most of the detected planets will allow for first estimates of their radii and effective temperatures and will help prioritize the targets for a second mission phase to obtain high-S/N thermal emission spectra, leveraging the superior diagnostic power of the MIR regime compared to shorter wavelengths.
• Spalding, E., Ertel, S., & Defrère, D. (2022). Unveiling exozodiacal light. Physics Today, 75(4). doi:10.1063/pt.3.4982
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  Nulling interferometry draws aside bright stellar glare to probe fine dust in extrasolar systems that may hamper future searches for Earthlike worlds. Under a dark sky and with the proper celestial orientation, stargazers can see the plane of the Milky Way as a soaring thoroughfare of glowing stars and the silhouettes of dust clumps and tendrils.
• Absil, O., Marion, L., Ertel, S., Kennedy, G., Romagnolo, A., Le Bouquin, J., Christiaens, V., Milli, J., Bonsor, A., Olofsson, J., Su, K., Augereau, J., & Defrère, D. (2021). A near-infrared interferometric survey of debris-disk stars: VII. The hot-to-warm dust connection. Astronomy and Astrophysics, 651(Issue). doi:10.1051/0004-6361/202140561
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  Context. Hot exozodiacal dust has been shown to be present in the innermost regions of an increasing number of main sequence stars over the past 15 yr. However, the origin of hot exozodiacal dust and its connection with outer dust reservoirs remains unclear. Aims. We aim to explore the possible connection between hot exozodiacal dust and warm dust reservoirs (>100 K) in asteroid belts. Methods. We use precision near-infrared interferometry with VLTI/PIONIER to search for resolved emission at H-band around a selected sample of 62 nearby stars that show possible signs of warm dust populations. Results. Our observations reveal the presence of resolved near-infrared emission around 17 out of 52 stars with sufficient data quality. For four of these, the emission is shown to be due to a previously unknown stellar companion. The 13 other H-band excesses are thought to originate from the thermal emission of hot dust grains, close to their sublimation temperature. Taking into account earlier PIONIER observations, where some stars with warm dust were also observed, and after re-evaluating the warm dust content of all our PIONIER targets through spectral energy distribution modeling, we find a detection rate of 17:1+8:1-4:6% for H-band excess around main sequence stars hosting warm dust belts, which is statistically compatible with the occurrence rate of 14:6+4:3-2:8% found around stars showing no signs of warm dust. After correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we find tentative evidence at the 3s level that H-band excesses around stars with outer dust reservoirs (warm or cold) could be statistically larger than H-band excesses around stars with no detectable outer dust. Conclusions. Our observations do not suggest a direct connection between warm and hot dust populations at the sensitivity level of the considered instruments, although they bring to light a possible correlation between the level of H-band excess and the presence of outer dust reservoirs in general.
• Crass, J., Bechter, A., Sands, B., King, D., Ketterer, R., Engstrom, M., Hamper, R., Kopon, D., Smous, J., Crepp, J., Montoya, M., Durney, O., Cavalieri, D., Reynolds, R., Vansickle, M., Onuma, E., Thomes, J., Mullin, S., Shelton, C., , Wallace, K., et al. (2021). Final design and on-sky testing of the iLocater SX acquisition camera: broad-band single-mode fibre coupling. \mnras, 501(2), 2250-2267.
• Defr{\`ere}, D., Hinz, P., Kennedy, G., Stone, J., Rigley, J., Ertel, S., Gaspar, A., Bailey, V., Hoffmann, W., Mennesson, B., Millan-Gabet, R. .., Danchi, W., Absil, O., Arbo, P., Beichman, C., Bonavita, M., Brusa, G., Bryden, G., Downey, E., , Esposito, S., et al. (2021). The HOSTS Survey: Evidence for an Extended Dust Disk and Constraints on the Presence of Giant Planets in the Habitable Zone of \ensuremath{\beta} Leo. \aj, 161(4), 186.
• Musso, B. A., Launhardt, R., M{\"uller}, A., Kennedy, G. M., Boekel, R., Henning, T., Ruh, H. L., Marino, S., Pearce, T. D., Brems, S. S., Ertel, S., & Spalding, E. A. (2021). LIStEN: L' band Imaging Survey for Exoplanets in the North. \aap, 645, A88.
• Pinna, E., Rossi, F., Puglisi, A., Agapito, G., Bonaglia, M., Plantet, C., Mazzoni, T., Briguglio, R., Carbonaro, L., Xompero, M., Grani, P., Riccardi, A., Esposito, S., Hinz, P., Vaz, A., Ertel, S., Montoya, O. M., Durney, O., Christou, J., , Miller, D. L., et al. (2021). Bringing SOUL on sky. arXiv e-prints, arXiv:2101.07091.
• collaboration, L., Quanz, S., Ottiger, M., Fontanet, E., Kammerer, J., Menti, F., Dannert, F., Gheorghe, A., Absil, O., Airapetian, V., Alei, E., Allart, R., Angerhausen, D., Blumenthal, S., Cabrera, J., Carri{\'on-Gonz\'alez}, \., Chauvin, G., Danchi, W., Dandumont, C., , Defr{\`ere}, D., et al. (2021). Large Interferometer For Exoplanets (LIFE): I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission. arXiv e-prints, arXiv:2101.07500.
• Bechter, E., Bechter, A., Cavalieri, D., Crass, J., Crepp, J. R., Durney, O., Engstrom, M., Ertel, S., Hamper, R., Ketterer, R., King, D., Kopon, D., Montoya, M., Mullin, S., Onuma, E., Power, J., Rahmer, G., Reynolds, R., Sands, B., , Shelton, C., et al. (2020). Final design and on-sky testing of the iLocater SX acquisition camera: broad-band single-mode fibre coupling. Monthly Notices of the Royal Astronomical Society, 501(2), 2250-2267. doi:10.1093/mnras/staa3355
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  Enabling efficient injection of light into single-mode fibres (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fibre injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broad-band SMF coupling in excess of 35 per cent (absolute) in the near-infrared (0.97-1.31 ${\mu {\rm m}}$) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality.
• Bostroem, K. A., Valenti, S., Sand, D. J., Andrews, J. E., Van Dyk, S. D., Galbany, L., Pooley, D., Amaro, R. C., Smith, N., Yang, S., Anupama, G. C., Arcavi, I., Baron, E., Brown, P. J., Burke, J., Cartier, R., Hiramatsu, D., Dastidar, R., Derkacy, J. M., , Dong, Y., et al. (2020). Discovery and Rapid Follow-up Observations of the Unusual Type II SN 2018ivc in NGC 1068. Astrophysical Journal, 895(Issue 1). doi:10.3847/1538-4357/ab8945
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  We present the discovery and high-cadence follow-up observations of SN 2018ivc, an unusual SNe II that exploded in NGC 1068 (D = 10.1 Mpc). The light curve of SN 2018ivc declines piecewise-linearly, changing slope frequently, with four clear slope changes in the first 30 days of evolution. This rapidly changing light curve indicates that interaction between the circumstellar material and ejecta plays a significant role in the evolution. Circumstellar interaction is further supported by a strong X-ray detection. The spectra are rapidly evolving and dominated by hydrogen, helium, and calcium emission lines. We identify a rare high-velocity emission-line feature blueshifted at ∼7800 km, s-1 (in Hα, Hβ, Pβ, Pγ, He i, and Ca ii), which is visible from day 18 until at least day 78 and could be evidence of an asymmetric progenitor or explosion. From the overall similarity between SN 2018ivc and SN 1996al, the Hα equivalent width of its parent H ii region, and constraints from pre-explosion archival Hubble Space Telescope images, we find that the progenitor of SN 2018ivc could be as massive as 52 M⊙ but is more likely
• 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.
• Ertel, S., Defr{\`ere}, D., Hinz, P., Mennesson, B., Kennedy, G., Danchi, W., Gelino, C., Hill, J., Hoffmann, W., Mazoyer, J., Rieke, G., Shannon, A., Stapelfeldt, K., Spalding, E., Stone, J., Vaz, A., Weinberger, A., Willems, P., Absil, O., , Arbo, P., et al. (2020). The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey. \aj, 159(4), 177.
• Kirchschlager, F., Ertel, S., Wolf, S., Matter, A., & Krivov, A. V. (2020). First L band detection of hot exozodiacal dust with VLTI/MATISSE. \mnras, 499(1), L47-L52.
• Lazzoni, C., Zurlo, A., Desidera, S., Mesa, D., Fontanive, C., Bonavita, M., Ertel, S., Rice, K., Vigan, A., Boccaletti, A., Bonnefoy, M., Chauvin, G., Delorme, P., Gratton, R., Houll{\'e}, M., Maire, A., Meyer, M., Rickman, E., Spalding, E., , Asensio-Torres, R. .., et al. (2020). The search for disks or planetary objects around directly imaged companions: a candidate around DH Tauri B. \aap, 641, A131.
• Maier, E. R., Hinz, P., Defr{\`ere}, D., Grenz, P., Downey, E., Ertel, S., Morzinski, K., & Douglas, E. S. (2020). Implementing multiwavelength fringe tracking for the Large Binocular Telescope Interferometer's phase sensor, PHASECam. Journal of Astronomical Telescopes, Instruments, and Systems, 6, 035001.
• Rebollido, I., Eiroa, C., Montesinos, B., Maldonado, J., Villaver, E., Absil, O., Bayo, A., Canovas, H., Carmona, A., Chen, C., Ertel, S., Henning, T., Iglesias, D., Launhardt, R., Liseau, R., Meeus, G., Mo{\'or}, A., Mora, A., Olofsson, J., , Rauw, G., et al. (2020). Exocomets: A spectroscopic survey. \aap, 639, A11.
• Scicluna, P., Kemper, F., Trejo, A., Marshall, J., Ertel, S., & Hillen, M. (2020). Rapid grain growth in post-AGB disc systems from far-infrared and sub-millimetre photometry. \mnras, 494(2), 2925-2936.
• Wagner, K., Stone, J., Dong, R., Ertel, S., Apai, D., Doelman, D., Bohn, A., Najita, J., Brittain, S., Kenworthy, M., Keppler, M., Webster, R., Mailhot, E., & Snik, F. (2020). First Images of the Protoplanetary Disk around PDS 201. Astronomical Journal, 159(Issue 6). doi:10.3847/1538-3881/ab893f
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  Scattered light imaging has revealed nearly a dozen circumstellar disks around young Herbig Ae/Be stars-enabling studies of structures in the upper disk layers as potential signs of ongoing planet formation. We present the first images of the disk around the variable Herbig Ae star PDS 201 (V∗ V351 Ori) and an analysis of the images and spectral energy distribution through 3D Monte Carlo radiative transfer simulations and forward modeling. The disk is detected in three data sets with the Large Binocular Telescope Interferometer/Large Binocular Telescope mid-infrared camera at the Large Binocular Telescope, including direct observations in the Ks and L′ filters, and an L′ observation with the 360° vector apodizing phase plate coronagraph. The scattered light disk extends to a very large radius of ∼250 au, which places it among the largest of such disks. Exterior to the disk, we establish detection limits on substellar companions down to ∼5 M Jup at ⪆1.″5 (⪆500 au), assuming the Baraffe et al. models. The images show a radial gap extending to ∼0.″4 (∼140 au at a distance of 340 pc) that is also evident in the spectral energy distribution. The large gap is a possible signpost of multiple high-mass giant planets at orbital distances (∼60-100 au) that are unusually massive and widely separated compared to those of planet populations previously inferred from protoplanetary disk substructures.
• Wagner, K., Stone, J., Dong, R., Ertel, S., Apai, D., Doelman, D., Bohn, A., Najita, J., Brittain, S., Kenworthy, M., Keppler, M., Webster, R., Mailhot, E., & Snik, F. (2020). First Images of the Protoplanetary Disk around PDS 201. \aj, 159(6), 252.
• Wang, J. i., Wang, J. J., Ma, B. o., Chilcote, J., Ertel, S., Guyon, O., Ilyin, I., Jovanovic, N., Kalas, P., Lozi, J., Macintosh, B., Strassmeier, K. G., & Stone, J. (2020). On the Chemical Abundance of HR 8799 and the Planet c. \aj, 160(3), 150.
• Apai, D., Beichman, C., Krijt, S., Nesvold, E., Augereau, J., Ballering, N. P., Beichman, C. A., Boccaletti, A., Booth, M., Bowler, B. P., Bryden, G., Chen, C., Currie, T., Danchi, W. C., Debes, J. H., Defrere, D., Ertel, S., Gaspar, A., Jackson, A. P., , Kalas, P., et al. (2019). Modeling Debris Disk Evolution. Bulletin of the American Astronomical Society, 51(3).
• Ballering, N. P., Ertel, S., Gaspar, A., Kennedy, G. M., Leisawitz, D., Macgregor, M. A., Matthews, B. C., Moro-martin, A., Rieke, G. H., Su, K. Y., White, J. A., Wilner, D. J., & Wyatt, M. (2019). Probing Unseen Planet Populations with Resolved Debris Disk Structures. Bulletin of the American Astronomical Society, 51(3).
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  This white paper focuses on resolving debris structures in thermal emission that is applicable to a large unbiased sample. We summarize the properties of the known debris disks and assess the feasibility of resolving them within our current and future infrared and millimeter facilities by adopting uniform criteria.
• Bertrang, G. H., Boffin, H. M., Ertel, S., Guzman-ramirez, L., Hillen, M., Horner, J., Kamath, D., Manick, R., Marshall, J. P., Milli, J., Okumura, J., Scicluna, P., Vaz, A., Villaver, E., Wesson, R., Winckel, H. V., & Xu, S. (2019). Resolved imaging of the AR Puppis circumbinary disk. The Astronomical Journal, 157(3), 110. doi:10.3847/1538-3881/aafe04
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  Circumbinary disks are common around post-asymptotic giant branch (post- AGB) stars with a stellar companion on orbital timescales of a few 100 to few 1000 days. The presence of a disk is usually inferred from the system’s spectral energy distribution and confirmed, for a sub-sample, by interferometric observations. We used the Spectro-Polarimetric High- contrast Exoplanet REsearch (SPHERE) instrument on the Very Large Telescope to obtain extreme adaptive optics assisted scattered light images of the post-AGB binary system AR Puppis. Data have been obtained in the V, I, and H bands. Our observations have produced the first resolved images of AR Puppis’s circumbinary disk and confirm its edge-on orientation. In our high-angular-resolution and high-dynamic-range images we identify several structural components such as a dark mid- plane, the disk surface, and arc-like features. We discuss the nature of these components and use complementary photometric monitoring to relate them to the orbital phase of the binary system. Because the star is completely obscured by the disk at visible wavelengths, we conclude that the long-term photometric variability of the system must be caused by variable scattering, not extinction, of starlight by the disk over the binary orbit. Finally, we discuss how the short disk lifetimes and fast evolution of the host stars compared to the ages at which protoplanetary disks are typically observed make systems like AR Puppis valuable extreme laboratories to study circumstellar disk evolution and constrain the timescale of dust grain growth during the planet formation process. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 097.D-0385 (SPHERE) and 094.D-0865 (PIONIER).
