Uwe Fink

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• Fink, U., & Rubin, M. (2012). The calculation of Afρ and mass loss rate for comets. Icarus, 221(2), 721-734.
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  Abstract: Ab initio calculations of Afρ are presented using Mie scattering theory and a Direct Simulation Monte Carlo (DSMC) dust outflow model in support of the Rosetta mission and its target 67P/. Churyumov-Gerasimenko (CG). These calculations are performed for particle sizes ranging from 0.010. μm to 1.0. cm. The present status of our knowledge of various differential particle size distributions is reviewed and a variety of particle size distributions is used to explore their effect on Afρ, and the dust mass production m A new simple two parameter particle size distribution that curtails the effect of particles below 1. μm is developed. The contributions of all particle sizes are summed to get a resulting overall Afρ. The resultant Afρ could not easily be predicted a priori and turned out to be considerably more constraining regarding the mass loss rate than expected. It is found that a proper calculation of Afρ combined with a good Afρ measurement can constrain the dust/gas ratio in the coma of comets as well as other methods presently available. Phase curves of Afρ versus scattering angle are calculated and produce good agreement with observational data.The major conclusions of our calculations are:. -The original definition of A in Afρ is problematical and Afρ should be: q sca(n, λ) × p(g) × f × ρ.Nevertheless, we keep the present nomenclature of Afρ as a measured quantity for an ensemble of coma particles.-The ratio between Afρ and the dust mass loss rate m is dominated by the particle size distribution.-For most particle size distributions presently in use, small particles in the range from 0.10 to 1.0μm contribute a large fraction to Afρ.-Simplifying the calculation of Afρ by considering only large particles and approximating q sca does not represent a realistic model. Mie scattering theory or if necessary, more complex scattering calculations must be used.-For the commonly used particle size distribution, dn/da∼a -3.5 to a -4, there is a natural cut off in Afρ contribution for both small and large particles.-The scattering phase function must be taken into account for each particle size; otherwise the contribution of large particles can be over-estimated by a factor of 10.-Using an imaginary index of refraction of i=0.10 does not produce sufficient backscattering to match observational data.-A mixture of dark particles with i0.10 and brighter silicate particles with i0.04 matches the observed phase curves quite well.-Using current observational constraints, we find the dust/gas mass-production ratio of CG at 1.3 AU is confined to a range of 0.03-0.5 with a reasonably likely value around 0.1. © 2012 Elsevier Inc.
• Coradini, A., Capaccioni, F., Erard, S., Arnold, G., Sanctis, M. D., Filacchione, G., Tosi, F., Barucci, M. A., Capria, M. T., Ammannito, E., Grassi, D., Piccioni, G., Giuppi, S., Bellucci, G., Benkhoff, J., Bibring, J. P., Blanco, A., Blecka, M., Bockelee-Morvan, D., , Carraro, F., et al. (2011). The surface composition and temperature of asteroid 21 lutetia as observed by Rosetta/VIRTIS. Science, 334(6055), 492-494.
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  PMID: 22034430;Abstract: The Visible, InfraRed, and Thermal Imaging Spectrometer (VIRTIS) on Rosetta obtained hyperspectral images, spectral reflectance maps, and temperature maps of the asteroid 21 Lutetia. No absorption features, of either silicates or hydrated minerals, have been detected across the observed area in the spectral range from 0.4 to 3.5 micrometers. The surface temperature reaches a maximum value of 245 kelvin and correlates well with topographic features. The thermal inertia is in the range from 20 to 30 joules meter -2 kelvin -1 second -0.5, comparable to a lunarlike powdery regolith. Spectral signatures of surface alteration, resulting from space weathering, seem to be missing. Lutetia is likely a remnant of the primordial planetesimal population, unaltered by differentiation processes and composed of chondritic materials of enstatitic or carbonaceous origin, dominated by iron-poor minerals that have not suffered aqueous alteration.
• Coradini, A., Grassi, D., Capaccioni, F., Filacchione, G., Tosi, F., Ammannito, E., Sanctis, M. D., Formisano, V., Wolkenberg, P., Rinaldi, G., Arnold, G., Barucci, M. A., Bellucci, G., Benkhoff, J., Bibring, J. P., Blanco, A., Bockelee-Morvan, D., Capria, M. T., Carlson, R., , Carsenty, U., et al. (2010). Martian atmosphere as observed by VIRTIS-M on Rosetta spacecraft. Journal of Geophysical Research E: Planets, 115(4).
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  Abstract: The Rosetta spacecraft accomplished a flyby of Mars on its way to 67P/Churyumov-Gerasimenko on 25 February 2007. In this paper we describe the measurements obtained by the M channel of the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS-M) and the first scientific results derived from their analysis. The broad spectral coverage of the VIRTIS-M in the IR permitted the study of various phenomena occurring in the Martian atmosphere; observations were further exploited to achieve accurate absolute radiometric calibration. Nighttime data from the VIRTIS-M constrain the air temperature profile in the lower atmosphere (5-30 km), using variations in CO2 opacity at 4.3 mm. A comparison of this data with the global circulation model (GCM) by Forget et al. (1999) shows a trend of slightly higher air temperature in the VIRTIS-M retrievals; this is accompanied by the presence of moderate decreases (∼5 K) in large sections of the equatorial region. This is potentially related to the occurrence of water ice cl uds. Daytime data from the VIRTIS-M reveal CO 2 non-local thermodynamic equilibrium emission in the high atmosphere. A mapping of emission intensity confirms its strict dependence on solar zenith angle. Additionally, devoted limb observations allowed the retrieval of vertical emission intensity profiles, indicating a peak around 105 km in southern tropical regions. Ozone content can be effectively monitored by the emission of O2 (a1Δg) at 1.27 μm. Retrieved emission intensity shows that polar regions are particularly rich in ozone. Aerosol scattering was observed in the 1-2.5 μm region above the night region above the night disk, suggesting the occurrence of very high noctilucent clouds. Copyright 2010 by the American Geophysical Union.
• Fink, U. (2009). A taxonomic survey of comet composition 1985-2004 using CCD spectroscopy. Icarus, 201(1), 311-334.
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  Abstract: A summary is presented of our spectroscopic survey of comets extending for roughly 19 years from 1985 to 2004 comprising data for 92 comets of which 50 showed good emissions. All data were re-analyzed using consistent reduction techniques. Our observations of comets over several apparitions and comets observed over an extended period indicate no major changes in compositional classification. To our regret, no major unidentified cometary features were found in our surveyed spectral region of 5200-10400 Å. Absolute production rates for the dominant parent molecule H2O and the daughter species C2, NH2 and CN are determined within the limits of the Haser model as are values for the dust continuum, Afρ. From these data, production rate ratios are calculated for C2/H2O, NH2/H2O, CN/H2O and Afρ/H2O. Excluding the odd Comets Yanaka (1988r), 43P/Wolf-Harrington and 19P/Borrelly, with unusual spectra, our set of comets exhibited relatively uniform composition. Detailed analyses of our data resulted in four taxonomic classes:-Comets of typical composition (∼70%); exhibiting typical ratios with respect to water of C2, NH2, and CN.-Tempel 1 type (∼22%); having a deficiency in C2 but normal NH2 abundance.-G-Z type (∼6%); having both low C2 and NH2 ratios.-The unusual object Yanaka (1988r) (∼2%?); no detectable C2 or CN emission but normal NH2. It is uncertain whether there is a clear separation between the comets of typical composition and those with C2 depletion, or whether the latter consists of a group showing a continuum of decreasing C2/CN ratios. Our spectroscopic investigations result in a visual record of the various compositional classes, which are illustrated in a number of figures. Production rate comparisons with the comet photometry program of Schleicher and A'Hearn [A'Hearn, M.F., and 4 colleagues, 1995. Icarus 118, 223-270] for 13 comets in common yielded good agreement once the different scale lengths are taken into account. An investigation into the possible origin of our compositional groups with respect to dynamical families of comets shows that the Halley family exhibits essentially no C2 depletion. These objects were presumably formed in the region of Saturn and Uranus and scattered into the Oort cloud. Comets formed in the space near Neptune, responsible for the scattered Kuiper Belt show a mixture of "typical" and C2 depleted objects, while we associate comets formed in-situ in the classical Kuiper belt with our C2 depleted group. © 2009 Elsevier Inc. All rights reserved.
• Fink, U. (2009). How tempel 1 fits into the ensemble of comets: A spectrosopic perspective. ESO Astrophysics Symposia, 2009, 311-316.
• Coradini, A., Capaccioni, F., Drossart, P., Arnold, G., Ammannito, E., Angrilli, F., Barucci, A., Bellucci, G., Benkhoff, J., Bianchini, G., Bibring, J. P., Blecka, M., Bockelee-Morvan, D., Capria, M. T., Carlson, R., Carsenty, U., Cerroni, P., Colangeli, L., Combes, M., , Combi, M., et al. (2007). Virtis: An imaging spectrometer for the Rosetta mission. Space Science Reviews, 128(1-4), 529-559.
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  Abstract: The VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe for Planetary Exploration. VIRTIS, developed in cooperation among Italy, France and Germany, has been already selected as a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison - using the same combination of sophisticated experiments - of targets that are poorly differentiated and are representative of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the "in situ" measurements will provide "ground-truth" for the remote sensing information, and, in turn, the locally collected data will be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures - such as the typical spectral bands of minerals and molecules - arising from surface components and from materials dispersed in the coma. The identification of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied. © Springer Science+Business Media, Inc. 2007.
• Fevig, R. A., & Fink, U. (2007). Spectral observations of 19 weathered and 23 fresh NEAs and their correlations with orbital parameters. Icarus, 188(1), 175-188.
