Boogert, A. C. A. and Pontoppidan, K. M. and Knez, C. and Lahuis, F. and Kessler-Silacci, J. and van Dishoeck, E. F. and Blake, G. A. and Augereau, J.-C. and Bisschop, S. E. and Bottinelli, S. and Brooke, T. Y. and Brown, J. and Crapsi, A. and Evans, N. J., II and Fraser, H. J. and Geers, V. and Huard, T. L. and Jørgensen, J. K. and Öberg, K. I. and Allen, L. E. and Harvey, P. M. and Koerner, D. W. and Mundy, L. G. and Padgett, D. L. and Sargent, A. I. and Stapelfeldt, K. R. (2008) The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects. I. H₂O and the 5-8 μm bands. Astrophysical Journal, 678 (2). pp. 985-1004. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:BOOapj08
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To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L ~ 0.1 - 10 L☉) using 3 - 38 μm Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L ~ 10⁵ L☉). The long-known 6.0 and 6.85 μm bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. The 6.0 μm band is often deeper than expected from the bending mode of pure solid H₂O. The additional 5 - 7 μm absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%-30% for CH₃OH, 3%-8% for NH₃, 1%-5% for HCOOH, ~6% for H₂CO, and ~0.3% for HCOO⁻ relative to solid H₂O. The 6.85 μm band has one or two carriers, of which one may be less volatile than H₂O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH4^+-containing salt is the carrier, its abundance relative to solid H₂O is ~7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-ray-induced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8 μm. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution.
|Additional Information:||© 2008 American Astronomical Society. Received 2007 September 23; accepted 2008 January 5. We thank the anonymous referee for thoughtful comments on the manuscript and Alberto Noriega-Crespo for help in identifying the emission lines. Support for this work, part of the Spitzer Legacy Science Program, was provided by NASA through contracts 1224608, 1230779, 1230782, 1256316, and 1279952 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Astrochemistry in Leiden is supported by an NWO Spinoza grant, a NOVA grant, and by the European Research Training Network "The Origin of Planetary Systems" (PLANETS, contract HPRN-CT-2002-00308). The work of J. K. J. is supported by NASA Origins grant NAG5-13050. K. M. P. is supported by NASA through Hubble Fellowship grant 01201.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5- 26555. We thank the Lorentz Center in Leiden for hosting several meetings that contributed to this paper. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.|
|Subject Keywords:||astrochemistry; infrared: ISM; infrared: stars; ISM: abundances; ISM: molecules; stars: formation|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||02 Apr 2009 22:35|
|Last Modified:||26 Dec 2012 10:55|
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