• Ertel, S., Kamath, D., Hillen, M., Winckel, H., Okumura, J., Manick, R., Boffin, H., Milli, J., Bertrang, G. -., Guzman-Ramirez, L. .., Horner, J., Marshall, J., Scicluna, P., Vaz, A., Villaver, E., Wesson, R., & Xu, S. (2019). Resolved Imaging of the AR Puppis Circumbinary Disk. \aj, 157(3), 110.
• Gordon, M. S., Jones, T. J., Humphreys, R. M., Ertel, S., Hinz, P. M., Hoffmann, W. F., Stone, J., Spalding, E., & Vaz, A. (2019). Thermal Emission in the Southwest Clump of VY CMa. \aj, 157(2), 57.
• Jones, T. J., Williams, L. L., Ertel, S., Hinz, P. M., Vaz, A., Walsh, S., & Webster, R. (2019). Image Flux Ratios of Gravitationally Lensed HS 0810+2554 with High-resolution Infrared Imaging. \aj, 158(6), 237.
• Matter, A., Labadie, L., Kreplin, A., Lopez, B., Wolf, S., Weigelt, G., Ertel, S., Pott, J. -., & Danchi, W. (2019). Evidence of a discontinuous disk structure around the Herbig Ae star HD 139614 (Corrigendum). \aap, 632, C2.
• Montesinos, B., Eiroa, C., Lillo-Box, J. .., Rebollido, I., Djupvik, A., Absil, O., Ertel, S., Marion, L., Kajava, J., Redfield, S., Isaacson, H., C{\'anovas}, H., Meeus, G., Mendigut{\'\ia}, I., Mora, A., Rivi{\`ere-Marichalar}, P., Villaver, E., Maldonado, J., & Henning, T. (2019). HR 10: a main-sequence binary with circumstellar envelopes around both components. Discovery and analysis. \aap, 629, A19.
• Quanz, S. P., Absil, O., Angerhausen, D., Benz, W., Bonfils, X., Berger, J., Brogi, M., Cabrera, J., Danchi, W. C., Defr{\`ere}, D., Dishoeck, E., Ehrenreich, D., Ertel, S., Fortney, J., Gaudi, S., Girard, J., Glauser, A., Grenfell, J. L., Ireland, M., , Janson, M., et al. (2019). Atmospheric characterization of terrestrial exoplanets in the mid-infrared: biosignatures, habitability \& diversity. arXiv e-prints, arXiv:1908.01316.
• Rebollido, I., Eiroa, C., Montesinos, B., Maldonado, J., Villaver, E., Absil, O., Bayo, A., Canovas, H., Carmona, A., Chen, C., Ertel, S., Garufi, A., Henning, T., Iglesias, D. P., Launhardt, R., Liseau, R., Meeus, G., Moór, A., Mora, A., , Olofsson, J., et al. (2019). Erratum: The co-existence of hot and cold gas in debris discs (Astronomy and Astrophysics (2018) 614 (A3) DOI: 10.1051/0004-6361/201732329). Astronomy and Astrophysics, 625(Issue). doi:10.1051/0004-6361/201732329e
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  Due to a bad correction of telluric lines some Na I absorptions detected towards some stars were not mentioned in the original paper. This corrigendum presents a proper telluric subtraction, carried out with MOLECFIT1 (Smette et al. 2015, Kausch et al. 2015). Tables 3 and 4 from the original paper are rectified below with the corrected Na I absorptions shown in boldface text. Figure 4 of the original paper showed an incorrect plot of the Na I D line features observed towards HD 138813. Figure 1 is the corrected version of the original paper s Fig. 4. Below we summarize the corrected Na I absorptions of each concerned star: - HD 9672: the Na I D absorption at 11.5 km s1 coincides with the Ca II feature and the radial velocity of the ISM. - HD 131488: besides the already reported non-photospheric absorptions at 5.3 km s1, a Na I D2 feature at -13.9 km s1 is detected. A similar feature is detected towards field stars and most likely has an interstellar medium origin. - HD 138813: two new non-photospheric features are detected in the Na I D lines (see Fig. 1). The approximately 22.2 km s1 absorption is close to the Ca II K nonphotospheric absorption and the G ISM cloud; thus, an interstellar origin is more plausible. A feature in emission at 0.1 km s1 is detected in both Na I D lines at the radial velocity of the star; this feature is related to the star. (Figure Presented).
• Rebollido, I., Eiroa, C., Montesinos, B., Maldonado, J., Villaver, E., Absil, O., Bayo, A., Canovas, H., Carmona, A., Chen, C., Ertel, S., Garufi, A., Henning, T., Iglesias, D., Launhardt, R., Liseau, R., Meeus, G., Mo{\'or}, A., Mora, A., , Olofsson, J., et al. (2019). The co-existence of hot and cold gas in debris discs (Corrigendum). \aap, 625, C2.
• Sepulveda, A. G., Matr{\`a}, L., Kennedy, G. M., Burgo, C., {\"Oberg}, K. I., Wilner, D. J., Marino, S., Booth, M., Carpenter, J. M., Davies, C. L., Dent, W. R., Ertel, S., Lestrade, J., Marshall, J. P., Milli, J., Wyatt, M. C., MacGregor, M. A., & Matthews, B. C. (2019). The REASONS Survey: Resolved Millimeter Observations of a Large Debris Disk around the Nearby F Star HD 170773. \apj, 881(1), 84.
• Stark, C. C., Belikov, R., Bolcar, M. R., Cady, E., Crill, B. P., Ertel, S., Groff, T., Hildebrandt, S., Krist, J., Lisman, P. D., Mazoyer, J., Mennesson, B., Nemati, B., Pueyo, L., Rauscher, B. J., Riggs, A. J., Ruane, G., Shaklan, S. B., Sirbu, D., , Soummer, R., et al. (2019). ExoEarth yield landscape for future direct imaging space telescopes. Journal of Astronomical Telescopes, Instruments, and Systems, 5(Issue 2). doi:10.1117/1.jatis.5.2.024009
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  The expected yield of potentially Earth-like planets is a useful metric for designing future exoplanet-imaging missions. Recent yield studies of direct-imaging missions have focused primarily on yield methods and trade studies using "toy" models of missions. Here, we increase the fidelity of these calculations substantially, adopting more realistic exoplanet demographics as input, an improved target list, and a realistic distribution of exozodi levels. Most importantly, we define standardized inputs for instrument simulations, use these standards to directly compare the performance of realistic instrument designs, include the sensitivity of coronagraph contrast to stellar diameter, and adopt engineering-based throughputs and detector parameters. We apply these new high-fidelity yield models to study several critical design trades: monolithic versus segmented primary mirrors (PMs), on-axis versus off-axis secondary mirrors, and coronagraphs versus starshades. We show that as long as the gap size between segments is sufficiently small (
• Stark, C. C., Belikov, R., Bolcar, M. R., Cady, E., Crill, B. P., Ertel, S., Groff, T., Hildebrandt, S., Krist, J., Lisman, P. D., Mazoyer, J., Mennesson, B., Nemati, B., Pueyo, L., Rauscher, B. J., Riggs, A., Ruane, G., Shaklan, S. B., Sirbu, D., , Soummer, R., et al. (2019). ExoEarth yield landscape for future direct imaging space telescopes. Journal of Astronomical Telescopes, Instruments, and Systems, 5, 024009.
• Wagner, K., Stone, J. M., Spalding, E., Apai, D., Dong, R., Ertel, S., Leisenring, J., & Webster, R. (2019). Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms?. \apj, 882(1), 20.
• Absil, O., Arbo, P., Bailey, V. P., Beichman, C., Bryden, G., Danchi, W. C., Defrere, D., Downey, E. C., Durney, O., Ertel, S., Esposito, S., Gaspar, A., Gelino, C. R., Grenz, P., Haniff, C. A., Hill, J. M., Hinz, P. M., Hoffmann, W. F., Kennedy, G. M., , Leisenring, J. M., et al. (2018). The HOSTS survey - Exozodiacal dust measurements for 30 stars. The Astronomical Journal, 155(5), 194. doi:10.3847/1538-3881/aab717
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  The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from 60^(+16)_(-21)% for stars with previously detected cold dust to 8^(+10)_(-3)% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.
• Apai, D., Bailey, V. P., Bass, B., Biller, B., Bonavita, M., Bonnefoy, M., Brandner, W., Brems, S. S., Buenzli, E., Close, L. M., Crepp, J. R., Defrere, D., Desidera, S., Eisner, J. A., Ertel, S., Fortney, J. J., Henning, T., Hinz, P. M., Hofmann, K., , Kratter, K. M., et al. (2018). The LEECH exoplanet imaging survey: Limits on planet occurrence rates under conservative assumptions. The Astronomical Journal, 156(6), 286. doi:10.3847/1538-3881/aaec00
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  We present the results of the largest $L^{\prime}$ ($3.8~\mu$m) direct imaging survey for exoplanets to date, the Large Binocular Telescope Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98 stars with spectral types from B to M. Cool planets emit a larger share of their flux in $L^{\prime}$ compared to shorter wavelengths, affording LEECH an advantage in detecting low-mass, old, and cold-start giant planets. We emphasize proximity over youth in our target selection, probing physical separations smaller than other direct imaging surveys. For FGK stars, LEECH outperforms many previous studies, placing tighter constraints on the hot-start planet occurrence frequency interior to $\sim20$ au. For less luminous, cold-start planets, LEECH provides the best constraints on giant-planet frequency interior to $\sim20$ au around FGK stars. Direct imaging survey results depend sensitively on both the choice of evolutionary model (e.g., hot- or cold-start) and assumptions (explicit or implicit) about the shape of the underlying planet distribution, in particular its radial extent. Artificially low limits on the planet occurrence frequency can be derived when the shape of the planet distribution is assumed to extend to very large separations, well beyond typical protoplanetary dust-disk radii ($\lesssim50$ au), and when hot-start models are used exclusively. We place a conservative upper limit on the planet occurrence frequency using cold-start models and planetary population distributions that do not extend beyond typical protoplanetary dust-disk radii. We find that $\lesssim90\%$ of FGK systems can host a 7 to 10 $M_{\mathrm{Jup}}$ planet from 5 to 50 au. This limit leaves open the possibility that planets in this range are common.
• Bonsor, A., Wyatt, M. C., Kral, Q., Kennedy, G., Shannon, A., & Ertel, S. (2018). Using warm dust to constrain unseen planets. Monthly Notices of the Royal Astronomical Society, 480(Issue 4). doi:10.1093/mnras/sty2200
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  Cold outer debris belts orbit a significant fraction of stars, many of which are planet hosts. Radiative forces from the star lead to dust particles leaving the outer belts and spiralling inwards under Poynting-Robertson drag. We present an empirical model fitted to N-body simulations that allows the fate of these dust particles when they encounter a planet to be rapidly calculated. High-mass planets eject most particles, whilst dust passes low-mass planets relatively unperturbed. Close-in, high-mass planets (hot Jupiters) are best at accreting dust. The model predicts the accretion rate of dust on to planets interior to debris belts, with mass accretion rates of up to hundreds of kilograms per second predicted for hot Jupiters interior to outer debris belts, when collisional evolution is also taken into account. The model can be used to infer the presence and likely masses of as yet undetected planets in systems with outer belts. The non-detection of warm dust with the Large Binocular Telescope Interferometer (LBTI) around Vega could be explained by the presence of a single Saturn mass planet, or a chain of lower mass planets. Similarly, the detection of warm dust in such systems implies the absence of planets above a quantifiable level, which can be lower than similar limits from direct imaging. The level of dust detected with LBTI around β Leo can be used to rule out the presence of planets more massive than a few Saturn masses outside of ~5 au.
• Bonsor, A., Wyatt, M. C., Kral, Q., Kennedy, G., Shannon, A., & Ertel, S. (2018). Using warm dust to constrain unseen planets. \mnras, 480(4), 5560-5579.
• Boyajian, T. S., Alonso, R., Ammerman, A., Armstrong, D., Asensio Ramos, A., Barkaoui, K., Beatty, T. G., Benkhaldoun, Z., Benni, P., Bentley, R. O., Berdyugin, A., Berdyugina, S., Bergeron, S., Bieryla, A., Blain, M. G., Capetillo, B. A., Bodman, E. H., Boucher, A., Bradley, M., , Brincat, S. M., et al. (2018). The First Post-Kepler Brightness Dips of KIC 8462852. \apjl, 853(1), L8.
• Crepp, J. R., Gonzales, E. J., Bowler, B. P., Morales, F., Stone, J., Spalding, E., Vaz, A., Hinz, P., Ertel, S., Howard, A., & Isaacson, H. (2018). The TRENDS High-contrast Imaging Survey. VII. Discovery of a Nearby Sirius-like White Dwarf System (HD 169889). \apj, 864(1), 42.
• Defr{\`ere}, D., Absil, O., Berger, J. -., Boulet, T., Danchi, W., Ertel, S., Gallenne, A., H{\'enault}, F., Hinz, P., Huby, E., Ireland, M., Kraus, S., Labadie, L., Le, B., Martin, G., Matter, A., M{\'erand}, A., Mennesson, B., Minardi, S., , Monnier, J., et al. (2018). The path towards high-contrast imaging with the VLTI: the Hi-5 project. Experimental Astronomy, 46(3), 475-495.