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  Abstract: Results of our visible to near-infrared spectrophotometric observations of 41 near-Earth asteroids (NEAs) are reported. These moderate-resolution spectra, along with 14 previously published spectra from our earlier survey [Hicks, M.D., Fink, U., Grundy, W.M., 1998. Icarus 133, 69-78] show a preponderance of spectra consistent with ordinary chondrites (23 NEAs with this type of spectrum, along with 19 S-types and 13 in other taxonomic groups). There exists statistically significant evidence for orbit-dependent trends in our data. While S-type NEAs from our survey reside primarily in (1) Amor orbits or (2) Aten or Apollo orbits which do not cross the asteroid main-belt, the majority of objects with spectra consistent with ordinary chondrites in our survey are in highly eccentric Apollo orbits which enter the asteroid main-belt. This trend toward fresh, relatively unweathered NEAs with ordinary chondrite type spectra in highly eccentric Apollo orbits is attributed to one or a combination of three possible causes: (1) the chaotic nature of NEA orbits can easily result in high eccentricity orbits/large aphelion distances so that they can enter the collisionally enhanced environment in the main-belt, exposing fresh surfaces, (2) they have recently been injected into such orbits after a collision in the main-belt, or (3) such objects cross the orbits of several terrestrial planets, causing tidal disruption events that expose fresh surfaces. © 2006 Elsevier Inc. All rights reserved.
• Dusseau, L., Vaillé, J., Saigne, F., Gasiot, J., Cresciucci, L., Campillo, D., Chatry, C., Fink, U., Gruenenfelder, J., Calvel, P., & Gayrard, J. D. (2005). CUBE SAT SACRED: A student project to investigate radiation effects. Proceedings of the European Conference on Radiation and its Effects on Components and Systems, RADECS, H21-H24.
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  Abstract: The SACRED project is a nano-satellite designed by students to study the radiation effects on electronic devices in flight. The mission goals, the expected environment and the payload experiment are described.
• Lisse, C. M., A'Hearn, M., Farnham, T. L., Groussin, O., Meech, K. J., Fink, U., & Schleicher, D. G. (2005). The coma of comet 9P/Tempel 1. Deep Impact Mission: Looking Beneath the Surface of a Cometary Nucleus, 161-192.
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  Abstract: As comet 9P/Tempel 1 approaches the Sun in 2004-2005, a temporary atmosphere, or coma, will form, composed of molecules and dust expelled from the nucleus as its component icy volatiles sublimate. Driven mainly by water ice sublimation at surface temperatures T > 200 K, this coma is a gravitationally unbound atmosphere in free adiabatic expansion. Near the nucleus (≤10 2 km), it is in collisional equilibrium, at larger distances (≥104 km) it is in free molecular flow. Ultimately the coma components are swept into the comet's plasma and dust tails or simply dissipate into interplanetary space. Clues to the nature of the cometary nucleus are contained in the chemistry and physics of the coma, as well as with its variability with time, orbital position, and heliocentric distance. The DI instrument payload includes CCD cameras with broadband filters covering the optical spectrum, allowing for sensitive measurement of dust in the comet's coma, and a number of narrowband filters for studying the spatial distribution of several gas species. DI also carries the first near-infrared spectrometer to a comet flyby since the VEGA mission to Halley in 1986. This spectrograph will allow detection of gas emission lines from the coma in unprecedented detail. Here we discuss the current state of understanding of the 9P/Tempel 1 coma, our expectations for the measurements DI will obtain, and the predicted hazards that the coma presents for the spacecraft. © 2005 Springer.
• Lisse, C. M., A'Hearn, M., Farnham, T. L., Groussin, O., Meech, K. J., Fink, U., & Schleicher, D. G. (2005). The coma of comet 9P/Tempel 1. Space Science Reviews, 117(1-2), 161-192.
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  Abstract: As comet 9P/Tempel 1 approaches the Sun in 2004-2005, a temporary atmosphere, or "coma," will form, composed of molecules and dust expelled from the nucleus as its component icy volatiles sublimate. Driven mainly by water ice sublimation at surface temperatures T > 200 K, this coma is a gravitationally unbound atmosphere in free adiabatic expansion. Near the nucleus (≤ 102 km), it is in collisional equilibrium, at larger distances (≥104 km) it is in free molecular flow. Ultimately the coma components are swept into the comet's plasma and dust tails or simply dissipate into interplanetary space. Clues to the nature of the cometary nucleus are contained in the chemistry and physics of the coma, as well as with its variability with time, orbital position, and heliocentric distance. The DI instrument payload includes CCD cameras with broadband filters covering the optical spectrum, allowing for sensitive measurement of dust in the comet's coma, and a number of narrowband filters for studying the spatial distribution of several gas species. DI also carries the first near-infrared spectrometer to a comet flyby since the VEGA mission to Halley in 1986. This spectrograph will allow detection of gas emission lines from the coma in unprecedented detail. Here we discuss the current state of understanding of the 9P/Tempel 1 coma, our expectations for the measurements DI will obtain, and the predicted hazards that the coma presents for the spacecraft. © Springer 2005.
• Fink, U., & Combi, M. R. (2004). The effect of using different scale lengths on the production rates of Comet 46P/Wirtanen. Planetary and Space Science, 52(7), 573-580.
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  Abstract: The variations in production rates for Comet 46P/Wirtanen for the species H2O and the parents of C2 and CN are examined from the point of view of a variety of commonly used scale lengths. The calculations are carried out as a function of heliocentric distance. It is shown that, by using a common set of scale lengths, the results of various investigators can be brought into acceptable accord. The resulting production rates of H 2O and the parents of C2 and CN versus heliocentric distance are recalculated and plotted versus the heliocentric distance r H. The curves show reasonable agreement with a slope of ∼r H-4. The water production rate near perihelion of 46P/Wirtanen is close to 2 × 1028 mol s-1. © 2003 Elsevier Ltd. All rights reserved.
• Fink, U., Hicks, M. P., & Fevig, R. A. (1999). Production rates for the stardust mission target: 81P/Wild 2. Icarus, 141(2), 331-340.
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  Abstract: We observed 81P/Wild 2 from February 01 to June 01, 1997, during five observing runs spaced roughly 1 month apart straddling perihelion 1997 May 06.6. A considerable volume of spectroscopic data was collected and is analyzed in the present paper. In units of 1025 molecules/s the following gas production rates were measured: H2O, 1500; CN, 3.3; NH2, 4.0; C2, ≤0.9. Emissions by C2 appear to be present in our data but this is not certain. The gas production stayed relatively constant throughout our observation period but the dust production as measured by Afρdropped from 564 to 311 cm. Comparison with other comets in our sample shows that Wild 2 is a Borrelly-type comet depleted in C2, but with average to slightly high NH2 abundance. Our imaging data indicate noticeable coma activity around February 01 followed by relatively constant outgassing. Our V+R magnitudes are compared with visual data and their different behavior is discussed and explained. The comet's visual magnitude brightness dependence shows a steep 25 log rH dependence, indicating a mature crust. © 1999 Academic Press.
• Coradini, A., Capaccioni, F., Drossart, P., Semery, A., Arnold, G., Schade, U., Angrilli, F., Barucci, M. A., Bellucci, G., Bianchini, G., Bibring, J. P., Blanco, A., Blecka, M., Bockelee-Morvan, D., Bonsignori, R., Bouye, M., Bussoletti, E., Capria, M. T., Carlson, R., , Carsenty, U., et al. (1998). VIRTIS: An imaging spectrometer for the ROSETTA mission. Planetary and Space Science, 46(9-10), 1291-1304.
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  Abstract: The VIRTIS scientific and technical teams will take advantage of their previous experience in the design and development of spectrometers for space applications. In fact, the various groups contributing to the VIRTIS experiment, from Italy, France and Germany, have been deeply involved in the CASSINI mission, with the experiments VIMS and CIRS. The targets of the ROSETTA mission are the most primitive solar system bodies: comets and asteroids. ROSETTA will study in detail a comet nucleus, the prime target of the mission, and will fly by one or two asteroids. The small bodies of the solar system are of great interest for planetary science and their study is crucial to understand the solar system formation. In fact it is believed that comets and, to a lesser extent, asteroids underwent a moderate evolution so that they preserve some pristine solar system material. Comets and asteroids are in close relationship with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The global characterisation of one comet nucleus and one or two asteroids will provide basic information on the origin of the solar system and on the interrelation between the solar system and the interstellar dust environment. The ROSETTA mission is designed to obtain the above mentioned scientific goals by: (a) in situ analysis of comet material; (b) long period of remote sensing of the comet. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the "in situ" measurements will give relevant "ground-truth" for the remote sensing information, and, in turn, the locally collected data will be interpreted in the appropriate scenario provided by remote sensing investigation. The scientific payload of ROSETTA includes a Visual InfraRed Spectral and Thermal Spectrometer (VIRTIS) among the instrument on board the spacecraft orbiting around the comet. This instrument is fundamental to detect and study the evolution of specific fingerprints - such as the typical spectral bands of minerals and molecules - arising from surface components and from materials dispersed in the coma. Their identification is a primary goal of the ROSETTA mission as it will allow us to identify the nature of the main constituent of the comets. Moreover, the surface thermal evolution during comet approach to Sun is important information that can be obtained by means of spectroscopic observation. The VIRTIS design and its detailed science goals are reported hereafter. © 1998 Elsevier Science Ltd. All rights reserved.
• Fink, U., Hicks, M. D., Fevig, R. A., & Collins, J. (1998). Spectroscopy of 46 P/Wirtanen during its 1997 apparition. Astronomy and Astrophysics, 335(2), L37-L45.
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  Abstract: Comet 46P/Wirtanen was observed during five observing runs around its perihelion passage from 1997 January 28 to June 02. The spectra acquired extend from 5200 to 10000 Å at spectral resolutions of 12 Å and 18Å. A total of 16 spectral averages, each comprising about 40 minutes of integration time, were obtained. The production rate of H2O near perihelion averaged 2.7 × 1028 molecules/sec. The continuum strength Afρ was 129 cm while the production rates respectively of the parents of C2, CN and NH2 were 5.7, 3.2 and 5.6 × 1025 molecules/sec. Our estimated error for all these quantities is 20%. The production rate ratios relative to water can be compared to our larger sample of comets (Fink & Hicks 1996) with the following results: the C2 and CN abundance ratios are slightly below average but the NH2 ratio is definitely enhanced putting P/Wirtanen among the top few comets in that category. Its Afρ/H2O ratio is very close but slightly below the median of our comet sample. Reduced to 1 AU P/Wirtanen ranks near the 40% level of our ordered list of the H2O production rates of 20 comets. If the production rate of water is combined with P/Wirtanen's estimated radius of 0.6 km, it implies that virtually the whole surface area of the comet is active. Our measured Afρ values combined with those obtained by photometry yield a fairly tight heliocentric activity dependence of r-3.8 with no pre-post perihelion asymmetry. This agrees well with the general heliocentric brightness dependence of Jupiter family comets. Taking all this data together, P/Wirtanen appears to be a rather typical member of the Jupiter family of comets.
