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Ice and dust in the quiescent medium of isolated dense cores

Boogert, A. C. A. and Huard, T. L. and Cook, A. M. and Chiar, J. E. and Knez, C. and Decin, L. and Blake, G. A. and Tielens, A. G. G. M. and van Dishoeck, E. F. (2011) Ice and dust in the quiescent medium of isolated dense cores. Astrophysical Journal, 729 (2). Art. No. 92. ISSN 0004-637X.

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The relation between ices in the envelopes and disks surrounding young stellar objects (YSOs) and those in the quiescent interstellar medium (ISM) is investigated. For a sample of 31 stars behind isolated dense cores, ground-based and Spitzer spectra and photometry in the 1-25 μm wavelength range are combined. The baseline for the broad and overlapping ice features is modeled, using calculated spectra of giants, H_2O ice and silicates. The adopted extinction curve is derived empirically. Its high resolution allows for the separation of continuum and feature extinction. The extinction between 13 and 25 μm is ~50% relative to that at 2.2 μm. The strengths of the 6.0 and 6.85 μm absorption bands are in line with those of YSOs. Thus, their carriers, which, besides H_2O and CH_3OH, may include NH^+_4, HCOOH, H_2CO, and NH_3, are readily formed in the dense core phase, before stars form. The 3.53 μm C-H stretching mode of solid CH_3OH was discovered. The CH_3OH/H_2O abundance ratios of 5%-12% are larger than upper limits in the Taurus molecular cloud. The initial ice composition, before star formation occurs, therefore depends on the environment. Signs of thermal and energetic processing that were found toward some YSOs are absent in the ices toward background stars. Finally, the peak optical depth of the 9.7 μm band of silicates relative to the continuum extinction at 2.2 μm is significantly shallower than in the diffuse ISM. This extends the results of Chiar et al. to a larger sample and higher extinctions.

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Blake, G. A.0000-0003-0787-1610
van Dishoeck, E. F.0000-0001-7591-1907
Additional Information:© 2011 American Astronomical Society. Received 2010 September 15; accepted 2011 January 6; published 2011 February 14. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank the anonymous referee for comments that helped with improving the presentation and conclusions of this work. T.L.H. acknowledges support for this work provided by NASA through contract 1316720 issued by JPL/Caltech. A.M.C. acknowledges support from the NASA Astrobiology Institute (grant NNA09DA80A) and the IPAC Visiting Graduate Student Fellowship Program. 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.
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IPAC Visiting Graduate Student Fellowship ProgramUNSPECIFIED
Subject Keywords:astrochemistry; infrared: ISM; infrared: stars; ISM: abundances; ISM: molecules; stars: formation
Issue or Number:2
Classification Code:PACS: 97.21.+a; 98.38.Bn; 95.30.Ft; 97.10.Fy; 95.30.Ky; 98.38.Dq
Record Number:CaltechAUTHORS:20110413-081502145
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Official Citation:Ice and Dust in the Quiescent Medium of Isolated Dense Cores A. C. A. Boogert, T. L. Huard, A. M. Cook, J. E. Chiar, C. Knez, L. Decin, G. A. Blake, A. G. G. M. Tielens and E. F. van Dishoeck doi: 10.1088/0004-637X/729/2/92
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23297
Deposited By: Ruth Sustaita
Deposited On:13 Apr 2011 16:47
Last Modified:03 Oct 2019 02:45

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