• Defr{\`ere}, D., L{\'eger}, A., Absil, O., Beichman, C., Biller, B., Danchi, W., Ergenzinger, K., Eiroa, C., Ertel, S., Fridlund, M., Mu{\~noz}, A. G., Gillon, M., Glasse, A., Godolt, M., Grenfell, J., Kraus, S., Labadie, L., Lacour, S., Liseau, R., , Martin, G., et al. (2018). Space-based infrared interferometry to study exoplanetary atmospheres. Experimental Astronomy, 46(3), 543-560.
• Ertel, S., Absil, O., Defr{\`ere}, D., Augereau, J. -., & Mennesson, B. (2018). Prospects for the characterisation of exo-zodiacal dust with the VLTI. Experimental Astronomy, 46(3), 401-411.
• Ertel, S., Defr{\`ere}, D., Hinz, P., Mennesson, B., Kennedy, G., Danchi, W., Gelino, C., Hill, J., Hoffmann, W., Rieke, G., Shannon, A., Spalding, E., Stone, J., Vaz, A., Weinberger, A., Willems, P., Absil, O., Arbo, P., Bailey, V., , Beichman, C., et al. (2018). The HOSTS Survey\textemdashExozodiacal Dust Measurements for 30 Stars. \aj, 155(5), 194.
• Marshall, J., Milli, J., Choquet, \., Burgo, C., Kennedy, G., Matr{\`a}, L., Ertel, S., & Boccaletti, A. (2018). Comprehensive Analysis of HD 105, A Young Solar System Analog. \apj, 869(1), 10.
• Martin, D. M., Ertel, S., Schneider, G., Kamath, D., & Choquet, \. (2018). Two Newly Imaged, Faint Protoplanetary Nebulae from Contrast Enhanced Hubble Archival Observations. Research Notes of the American Astronomical Society, 2(4), 219.
• Rebollido, I., Eiroa, C., Montesinos, B., Maldonado, J., Villaver, E., Absil, O., Bayo, A., Canovas, H., Carmona, A., Chen, C., Ertel, S., Garufi, A., Henning, T., Iglesias, D., Launhardt, R., Liseau, R., Meeus, G., Mo{\'or}, A., Mora, A., , Olofsson, J., et al. (2018). The co-existence of hot and cold gas in debris discs. \aap, 614, A3.
• Stone, J. M., Skemer, A. J., Hinz, P. M., Bonavita, M., Kratter, K. M., Maire, A., Defrere, D., Bailey, V. P., Spalding, E., Leisenring, J. M., Desidera, S., Bonnefoy, M., Biller, B., Woodward, C. E., Henning, T., Skrutskie, M. F., Eisner, J., Crepp, J. R., Patience, J., , Weigelt, G., et al. (2018). The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates under Conservative Assumptions. \aj, 156(6), 286.
• Booth, M., Dent, W. R., Jord{\'an}, A., Lestrade, J., Hales, A. S., Wyatt, M. C., Casassus, S., Ertel, S., Greaves, J. S., Kennedy, G. M., Matr{\`a}, L., Augereau, J., & Villard, E. (2017). The Northern arc of ɛ Eridani's Debris Ring as seen by ALMA. \mnras, 469(3), 3200-3212.
• Brunngr{\"aber}, R., Wolf, S., Kirchschlager, F., & Ertel, S. (2017). The influence of dust grain porosity on the analysis of debris disc observations. \mnras, 464(4), 4383-4389.
• Choquet, \., Milli, J., Wahhaj, Z., Soummer, R., Roberge, A., Augereau, J., Booth, M., Absil, O., Boccaletti, A., Chen, C. H., Debes, J. H., Burgo, C., Dent, W. R., Ertel, S., Girard, J. H., Gofas-Salas, E., Golimowski, D. A., G{\'omez, G., Hagan, J. B., , Hibon, P., et al. (2017). First Scattered-light Images of the Gas-rich Debris Disk around 49 Ceti. \apjl, 834(2), L12.
• Faramaz, V., Ertel, S., Booth, M., Cuadra, J., & Simmonds, C. (2017). Inner mean-motion resonances with eccentric planets: a possible origin for exozodiacal dust clouds. \mnras, 465(2), 2352-2365.
• Kral, Q., Krivov, A. V., Defr{\`ere}, D., Lieshout, R., Bonsor, A., Augereau, J., Th{\'ebault}, P., Ertel, S., Lebreton, J., & Absil, O. (2017). Exozodiacal clouds: hot and warm dust around main sequence stars. The Astronomical Review, 13(2), 69-111.
• Le, B., Sana, H., Gosset, E., De Becker, M., Duvert, G., Absil, O., Anthonioz, F., Berger, J. -., Ertel, S., Grellmann, R., Guieu, S., Kervella, P., Rabus, M., & Willson, M. (2017). Resolved astrometric orbits of ten O-type binaries. \aap, 601, A34.
• Milli, J., Hibon, P., Christiaens, V., Choquet, \., Bonnefoy, M., Kennedy, G., Wyatt, M., Absil, O., G{\'omez, G. C., Burgo, C., Matr{\`a}, L., Augereau, J. -., Boccaletti, A., Delacroix, C., Ertel, S., Dent, W., Forsberg, P., Fusco, T., Girard, J., , Habraken, S., et al. (2017). Discovery of a low-mass companion inside the debris ring surrounding the F5V star HD 206893. \aap, 597, L2.
• Milli}, J., Vigan, A., Mouillet, D., Lagrange, A. -., Augereau, J. -., Pinte, C., Mawet, D., Schmid, H., Boccaletti, A., Matr{\`a}, L., Kral, Q., Ertel, S., Chauvin, G., Bazzon, A., M{\'enard}, F., Beuzit, J. -., Thalmann, C., Dominik, C., Feldt, M., , Henning, T., et al. (2017). Near-infrared scattered light properties of the HR 4796 A dust ring. A measured scattering phase function from 13.6\textdegree to 166.6\textdegree. \aap, 599, A108.
• Nu{\~nez}, P., Scott, N., Mennesson, B., Absil, O., Augereau, J. -., Bryden, G., Brummelaar, T., Ertel, S., Foresto}, V., Ridgway, S., Sturmann, J., Sturmann, L., Turner, N., & Turner, N. (2017). A near-infrared interferometric survey of debris-disc stars. VI. Extending the exozodiacal light survey with CHARA/JouFLU. \aap, 608, A113.
• Nuñez, P. D., Scott, N. J., Mennesson, B., Absil, O., Augereau, J. C., Bryden, G., Ten Brummelaar, T., Ertel, S., Coudé Du Foresto, V., Ridgway, S. T., Sturmann, J., Sturmann, L., Turner, N. J., & Turner, N. H. (2017). A near-infrared interferometric survey of debris-disc stars: VI. Extending the exozodiacal light survey with CHARA/JouFLU. Astronomy and Astrophysics, 608(Issue). doi:10.1051/0004-6361/201730859
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  We report the results of high-angular-resolution observations that search for exozodiacal light in a sample of main sequence stars and sub-giants. Using the "jouvence" of the fiber linked unit for optical recombination (JouFLU) at the center for high angular resolution astronomy (CHARA) telescope array, we have observed a total of 44 stars. Out of the 44 stars, 33 are new stars added to the initial, previously published survey of 42 stars performed at CHARA with the fiber linked unit for optical recombination (FLUOR). Since the start of the survey extension, we have detected a K-band circumstellar excess for six new stars at the 1% level or higher, four of which are known or candidate binaries, and two for which the excess could be attributed to exozodiacal dust. We have also performed follow-up observations of 11 of the stars observed in the previously published survey and found generally consistent results. We do however detect a significantly larger excess on three of these follow-up targets: Altair, υ And and κ CrB. Interestingly, the last two are known exoplanet host stars. We perform a statistical analysis of the JouFLU and FLUOR samples combined, which yields an overall exozodi detection rate of. We also find that the K-band excess in FGK-type stars correlates with the existence of an outer reservoir of cold (100 K) dust at the 99% confidence level, while the same cannot be said for A-type stars.
• Su, K. Y., MacGregor, M. A., Booth, M., Wilner, D. J., Flaherty, K., Hughes, A. M., Phillips, N. M., Malhotra, R., Hales, A. S., Morrison, S., Ertel, S., Matthews, B. C., Dent, W. R., & Casassus, S. (2017). ALMA 1.3 mm Map of the HD 95086 System. \aj, 154(6), 225.
• Absil, O., Bailey, J., Bott, K., Burgo, C. D., Cotton, D. V., Ertel, S., Kedziora-chudczer, L., Kennedy, G. M., Marshall, J. P., & Wyatt, M. C. (2016). POLARIZATION MEASUREMENTS OF HOT DUST STARS AND THE LOCAL INTERSTELLAR MEDIUM. The Astrophysical Journal, 825(2), 124. doi:10.3847/0004-637x/825/2/124
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  UNSW Vice-Chancellor's postdoctoral fellowship; Mexican CONACyT research grant [CB-2012-183007]; European Union through ERC [279973]
• Bailey, V. P., Bryden, G., Danchi, W. C., Defrere, D., Ertel, S., Haniff, C. A., Hinz, P. M., Kennedy, G. M., Mennesson, B., Millan-gabet, R., Rieke, G. H., Roberge, A., Serabyn, E., Skemer, A., Stapelfeldt, K. R., Vaz, A., Weinberger, A. J., Wyatt, M. C., & Wyatt, M. C. (2016). Enabling the Direct Detection of Earth-Sized Exoplanets with the LBTI HOSTS Project: A Progress Report. Proceedings of SPIE, 9907. doi:10.1117/12.2233397
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  NASA has funded a project called the Hunt for Observable Signatures of Terrestrial Systems (HOSTS) to survey nearby solar type stars to determine the amount of warm zodiacal dust in their habitable zones. The goal is not only to determine the luminosity distribution function but also to know which individual stars have the least amount of zodiacal dust. It is important to have this information for future missions that directly image exoplanets as this dust is the main source of astrophysical noise for them. The HOSTS project utilizes the Large Binocular Telescope Interferometer (LBTI), which consists of two 8.4-m apertures separated by a 14.4-m baseline on Mt. Graham, Arizona. The LBTI operates in a nulling mode in the mid-infrared spectral window (8-13 μm), in which light from the two telescopes is coherently combined with a 180 degree phase shift between them, producing a dark fringe at the location of the target star. In doing so the starlight is greatly reduced, increasing the contrast, analogous to a coronagraph operating at shorter wavelengths. The LBTI is a unique instrument, having only three warm reflections before the starlight reaches cold mirrors, giving it the best photometric sensitivity of any interferometer operating in the mid-infrared. It also has a superb Adaptive Optics (AO) system giving it Strehl ratios greater than 98% at 10 μm. In 2014 into early 2015 LBTI was undergoing commissioning. The HOSTS project team passed its Operational Readiness Review (ORR) in April 2015. The team recently published papers on the target sample, modeling of the nulled disk images, and initial results such as the detection of warm dust around η Corvi. Recently a paper was published on the data pipeline and on-sky performance. An additional paper is in preparation on β Leo. We will discuss the scientific and programmatic context for the LBTI project, and we will report recent progress, new results, and plans for the science verification phase that started in February 2016, and for the survey.
• Bailey, V. P., Danchi, W. C., Defrere, D., Downey, E., Durney, O., Ertel, S., Esposito, S., Grenz, P., Hill, J. M., Hinz, P. M., Hoffmann, W. F., Leisenring, J., Mennesson, B., Millan-gabet, R., Montoya, M., Morzinski, K. M., Pinna, E., Puglisi, A., Skemer, A., , Skrutskie, M., et al. (2016). Overview of LBTI: A Multipurpose Facility for High Spatial Resolution Observations. Proceedings of SPIE, 9907. doi:10.1117/12.2233795
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  The Large Binocular Telescope Interferometer (LBTI) is a high spatial resolution instrument developed for coherent imaging and nulling interferometry using the 14.4 m baseline of the 2×8.4 m LBT. The unique telescope design, comprising of the dual apertures on a common elevation-azimuth mount, enables a broad use of observing modes. The full system is comprised of dual adaptive optics systems, a near-infrared phasing camera, a 1-5 μm camera (called LMIRCam), and an 8-13 μm camera (called NOMIC). The key program for LBTI is the Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS), a survey using nulling interferometry to constrain the typical brightness from exozodiacal dust around nearby stars. Additional observations focus on the detection and characterization of giant planets in the thermal infrared, high spatial resolution imaging of complex scenes such as Jupiter's moon, Io, planets forming in transition disks, and the structure of active Galactic Nuclei (AGN). Several instrumental upgrades are currently underway to improve and expand the capabilities of LBTI. These include: Improving the performance and limiting magnitude of the parallel adaptive optics systems; quadrupling the field of view of LMIRcam (increasing to 20"x20"); adding an integral field spectrometry mode; and implementing a new algorithm for path length correction that accounts for dispersion due to atmospheric water vapor. We present the current architecture and performance of LBTI, as well as an overview of the upgrades.
• Bohm, M. C., Danchi, W. C., Defrere, D., Downey, E., Durney, O., Ertel, S., Hill, J. M., Hinz, P. M., Hoffmann, W. F., Mennesson, B., Millan-gabet, R., Montoya, M., Pott, J. U., Skemer, A., Spalding, E., Stone, J. M., & Vaz, A. (2016). Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer. Proceedings of SPIE, 9907. doi:10.1117/12.2233884
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  The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 microns). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the new sensing approach that has been developed at the LBT to measure and monitor the optical path length fluctuations due to dry air and water vapor separately. After reviewing the current performance of the system for dry air seeing compensation, we present simultaneous H-, K-, and N-band observations that illustrate the feasibility of our feedforward approach to stabilize the path length fluctuations seen by the LBTI nuller.
• Eiroa, C., Rebollido, I., Montesinos, B., Villaver, E., Absil, O., Henning, T., Bayo, A., Canovas, H., Carmona, A., Chen, C., Ertel, S., Iglesias, D., Launhardt, R., Maldonado, J., Meeus, G., Mo{\'or}, A., Mora, A., Mustill, A., Olofsson, J., , Riviere-Marichalar, P. .., et al. (2016). Exocomet signatures around the A-shell star \ensuremath{\varphi} Leonis?. \aap, 594, L1.
• Ertel, S., Defr{\`ere}, D., Absil, O., Le, B., Augereau, J. -., Berger, J. -., Blind, N., Bonsor, A., Lagrange, A. -., Lebreton, J., Marion, L., Milli, J., & Olofsson, J. (2016). A near-infrared interferometric survey of debris-disc stars. V. PIONIER search for variability. \aap, 595, A44.