• Hicks, M. D., Fink, U., & Grundy, W. M. (1998). The Unusual Spectra of 15 Near-Earth Asteroids and Extinct Comet Candidates. Icarus, 133(1), 69-78.
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  Abstract: We present moderate resolution reflectance spectra from 0.55 to 1.0 μm for 15 near-Earth asteroids and extinct cometary nuclei candidates obtained at the Catalina Station 1.54-m telescope near Tucson, Arizona. Though our limited wavelength coverage often makes firm classification difficult, an analysis of our measurements reveals that there is an over-representation of asteroids with unusually deep 0.9- to 1-μm absorption features. Several of our objects have spectra consistent with Q-type asteroids and within the limits of our signal-to-noise ratio, are compatible with a chondritic composition. It is apparent that the near-Earth asteroids as a population have an unusual taxonomic distribution, one that is much closer to that of meteoritic falls than may have been previously assumed. © 1998 Academic Press.
• Combi, M. R., & Fink, U. (1997). A critical study of molecular photodissociation and chon grain sources for cometary C₂. Astrophysical Journal Letters, 484(2), 879-890.
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  Abstract: The spatial distribution of C2 in the very inner comae of comets (< 104 km) often shows a profile which is flatter than can be reproduced by standard two-generation models. Because of this it has been suspected that a source other than the typical two-generation photodissociation is responsible. Previous investigators have suggested that either grains, most likely CHON grains, or a three-generation photodissociation may the source for cometary C2. We have performed an analysis of a set of spatial profiles of C2 in comet P/Halley to investigate this question. A three-generation dissociation model that unlike previous attempts can include the ejection velocity of daughter fragments at each dissociation is compared with published results of a purely radial three-generation model. We find that the addition of ejection velocities has a similar effect on three-generation models as has been shown already in two-generations by the vectoral and Monte Carlo models. Specifically, the addition of typical ejection velocities which are usually on the order of 1 km s-1 for a heavy species essentially fills in the "hole" in the inner coma which would otherwise be left by three-generation models that are purely radial, yielding profiles that are not easily distinguishable from two-generation model (Haser, vectorial, or Monte Carlo). We have also constructed a CHON Grain Halo (CGH) model that also produces flat inner profiles. The inferred size of the CGH is 88,000 km at 1 AU. This is consistent with some estimates of the depletion of small grains in comet Halley but is much larger than the extended source for H2CO and CO (∼104 km). The strict r2 variation for the heliocentric distance dependence for the C2 source is better explained by a direct CGH source. A combination of either grandparent-parent molecule scale lengths or grandparent CHON grains and an intermediate molecule would yield parent scale length variations closer to r1.5 (more like CN and NH2) than r2 which is found for C2. © 1997. The American Astronomical Society. All rights reserved.
• Combi, M. R., DiSanti, M. A., & Fink, U. (1997). The spatial distribution of gaseous atomic sodium in the comae of comets: Evidence for direct nucleus and extended plasma sources. Icarus, 130(2), 336-354.
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  Abstract: Sodium D-line emission (5890 and 5896 Å) has been observed in bright comets at small to moderate heliocentric distances for many years. We present here the first in depth study of a set of spatial profiles of the sodium D-line emission constructed from long-slit spectroscopic observations of Comets Bennett C/1969 Y1, Kohoutek C/1973 D1, and 1P/Halley. Preliminary analysis of these data lead to the suggestion by Combiet al.(1996,A Plasmagenic Source for Gaseous Sodium in Comets.Presented at Asteroids, Comets, Meteors) that a major fraction of the gaseous sodium was produced by an extended source in the tail and that the source was likely to be some charged species. Dissociative recombination of a molecular ion was suggested. The spatial profiles of sodium are not like typical neutral species. The inner region from the nucleus (
• Fink, U., Fevig, R. A., Tegler, S. C., & Romanishin, W. (1997). CCD imaging and photometry of 46P/Wirtanen during October 1996. Planetary and Space Science, 45(11), 1383-1387.
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  Abstract: During the period of 96 Oct. 7.16 to Oct. 12.14 comet P/Wirtanen was observed with our CCD system at the 154 cm Catalina Observatory telescope at a heliocentric distance near 2.1 AU. The comet exhibited a coma of about 7 in ia diameter with a tail of about 14 in. The observed B, V and R magnitudes within a 9.3 in diameter aperture were 19.94, 19.11 and 18.73, respectively. The large majority of our observations were carried out with a filter combining the V and R passbands (V + R). The average V + R magnitudes for Oct. 7.16, 8.14, 9.12 and 10.15, respectively, were 18.91, 18.87, 18.87 and 18.86, the data did not allow the extraction of a lightcurve but hopefully can be used in conjunction with other observations to constrain the comet's rotation period. An attempt to separate the nucleus contribution from the coma resulted in an upper limit to the nuclear magnitude of ≈20.6 in V + R at a phase of 26° or ≈19.6 at 0° phase angle. This results in an upper limit of 1.2 km for the comet's radius assuming a geometric albedo of 0.04. Calculating the Afp yielded a value of 7 cm which is a factor of 170 smaller than P/Halley at a comparable heliocentric distance and phase angle. Making the simple assumption that the comet's activity is proportional to its surface area makes the surface area of Wirtanen about 2.4 km2, equivalent to an effective radius of ≈0.44 km. © 1997 Published by Elsevier Science Ltd. All rights reserved.
• Hicks, M. D., & Fink, U. (1997). Spectrophotometry and the development of emissions for C/1996 B2 (Comet Hyakutake). Icarus, 127(2), 307-318.
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  Abstract: An analysis of the spectrophotometry of C/1996 B2 (Hyakutake) from 0.55 μm to 1.05 μm recorded between February 17 and April 17, 1996, is presented. We derive Afρ values and production rates of H2O, C2, NH2, and CN. In general we find the Haser model to be substantiated with no inconsistencies for different aperture sizes and different heliocentric and geocentric distances. Comet Hyakutake is the dustiest comet in our database of 39 comets (U. Fink and M. Hicks 1996.Astrophys. J.459,729-743) and both the dust and the H2O production rates follow a heliocentric dependence of ~r-1.5, lower than the ~r-2.5dependence found for P/Halley by U. Fink (1994.Astrophys. J.423,461-472). The Afρ values and the H2O production rates track the visual lightcurve quite well. Strong evidence for quenching of OI emissions close to the nucleus was observed in the March data due to the comet's small geocentric distance. While the CN production rate also has a dependence of ~r-1.5with a CN/H2O ratio typical of most comets, the C2production rate has a much steeper slope, ~r-2.5, and the C2/H2O ratio evolves from a typical cometary ratio to one that is exceedingly rich in C2. We feel that this is evidence for a significant CHON contribution to the overall C2production. The NH2production is considerably flatter and follows roughly a ~r-0.85law. In February and March, Comet Hyakutake exhibited the highest relative NH2abundance of any comet in our database, but reverts to more a normal value in April. All together, we feel that the behavior of the comet's Afρ and production rates throughout its apparition argue for a more primordial comet than may be suggested by the orbital elements alone. © 1997 Academic Press.
• Sprague, A. L., Kozlowski, R. W., Hunten, D. M., Schneider, N. M., Domingue, D. L., Wells, W. K., Schmitt, W., & Fink, U. (1997). Distribution and abundance of sodium in Mercury's atmosphere, 1985-1988. Icarus, 129(2), 506-527.
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  Abstract: We report spectroscopic measurements of sodium in Mercury's atmosphere for the period July 1985-May 1988. Na abundance varies from
• Tegler, S. C., Romanishin, W., Stone, A., Tryka, K., Fink, U., & Fevig, R. (1997). Photometry of the Trans-Neptunian Object 1993 SC. Astronomical Journal, 114(3), 1230-1233.
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  Abstract: We obtained broadband photometry of the Trans-Neptunian Object 1993 SC with the Steward Observatory 1.5-m telescope near Mt. Bigelow, Arizona and the Lunar and Planetary Laboratory CCD on 1996 October 8. 1993 SC exhibited a constant brightness (V= 22.67) with a 1σ scatter about the average of 0.06 magnitudes during a five hour interval. In addition, we obtained observations of 1993 SC with the Steward Observatory 2.3-m telescope on Kitt Peak, Arizona during 1995 November 24-27. Once again 1993 SC exhibited a constant brightness (V= 22.73) with a 1σ scatter about the average of 0.04 magnitude. If 1993 SC has a lightcurve, the amplitude must be at the level of 0.12 magnitude or less. If the obliquity of 1993 SC is near zero degrees, then 1993 SC is spherical with a semi-major to semi-minor axis ratio less than or equal to 1.12. A spherical nature for 1993 SC may be the result of self-gravity exceeding the tensile strength of the material in the interior of 1993 SC. If the obliquity of 1993 SC is large, then 1993 SC could have an irregular shape. The steady intrinsic brightness for 1993 SC suggests that the object has a relatively uniform surface albedo. Our photometry and the assumption of a comet-like albedo (0.04) indicates that the diameter of 1993 SC is ∼240 km. © 1997 American Astronomical Society.
• Fink, U., & Hicks, M. D. (1996). A survey of 39 comets using CCD spectroscopy. Astrophysical Journal Letters, 459(2 PART I), 729-743.
