Cook, A. M. and Whittet, D. C. B. and Shenoy, S. S. and Gerakines, P. A. and White, D. W. and Chiar, J. E. (2011) The Thermal Evolution of Ices in the Environments of Newly Formed Stars: The CO_2 Diagnostic. Astrophysical Journal, 730 (2). Art. No. 124. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110413-081503154
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Archival data from the Infrared Spectrometer of the Spitzer Space Telescope are used to study the 15 μm absorption feature of solid CO_2 toward 28 young stellar objects (YSOs) of approximately solar mass. Fits to the absorption profile using laboratory spectra enable categorization according to the degree of thermal processing of the ice matrix that contains the CO_2. The majority of YSOs in our sample (20 out of 28) are found to be consistent with a combination of polar (H_2O-rich) and nonpolar (CO-rich) ices at low temperature; the remainder exhibit profile structure consistent with partial crystallization as the result of significant heating. Ice-phase column densities of CO_2 are determined and compared with those of other species. Lines of sight with crystallization signatures in their spectra are found to be systematically deficient in solid-phase CO, as expected if CO is being sublimated in regions where the ices are heated to crystallization temperatures. Significant variation is found in the CO2 abundance with respect to both H_2O (the dominant ice constituent) and total dust column (quantified by the extinction, AV ). YSOs in our sample display typically higher CO_2 concentrations (independent of evidence for thermal processing) in comparison to quiescent regions of the prototypical cold molecular cloud. This suggests that enhanced CO_2 production is driven by photochemical reactions in proximity to some YSOs, and that photoprocessing and thermal processing may occur independently.
|Additional Information:||© 2011 American Astronomical Society. Received 2010 July 22; accepted 2011 February 4; published 2011 March 11. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Financial support for this research was provided by the Spitzer General Observer and Archival Research Programs (JPL/Caltech Support Agreements nos. 1264149 and 1290823), the NASA Exobiology and Evolutionary Biology program (grant NNX07AK38G), the NASA Astrobiology Institute (grant NNA09DA80A), and the NASA New York Space Grant Consortium. We are grateful to an anonymous referee for helpful comments. Facilities: Spitzer (IRS), IRTF (SpeX), FLWO:2MASS, CTIO:2MASS|
|Subject Keywords:||astrochemistry; dust, extinction; evolution; infrared: ISM; ISM: molecules; stars: pre-main sequence|
|Classification Code:||PACS: 97.21.+a; 95.30.Ky; 98.58.Ay; 98.58.Db; 98.58.Ca|
|Official Citation:||The Thermal Evolution of Ices in the Environments of Newly Formed Stars: The CO2 Diagnostic A. M. Cook, D. C. B. Whittet, S. S. Shenoy, P. A. Gerakines, D. W. White and J. E. Chiar doi: 10.1088/0004-637X/730/2/124|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||14 Apr 2011 14:53|
|Last Modified:||26 Dec 2012 13:09|
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