• Ertel, S., Defrère, D., Absil, O., Le Bouquin, J. B., Augereau, J. C., Berger, J. P., Blind, N., Bonsor, A., Lagrange, A. M., Lebreton, J., Marion, L., Milli, J., & Olofsson, J. (2016). A near-infrared interferometric survey of debris-disc stars: V. PIONIER search for variability. Astronomy and Astrophysics, 595(Issue). doi:10.1051/0004-6361/201527721
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  Context. Extended circumstellar emission has been detected within a few 100 milli-arcsec around ≳ 10% of nearby main sequence stars using near-infrared interferometry. Follow-up observations using other techniques, should they yield similar results or non-detections, can provide strong constraints on the origin of the emission. They can also reveal the variability of the phenomenon. Aims. We aim to demonstrate the persistence of the phenomenon over the timescale of a few years and to search for variability of our previously detected excesses. Methods. Using Very Large Telescope Interferometer (VLTI)/Precision Integrated Optics Near Infrared ExpeRiment (PIONIER) in H band we have carried out multi-epoch observations of the stars for which a near-infrared excess was previously detected using the same observation technique and instrument. The detection rates and distribution of the excesses from our original survey and the follow-up observations are compared statistically. A search for variability of the excesses in our time series is carried out based on the level of the broadband excesses. Results. In 12 of 16 follow-up observations, an excess is re-detected with a significance of > 2σ, and in 7 of 16 follow-up observations significant excess (> 3σ) is re-detected. We statistically demonstrate with very high confidence that the phenomenon persists for the majority of the systems. We also present the first detection of potential variability in two sources. Conclusions. We conclude that the phenomenon responsible for the excesses persists over the timescale of a few years for the majority of the systems. However, we also find that variability intrinsic to a target can cause it to have no significant excess at the time of a specific observation.
• Marshall, J., Cotton, D., Bott, K., Ertel, S., Kennedy, G., Wyatt, M., Burgo, C., Absil, O., Bailey, J., & Kedziora-Chudczer, L. .. (2016). Polarization Measurements of Hot Dust Stars and the Local Interstellar Medium. \apj, 825(2), 124.
• Montesinos, B., Eiroa, C., Krivov, A., Marshall, J., Pilbratt, G., Liseau, R., Mora, A., Maldonado, J., Wolf, S., Ertel, S., Bayo, A., Augereau, J. -., Heras, A., Fridlund, M., Danchi, W., Solano, E., Kirchschlager, F., Burgo, C., & Montes, D. (2016). Incidence of debris discs around FGK stars in the solar neighbourhood. \aap, 593, A51.
• Thompson, M., Scicluna, P., Kemper, F., Geach, J., Dunham, M., Morata, O., Ertel, S., Ho, P., Dempsey, J., Coulson, I., Petitpas, G., & Kristensen, L. (2016). Constraints on the circumstellar dust around KIC 8462852. \mnras, 458(1), L39-L43.
• Wahhaj, Z., Milli, J., Kennedy, G., Ertel, S., Matr{\`a}, L., Boccaletti, A., Burgo, C., Wyatt, M., Pinte, C., Lagrange, A., Absil, O., Choquet, E., G{\'omez, G., Kobayashi, H., Mawet, D., Mouillet, D., Pueyo, L., Dent, W. R., Augereau, J., & Girard, J. (2016). The SHARDDS survey: First resolved image of the HD 114082 debris disk in the Lower Centaurus Crux with SPHERE. \aap, 596, L4.
• Ertel, S., Augereau, J. -., Absil, O., Defr{\`ere}, D., Le, B., Marion, L., Bonsor, A., & Lebreton, J. (2015). An Unbiased Near-infrared Interferometric Survey for Hot Exozodiacal Dust. The Messenger, 159, 24-29.
• Liseau, R., Vlemmings, W., Bayo, A., Bertone, E., Black, J., Burgo, C., Chavez, M., Danchi, W., Luz, V., Eiroa, C., Ertel, S., Fridlund, M., Justtanont, K., Krivov, A., Marshall, J., Mora, A., Montesinos, B., Nyman, L. -., Olofsson, G., , Sanz-Forcada, J. .., et al. (2015). ALMA observations of \ensuremath{\alpha} Centauri. First detection of main-sequence stars at 3 mm wavelength. \aap, 573, L4.
• Sch{\"uppler}, C., L{\"ohne}, T., Krivov, A., Ertel, S., Marshall, J., Wolf, S., Wyatt, M., Augereau, J. -., & Metchev, S. (2015). Collisional modelling of the AU Microscopii debris disc. \aap, 581, A97.
• Xu, S., Ertel, S., Wahhaj, Z., Milli, J., Scicluna, P., & Bertrang, G. -. (2015). An extreme-AO search for giant planets around a white dwarf. VLT/SPHERE performance on a faint target GD 50. \aap, 579, L8.
• Beust, H., Augereau, J. -., Bonsor, A., Graham, J., Kalas, P., Lebreton, J., Lagrange, A. -., Ertel, S., Faramaz, V., & Th{\'ebault}, P. (2014). An independent determination of Fomalhaut b's orbit and the dynamical effects on the outer dust belt. \aap, 561, A43.
• Ertel, S., Absil, O., Defr{\`ere}, D., Le, B., Augereau, J. -., Marion, L., Blind, N., Bonsor, A., Bryden, G., Lebreton, J., & Milli, J. (2014). A near-infrared interferometric survey of debris-disk stars. IV. An unbiased sample of 92 southern stars observed in H band with VLTI/PIONIER. \aap, 570, A128.
• Ertel, S., Marshall, J., Augereau, J. -., Krivov, A., L{\"ohne}, T., Eiroa, C., Mora, A., Burgo, C., Montesinos, B., Bryden, G., Danchi, W., Kirchschlager, F., Liseau, R., Maldonado, J., Pilbratt, G., Sch{\"uppler}, C., Th{\'ebault}, P., White, G., & Wolf, S. (2014). Potential multi-component structure of the debris disk around HIP 17439 revealed by Herschel/DUNES. \aap, 561, A114.
• Faramaz, V., Beust, H., Th{\'ebault}, P., Augereau, J. -., Bonsor, A., Burgo, C., Ertel, S., Marshall, J., Milli, J., Montesinos, B., Mora, A., Bryden, G., Danchi, W., Eiroa, C., White, G., & Wolf, S. (2014). Can eccentric debris disks be long-lived?. A first numerical investigation and application to \ensuremath{\zeta}$^2$ Reticuli. \aap, 563, A72.
• Greaves, J., Kennedy, G., Thureau, N., Eiroa, C., Marshall, J., Maldonado, J., Matthews, B., Olofsson, G., Barlow, M., Moro-Mart{\'\in}, A., Sibthorpe, B., Absil, O., Ardila, D., Booth, M., Broekhoven-Fiene, H. .., Brown, D., Collier Cameron, A., Burgo, C., Di Francesco, J., , Eisl{\"offel}, J., et al. (2014). Alignment in star-debris disc systems seen by Herschel. \mnras, 438(1), L31-L35.
• Marion, L., Absil, O., Ertel, S., Le, B., Augereau, J. -., Blind, N., Defr{\`ere}, D., Lebreton, J., & Milli, J. (2014). Searching for faint companions with VLTI/PIONIER. II. 92 main sequence stars from the Exozodi survey. \aap, 570, A127.
• Marshall, J., Kirchschlager, F., Ertel, S., Augereau, J. -., Kennedy, G., Booth, M., Wolf, S., Montesinos, B., Eiroa, C., & Matthews, B. (2014). Interpreting the extended emission around three nearby debris disc host stars. \aap, 570, A114.
• Matter, A., Labadie, L., Kreplin, A., Lopez, B., Wolf, S., Weigelt, G., Ertel, S., Pott, J. -., & Danchi, W. (2014). Evidence of a discontinuous disk structure around the Herbig Ae star HD 139614. \aap, 561, A26.
• Sch{\"uppler}, C., L{\"ohne}, T., Krivov, A., Ertel, S., Marshall, J., & Eiroa, C. (2014). Collisional modelling of the debris disc around HIP 17439. \aap, 567, A127.
• Wiegert, J., Liseau, R., Th{\'ebault}, P., Olofsson, G., Mora, A., Bryden, G., Marshall, J., Eiroa, C., Montesinos, B., Ardila, D., Augereau, J., Bayo Aran, A., Danchi, W., Burgo, C., Ertel, S., Fridlund, M., Hajigholi, M., Krivov, A., Pilbratt, G., , Roberge, A., et al. (2014). How dusty is \ensuremath{\alpha} Centauri?. Excess or non-excess over the infrared photospheres of main-sequence stars. \aap, 563, A102.
• Wiegert, J., Liseau, R., Thébault, P., Olofsson, G., Mora, A., Bryden, G., Marshall, J. P., Eiroa, C., Montesinos, B., Ardila, D., Augereau, J. C., Bayo Aran, A., Danchi, W. C., Del Burgo, C., Ertel, S., Fridlund, M. C., Hajigholi, M., Krivov, A. V., Pilbratt, G. L., , Roberge, A., et al. (2014). How dusty is α Centauri?: Excess or non-excess over the infrared photospheres of main-sequence stars. Astronomy and Astrophysics, 563(Issue). doi:10.1051/0004-6361/201321887
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  Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary α Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the α Cen system. This requires knowledge of their photospheres. Having already detected the temperature minimum, T min, of α Cen A at far-infrared wavelengths, we here attempt to do the same for the more active companion α Cen B. Using the α Cen stars as templates, we study the possible effects that Tmin may have on the detectability of unresolved dust discs around other stars. Methods. We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in the far infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around α Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunction with radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than α Cen, a fractional dust luminosity fd ≡ L dust/Lstar2×10-7 could account for SEDs that do not exhibit the Tmin effect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared, slight excesses at the 2.5σ level are observed at 24 μm for both α Cen A and B, which, if interpreted as due to zodiacal-type dust emission, would correspond to fd ∼ (1-3) × 10-5, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dust grains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the α Cen stars, viz. ≲4x10-6,M- of 4 to 1000 μm size grains, distributed according to n(a) a-3.5. Similarly, for filled-in Tmin emission, corresponding Edgeworth-Kuiper belts could account for ∼ 10-3M- of dust. Conclusions. Our far-infrared observations lead to estimates of upper limits to the amount of circumstellar dust around the stars α Cen A and B. Light scattered and/or thermally emitted by exo-Zodi discs will have profound implications for future spectroscopic missions designed to search for biomarkers in the atmospheres of Earth-like planets. The far-infrared spectral energy distribution of α Cen B is marginally consistent with the presence of a minimum temperature region in the upper atmosphere of the star. We also show that an α Cen A-like temperature minimum may result in an erroneous apprehension about the presence of dust around other, more distant stars. © 2014 ESO.
• Absil, O., Defr{\`ere}, D., Foresto}, V., Di Folco, E., M{\'erand}, A., Augereau, J. -., Ertel, S., Hanot, C., Kervella, P., Mollier, B., Scott, N., Che, X., Monnier, J., Thureau, N., Tuthill, P., Brummelaar, T., McAlister, H., Sturmann, J., Sturmann, L., & Turner, N. (2013). A near-infrared interferometric survey of debris-disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR. \aap, 555, A104.
• Eiroa, C., Marshall, J., Mora, A., Montesinos, B., Absil, O., Augereau, J. C., Bayo, A., Bryden, G., Danchi, W., Burgo, C., Ertel, S., Fridlund, M., Heras, A., Krivov, A., Launhardt, R., Liseau, R., L{\"ohne}, T., Maldonado, J., Pilbratt, G., , Roberge, A., et al. (2013). DUst around NEarby Stars. The survey observational results. \aap, 555, A11.
• Krivov, A. V., Eiroa, C., Löhne, T., Marshall, J. P., Montesinos, B., Del Burgo, C., Absil, O., Ardila, D., Augereau, J. C., Bayo, A., Bryden, G., Danchi, W., Ertel, S., Lebreton, J., Liseau, R., Mora, A., Mustill, A. J., Mutschke, H., Neuhäuser, R., , Pilbratt, G. L., et al. (2013). Herschel's "cold debris disks": Background galaxies or quiescent rims of planetary systems?. Astrophysical Journal, 772(Issue 1). doi:10.1088/0004-637x/772/1/32
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  Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around 100 μm or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant - and in some cases extended - excess emission at 160 μm, which is larger than the 100 μm excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than 100 μm, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before "cometary" or "asteroidal" sizes were reached. © 2013. The American Astronomical Society. All rights reserved.
• Krivov, A., Eiroa, C., L{\"ohne}, T., Marshall, J., Montesinos, B., Burgo, C., Absil, O., Ardila, D., Augereau, J. -., Bayo, A., Bryden, G., Danchi, W., Ertel, S., Lebreton, J., Liseau, R., Mora, A., Mustill, A., Mutschke, H., Neuh{\"auser}, R., , Pilbratt, G., et al. (2013). Herschel's ``Cold Debris Disks'': Background Galaxies or Quiescent Rims of Planetary Systems?. \apj, 772(1), 32.
• Lebreton, J., Lieshout, R., Augereau, J. -., Absil, O., Mennesson, B., Kama, M., Dominik, C., Bonsor, A., Vandeportal, J., Beust, H., Defr{\`ere}, D., Ertel, S., Faramaz, V., Hinz, P., Kral, Q., Lagrange, A. -., Liu, W., & Th{\'ebault}, P. (2013). An interferometric study of the Fomalhaut inner debris disk. III. Detailed models of the exozodiacal disk and its origin. \aap, 555, A146.