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  Abstract: An analysis of our spectra of 39 comets from 0.55 to 1.0 μm collected over the last decade is presented. All spectra were obtained with the 154 cm Mount Bigelow telescope of the University of Arizona Observatories, using our fast f/1.2 spectrograph and an 800 × 800 TI CCD detector. Roughly 21 of the objects observed displayed emissions while the other 18 simply yielded a continuum, although three of these gave a suggestion of possible CN emission. Emission fluxes were measured for the Δν = - 1 C2 Swan band, the 0,10,0 and 0,8,0 NH2 bands, the O I 1D line at 6300 Å and the red CN system 2-0 and 1-0 bands. From these fluxes, production rates for the parents of C2, NH2, O I, and CN were determined and mixing ratios of the parents of C2, NH2, and CN with respect to H2O were calculated. We estimate our standard deviation error in these numbers to be about 10%. We find that about 10% of the comets have deviant composition with the most common being the P/Giacobini-Zinner class and the most unusual represented by Yanaka (1988r). The other 90% of our comet sample shows reasonably uniform mixing ratios with maximum comet-to-comet variations of a factor of 2-3 and a standard deviation of ∼ 30%. No distinct compositional classes could be discerned within that group. We interpret the observed spread in production rate ratios as chemical composition variations between individual comets and a measure of the nonuniformity of the solar nebula during the time of the solar system formation. © 1996. The American Astronomical Society. All rights reserved.
• Fink, U., Rostalski, H. -., & Hirsch, H. (1996). Applications of holographic gratings to two-dimensional spectroscopy. Applied Optics, 35(7), 1047-1055.
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  PMID: 21085214;Abstract: Calculations are presented for a set of aberration-corrected holographic concave gratings for possible use in space mission instruments. It is concluded that, for the visible range 0.26-1.02 μm when detectors with a 15-μm pixel size are used, a total field of view of ∼1° is possible at an aperture of f/7.0. For the infrared regions 0.9-2.5 μm and 2.4-4.2 μm, in which detector arrays have larger pixel sizes of 30-40 μm, a spatial field of view of ∼2° at f/7.0 and ∼1.0° at f/3.5 can be achieved. An exploration of spectrum lengths showed that performance starts to fall off sharply for lengths over 15 mm at a focal length of 150 mm (i.e., a spectral angular extent of ∼6°). © 1996 Optical Society of America.
• Grundy, W. M., & Fink, U. (1996). Synoptic CCD spectrophotometry of Pluto over the past 15 years. Icarus, 124(1), 329-343.
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  Abstract: Over the 15 years from 1980 to 1994, the same spectrometer has been used to obtain spectrophotometric observations of Pluto+Charon over the wavelength range from 0.5 to 1.0 μm. This time period spanned Pluto's perihelion passage in 1989, as well as the Pluto-Charon mutual event season. The data set is presented and a search made for variations in Pluto's methane absorptions and continuum slope correlating with Pluto's 6.4-day lightcurve as well as possible longer term secular evolution. Four quantities derived from Pluto's spectrum are examined for variation with Pluto's rotational phase. Although the depths of the methane bands are generally deeper away from the lightcurve minimum, they are found not to correlate in a simple way with the lightcurve, in contrast with the behavior of the stronger methane bands at longer wavelengths. This behavior implies that Pluto's CH4 is not exclusively associated with the brightest or the darkest terrain, and that weak and strong methane bands are sensitive to different methane reservoirs on Pluto's surface. The wavelengths of CH4 bands also change, being longest at the rotational phases where the CH4 bands are deepest. The wavelength shifts can be attributed to variable concentration of CH4 dissolved in N2 ice. No statistically significant trend of bandwidth with longitude is detected. It is confirmed that the reddest slope of the continuum coincides with the darkest surface terrain. Examining spectral data pairs taken at similar Pluto longitudes, a modest but consistent secular trend is seen, with the depth of the 0.73 -μm CH4 absorption diminishing relative to that of the stronger 0.89-μm band. The observations are interpreted by means of Hapke scattering models. While unique solutions are not possible, it is found that the observed spectra can be matched by geographically diverse models possessing both methane rich and methane poor terrains. Terrain types proposed are a high albedo, CH4 poor, N2 dominated surface, a dark, red, tholin-rich surface, and a transitional zone, rich in CH4, with an intermediate albedo. The slight secular weakening of the 0.73-μm CH4 band can be interpreted as resulting from differences between Pluto's southern and northern hemispheres or from a temporal evolution in the geographic proportions of the CH4 rich and CH4 poor terrains. © 1996 Academic Press, Inc.
• Magnusson, P., Dahlgren, M., Barucci, M. A., Jorda, L., Binzel, R. P., Slivan, S. M., Blanco, C., Riccioli, D., Buratti, B. J., Colas, F., Berthier, J., Angelis, G. D., Martino, M. D., Dotto, E., Drummond, J. D., Fink, U., Hicks, M., Grundy, W., Wisniewski, W., , Gaftonyuk, N. M., et al. (1996). Photometric observations and modeling of asteroid 1620 Geographos. Icarus, 123(1), 227-244.
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  Abstract: Photometric observations of 1620 Geographos in 1993 and 1994 are presented and, in combination with previously published data, are used to derive models of Geographos. We estimate that the sidereal period of rotation is 0.21763860 ± 0.00000003 days (5h13m23.975s ± 0.003s). The sense of rotation is retrograde. The ecliptic coordinates of the spin angular velocity vector are estimated to λp = 56° ± 6° and βp = -47° ± 4° (equinox J2000.0). The lightcurve amplitudes are well-explained by an ellipsoidal model with axis ratios a/b = 2.58 ± 0.16 and b/c = 1.00 ± 0.15. Models that have one or both ends more sharply pointed than the ellipsoid improve the fit to the observations. There are no significant indications of albedo variegation, but non-geometric scattering effects are tentatively suggested based on significant rotational color variation. © 1996 Academic Press, Inc.
• Cosmovici, C. B., Schwarz, G., Ip, W. H., & Fink, U. (1995). Imaging of H₂O⁺ in the coma of comet Halley. Planetary and Space Science, 43(6), 699-703.
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  Abstract: Previous investigations applying the "ring masking" technique to CCD images obtained at the South African Observatory in the period 13-18 March 1986, led to the detection of CN, C2, C3 and ([OI] + NH2) jet features in the coma of comet Halley (Cosmovici et al., Nature 332, 705-709, 1988). In complement to these results we report here the detection of new features in water ion emission at 6193 Å which may be used as a tracer for the time-dependent anisotropic emission profile of the water vapour from the cometary nucleus. South Africa images, as well as Catalina Observatory data with identical filters on 20 January and 7, 8 and 24 March 1986, are utilized in order to exclude instrumental errors. Because of the narrow bandwidth of the filter (6192±44 Å) other significant molecular contaminations are considerably reduced. The observed peculiar H2O features can be explained by the stronger H2O+/dust contrast in the ion tail or by a possible mechanism of negative charging of the dust in the cometary coma. © 1995.
• Hicks, M., Grundy, W., Fink, U., Mottola, S., & Neukum, G. (1995). Rotationally Resolved Spectra of 1620 Geographos. Icarus, 113(2), 456-459.
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  Abstract: We present CCD spectra (0.54-0.98 μm) as a function of rotational phase of the Clementine target 1620 Geographos. We confirm the asteroid's S-type taxonomic classification (more precisely, SII-SIII). The surface mineral assemblage appears to be a metal and pyroxene/olivine mixture. Though our spectral observations sampled the rotational lightcurve well, we were unable to detect significant color variations across the surface of the asteroid. © 1995 Academic Press. All rights reserved.
• Rodrigue, M., Schultz, A., Thompson, J., Colegrove, T., Spight, L. D., Disanti, M., Fink, U., Grundy, W., Fricke, K., & Papaderos, P. (1995). A multiwavelength investigation of the merging galaxy HCG 95C. Astronomical Journal, 109(6), 2362-2367.
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  Abstract: The compact group HCG 95 consists of four galaxies in which two of the members, HCG 95a and HCG 95c, are interacting. The morphology suggests the interaction is well evolved with the Northern tidal arm of HCG 95c overlapping the Eastern edge of HCG 95a. A linear bridge connecting the two galaxies hints at nuclear activity within HCG 95c. Our color indices indicate an older stellar population for both HCG 95a and HCG 95c, with the exception of the Northern tidal arm of HCG 95c. Long slit spectra of HCG 95a exhibits red-shifted H-alpha +[N II] and [S II] emission lines indicative of a LINER-type AGN. Spatial profiles indicate non-nuclear starburst activity triggered by tidal forces, while the nuclear spectrum indicates nonthermal activity. IUE observations of HCG 95c exhibit a featureless continuum with a transient outburst captured in one IUE observation which shows characteristic galactic emissions of red-shifted N V (1240 Å) and C IV (1550 Å). These results suggest that HCG 95c is in an early stage of merging with HCG 95a. © 1995 American Astronomical Society.
• Combi, M., Huang, B., Cochran, A., Fink, U., & Schulz, R. (1994). Time-dependent analysis of 8 days of CN spatial profiles in comet P/Halley. Astrophysical Journal Letters, 435(2), 870-873.
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  Abstract: CN profiles in comet P/Halley were constructed from observations taken at three observatories during an 8 day period in April 1986. These data provide a time series of CN spatial profiles spanning just over one 7.37 day period from 1986 April 7 to April 15 and sample distances from the nucleus from just over 103 km to 106 km. The effect of the 7.37 day periodic variation on the CN distribution in P/Halley has been examined by using the time-dependent model applied earlier to a subset of the data. Because of the large spatial scale of the data on April 7, 8, and 9 (∼106 km), and the corresponding transport time in the coma, information present in the spatial profiles regarding the gas production rate actually covers nearly two full periods. These spatially extended profiles clearly show the wavy structures outside 105 km. Such structures were predicted in a previous analysis (Combi & Fink 1993) that was based solely on the photometric light curve and on profiles which only extended to distances less than 105 km. We are now able to reproduce the highly variable Halley CN profiles using the same model as before, with the same standard scale lengths, phase lag, and amplitude correction for the variation in gas production rate.