• Liseau, R., Montesinos, B., Olofsson, G., Bryden, G., Marshall, J. P., Ardila, D., Bayo Aran, A., Danchi, W. C., Del Burgo, C., Eiroa, C., Ertel, S., Fridlund, M. C., Krivov, A. V., Pilbratt, G. L., Roberge, A., Thébault, P., Wiegert, J., & White, G. J. (2013). α Centauri A in the far infrared : First measurement of the temperature minimum of a star other than the Sun. Astronomy and Astrophysics, 549(Issue). doi:10.1051/0004-6361/201220776
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  Context. Chromospheres and coronae are common phenomena on solar-type stars. Understanding the energy transfer to these heated atmospheric layers requires direct access to the relevant empirical data. Study of these structures has, by and large, been limited to the Sun thus far. Aims. The region of the temperature reversal can be directly observed only in the far infrared and submillimetre spectral regime. We aim at determining the characteristics of the atmosphere in the region of the temperature minimum of the solar sister star α Cen A. As a bonus this will also provide a detailed mapping of the spectral energy distribution, i.e. knowledge that is crucial when searching for faint, Kuiper belt-like dust emission around other stars. Methods. For the nearby binary system α Cen, stellar parameters are known with high accuracy from measurements. For the basic model parameters Teff, log g and [Fe/H], we interpolate stellar model atmospheres in the grid of Gaia/PHOENIX and compute the corresponding model for the G2 V star α Cen A. Comparison with photometric measurements shows excellent agreement between observed photospheric data in the optical and infrared. For longer wavelengths, the modelled spectral energy distribution is compared to Spitzer-MIPS, Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry. A specifically tailored Uppsala model based on the MARCS code and extending further in wavelength is used to gauge the emission characteristics of α Cen A in the far infared. Results. Similar to the Sun, the far infrared (FIR) emission of α Cen A originates in the minimum temperature region above the stellar photosphere in the visible. However, in comparison with the solar case, the FIR photosphere of α Cen A appears marginally cooler, Tmin ∼ T160 μm = 3920 ± 375 K. Beyond the minimum near 160 μm, the brightness temperatures increase, and this radiation very likely originates in warmer regions of the chromosphere of α Cen A. Conclusions. To the best of our knowledge, this is the first time a temperature minimum has been directly measured on a main-sequence star other than the Sun. © ESO, 2013.
• Liseau, R., Montesinos, B., Olofsson, G., Bryden, G., Marshall, J., Ardila, D., Bayo Aran, A., Danchi, W., Burgo, C., Eiroa, C., Ertel, S., Fridlund, M., Krivov, A., Pilbratt, G., Roberge, A., Th{\'ebault}, P., Wiegert, J., & White, G. (2013). \ensuremath{\alpha} Centauri A in the far infrared. First measurement of the temperature minimum of a star other than the Sun. \aap, 549, L7.
• Marshall, J., Krivov, A., Burgo, C., Eiroa, C., Mora, A., Montesinos, B., Ertel, S., Bryden, G., Liseau, R., Augereau, J. -., Bayo, A., Danchi, W., L{\"ohne}, T., Maldonado, J., Pilbratt, G., Stapelfeldt, K., Thebault, P., White, G., & Wolf, S. (2013). Herschel observations of the debris disc around HIP 92043. \aap, 557, A58.
• Defr{\`ere}, D., Lebreton, J., Le, B., Lagrange, A. -., Absil, O., Augereau, J. -., Berger, J. -., Folco, E., Ertel, S., Kluska, J., Montagnier, G., Millan-Gabet, R. .., Traub, W., & Zins, G. (2012). Hot circumstellar material resolved around \ensuremath{\beta} Pic with VLTI/PIONIER. \aap, 546, L9.
• Ertel, S., Wolf, S., & Rodmann, J. (2012). Observing planet-disk interaction in debris disks. Astronomy and Astrophysics, 544(Issue). doi:10.1051/0004-6361/201219236
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  Context. Debris disks are commonly considered to be a by-product of planet formation. Structures in debris disks induced by planet-disk interaction are promising to provide valuable constraints on the existence and properties of embedded planets. Aims. We investigate the observability of structures in debris disks induced by planet-disk interaction with future facilities in a systematic way. High-sensitivity, high angular resolution observations with large (sub-)mm interferometers and large space-based telescopes operating in the near-to mid-infrared wavelength range are considered. Methods. The observability of debris disks with the Atacama Large Millimeter/submillimeter Array (ALMA) is studied on the basis of a simple analytical disk model. Furthermore, N-body simulations are used to model the spatial dust distribution in debris disks under the influence of planet-disk interaction. From these simulations, images at optical scattered light to millimeter thermal re-emission are computed. Available information about the expected capabilities of ALMA and the James Webb Space Telescope (JWST) are used to investigate the observability of characteristic disk structures with these facilities through spatially resolved imaging. Results. Our simulations show that planet-disk interaction can result in prominent structures in the whole considered wavelength range. The exact result depends on the configuration of the planet-disk system and on the observing wavelength which provides the opportunity of detecting and characterizing extrasolar planets in a range of masses and radial distances from the star that is not accessible to other techniques. Facilities that will be available in the near future at both considered wavelength ranges are shown to provide the capabilities to spatially resolve and characterize structures in debris disks that arise because of planet-disk interaction. Limitations are revealed and suggestions for possible instrument setups and observing strategies are given. In particular, ALMA is limited by its sensitivity to surface brightness, which requires a trade-off between sensitivity and spatial resolution. Space-based mid-infrared observations will be able to detect and spatially resolve regions in debris disks even at a distance of several tens of AU from the star, where the emission from debris disks in this wavelength range is expected to be low. Conclusions. Both ALMA and the planned space-based near-to mid-infrared telescopes will provide unprecedented capabilities to study planet-disk interaction in debris disks. In particular, a combination of observations at both wavelengths will provide very strong constraints on the planetary/planetesimal systems. © 2012 ESO.
• Ertel, S., Wolf, S., & Rodmann, J. (2012). Observing planet-disk interaction in debris disks. \aap, 544, A61.
• Ertel, S., Wolf, S., Marshall, J. P., Eiroa, C., Augereau, J. C., Krivov, A. V., Löhne, T., Absil, O., Ardila, D., Arévalo, M., Bayo, A., Bryden, G., Del Burgo, C., Greaves, J., Kennedy, G., Lebreton, J., Liseau, R., Maldonado, J., Montesinos, B., , Mora, A., et al. (2012). A peculiar class of debris disks from Herschel/DUNES: A steep fall off in the far infrared. Astronomy and Astrophysics, 541(Issue). doi:10.1051/0004-6361/201118077
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  Context. The existence of debris disks around old main sequence stars is usually explained by continuous replenishment of small dust grains through collisions from a reservoir of larger objects. Aims. We present photometric data of debris disks around HIP 103389 (HD199260), HIP 107350 (HNPeg, HD206860), and HIP 114948 (HD219482), obtained in the context of our Herschel open time key program DUNES (DUst around NEarby Stars). Methods. We used Herschel/PACS to detect the thermal emission of the three debris disks with a 3s sensitivity of a few mJy at 100 μ m and 160 μ m. In addition, we obtained Herschel/PACS photometric data at 70 μ m for HIP 103389. These observations are complemented by a large variety of optical to far-infrared photometric data. Two different approaches are applied to reduce the Herschel data to investigate the impact of data reduction on the photometry. We fit analytical models to the available spectral energy distribution (SED) data using the fitting method of simulated thermal annealing as well as a classical grid search method. Results. The SEDs of the three disks potentially exhibit an unusually steep decrease at wavelengths ≥70 μ m. We investigate the significance of the peculiar shape of these SEDs and the impact on models of the disks provided it is real. Using grain compositions that have been applied successfully for modeling of many other debris disks, our modeling reveals that such a steep decrease of the SEDs in the long wavelength regime is inconsistent with a power-law exponent of the grain size distribution-3.5 expected from a standard equilibrium collisional cascade. In contrast, a steep grain size distribution or, alternatively an upper grain size in the range of few tens of micrometers are implied. This suggests that a very distinct range of grain sizes would dominate the thermal emission of such disks. However, we demonstrate that the understanding of the data of faint sources obtained with Herschel is still incomplete and that the significance of our results depends on the version of the data reduction pipeline used. Conclusions. A new mechanism to produce the dust in the presented debris disks, deviations from the conditions required for a standard equilibrium collisional cascade (grain size exponent of-3.5), and/or significantly different dust properties would be necessary to explain the potentially steep SED shape of the three debris disks presented. © 2012 ESO.
• Ertel, S., Wolf, S., Marshall, J., Eiroa, C., Augereau, J. -., Krivov, A., L{\"ohne}, T., Absil, O., Ardila, D., Ar{\'evalo}, M., Bayo, A., Bryden, G., Burgo, C., Greaves, J., Kennedy, G., Lebreton, J., Liseau, R., Maldonado, J., Montesinos, B., , Mora, A., et al. (2012). A peculiar class of debris disks from Herschel/DUNES. A steep fall off in the far infrared. \aap, 541, A148.
• L{\"ohne}, T., Augereau, J. -., Ertel, S., Marshall, J., Eiroa, C., Mora, A., Absil, O., Stapelfeldt, K., Th{\'ebault}, P., Bayo, A., Del Burgo, C., Danchi, W., Krivov, A., Lebreton, J., Letawe, G., Magain, P., Maldonado, J., Montesinos, B., Pilbratt, G., , White, G., et al. (2012). Modelling the huge, Herschel-resolved debris ring around HD 207129. \aap, 537, A110.
• L{\"ohne}, T., Eiroa, C., Augereau, J. -., Ertel, S., Marshall, J., Mora, A., Absil, O., Stapelfeldt, K., Th{\'ebault}, P., Bayo, A., Burgo, C., Danchi, W., Krivov, A., Lebreton, J., Letawe, G., Magain, P., Maldonado, J., Montesinos, B., Pilbratt, G., , White, G., et al. (2012). Debris disks as seen by Herschel/DUNES. Astronomische Nachrichten, 333(5-6), 441.
• Thebault, P., Kral, Q., & Ertel, S. (2012). Planet signatures in collisionally active debris discs: scattered light images. \aap, 547, A92.
• Eiroa, C., Marshall, J., Mora, A., Krivov, A., Montesinos, B., Absil, O., Ardila, D., Ar{\'evalo}, M., Augereau, J. -., Bayo, A., Danchi, W., Del Burgo, C., Ertel, S., Fridlund, M., Gonz{\'alez-Garc\'\ia}, B., Heras, A., Lebreton, J., Liseau, R., Maldonado, J., , Meeus, G., et al. (2011). Herschel discovery of a new class of cold, faint debris discs. \aap, 536, L4.
• Ertel, S., Wolf, S., Metchev, S., Schneider, G., Carpenter, J., Meyer, M., Hillenbrand, L., & Silverstone, M. (2011). Multi-wavelength modeling of the spatially resolved debris disk of HD 107146. \aap, 533, A132.
• Gr{\"afe}, C., Wolf, S., Roccatagliata, V., Sauter, J., & Ertel, S. (2011). Mid-infrared observations of the transitional disks around DH Tauri, DM Tauri, and GM Aurigae. \aap, 533, A89.
• Gräfe, C., Wolf, S., Roccatagliata, V., Sauter, J., & Ertel, S. (2011). Mid-infrared observations of the transitional disks around DHTauri, DMTauri, and GMAurigae. Astronomy and Astrophysics, 533(Issue). doi:10.1051/0004-6361/201015927
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  Aims. We present mid-infrared observations and photometry of the transitional disks around the young stellar objects DHâ Tau, DM Tau, and GM Aur, obtained with VISIR/VLT in N band. Our aim is to resolve the inner region and the large-scale structures of these transitional disks, carrying potential signatures of intermediate or later stages of disk evolution and ongoing planet formation. Methods. We use the simultaneously observed standard-stars as PSF reference to constrain the radial flux profiles of our target objects. Subtracting the obtained standard-star profile from the corresponding science object profile yields the flux residuals produced by the star-disk system. A detection threshold takes into account the background standard deviation and also the seeing variations during the observations to evaluate the significance of these flux residuals. On the basis of a simple model for the dust re-emission, we derive constraints on the inner radius of the dust disk. Results. We spatially resolve the transitional disk around GM Aur and determine an inner-disk hole radius of 20.5+1.0-0.5} AU. The circumstellar disks around DH Tau and DM Tau are not spatially resolved but we are able to constrain the inner-disk hole radius to
• Marshall, J., L{\"ohne}, T., Montesinos, B., Krivov, A., Eiroa, C., Absil, O., Bryden, G., Maldonado, J., Mora, A., Sanz-Forcada, J. .., Ardila, D., Augereau, J. -., Bayo, A., Del Burgo, C., Danchi, W., Ertel, S., Fedele, D., Fridlund, M., Lebreton, J., , Gonz{\'alez-Garc\'\ia}, B., et al. (2011). A Herschel resolved far-infrared dust ring around HD 207129. \aap, 529, A117.
• Eiroa, C., Fedele, D., Maldonado, J., Gonz{\'alez-Garc\'\ia}, B., Rodmann, J., Heras, A., Pilbratt, G., Augereau, J. -., Mora, A., Montesinos, B., Ardila, D., Bryden, G., Liseau, R., Stapelfeldt, K., Launhardt, R., Solano, E., Bayo, A., Absil, O., Ar{\'evalo}, M., , Barrado, D., et al. (2010). Cold DUst around NEarby Stars (DUNES). First results. A resolved exo-Kuiper belt around the solar-like star \ensuremath{\zeta}$^2$ Ret. \aap, 518, L131.
• Liseau, R., Eiroa, C., Fedele, D., Augereau, J. -., Olofsson, G., Gonz{\'alez}, B., Maldonado, J., Montesinos, B., Mora, A., Absil, O., Ardila, D., Barrado, D., Bayo, A., Beichman, C., Bryden, G., Danchi, W., Del Burgo, C., Ertel, S., Fridlund, C., , Heras, A., et al. (2010). Resolving the cold debris disc around a planet-hosting star . PACS photometric imaging observations of q$^1$ Eridani (HD 10647, HR 506). \aap, 518, L132.
• Meusinger, H., Henze, M., Birkle, K., Pietsch, W., Williams, B., Hatzidimitriou, D., Nesci, R., Mandel, H., Ertel, S., Hinze, A., & Berthold, T. (2010). J004457+4123 (Sharov 21): not a remarkable nova in M 31 but a background quasar with a spectacular UV flare. \aap, 512, A1.

Proceedings Publications

• Barbato, D., Farinato, J., Baruffolo, A., Bergomi, M., Bianco, A., Biondi, F., Briegel, F., Carolo, E., Cerpelloni, P., Carlotti, A., Chinellato, S., Conrad, A., De Pascale, M., Di Filippo, S., Dima, M., D'Orazi, V., Ertel, S., Machado, T., Greggio, D., , Guerra, J., et al. (2024). SHARK-NIR commissioning and early science runs. In Ground-Based and Airborne Instrumentation for Astronomy X 2024, 13096.
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  SHARK-NIR is an instrument providing high-contrast coronagraphic imaging, dual band imaging and low resolution spectroscopy in Y, J and H bands, taking advantage of the high performance of the Large Binocular Telescope (LBT) AO systems. Its main scientific drivers is the detection and characterization of exoplanets, circumstellar disks, Solar System small bodies and acrive galactic nuclei. Binocular observations are provided by exploiting the synergy with SHARK-VIS (operating in V band) and LMIRCam of LBTI (operating from K to M band). SHARK-NIR was shipped to LBT in June 2022, and up to November 2022 was the subject of the three pre-commissioning runs: the first to install and test the instrument in the high-bay LBT clean tent, the second to install and align the instrument to the telescope and the third to perform daytime testing. This pre-commissioning phase resulted in the successful alignment of the instrument with a very good internal optical quality and the performance of additional tests using simulated turbulence injected through LBT Adaptive Secondary Mirror. In January 2023 we had the first commissioning run and the instrument first light, in which we successfully tested the imaging capabilities with and without the Gaussian Lyot coronagraph. In March 2023 we had the second commissioning run, in which despite the bad weather we successfully performed a variety of technical activities, as well as preliminary testing of the Shaped Pupil coronagraph. After two additional commissioning runs in May and October, our first early scientific run in October 2023 focused on the Taurus star formation region, a region populated by targets of considerable scientific interest. In this paper we will give an overview of commissioning and the early science phases running from October 2023 to May 2024, focusing on the technical challenges we overcame and future work needed to push the instrument to its very limit, as well as presenting the first preliminary scientific results.
• Glauser, A., Quanz, S., Hansen, J., Dannert, F., Ireland, M., Linz, H., Absil, O., Alei, E., Angerhausen, D., Birbacher, T., Fortier, A., Huber, P., Kammerer, J., Laugier, R., Lichtenberg, T., Noack, L., Ranganathan, M., Rugheimer, S., Airapetian, V., , Alibert, Y., et al. (2024). The Large Interferometer For Exoplanets (LIFE): A space mission for mid-infrared nulling interferometry. In Optical and Infrared Interferometry and Imaging IX 2024, 13095.
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  The Large Interferometer For Exoplanets (LIFE) is a proposed space mission that enables the spectral characterization of the thermal emission of exoplanets in the solar neighborhood. The mission is designed to search for global atmospheric biosignatures on dozens of temperate terrestrial exoplanets and it will naturally investigate the diversity of other worlds. Here, we review the status of the mission concept, discuss the key mission parameters, and outline the trade-offs related to the mission's architecture. In preparation for an upcoming concept study, we define a mission baseline based on a free-formation flying constellation of a double Bracewell nulling interferometer that consists of 4 collectors and a central beam-combiner spacecraft. The interferometric baselines are between 10-600 m, and the estimated diameters of the collectors are at least 2 m (but will depend on the total achievable instrument throughput). The spectral required wavelength range is 6-16 µm (with a goal of 4-18.5 µm), hence cryogenic temperatures are needed both for the collectors and the beam combiners. One of the key challenges is the required deep, stable, and broad-band nulling performance while maintaining a high system throughput for the planet signal. Among many ongoing or needed technology development activities, the demonstration of the measurement principle under cryogenic conditions is fundamentally important for LIFE.
• Isbell, J., Ertel, S., Wagner, K., Rousseau, H., Power, J., Carlson, J., Becker, A., Rupert, J., Hinz, P., Hoffmann, W., Leisenring, J., Stone, J., & Spalding, E. (2024). The LBTI - Pioneering the ELT Era. In Optical and Infrared Interferometry and Imaging IX 2024, 13095.
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  The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument which combines the two 8.4m apertures of the LBT for sensitive, high-angular-resolution imaging and interferometric observations in the thermal infrared. Through its observing modes utilizing adaptive optics, Fizeau imaging, and nulling interferometry, the LBTI is in many respects the first ELT; it serves as a pioneer for upcoming ELTs in terms of both science and instrumentation. LBTI has completed a large survey for habitable-zone dust around main sequence stars, exploiting its angular resolution to obtain 100x better sensitivity than space-based photometric observations. Recently we have emphasized Fizeau imaging, supporting high-contrast and precision-astrometric observations. We obtained the first extragalactic and N band observations in this mode, demonstrating high-fidelity, high-sensitivity imaging on a 23 m baseline. We are now pushing to image the first rocky planet in the habitable zone around a nearby Sun-like star. In this paper we present an overview of the LBTI's design and capabilities as a 23 m telescope. In particular, we focus on open loop Fizeau imaging, presenting the state of the art. We measure the stability of the Fizeau PSF, test frame selection criteria, and demonstrate PSF deconvolution. Finally, we outline future developments and synergies with current and upcoming facilities.
• Laugier, R., Martinod, M., Garreau, G., Missiaen, K., Salman, M., Raskin, G., Dandumont, C., Ertel, S., Ireland, M., Kraus, S., Labadie, L., Mazzoli, A., Medgyesi, G., Sanny, A., Absil, O., Berger, J., Bonduelle, M., Bigioli, A., Bouzerand, E., , Carter, J., et al. (2024). L-band nulling interferometry at the VLTI with Asgard/NOTT: status and plans. In Optical and Infrared Interferometry and Imaging IX 2024, 13095.
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  NOTT (formerly Hi-5) is the L'-band (3.5-4.0 µm) nulling interferometer of Asgard, an instrument suite in preparation for the VLTI visitor focus. The primary scientific objectives of NOTT include characterizing (i) young planetary systems near the snow line, a critical region for giant planet formation, and (ii) nearby main-sequence stars close to the habitable zone, with a focus on detecting exozodiacal dust that could obscure Earth-like planets. In 2023-2024, the final warm optics have been procured and assembled in a new laboratory at KU Leuven. First fringes and null measurements were obtained using a Gallium Lanthanum Sulfide (GLS) photonic chip that was also tested at cryogenic temperatures. In this paper, we present an overall update of the NOTT project with a particular focus on the cold mechanical design, the first results in the laboratory with the final NOTT warm optics, and the ongoing Asgard integration activities. We also report on other ongoing activities such as the characterization of the photonic chip (GLS, LiNbO3, SiO), the development of the exoplanet science case, the design of the dispersion control module, and the progress with the self-calibration data reduction software.
• Martinod, M., Ireland, M., Kraus, S., Martinache, F., Tuthill, P., Allouche, F., Bouzerand, E., Bryant, J., Carter, J., Chhabra, S., Courtney-Barrer, B., Crous, F., Cvetojevic, N., Dandumont, C., Ertel, S., Gardner, T., Garreau, G., Glauser, A., Haubois, X., , Labadie, L., et al. (2024). Pushing high angular resolution and high contrast observations on the VLTI from Y to L band with the Asgard instrumental suite: integration status and plans. In Optical and Infrared Interferometry and Imaging IX 2024, 13095.
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  ESO's Very Large Telescope Interferometer has a history of record-breaking discoveries in astrophysics and significant advances in instrumentation. The next leap forward is its new visitor instrument, called Asgard. It comprises four natively collaborating instruments: HEIMDALLR, an instrument performing both fringe tracking and stellar interferometry simultaneously with the same optics, operating in the K band; Baldr, a Strehl optimizer in the H band; BIFROST, a spectroscopic combiner to study the formation processes and properties of stellar and planetary systems in the Y-J-H bands; and NOTT, a nulling interferometer dedicated to imaging nearby young planetary systems in the L band. The suite is in its integration phase in Europe and should be shipped to Paranal in 2025. In this article, we present details of the alignment and calibration unit, the observing modes, the integration plan, the software architecture, and the roadmap to completion of the project.
• Martinod, M., Laugier, R., Ertel, S., Absil, O., Norris, B., Garreau, G., Mennesson, B., & Defrère, D. (2024). Generic data reduction for nulling interferometry package: the grip of a single data reduction package on all the nulling interferometers. In Optical and Infrared Interferometry and Imaging IX 2024, 13095.
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  Nulling interferometry is a powerful observing technique to reach exoplanets and circumstellar dust at separations too small for direct imaging with single-dish telescopes and too large for indirect methods. With near-future instrumentation, it bears the potential to detect young, hot planets near the snow lines of their host stars. A future space mission could detect and characterize a large number of rocky, habitable-zone planets around nearby stars at thermal-infrared wavelengths. The null self-calibration is a method aiming at modelling the statistical distribution of the nulled signal. It has proven to be more sensitive and accurate than average-based data reduction methods in nulling interferometry. This statistical approach opens the possibility of designing a GPU-based Python package to reduce the data from any of these instruments, by simply providing the data and a simulator of the instrument. GRIP is a toolbox to reduce nulling and interferometric data based on the statistical self-calibration method. In this article, we present the main features of GRIP as well as applications on real data.
• Miles, B., Ertel, S., Wagner, K., & Apai, D. (2024). Sensitivity and Performance of LBTI/NOMIC Spectroscopy: Prospects for 10- and 30- meter class Mid-IR Exoplanet Science. In Ground-Based and Airborne Instrumentation for Astronomy X 2024, 13096.
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  Long wavelength infrared (8-13 µm) spectroscopy is invaluable for detecting molecular features in the atmospheres of gas giant and terrestrial exoplanets. The nulling-optimized mid-infrared camera (NOMIC) on the Large Binocular Telescope Interferometer (LBTI) has a low resolution (R∼200) germanium grism that was previously installed but has not been characterized and commissioned for scientific observations. Using a 1.27 mm slit and broadband filter in combination with the grism, the infrared window between 8-13 µm can be captured. We describe initial on sky testing of the LBTI/NOMIC grism mode with adaptive optics to study standard stars and binaries. We discuss the impact of observational strategy and telluric calibration on the spectral reduction process. We infer the impact of existing mid-infrared detectors on NOMIC's spectroscopic mode and discuss requirements to enable higher resolution 8-13 µm spectroscopy on current and future facilities.
• Pedichini, F., Piazzesi, R., Causi, G., Antoniucci, S., Testa, V., Vaccari, P., Farinato, J., Bergomi, M., Mesa, D., Esposito, S., Pinna, E., Cardwell, A., Guerra, J., Power, J., Ertel, S., Montoya, M., Carlson, J., & D’Orazi, V. (2024). Early results from AO assisted visible observations with the new high contrast imager SHARK-VIS at the Large Binocular Telescope. In Adaptive Optics Systems IX 2024, 13097.
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  SHARK-VIS, the Large Binocular Telescope (LBT) optical high-contrast imager, had its first light in October 2023. Thanks to the high performance of the refurbished LBT adaptive optics system SOUL, SHARK-VIS extends the capabilities of one arm of the LBT telescope down to 400 nm, delivering images with a spatial resolution in the order of 20 mas, which in the infrared bands will be achieved only by future Extremely Large Telescopes. This document reports the instrument’s preliminary performance on-sky, which confirms that SHARK-VIS is ready for its main science applications. Specifically, we will show that the instrument is able to provide views of minor bodies and satellites in the Solar System with an unprecedented level of detail and that it achieves contrasts of the order 1e-4 with its H-alpha filter (1nm FWHM) at 150 mas separation from a mag G14 star, even under non-optimal weather conditions.
• Shields, J., Chu, J., Conrad, A., Crass, J., Crepp, J., Ertel, S., Farinato, J., Ilyin, I., Kuhn, O., Marafatto, L., Pedichini, F., Piazzesi, R., Pogge, R., Power, J., Ragland, S., Reynolds, R., Riedl, J., Smithwright, M., Strassmeier, K., & Thompson, D. (2024). The instrumentation program at the Large Binocular Telescope Observatory in 2024. In Ground-Based and Airborne Instrumentation for Astronomy X 2024, 13096.
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  The Large Binocular Telescope, with its expansive collecting area, angular resolving power, and advanced optical design, provides a robust platform for development and operation of advanced instrumentation for astronomical research.The LBT currently hosts a mature suite of instruments for spectroscopy and imaging at optical through mid-infrared wavelengths, supported by sophisticated adaptive optics systems.This contribution summarizes the current state of instrumentation, including upgrades to existing instruments and commissioning of second generation instruments now in progress.The LBT is soliciting proposals for next generation instrument concepts, with participation open to consortium members and others interested in participation in the Observatory.
• Tamura, N., Yabe, K., Koshida, S., Moritani, Y., Tanaka, M., Ishigaki, M., Ishizuka, Y., Kamata, Y., Allaoui, A., Arai, A., Arnouts, S., Barette, R., Barkhouser, R., Bergeron, E., Blanchard, P., Caplar, N., Carle, M., Chabaud, P., Chang, Y., , Chen, H., et al. (2024). Prime Focus Spectrograph (PFS) for the Subaru telescope: Progressing final steps to science operation. In Ground-Based and Airborne Instrumentation for Astronomy X 2024, 13096.
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  The instrumentation of the Prime Focus Spectrograph (PFS), a next generation facility instrument on the Subaru telescope, is now in the final phase of its commissioning process and its general, open-use operations for sciences will provisionally start in 2025.The instrument enables simultaneous spectroscopy with 2386 individual fibers distributed over a very wide (∼1.3 degrees in diameter) field of view on the Subaru's prime focus.The spectra cover a wide range of wavelengths from 380nm to 1260nm in one exposure in the Low-Resolution (LR) mode (while the visible red channel has the Medium-Resolution (MR) mode as well that covers 710−885nm).The system integration activities at the observatory on Maunakea in Hawaii have been continuing since the arrival of the Metrology Camera System in 2018.On-sky engineering tests and observations have also been carried out continually since September 2021 and, despite various difficulties in interlacing commissioning processes with development activities on the schedule and addressing some major issues on hardware and software, the team successfully observed many targeted stars as intended over the entire field of view (Engineering First Light) in September 2022.Then in parallel to the arrival, integration and commissioning of more hardware components, validations and optimizations of the performance and operation of the instrument are ongoing.The accuracy of the fiber positioning process and the speed of the fiber reconfiguration process have been recently confirmed to be ∼ 20−30µm for 95% of allocated fibers, and ∼130 seconds, respectively.While precise quantitative analyses are still in progress, the measured throughput has been confirmed to be consistent with the model where the information from various sub-components and sub-assemblies is integrated.Long integration of relatively faint objects are being taken to validate an expected increase of signal-to-noise ratio as more exposures are taken and co-added without any serious systematic errors from, e.g., sky subtraction process.The PFS science operation will be carried out in a queue mode by default and various developments, implementations and validations have been underway accordingly in parallel to the instrument commissioning activities.Meetings and sessions are arranged continually with the communities of potential PFS users on multiple scales, and discussions are iterated for mutual understanding and possible optimization of the rules and procedures over a wide range of processes such as proposal submission, observation planning, data acquisition and data delivery.The end-to-end processes of queue observations including successive exposures with updated plans based on assessed qualities of the data from past observations are being tested during engineering observations, and further optimizations are being undertaken.In this contribution, a top-level summary of these achievements and ongoing progresses and future perspectives will be provided.