• Fink, U. (1994). The trend of production rates with heliocentric distance for comet P/Halley. Astrophysical Journal Letters, 423(1), 461-473.
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  Abstract: Comet P/Halley was observed spectroscopically in the wavelength range 5200-10,400 Å during 10 observing runs, roughly a month apart from 1985 August 28 to 1986 June 6. The observations span a heliocentric distance from 0.73 to 2.52 AU. This data set is analyzed to determine the course of the production rate with heliocentric distance for C2, NH2, CN, and the continuum. The effect of changing the Haser scale lengths and their heliocentric distance dependence is examined. The production rate ratios to water change only in a minor way, but the absolute values of the production rates are more severly affected. Fluorescent efficiencies, or g-factors for the CN red system are calculated, and band intensity ratios for NH2 and CN are presented. Using presently available fluorescence efficiencies and Haser scale lengths, mixing ratios for the parents of C2, CN, and NH2 with respect to water are: 0.34 ± 0.07%, 0.15 ± 0.04%, and 0.13 ± 0.05%. It is found that these mixing ratios are essentially constant over the heliocentric distance range of the observations, implying a rather uniform nucleus and uniform outgassing characteristics, although there are indications of smaller scale day-to-day variations. The results provide strong observational confirmation that water evaporation controls the activity of the comet over the distance range studied. Continuum values Afρ are determined, and their ratios to QH2O are found to have a clear dependence with heliocentric distance ∼r̄1.0 with a post-perihelion enhancement. No correlation of the production rate ratios with light curve of P/Halley were found, nor was there any correlation of the C2 or CN production with the dust.
• Combi, M. R., & Fink, U. (1993). P/Halley: Effects of time-dependent production rates on spatial emission profiles. Astrophysical Journal Letters, 409(2), 790-797.
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  Abstract: Spatial profiles of C2, CN, NH2, and O(1D) in comet P/Halley taken on 1986 March 1.54 and 2.55 and April 14.32 and 15.30 clearly show the effect of the 7 day periodic variation seen in photometric observations. With a time-dependent model based upon the light curve and employing standard scale lengths for each species reduced to the appropriate heliocentric distance, we are able to reproduce the highly variable profiles for all species. We computed the phase lag and amplitude correction between the actual gas production at the nucleus and the temporal/spatial filter imposed by the finite aperture photometry. For early March we find a phase lag and amplitude correction of 12 hr and -9%, respectively, whereas in mid-April the values are 6 hr and -27%. The same phase lag and amplitude correction work equally well for all four species despite their wide variation in photochemical lifetimes for production and decay. The same model integrated over circular apertures is able to reproduce the entire published March and April photometric light curves for C2. Our results require the use of the 7.60 day period for the March data as opposed to the 7.37 day period that is relevant for the April data, in agreement with the published analysis of the photometric data. Our results will help to reconcile the placement of active areas on the surface of Halley's comet with various remote observations and spacecraft images of the nucleus.
• Fink, U. (1992). Comet Yanaka (1988r): A new class of carbon-poor comet. Science, 257(5078), 1926-1929.
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  Abstract: As part of a program to determine the chemical composition of a sample population of comets, a very unusual comet, Yanaka (1988r), was observed in January 1989. Although the comet showed the usual emissions of OI and NH 2, it did not display any hint of C2 or CN emission. The comet is depleted in C2 by at least a factor of 100 and in CN by a factor of 25 relative to typical comets. If comets originate from interstellar clouds, Yanaka (1988r) could be an interloper from a cloud of different composition. If Yanaka (1988r) was formed within our solar system, the solar nebula was less uniform than assumed by most present models of formation.
• Fink, U., Hoffmann, M., Grundy, W., Hicks, M., & Sears, W. (1992). The steep red spectrum of 1992 AD: An asteroid covered with organic material?. Icarus, 97(1), 145-149.
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  Abstract: A spectrum of the newly discovered asteroid 1992 AD (now numbered 5145) was obtained by us with our CCD camera and spectrometer 1992 February 01.23. The reflection spectrum of 1992 AD displays a very steep and constant red slope between 0.5 and 1.0 μm and exhibits no absorption nor emission features. The red slope is steeper than that of any presently known Solar System object. The reflectivity ratio between 1.0 and 0.55 μm is a factor of 3.5 (1.36 magnitudes), or using a slight extrapolation, a factor of 4.90 (1.72 magnitudes) for the wavelength octave 1.0 to 0.5 μm. The steep red slope is difficult to match with conventional silicate or meteoritic materials. While allotropes of sulfur may give a partial match, the best match is provided by the steep red spectra of mixtures of tholins, the residues left after subjecting organic molecules to an energetic radiation environment. © 1992.
• Larson, H. P., Timmermann, R., & Fink, U. (1992). High resolution observations of the 2.125-μm feature in Io's spectrum during 1975 and 1976. Icarus, 95(2), 325-328.
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  Abstract: We confirm the presence of a weak absorption feature in Io's spectrum at 2.125 μm using high resolution observations acquired in 1975 and 1976. If this feature is due to a new class of material on Io, it appears to be the only diagnostic spectral feature of it anywhere in those regions of Io's near-IR spectrum that are accessible at groundbased telescopes. We cannot definitively assign the feature to any atom or molecule. © 1992.
• Marcialis, R. L., Lebofsky, L. A., Disanti, M. A., Fink, U., Tedesco, E. F., & Africano, J. (1992). The albedos of Pluto and Charon: Wavelength dependence. Astronomical Journal, 103(4), 1389-1394.
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  Abstract: The 1987 March 03 occultation of Charon by Pluto was monitored simultaneously with three telescopes in the vicinity of Tucson, Arizona. Each site covered a distinct wavelength interval, with the total range spanning 0.44-2.4 μm. Observing the same event ensures an identical Sun-Pluto-Earth geometry for all three sites, and minimizes the assumptions which must be made to combine results. We have used this spectrophotometry to derive the individual geometric albedos of Pluto and Charon over a factor of ≥5 in wavelength. Combining our results with those of Binzel [Science, 241, 1070 (1988)], we obtain improved (B - V) color estimates (on the "Johnson Pluto" system) for the components of the system at rotational phase 0.75: (Pluto + Charon) = 0.843 ± 0.006; Pluto alone = 0.866 ± 0.007; and Charon alone = 0.702 ± 0.010.
• Tegler, S. C., Burke, L. F., Wyckoff, S., Womack, M., Fink, U., & Disanti, M. (1992). NH₃ and NH₂ in the coma of comet Brorsen-Metcalf. Astrophysical Journal Letters, 384(1), 292-297.
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  Abstract: Narrow-band CCD images of comet Brorsen-Metcalf have been obtained using interference filters (fwhm = 20 Å) centered at λ = 6250 and 6338 Å to isolate continuum and NH2 (8-0) Ã2A1-X̃2B1 emission, respectively. The 6338 Å images corrected for background sky and dust-scattered solar continuum isolate the NH2 coma in the comet. The distribution of NH2 is symmetric and shows no evidence for jet structure at the 3 σ significance level above background emission. An azimuthal average of the NH2 image produces an NH2 surface brightness profile for comet Brorsen-Metcalf which gives a factor of ∼ 10 improvement in the signal-to-noise ratio over previous one-dimensional long-slit NH2 observations, and provides a significant constraint on the NH2 photodissociation time scale in comets. A Monte Carlo simulation of the comet coma assuming that NH3 is the primary source of NH2 is described and compared with the observations. The effects on the surface brightness distribution of NH2 due to (1) collisions in the inner coma and (2) non-steady state production rates were investigated with the Monte Carlo model. For an observed production rate, Q(H2 O) ∼ 7 × 1028 molecules s-1, collisional effects on the NH3 and NH2 outflow had at most a ∼ 10% effect on the NH2 surface brightness profile. The models also indicate that large variations in the gas production rate on time scales ∼ τNH2 could cause significant differences from the steady state profiles. Because comet Brorsen-Metcalf showed no significant dust or gas production rate variability, we argue that steady state conditions best match the comet at the time of observations. We find for steady state conditions and a recently revised NH2 photodissociation time scale, τNH2 ∼ 3.3 × 104 s at 1 AU, a satisfactory match between the observed and computed NH2 surface brightness profiles. For a steady state model with τNH2 ∼ 5.0 × 104 s at 1 AU the observations are fitted to an estimated accuracy of ∼ 10%. We conclude that NH3 is probably the dominant source of NH2 in the coma of comet Brorsen-Metcalf. The conclusive identification of the NH2 percursor in comets will require (1) the direct detection of NH3 , (2) observations of NH2 emission over several successive nights to monitor possible production rate variations, or (3) accurate experimental photodissociation cross sections for NH2.
• DiSanti, M. A., & Fink, U. (1991). Composition comparison between Comets P/Halley and P/Brorsen-Metcalf. Icarus, 91(1), 105-111.
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  Abstract: Comet P/Brorsen-Metcalf was observed at heliocentric and geocentric distances very similar to those of Comet P/Halley. Notable differences in both absolute production rates and relative composition were found. Production rate ratios were derived without recourse to a model, thus minimizing model-dependent uncertainties. It was found that the active sun produces 1.23 times more OI 6300-Å flux than the quiet sun for equal H2O production rates. Taking this effect into account, the water production rate of Comet P/Brorsen-Metcalf was about 15% that of P/Halley, for the same heliocentric distance. Even more severe was the depletion in the continuum flux, which was a factor of 20 weaker for P/Brorsen-Metcalf than for P/Halley, when both were compared with their respective H2O production rates. The relative abundances of NH2, C2 and CN, again compared with H2O, were about 41, 75, and 70% that of Comet P/Halley. Both the C2 and CN abundances did not increase as quickly with decreasing heliocentric distances as for P/Halley, which is probably linked to their partial origin from the dust which was so much weaker for P/Brorsen-Metcalf. © 1991.
• Fink, U., Combi, M. R., & Disanti, M. A. (1991). Comet P/Halley: Spatial distributions and scale lengths for C₂, CN, NH₂, and H₂O. Astrophysical Journal Letters, 383(1), 356-371.
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  Abstract: Spatial profiles were obtained for emissions by C2, CN, NH2, and O I (1D) from comet P/Halley long-slit spectroscopic exposures on 12 dates, extending from 1985 October to 1986 May. Haser model scale lengths were fitted to these data. The extended time coverage allowed us to check for consistency between the various dates. Not unexpectedly, the time varying production rate of P/Halley severely affected the profiles after perihelion. This is demonstrated in two profile sequences on adjacent dates, March 1/2 and April 14/15. Because of the time-varying production rate, it was difficult to obtain reliable Haser model scale lengths after perihelion. Our preperihelion analysis yielded Haser model scale lengths of sufficient consistency that they can be used for production rate determinations. For C2 a slight flattening of the profiles close to the nucleus could not be fitted with a two-step Haser model. If the inner region is excluded from the fit, the daughter/parent scale length ratio changes from near 1 to about 6 which is close to previous results from other comets. However, when production rates are sought using a two-step Haser algorithm, only an equal scale-length model comes close to providing an acceptable fit. Only three observations yielded CN daughter scale lengths because our profiles did not extend sufficiently far. Additionally, the long daughter of CN makes this emission very sensitive to production rate variations causing greater scatter in the parent values. The preperihelion data where the effects of time-varying production rate were minimal yielded a parent of 24 × 103 km in agreement with previous values. A curious asymmetry of the scale lengths was exhibited by NH2, with the postperihelion parent being about twice the preperihelion value, but the daughter being less than half the preperihelion number. A Swings effect, as occurs for the OH lifetime, is the best explanation for this behavior. The average parent scale lengths found for NH2 are consistent with photodissociation lifetimes for NH3 and the dissociation chain NH3 → NH2 → NH is corroborated. Most of the O I 1D profiles, which effectively map out the comet's H2O distribution, deviated very little from a 1/r falloff so that it was not possible to obtain a reliable H2O parent scale length, although consistency with the nominal lifetime of 80 × 103 s is demonstrated.
• Grundy, W. M., & Fink, U. (1991). A new spectrum of Triton near the time of the Voyager encounter. Icarus, 93(2), 379-385.
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  Abstract: We present a new spectrum of Triton from 5200 to 10,000 Å in which the 8900-Å methane ice absorption band can be clearly seen and accurately measured. The data were obtained during the summer of 1989, just before the Voyager II spacecraft encountered the Neptune system. By combining data from the spacecraft with our telescopic data, we have shown that the absorption is entirely caused by CH4 ice on Triton's surface. We have modeled Triton's spectrum with a simple Hapke-type model which allowed us to set a 20-μm lower limit on the mean grain size of methane ice on Triton. We feel that the true grain size is probably somewhat larger, of the order 100 μm. Our model has led us to believe that methane ice is widely distributed on the surface of Triton's southern hemisphere. If CH4 condenses together with N2, the CH4 must be significantly more concentrated relative to N2 in the surface ice than it is in Triton's atmosphere. © 1991.
• Grundy, W. M., & Fink, U. (1991). The absorption coefficient of the liquid N₂ 2.15-μm band and application to triton. Icarus, 93(1), 169-173.
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  Abstract: We have measured the temperature dependence of the absorption coefficient and integrated absorption of the liquid nitrogen 2.15-μm (4647 cm-1) 2-0 collision-induced band. The integrated absorption of the liquid is observed to be smaller than that of the gas, and decreases slightly with decreasing temperature. The band gets sharper with decreasing temperature with a half-width proportional to the square root of the temperature. If this temperature-dependent behavior is extrapolated to the nominal surface temperature of Triton, a new estimate of the grain size of N2 ice on Triton's south polar cap can be made. We employ Hapke scattering theory with previously published IR spectra of Triton to estimate a mean nitrogen grain size of between 0.7 and 3 cm. This results is consistent with results from grain growth rate calculations. © 1991.
• Schneider, N. M., Hunten, D. M., Wells, W. K., Schultz, A. B., & Fink, U. (1991). The structure of Io's corona. Astrophysical Journal Letters, 368(1), 298-315.
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  Abstract: A spatial profile of the distribution of sodium in Io's corona has been constructed using measurements obtained during satellite mutual eclipses. The data reveal a fairly symmetric corona whose density falls steeply from the surface out to 6 rIo and more slowly outside. An upper limit of 700 km is placed on the exobase altitude, but the observations do not constrain the surface density. Several theoretical models adequately match some traits of the corona, but none satisfies all the observations. No strong upstream/downstream asymmetry of the corona is observed, so it is unlikely that the corona is primarily generated by the impact of corotating ions into the trailing hemisphere.
• Disanti, M. A., Fink, U., & Schultz, A. B. (1990). Spatial distribution of H₂O⁺ in comet P/Halley. Icarus, 86(1), 152-171.
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  Abstract: An analysis of the H2O+ distribution and near-nucleus ion physics is presented using our comet P/Halley spectroscopic and imaging data near the time of the Vega 1 spacecraft encounter 1986 March 02-06. An extensive data reduction procedure was necessary to extract accurate H2O+ column densities. This process is outlined in the paper and required such steps as flat fielding, sky removal, continuum subtraction, contamination corrections, absolute flux calibration, and conversion to ion column densities. The spectroscopic data used the H2O+ 0,8,0 red peak close to the nucleus and the sum of the 0,8,0 and 0,6,0 band farther from the nucleus. The filter imaging data employed a filter centered on the H2O+ 0,8,0 band at 6192 Å. A contour plot of the H2O+ column density, 9′ × 9′ in size, gives a quantitative map of the ion distribution near the Vega 1 encounter. Spectroscopic and imaging ion density profiles are also presented for radial cuts along the tail and transverse cuts various distances downstream from the nucleus. A collision zone of radius ∼25,000 km, within which collisions dominate the sweeping effect of the solar wind, is verified. The central part of this collision zone, ∼12,000 km in radius, shows a depletion of the ion density by about a factor of 3, in agreement with Vega 1 spacecraft data. This is probably caused by electron recombination. Our spatial distribution of H2O+ ions agrees well with the 1/R2 falloff reported by Vega 1. Our derived H2O+ number densities are about half those reported by Giotto, suggesting that fluorescence efficiencies for H2O+ may be too high by a factor of 2. A production rate of H2O+ ions is calculated from the average velocity and column density integral across the tail. To arrive at reasonable ion outflow velocities from the collision zone, an H2O+ production rate lower than theoretical expectations by about a factor of 10 is required. Much of this discrepancy may be resolved by including the ion destruction in the inner part of the collision zone. Further ameliorating factors are our proposed lower g factor and/or a somewhat lower photodissociation rate. Analysis of the tailward ion flow shows a constant acceleration beyond 130,000 km from the nucleus, with values ∼100 cm sec-2 (∼0.1g). © 1990.
• Fink, U., & DiSanti, M. A. (1990). The production rate and spatial distribution of H₂O for comet P/Halley. Astrophysical Journal, 364(2), 687-698.
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  Abstract: Spectroscopic observations of the OI 1D lines for comet P/Halley are used to derive water-production rates. Forty-three exposures during the period 1985 August to 1986 June are reduced. The reduction procedure involves sky subtraction, ratios with solar analog comparison stars, subtraction of contaminating NH2 emissions, and absolute flux calibration. The flux collected within our 2″.5 wide x 151″ long integration aperture is converted to a total comet OI 6300 Å luminosity using a cometary gas outflow model. Spatial OI profiles are extracted and illustrated but are not analyzed in this paper. Water-production rates for 10 preperihelion dates and seven postperihelion dates are derived. An error budget yields an estimated uncertainty of + 30% in H2O production rates with a maximum error of ±50%. For the preperihelion period a good fit of the water-production rate as a function of heliocentric distance can be obtained as Q(H2O) = 4.36 x 1029 x r-2.54. A postperihelion enhancement by about a factor of 1.8, which appears to dissipate by 1986 June, is observed. Several values of enhanced water production agree well with the observed lightcurve of P/Halley. Comparison of our H2O production rates with those deduced by other methods shows quite reasonable agreement.
• Buie, M. W., & Fink, U. (1987). Methane absorption variations in the spectrum of Pluto. Icarus, 70(3), 483-498.
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  Abstract: Absolute spectrophotometry of Pluto in the wavelength range of 5600 to 10,500 Å was obtained on 4 nights covering lightcurve phases of 0.18, 0.35, 0.49, and 0.98. The four phases included minimum light (0.98) and one near maximum light (0.49). The spectra reveal significant variations in the absorption depths of the methane bands at 6200, 7200, 7900, 8400, 8600, 8900, and 10,000 Å. The minimum amount of absorption was found to occur at minimum light. This variation would imply a 30° change in the column abundance of methane within 3 days. A model employing an anisotropic surface distribution of methane frost and a clear layer of CH4 gas was developed to explain the variation in absorption strength with rotational phase. The fit to the overall spectrum requires the presence of a frost with particle sizes on the order of a few millimeters. An upper limit of 5.5 m-am is derived for the one-way column abundance of CH4 gas. An equally good fit to the variation of the 7200-Å band is obtained if the atmosphere is removed from the model entirely. © 1987.
• Johnson, J. R., Fink, U., & Larson, S. M. (1984). Charge coupled device (CCD) spectroscopy of comets: Tuttle, Stephan-Oterma, Brooks 2, and Bowell. Icarus, 60(2), 351-372.