• Conrad, A., Stone, J., & Ertel, S. (2023). Increased sky coverage for the 23-meter LBT. In 7th Adaptive Optics for Extremely Large Telescopes Conference, AO4ELT7 2023.
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  Twin adaptive secondaries at the Large Binocular Telescope (LBT) enable powerful observing modes. Two of these, imaging (Fizeau) interferometry and nulling interferometry, make the LBT in many respects the first Extremely Large Telescope (ELT) [1]. Science programs that have been conducted using LBT as a 23-meter telescope include measuring habitable-zone dust around nearby stars and imaging planets during early stages of formation [2, 3]. To allow LBT to function as a 23-meter telescope, the light from its two 8.4-meter segments must be combined coherently. To this end, the Large Binocular Telescope Interferometer (LBTI) co-phases the two incoming beams via a piezo-electric path length corrector. This device is controlled by a fringe-tracking system that measures optical path difference in real time. Here we describe an upgrade to this system: the Fizeau Fringe Tracking Camera (FFTCam) [4]. New science will be enabled. For example, the number of exosolar systems in Taurus-Auriga that can be probed down to 3.5 AU∗ that can be studied with LBTI will increase by nearly two orders of magnitude.
• Farinato, J., Di Filippo, S., Baruffolo, A., Bergomi, M., Bianco, A., Biondi, F., Briegel, F., Carolo, E., Carlotti, A., Chinellato, S., Conrad, A., De Pascale, M., Dima, M., D’Orazi, V., Ertel, S., Greggio, D., Guerra, J. C., Henning, T., Hill, J. M., , Laudisio, F., et al. (2023). SHARK-NIR, first results of the commissioning at LBT. In 7th Adaptive Optics for Extremely Large Telescopes Conference, AO4ELT7 2023.
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  SHARK-NIR is an instrument which provides direct imaging, both coronagraphic and non-coronagraphic and with the possibility to perform dual-band imaging and low-resolution spectroscopy in Y, J and H bands, with the main scientific goal of detecting exoplanets, and characterizing already known planets, young stellar systems, jets and disks. SHARK-NIR takes advantage of the excellent performance of the Large Binocular Telescope AO systems, the wavefront sensors of which have been recently upgraded to SOUL. The latter is delivering a very good performance also at faint magnitude, opening to science otherwise difficult to be achieved, as for example AGN and QSO morphological studies. To fully exploit the just mentioned science cases, binocular observations will be performed using SHARK-NIR in combination with SHARK-VIS (operating in B, V, R and I bands) and LMIRCam of LBTI (operating from K to M bands), in a way to exploit coronagraphic observations in three different wavelengths. The instrument has passed the preliminary acceptance Europe in March 2022, being shipped immediately after at LBT, and re-integrated, installed and characterized daytime in three pre-commissioning run at the telescoped. SHARK-NIR had a very successful first light in January this year, and we will report of the results obtained in the three commissioning runs performed in the first half of 2023.
• Pinna, E., Rossi, F., Agapito, G., Puglisi, A., Plantet, C., Ghose, E., Bec, M., Bonaglia, M., Briguglio, R., Brusa, G., Carbonaro, L., Cavallaro, A., Christou, J., Durney, O., Hinz, P., Ertel, S., Esposito, S., Grani, P., Guerra, J. C., , Lefebvre, M., et al. (2023). SOUL at LBT: commissioning results, science and future. In 7th Adaptive Optics for Extremely Large Telescopes Conference, AO4ELT7 2023.
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  The SOUL systems at the Large Bincoular Telescope can be seen such as precursor for the ELT SCAO systems, combining together key technologies such as EMCCD, Pyramid WFS and adaptive telescopes. After the first light of the first upgraded system on September 2018, going through COVID and technical stops, we now have all the 4 systems working on-sky. Here, we report about some key control improvements and the system performance characterized during the commissioning. The upgrade allows us to correct more modes (500) in the bright end and increases the sky coverage providing SR(K) > 20% with reference stars GRP < 17, opening to extragalcatic targets with NGS systems. Finally, we review the first astrophysical results, looking forward to the next generation instruments (SHARK-NIR, SHARK-Vis and iLocater), to be fed by the SOUL AO correction.
• Rousseau, H., Ertel, S., Defrère, D., Faramaz, V., & Wagner, K. (2023). Pushing ELT’s sensitivity through PCA background subtraction. In 7th Adaptive Optics for Extremely Large Telescopes Conference, AO4ELT7 2023.
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  The thermal infrared is an important wavelength range for a wide variety of astronomical observations. At these wavelengths, the large ground-based telescopes such as the ELTs reach higher angular resolution than space-based telescopes. However, their sensitivity is limited by the high thermal background due to both photon noise and imperfect removal of background structures from the sky and warm telescope optics. Developing more effective methods for the removal of spatially and temporally variable background structure is paramount for unlocking the full potential of existing and future large and extremely large ground-based telescopes operating at thermal-infrared wavelength. As recent studies have shown, the Principal-Component-Analysis (PCA) method can significantly improve the background subtraction compared to the more common method of subtracting the mean image from dedicated background exposure. We developed and optimized background subtraction routine based on PCA. We used imaging data taken in nulling-interferometric mode from the Large Binocular Telescope Interferometer (LBTI) in the N band (11 µm). The LBTI connects the two aperture of the LBT to form the largest single-mount telescope in the word. This make the LBTI the best place to pioneer data reduction methods and procedures for future ELTs. We present a comparison of classical (mean) and PCA background subtraction for both aperture photometry (mean retrieval and RMS) and high contrast imaging (contrast curves). The PCA background subtraction allows for improvement factors of two to three for both observing techniques. This will allow for improving the sensitivity of suitable, existing data by the same factors. More importantly, it will reduce by a factor five to ten the extremely valuable integration time required to detect faint sources with future ELTs!
• Farinato, J., Baruffolo, A., Bergomi, M., Bianco, A., Biondi, F., Briegel, F., Carolo, E., Carlotti, A., Chavan, S., Chinellato, S., De Pascale, M., Dima, M., D'Orazi, V., Ertel, S., Greggio, D., Henning, T., Laudisio, F., Lessio, L., Magrin, D., , Marafatto, L., et al. (2022). SHARK-NIR, ready to “swim” in the LBT northern hemisphere “ocean”. In Adaptive Optics Systems VIII 2022, 12185.
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  SHARK-NIR is an instrument which provides direct imaging, coronagraphic imaging, dual band imaging and low resolution spectroscopy in Y, J and H bands, taking advantage of the outstanding performance of the Large Binocular Telescope AO systems. Binocular observations will be provided used in combination with SHARK-VIS (operating in V band) and LMIRCam of LBTI (operating from K to M bands), in a way to exploit coronagraphic simultaneous observations in three different wavelengths. A wide variety of coronagraphic techniques have been implemented in SHARK-NIR, ranging from conventional ones such as the Gaussian Lyot, to others quite robust to misalignments such as the Shaped Pupil, to eventually techniques more demanding in term of stability during the observation, as the Four Quadrant; the latter is giving in theory and simulations outstanding contrast, and it is supported in term of stability by the SHARK-NIR internal fast tip-tilt loop and local NCPA correction, which should ensure the necessary stability allowing this technique to operate at its best. The main science case is of course exoplanets search and characterization and young stellar systems, jets and disks characterization, although the LBT AO extreme performance, allowing to reach excellent correction even at very faint magnitudes, may open to science previously difficult to be achieved, as for example AGN and QSO morphological studies. The institutes participating to the SHARK-NIR consortium which designed and built the instrument are Istituto Nazionale di Astro Fisica (INAF, Italy), the Max Planck Institute for Astronomy (MPIA, Heidelberg, Germany) and University of Arizona/Steward Observatory (UoA/SO, Tucson, Az, USA). We report here about the SHARK-NIR status, that should achieve first light at LBT before the end of 2022.
• Stone, J., Skemer, A., Hinz, P., Ertel, S., Briesemeister, Z., Leisenring, J., Durney, O., Montoya, M., Woodward, C., Skrutskie, M., & Barman, T. (2022). On-sky Performance and Results of the Recently Upgraded ALES Integral Field Spectrograph. In Ground-based and Airborne Instrumentation for Astronomy IX 2022, 12184.
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  The Arizona Lenslets for Exoplanet Spectroscopy (ALES) is an integral field spectrograph implemented with a modular design comprising magnifiers, a lenslet array, and direct-vision prisms all installed in filterwheels within the LBTI/LMIRCam instrument. ALES is unique among high-contrast instruments for providing spatially resolved spectroscopy out to 5 microns. ALES has been operating with an upgraded lenslet array and prism assembly since late 2018. The new lenslet array includes larger lenslets to reduce diffraction losses and spatial crosstalk in the data. The lenslet array is fabricated with a unique sag surface for each lenslet, correcting for rotating off-axis astigmatism in the magnified intermediate focal plane. The result is tighter lenslet spots and better data. The new prism assembly provides increased spectral resolution in the 2.9 to 4.2 micron wavelength range. Here we characterize the performance of upgraded ALES, and report initial results probing the atmospheres of high-contrast companions to nearby stars. A calibration and data pre-processing strategy unique to the upgraded instrument is discussed. We also report laboratory tests of additional future upgrades including prism and blocking filter pairs for added bandpasses and magnification modes to facilitate Fizeau interferometry with LMIRCam and ALES.
• Wagner, K., Ertel, S., Stone, J., Leisenring, J., Apai, D., Kasper, M., Absil, O., Close, L., Defrère, D., Guyon, O., & Males, J. (2021). Imaging low-mass planets within the habitable zones of nearby stars with ground-based mid-infrared imaging. In Techniques and Instrumentation for Detection of Exoplanets X 2021, 11823.
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  Giant exoplanets on 10-100 au orbits have been directly imaged around young stars. The peak of the thermal emission from these warm young planets is in the near-infrared (a1/41-5 μm), whereas mature, temperate exoplanets (i.e., those within their stars' habitable zones) radiate primarily in the mid-infrared (mid-IR: A1/410 μm). If the background noise in the mid-IR can be mitigated, then exoplanets with low masses-including rocky exoplanets-can potentially be imaged in very deep exposures. Here, we review the recent results of the Breakthrough Watch/New Earths in the Alpha Centauri Region (NEAR) program on the Very Large Telescope (VLT) in Chile. NEAR pioneered a ground-based mid-IR observing approach designed to push the capabilities for exoplanet imaging with a specific focus on the closest stellar system, Centauri. NEAR combined several new optical technologies-including a mid-IR optimized coronagraph, adaptive optics system, and rapid chopping strategy to mitigate noise from the central star and thermal background within the habitable zone. We focus on the lessons of the VLT/NEAR campaign to improve future instrumentation specifically on strategies to improve noise mitigation through chopping. We also present the design and commissioning of the Large Binocular Telescope's Exploratory Survey for Super-Earths Orbiting Nearby Stars (LESSONS), an experiment in the Northern hemisphere that is building on what was learned from NEAR to further push the sensitivity of mid-IR imaging. Finally, we briefly discuss some of the possibilities that mid-IR imaging will enable for exoplanet science.
• Anugu, N., Morzinski, K. M., Eisner, J., Douglas, E., Marrone, D., Ertel, S., Haffert, S., Montoya, O., Stone, J., Kraus, S., Monnier, J., Lebouquin, J., Berger, J., Woillez, J., & Montarg{\`es}, M. (2020, aug). Betelgeuse scope: single-mode-fibers-assisted optical interferometer design for dedicated stellar activity monitoring. In Interferometry XX, 11490.
• Conrad, A. l., Walsh, S., Miller, D., Zhang, Y., Ertel, S., & Bec, M. (2020, dec). A program to monitor and improve routine AO operations. In Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 11448.
• Defr{\`ere}, D., Absil, O., Berger, J. -., Danchi, W., Dandumont, C., Eisenhauer, F., Ertel, S., Gardner, T., Glauser, A., Hinz, P., Ireland, M., Kammerer, J., Kraus, S., Labadie, L., Lacour, S., Laugier, R., Loicq, J., Martin, G., Martinache, F., , Martinod, M., et al. (2020, dec). Review and scientific prospects of high-contrast optical stellar interferometry. In Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 11446.
• Ertel, S. (2020, oct). Thermal infrared imaging with LBTI's LMIRCAM and NOMIC. In Ground-Based Thermal Infrared Astronomy - Past.
• Ertel, S., Hinz, P. M., Stone, J. M., Vaz, A., Montoya, O. M., West, G. S., Durney, O., Grenz, P., Spalding, E. A., Leisenring, J., Wagner, K., Anugu, N., Power, J., Maier, E. R., Defr{\`ere}, D., Hoffmann, W., Perera, S., Brown, S., Skemer, A. J., , Mennesson, B., et al. (2020, dec). Overview and prospects of the LBTI beyond the completed HOSTS survey. In Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 11446.
• Kirchschlager, F., Ertel, S., Wolf, S., Matter, A., & Krivov, A. (2020, oct). First L band detection of hot exozodiacal dust with VLTI/MATISSE. In Ground-Based Thermal Infrared Astronomy - Past.
• Perera, S., Pott, J., Woillez, J., Kulas, M., Brandner, W., Lacour, S., Widmann, F., Ertel, S., & Vaz, A. (2020, dec). Testing P-REx on VLTI data. In Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 11446.