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  Abstract: Spectra of the four comets, Tuttle, Stephan-Oterma, Brooks 2, and Bowell, were taken with a prototype space telescope charge coupled device (CCD) camera using a 500 × 500 Texas Instruments chip. The spectra extended from 5600 to 10,400 Å at a resolution of ∼25 A ̊. The spatial coverage along the slit was 180{upwards double arrow}; its resolution was defined by the seeing (2-3{upwards double arrow}). Both absolute flux scales and spectral albedos were determined with the data reduction procedure which included flat fielding and sky subtraction. Comet Tuttle displayed extensive emissions by NH2, the red system of CN, and the C2 Swan bands as well as emissions by the forbidden oxygen lines [OI] 1D at 6300 and 6364 Å, and the ionic species H2O+. A feature at 6851 Å has been tentatively identified as the 3-0 band of CS+. Notable is the absence of the C2 Phillips bands whose transitions are optimally placed in our spectrum. The much dustier comet, Stephan-Oterma showed emissions by CN, NH2, and [OI] while only [OI] could be discerned in the noisier Brooks 2 spectrum. The fresh comet Bowell exhibited an unusually extended coma with an albedo times cross section two orders of magnitude larger than the other comets, a very flat albedo spectrum, and no emission features. For Tuttle and Stephan-Oterma, CN and NH2 column densities using a number of bands were calculated. The CN band intensity ratios show good agreement with theoretical fluorescence models. The spatial profiles for CN and NH2 were compared to two step Haser model decay calculations. The scale lengths most consistent with the data were compared with values previously reported and with values expected for various photodissociation reactions. Production rates were calculated for CN and NH2. These should be less model dependent because of the simultaneous collection of spectral and spatial information. The production rate ratios of the parents of CN and NH2 to the parent of OH are several orders of magnitude smaller than the solar abundance ratios of C/O and N/O. © 1984.
• Johnson, J. R., Fink, U., Smith, B. A., & Reitsema, H. J. (1981). Spectrophotometry and upper limit of gaseous CH₄ for Triton. Icarus, 46(2), 288-291.
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  Abstract: Spectra of Triton with a CCD spectrometer yielded a relative spectral reflectivity curve from 0.56 to 1.05 μm at a resolution of 25 Å. Using low-temperature band model parameters from Fink et al. (1980), an upper limit for the one-way path gaseous CH4 abundance of 1 m-am was derived. © 1981.
• Sill, G., Fink, U., & Ferraro, J. R. (1981). The infrared spectrum of ammonia hydrate: Explanation for a reported ammonia phase. The Journal of Chemical Physics, 74(2), 997-1000.
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  Abstract: A number of anomalous spectra of solid NH3 deposited from the vapor phase have appeared in the literature. These spectra have been ascribed to a new phase of NH3. In the experiment reported here these anomalous spectra were reproduced by depositing a thin film from a mixture of gaseous NH3 and H2O and annealing this film at a temperature of 162°K. The thin film spectra showed excellent agreement with recent data on NH3·H2O. The anomalous "NH3" spectra are, therefore, seen to be caused by H2O contamination of solid NH3 with formation of NH3 hydrate. © 1981 American Institute of Physics.
• Benner, D., & Fink, U. (1980). Application of methane band-model parameters to the visible and near-infrared spectrum of Uranus. Icarus, 42(3), 343-353.
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  Abstract: Laboratory band-model absorption coefficients of CH4 are used to calculate the Uranus spectrum from 5400 to 10,400 Å. A good fit of both strong and weak bands for the Uranus spectrum over the entire wavelength interval is achieved for the first time. Three different atmospheric models are employed: a reflecting layer model, a homogeneous scattering layer model, and a clear atmosphere sandwiched between two scattering layers. The spectrum for the reflecting layer model exhibits serious discrepancies but shows that large amounts of CH4 (5-10 km-am) are necessary to reproduce the Uranus spectrum. Both scattering models give reasonably good fits. The homogeneous model requires a particle scattering albedo ( g ̃wp) ≥ 0.998 and an abundance per scattering mean free path ( a ̄) of a ̃1 km-am. The parameters derived from the sandwich layer model are: forsb the upper scattering layer a continuum single scattering albedo ( g ̃w0) of 0.995 and a scattering optical depth variable with wavelength consistent with Rayleigh scattering; for the clear layer they are a CH4 abundance (a) of 2.2 km-am and an effective pressure (p) ≥ 0.1 atm; for the lower cloud deck a Lambert reflectivity (L) of 0.9 resulted. A severe depletion of CH4 in the upper scattering layer is required. An enrichment of CH4/H2 over the solar ratio by a factor of 4-14 in the lower atmosphere is, however, indicated. © 1980.
• Feierberg, M. A., Larson, H. P., Fink, U., & Smith, H. A. (1980). Spectroscopic evidence for two achondrite parent bodies: asteroids 349 Dembowska and 4 Vesta. Geochimica et Cosmochimica Acta, 44(3), 513-524.
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  Abstract: A Fourier spectrometer was used to obtain IR spectra of asteroids 349 Dembowska and 4 Vesta (0.8-2.5μm; 25cm -1 resolution). The spectrum of Dembowska shows olivine and pyroxene (Fs24 ± 8) with an olivine/pyroxene abundance ratio greater than 2, and possibly as high as 10. This is probably an unsampled achondritic composition, similar to the unique achondrite ALHA 77005. Similar olivine-rich compositions have also been proposed for the mantles of basaltic achondrite parent bodies. Dembowska's mineralogy therefore appears related in some way to the achondrites. but a direct link cannot as yet be made. Our IR observations of Vesta have more complete spectral coverage than those first obtained by Larson and Fink (1975b). Pyroxene (Fs50 ± 5) and plagioclase feldspar are both seen, with a pyroxene/feldspar abundance ratio between 1.5 and 2.0. Vesta's mineralogy is consistent with a mixture of eucrites and howardites on its surface. Time-resolved observations over one-half of the rotation period show no spectral variations at the 2% level, indicating compositional homogeneity. Both 349 Dembowska and 4 Vesta can be considered as candidates for the parent bodies of igneous meteorites. © 1980.
• Larson, H. P., Feierberg, M. A., Fink, U., & Smith, H. A. (1979). Remote spectroscopic identification of carbonaceous chondrite mineralogies: Applications to Ceres and Pallas. Icarus, 39(2), 257-271.
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  Abstract: High-resolution spectroscopic observations of asteroids Ceres and Pallas have been obtained in the 1.0- to 2.6-μm region. Combined with previous spectralmeasurements at other wavelengths, this work presents the broadband spectral reflectances of these asteroids over the 0.4 to 3.6-um region. This extended coverage permits new analyses of the surface mineralogies of these objects. Using laboratory comparison spectra of meteorites and mixtures of terrestrial minerals, the surfaces of Ceres and Pallas are consistent with mixtures of opaques and hydrated silicates, such as are found in types C1 and C2 meteorites. This research emphasizes the importance of the 3-um spectral region for studying by remote methods the relationship of carbonaceous chondrite mineralogies to asteroid surfaces. © 1979.
• Benner, D. C., Fink, U., & Cromwell, R. H. (1978). Image tube spectra of pluto and triton from 6800 to 9000 Å. Icarus, 36(1), 82-91.
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  Abstract: To search for a possible atmosphere on Pluto and Triton, spectra of these objects as well as comparison stars were obtained with a three-stage Varo image tube for the spectral region from 6800 to 9000 Å. Ratio spectra indicate an absorption feature near 8900 Å, although the steeply diminishing response of the image tube at that wavelength casts some doubt on the reality of this feature. The feature appears more definitive in the spectrum of Pluto and less certain in the spectrum of Triton. The absorption was analyzed using our recently determined band-model parameters for methane. Under the assumption of a pressure higher than 0.01 atm an abundance of 3 m-amagat was determined. For pressures limited by the methane abundance itself, an abundance of 50 m-amagat and a pressure of 10-3 atm was derived (using g = 0.20 g⊕ for both Pluto and Triton). This pressure is close to the pressure that can be expected from the equilibrium vapor pressure of a methane frost. If the absorption at 8900 Å is spurious, our analysis will be applicable as an upper limit for the presence of methane gas on Pluto or Triton. © 1978.
• Fink, U., & Larson, H. P. (1978). Deuterated methane observed on Saturn. Science, 201(4353), 343-345.
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  Abstract: Absorptions for the v2 band of deuterated methane (CH 3D) have been observed in the 5-micron spectrum of Saturn, obtained with a Fourier transform spectrometer. Analysis of the band yields a CH 3D abundance of 2.6 ± 0.8 centimeter-amagat and a temperature of 175 ± 30 K for the mean level of spectroscopic line formation. This temperature indicates that a substantial portion of Saturn's flux at 5 microns is due to thermal radiation, and that we are therefore looking fairly deep into its atmosphere, as is the case for the Jupiter 5-micron window. This CH 3D abundance leads to a deuterium/hydrogen ratio of about 2 × 10-5 in Saturn's atmosphere. This ratio is much lower than the terrestrial value but comparable to that determined for Jupiter and may be taken as representative of the deuterium/hydrogen ratio in the solar system at the time of its formation. Copyright © 1978 AAAS.
• Fink, U., Larson, H. P., & Treffers, R. R. (1978). Germane in the atmosphere of Jupiter. Icarus, 34(2), 344-354.
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  Abstract: High-altitude spectra of Jupiter obtained from the Kuiper Airborne Observatory are analyzed for the presence of germane (GeH4) in Jupiter's atmosphere. Comparison with laboratory spectra shows that the strong Q branch of the ν3 band of germane at 2111 cm-1 is prominent in the Jovian spectra. The abundance of germane in Jupiter's atmosphere is 0.006 (±0.003) cm-am corresponding to a mixing ratio of 0.6 ppb. This trace amount of germane is consistent with chemical equilibrium calculations if the germane present at ∼1000°K is carried up by convection to the spectroscopically observable region at ∼300°K. © 1978.
• Treffers, R. R., Larson, H. P., Fink, U., & Gautier, T. N. (1978). Upper limits to trace constituents in Jupiter's atmosphere from an analysis of its 5-μm spectrum. Icarus, 34(2), 331-343.
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  Abstract: A high-resolution (0.6 cm-1) spectrum of Jupiter at 5 μm recorded at the Kuiper Airborne Observatory is used to determine upper limits to the column density of 19 molecules. The upper limits to the mixing ratios of SiH4, H2S, HCN, and simple hydrocarbons are discussed with respect to current models of Jupiter's atmosphere. These upper limits are compared to expectations based upon the solar abundance of the elements. This analysis permits upper limit measurements (SiH4), or actual detections (GeH4), of molecules with mixing ratios with hydrogen as low as 10-9. In future observations at 5 μm the sensitivity of remote spectroscopic analyses should permit the study of constituents with mixing ratios as low as 10-10, which would include the hydrides of such elements as Sn and As as well as numerous organic molecules. © 1978.
• Dick, K. A., & Fink, U. (1977). Photoelectric absorption spectra of methane (CH₄), methane and hydrogen (H₂) mixtures, and ethane (C₂H₆). Journal of Quantitative Spectroscopy and Radiative Transfer, 18(4), 433-446.
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  Abstract: Long path absorption spectra of methane have been recorded photoelectrically from 4200 to 10,600 Å. The region to the red of 6200 Å was studied with column abundances varying from approx. 0.001-1 km-amagat at a resolution of several Å. Ethane spectra in the same region were taken for abundances from about 0.1-1 km-amagat. Short scans at higher resolution and higher methane abundance were obtained for the 6800 Å absorption in the hope of discerning structure due to the presumed 5v3 band. The region below 6200 Å was recorded under a few high abundance conditions. It was also scanned with mixtures of methane and hydrogen in an attempt to detect absorption features attributable to simultaneous transitions in H2 and CH4. No such bands were detected under the pressures attained. Visual comparison with spectra of Uranus shows that pure methane explains the absorption features of Uranus quite well and that large laboratory amounts are necessary to match the weak absorptions below 6200 Å. A brief description of the complexity of the levels responsible for the methane transitions is given. © 1977.
• Dierenfeldt, K. E., Fink, U., & Larson, H. P. (1977). Temperature and pressure determinations in the Venus atmosphere by means of high-resolution spectra from 1 to 2.5 μm. Icarus, 31(1), 11-24.
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  Abstract: Twenty-one bands of CO2 and the 2-0 band of CO were analyzed for best temperature and pressure fits from Venus spectra obtained with the "Connes" interferometer at the Steward Observatory 2.25-m telescope during the spring of 1971. An average temperature of 241 ± 7°K, an effective pressure of 0.12 ± 0.06 atm, and an average two-way transmission abundance of 3 km-amagat were determined. No difference in temperature or pressure between hot bands, a double hot band, and regular bands was found. Our results were compared to model calculations for a reflecting layer and scattering atmosphere. The results indicate that, most likely, spectroscopic line formation occurs in a relatively clear space above a scattering cloud layer with a reasonably well-defined upper boundary. © 1977.
• Ferraro, J. R., & Fink, U. (1977). Near infrared reflectance spectra and analysis of H₂S frost as a function of temperature. The Journal of Chemical Physics, 67(2), 409-413.
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  Abstract: The reflection spectra of H2S frost in the near infrared region (1.6-4 μm), as a function of temperature to 62 °K, were measured. Analyses of these spectra were made, and assignments for the most intense combinations attempted. Dramatic changes in spectra are observed from 62-143 °K, connected with a phase transition between a tetragonal, low-temperature phase and a cubic, high-temperature phase, occurring at 125 ± 5 °K. The data present evidence for only two phases being involved for H2S frost. Copyright © 1977 American Institute of Physics.
• Fink, U., Benner, D., & Dick, K. A. (1977). Band model analysis of laboratory methane absorption spectra from 4500 to 10500 Å. Journal of Quantitative Spectroscopy and Radiative Transfer, 18(4), 447-457.
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  Abstract: Molecular band models are used to derive absorption and pressure coefficients for the methane absorption spectrum from 4500 to 10500 Å at intervals of 10 Å. These coefficients provide a necessary basis for the interpretation of the large methane absorptions in the atmospheres of the major planets. Although only coefficients for the "random" or "Goody" band model are derived, the equivalence between these and the "regular" of "Elasser" coefficients is demonstrated. The effects of pressure on the absorption are surprisingly small, leading to large values of the pressure coefficient quite unlike any previous application of the band-model theory. They indicate a pseudo-continuum character of the methane spectrum throughout the visible and near infrared. A spectrum synthesis calculation using the derived coefficients shows the close fit to experimental data that can be realized. © 1977.
• Larson, H. P., & Fink, U. (1977). APPLICATION OF FOURIER TRANSFORM SPECTROSCOPY TO THE REMOTE IDENTIFICATION OF SOLIDS IN THE SOLAR SYSTEM.. Applied Spectroscopy, 31(5), 386-402.
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  Abstract: The techniques of Fourier transform spectroscopy combined with large aperture telescopes and advances in detector technology now permit infrared observations of the surfaces of small solar system objects such as asteriods and satellites. The results demonstrate that this activity can produce important new compositional information related to the origin and evolution of the solar system. The detection of water ice in Saturn's rings and on some of the satellites of Jupiter and Saturn confirm expectations that ices are important mineralogical components in the chemistry of the outer solar system.
• Fink, U., Larson, H. P., & N., T. (1976). New upper limits for atmospheric constituents on Io. Icarus, 27(3), 439-446.
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  Abstract: A spectrum of the satellite of Jupiter, Io, from 0.86 to 2.7 μm at a resolution of 3.36 cm-1 and a signal to rms noise ratio of 120 is presented. No absorptions due to any atmospheric constituents on Io could be found on the spectrum. Upper limits of 0.12 cm-atm for NH3, 0.12cm-atm for CH4, 0.4cm-atm for N2O, and 24cm-atm for H2S were determined. Laboratory spectra of ammonia frosts as a function of temperature were compared with the spectrum of Io and showed as a frost not to be present at the surface of Io. A search for possible resonance lines of carbon, silicon, and sulfur as well as the 1.08μm line of helium proved negative and upper emission limits of 60, 18, 27, and 60 kilorayleighs, respectively, were established for these lines. © 1976.
• Larson, H. P., Fink, U., Treffers, R. R., & N., T. (1976). The infrared spectrum of asteroid 433 Eros. Icarus, 28(1), 95-103.
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  Abstract: The mineralogical composition of asteroid Eros has been determined from its infrared spectrum (0.9-2.7μm; 28cm-1 resolution). Major minerals include metallic NiFe and pyroxene; no spectroscopic evidence for olivine or plagioclase feldspar was found. The IR spectrum of Eros is most consistent with a stony-iron composition. © 1976.
• Fink, U., & Larson, H. P. (1975). Temperature dependence of the water-ice spectrum between 1 and 4 microns: Application to Europa, Ganymede and Saturn's rings. Icarus, 24(4), 411-420.
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  Abstract: Reflection spectra of water ice from 1 to 4 μm are presented as a function of temperature. It is found that a feature at 6056 cm-1 changes its intensity sufficiently that it can be used as a spectroscopic measure of the ice temperature. A temperature calibration curve of this feature down to 55 K is developed and is used to determine ice temperatures for the Galilean satellites Europa (95±10 K), Ganymede (103±10 K), and the rings of Saturn (80±5 K). The ice temperatures for the Galilean satellites are lower than their measured brightness temperatures, which can be explained by a higher albedo of the ice covered regions relative to the rest of the satellite and possibly a concentration of the ice near the polar caps. © 1975.
• Larson, H. P., & Fink, U. (1975). Infrared Fourier spectrometer for laboratory use and for astronomical studies from aircraft and ground based telescopes. Applied Optics, 14(9), 2085-2095.
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  Abstract: A portable, versatile, ir Fourier spectrometer is described that provides 0.5 cm-1 spectral resolution in the 0.87 5.6 μm region. This spectrometer is employed in a varied program of astronomical observations from ground based telescopes and from the NASA 91.5 cm airborne ir telescope. A number of spectral results are presented to illustrate the performance of this spectrometer in astronomical applications.
• Larson, H. P., & Fink, U. (1975). Infrared spectral observations of asteroid 4 Vesta. Icarus, 26(4), 420-427.
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  Abstract: An ir spectrum of asteroid Vesta, the first of any asteroid, has been recorded at a spectral resolution of 44 cm-1 with a Fourier spectrometer. An electronic absorption band is observed that is assigned to an iron-rich pyroxene (pigeonite) spectroscopically similar to that found in certain eucrites. Other important rock-forming minerals such as olivine and plagioclase feldspar are not observed. There is no evidence for compositional variation with rotational phase angle. This spectroscopic picture of Vesta suggests considerable evolution including the melting and differentiation of silicates. © 1975.
• Fink, U., Larson, H. P., Kuiper, G. P., & Poppen, R. F. (1972). Water vapor in the atmosphere of Venus. Icarus, 17(3), 617-631.
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  Abstract: Infrared spectra of Venus produced by a Fourier spectrometer flown aboard the NASA CV 990 jet aircraft were analyzed for water-vapor content by comparison with calculated model spectra. The reflecting layer model gave an abundance of 1.6 ± 0.4 μ of precipitable water for the two-way transmission of the Venus atmosphere. The scattering model resulted in a value of 0.25 ± 0.10 μ of water per scattering mean free path. Neither is regarded as a definitive model, but derived mixing ratios will not be significantly in error. An abundance of CO2 using an number of bands in our region was determined for both models. The volume mixing ratios of H2O to CO2 obtained were 0.6 × 10-6 and 1.0 × 10-6 for the reflecting layer and scattering model, respectively. © 1972.
• Fink, U., Bashkin, S., & Bickel, W. S. (1970). Transitions and level lifetimes in Ne II, III, Ar II, III, Kr II, III and Xe II. Journal of Quantitative Spectroscopy and Radiative Transfer, 10(12), 1241-1256.
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  Abstract: Beam-foil spectra of neon, argon, krypton, and xenon have been recorded photographically with a fast spectrograph. The particle energies ranged from 150 to 750 keV. Transitions in Ne II, III; Ar II, III; Kr II, III; and Xe II have been identified. In addition, new multiples were identified in Ne II and Xe II and a number of unidentified lines were observed in neon, argon, and krypton. Characteristic intensity decays of over 170 lines were measured, giving the mean lives of ≈ 80 levels, with an estimated error of 30 per cent. Tabulation of energy levels with similar electron configurations in neon, argon, krypton, and xenon shows a definite progression to larger mean lives as the nuclear change increases. © 1970.