• Hinz, P., Danchi, W. C., Defrere, D., Ertel, S., Kennedy, G. M., & Mennesson, B. (2019). The LBTI HOSTS Project: Instrumentation, Observations, and Results of the Survey of Exo-zodiacal Dust of >30 Nearby Stars. In 2019 IEEE Aerospace Conference, 2019-.
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  The Large Binocular Telescope Interferometer (LBTI) is a stellar interferometer consisting of two 8.4-m apertures on a 14.4 m baseline on a common mount at Mt. Graham, Arizona. The Hunt for Observable Signatures of Terrestrial Systems (HOSTS) is a NASA key project for the LBTI surveying the warm and hot dust in the inner regions of planetary systems, near the habitable zone (HZ) and closer in, commonly described as being ‘exo-zodiacal,’ analogous to the zodiacal light in our Solar System. The presence of large amounts of dust in the HZs of nearby stars poses a significant challenge for target selection and planning of future exo-Earth imaging missions. The HOSTS survey on the LBTI is designed to determine typical exozodi levels around a sample of nearby, bright main sequence stars. The LBTI operates in a nulling mode in the mid-infrared spectral window ( $8-13\ \epsilon\mathrm{m}$ ), in which light from the two telescopes is coherently combined with a 180-degree phase shift between them, producing a dark fringe at the location of the target star. In doing so the starlight is greatly reduced, increasing the contrast, analogous to a coronagraph operating at shorter wavelengths. The LBTI is a unique instrument, having only three warm reflections before the starlight reaches cold mirrors, giving it the best photometric sensitivity of any interferometer operating in the mid-infrared. It also has a superb Adaptive Optics (AO) system giving it Strehl ratios greater than 98% at $10\ \epsilon\mathrm{m}$ . Thus, nulling interferometry suppresses the bright stellar light and allows for the detection of faint, extended circumstellar dust emission. In this paper we present statistical results from 38 individual stars. We provide important new insights into the incidence rate, typical levels, and origin of HZ dust around main sequence stars. Our overall detection rate is 23%. While the inferred occurrence rates are comparable for early type and Sun-like stars, but decrease from [71 (+11/−20)] % for stars with previously detected mid to far infrared excess to [11 (+9/−4)]% for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 11.5 zodis (95% confidence) for all stars without cold dust and of 16 zodis when focussing on Sun-like stars without cold dust. We find first hints of a bimodal distribution where some stars have high HZ dust levels but the majority have dust levels below our sensitivity. Our results demonstrate the strength of LBTI for vetting potential targets for future exo-Earth imaging missions.
• Pinna, E., Rossi, F., Puglisi, A., Agapito, G., Bonaglia, M., Plantet, C., Mazzoni, T., Briguglio, R., Carbonaro, L., Xompero, M., Grani, P., Riccardi, A., Esposito, S., Hinz, P., Vaz, A., Ertel, S., Montoya, O. M., Durney, O., Christou, J., , Miller, D. L., et al. (2019). Bringing soul on sky. In 6th International Conference on Adaptive Optics for Extremely Large Telescopes, AO4ELT 2019.
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  The SOUL project is upgrading the 4 SCAO systems of LBT, pushing the current guide star limits of about 2 magnitudes fainter thanks to Electron Multiplied CCD detector. This improvement will open the NGS SCAO correction to a wider number of scientific cases from high contrast imaging in the visible to extra-galactic source in the NIR. The SOUL systems are today the unique case where pyramid WFS, adaptive secondary and EMCCD are used together. This makes SOUL a pathfinder for most of the ELT SCAO systems like the one of GMT, MICADO and HARMONI of E-ELT, where the same key technologies will be employed. Today we have 3 SOUL systems installed on the telescope in commissioning phase. The 4th system will be installed in a few months. We will present here the results achieved during daytime testing and commissioning nights up to the present date.
• Spalding, E., Hinz, P., Morzinksi, K., Ertel, S., Grenz, P., Maier, E., Stone, J., & Vaz, A. (2019, sep). Status of commissioning stabilized infrared Fizeau interferometry with LBTI. In Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 11117.
• Booth, M., Su, K., Macgregor, M., Wilner, D., Matr{\`a}, L., Flaherty, K., Hughes, M., Phillips, N., Malhotra, R., Hales, A., Morrison, S., Kral, Q., Ertel, S., Matthews, B., Dent, W., & Casassus, S. (2018, jul). Dust and Gas in the HD 95086 Planetary System. In Diversis Mundi: The Solar System in an Exoplanetary Context.
• Defr{\`ere}, D., Ireland, M., Absil, O., Berger, J. -., Danchi, W., Ertel, S., Gallenne, A., H{\'enault}, F., Hinz, P., Huby, E., Kraus, S., Labadie, L., Le, B., Martin, G., Matter, A., Mennesson, B., M{\'erand}, A., Minardi, S., Monnier, J., , Norris, B., et al. (2018, jul). Hi-5: a potential high-contrast thermal near-infrared imager for the VLTI. In Optical and Infrared Interferometry and Imaging VI, 10701.
• Ertel, S., Kennedy, G., Defr{\`ere}, D., Hinz, P., Shannon, A., Mennesson, B., Danchi, W., Gelino, C., Hill, J., Hoffman, W., Rieke, G., Spalding, E., Stone, J., Vaz, A., Weinberger, A., Willems, P., Absil, O., Arbo, P., Bailey, V., , Beichman, C., et al. (2018, jul). The HOSTS survey for exo-zodiacal dust: preliminary results and future prospects. In Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave, 10698.
• Maier, E., Hinz, P., Defr{\`ere}, D., Ertel, S., & Downey, E. (2018, jul). A two-band approach to n\ensuremath{\lambda} phase error corrections with LBTI's PHASECam. In Optical and Infrared Interferometry and Imaging VI, 10701.
• Spalding, E., Hinz, P., Ertel, S., Maier, E., & Stone, J. (2018, jul). Towards controlled Fizeau observations with the Large Binocular Telescope. In Optical and Infrared Interferometry and Imaging VI, 10701.
• Danchi, W., Bailey, V., Bryden, G., Defr{\`ere}, D., Ertel, S., Haniff, C., Hinz, P., Kennedy, G., Mennesson, B., Millan-Gabet, R. .., Rieke, G., Roberge, A., Serabyn, E., Skemer, A., Stapelfeldt, K., Weinberger, A., Wyatt, M., & Vaz, A. (2016, aug). Enabling the direct detection of earth-sized exoplanets with the LBTI HOSTS project: a progress report. In Optical and Infrared Interferometry and Imaging V, 9907.
• Defr{\`ere}, D., Hinz, P., Downey, E., B{\"ohm}, M., Danchi, W., Durney, O., Ertel, S., Hill, J., Hoffmann, W., Mennesson, B., Millan-Gabet, R. .., Montoya, M., Pott, J. -., Skemer, A., Spalding, E., Stone, J., & Vaz, A. (2016, aug). Simultaneous water vapor and dry air optical path length measurements and compensation with the large binocular telescope interferometer. In Optical and Infrared Interferometry and Imaging V, 9907.
• Hinz, P., Defr{\`ere}, D., Skemer, A., Bailey, V., Stone, J., Spalding, E., Vaz, A., Pinna, E., Puglisi, A., Esposito, S., Montoya, M., Downey, E., Leisenring, J., Durney, O., Hoffmann, W., Hill, J., Millan-Gabet, R. .., Mennesson, B., Danchi, W., , Morzinski, K., et al. (2016, aug). Overview of LBTI: a multipurpose facility for high spatial resolution observations. In Optical and Infrared Interferometry and Imaging V, 9907.
• Defrere, D., Ertel, S., Absil, O., Danchi, W., Eiroa, C., Greaves, J., Hinz, P., Grant, K., Leger, A., Roberge, A., Stapelfeldt, K., & Wolf, S. (2015, jul). SatMeet6- Prevalence of exozodiacal dust. In Pathways Towards Habitable Planets.
• Ertel, S., Augereau, J. -., Th{\'ebault}, P., Absil, O., Bonsor, A., Defr{\`ere}, D., Kral, Q., Le, B., Lebreton, J., & Foresto}, V. (2014, jan). Unraveling the Mystery of Exozodiacal Dust. In Exploring the Formation and Evolution of Planetary Systems, 299.
• Faramaz, V., Beust, H., Augereau, J. -., Bonsor, A., Th{\'ebault}, P., Wu, Y., Marshall, J., Burgo, C., Ertel, S., Eiroa, C., Montesinos, B., & Mora, A. (2014, jan). Planetary Systems Dynamics Eccentric patterns in debris disks \& Planetary migration in binary systems. In Exploring the Formation and Evolution of Planetary Systems, 299.
• Labadie, L., Matter, A., Kreplin, A., Lopez, B., Wolf, S., Weigelt, G., Ertel, S., Berger, J., Pott, J., & Danchi, W. C. (2014, jul). HD 139614: the interferometric case for a group-Ib pre-transitional young disk. In Optical and Infrared Interferometry IV, 9146.
• Marion, L., Absil, O., Ertel, S., Le, B., & Defr{\`ere}, D. (2014, jul). Unveiling new stellar companions from the PIONIER exozodi survey. In Optical and Infrared Interferometry IV, 9146.
• Montesinos, B., Liseau, R., Absil, O., Ardila, D., Augereau, J. C., Barrado, D., Bayo, A., Beichman, C., Bryden, G., Danchi, W., del Burgo, C., Eiroa, C., Ertel, S., Fedele, D., Fridlund, M., Fukagawa, M., González, B. M., Grun, E., Heras, A. M., , Kamp, I., et al. (2014). The chromosphere of α Cen A as seen by the herschel space observatory. In 11th Scientific Meeting of the Spanish Astronomical Society - Highlights of Spanish Astrophysics VIII, SEA 2014.
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  Chromospheres and coronae are common phenomena on solar-type stars. Understanding the heating of those layers requires the direct access to the relevant empirical data. In particular, the chromospheric temperature minimum, i.e. the region of the atmosphere where the temperature undergoes a reversal and starts increasing to reach values of the order of MK in the corona, can be observed directly in the far infrared and in the submillimetre spectral regime. In this paper we present the results of the observations obtained in those ranges of the solar twin α Cen A. Similar to the Sun, the far infrared emission of this star originates in the temperature minimum above the stellar photosphere. To our knowledge, this is the first time a temperature minimum has been directly measured on a main-sequence star other than the Sun. This contribution is a summary of the the results presented in “α Centauri in the far infrared. First measurements of the temperature minimum of a star other than the Sun” [9] based on results from the Herschel Open Time Key Project DUNES and APEX/LABOCA observations.
• M{\'erand}, A., Abuter, R., Aller-Carpentier, E., Andolfato, L., Alonso, J., Berger, J., Blanchard, G., Boffin, H., Bourget, P., Bristow, P., Cid, C., Wit, W., Valle, D., Delplancke-Str{\"obele}, F., Derie, F., Faundez, L., Ertel, S., Grellmann, R., Gitton, P., , Glindemann, A., et al. (2014, jul). VLTI status update: a decade of operations and beyond. In Optical and Infrared Interferometry IV, 9146.
• Ertel, S., Augereau, J., Thebault, P., Absil, O., Bonsor, A., Defrere, D., Kral, Q., Le, B. J., Lebreton, J., & Foresto, V. (2013, jul). Unraveling the mystery of exozodiacal dust. In Protostars and Planets VI Posters.
• Matter, A., Labadie, L., Kreplin, A., Lopez, B., Wolf, S., Weigelt, G., Ertel, S., Pott, J., & Danchi, W. C. (2013, jul). Evidence of a discontinuous inner disk structure around the Herbig star HD 139 614. In Protostars and Planets VI Posters.
• Absil, O., Defr{\`ere}, D., Le, B. J., Mollier, B., Augereau, J., Foresto}, V., Di, F. E., Ertel, S., & Brummelaar, T. (2012, jul). Studying hot exozodiacal dust with near-infrared interferometry. In Optical and Infrared Interferometry III, 8445.
• Meusinger, H., Henze, M., Birkle, K., Pietsch, W., Williams, B., Hatzidimitriou, D., Nesci, R., Ertel, S., Hinze, A., Bertold, T., & Kaminsky, B. (2012, dec). A unique UV flare in the optical light curve of the quasar J004457.9+412344. In European Physical Journal Web of Conferences, 39.
• Ertel, S., Wolf, S., Eiroa, C., Augereau, J. -., Metchev, S., Schneider, G., Silverstone, M., & Rodmann, J. (2011, oct). Modeling the spatial structure of debris disks. In EPSC-DPS Joint Meeting 2011, 2011.

Others

• Gaspar, A., Apai, D., Augereau, J., Ballering, N. P., Beichman, C. A., Boccaletti, A., Booth, M., Bowler, B. P., Bryden, G., Chen, C. H., Currie, T., Danchi, W. C., Debes, J., Defr{\`ere}, D., Ertel, S., Jackson, A. P., Kalas, P. G., Kennedy, G. M., Kenworthy, M. A., , Kim, J. S., et al. (2019, may). Modeling Debris Disk Evolution. \baas.
• Mennesson, B., Bailey, V., Kasdin, J., Trauger, J., Absil, O., Akeson, R., Armus, L., Baudino, J., Baudoz, P., Bellini, A., Bennett, D., Berriman, B., Boccaletti, A., Calchi-Novati, S. .., Carpenter, K., Chen, C., Danchi, W., Debes, J., Defrere, D., , Ertel, S., et al. (2019, sep). The Potential of Exozodiacal Disks Observations with the WFIRST Coronagraph Instrument. arXiv e-prints.
• Mennesson, B., Kennedy, G., Ertel, S., Wyatt, M., Defr{\`ere}, D., Debes, J., Stark, C., Kasdin, J., Macintosh, B., Hinz, P., Bailey, V., Stapelfeldt, K., Mawet, D., Scott, N., Roberge, A., Lisse, C., Lyra, W., Hasegawa, Y., Gaspar, A., , Danchi, W., et al. (2019, may). Interplanetary dust around main sequence stars: origin, magnitude, and implications for exoplanet habitability searches. \baas.
• Su, K., Ballering, N., Ertel, S., Gaspar, A., Kennedy, G., Leisawitz, D., MacGregor, M., Matthews, B., Moro-Martin, A., Rieke, G., White, J., Wilner, D., & Wyatt, M. (2019). Probing Unseen Planet Populations with Resolved Debris Disk Structures.