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The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. III. CH4

Öberg, Karin I. and Boogert, A. C. Adwin and Pontoppidan, Klaus M. and Blake, Geoffrey A. and Evans, Neal J., II and Lahuis, Fred and van Dishoeck, Ewine F. (2008) The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. III. CH4. Astrophysical Journal, 678 (2). pp. 1032-1041. ISSN 0004-637X. doi:10.1086/533432.

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CH4 is proposed to be the starting point of a rich organic chemistry. Solid CH4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH4 toward low-mass star-forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH4 abundance toward a large sample of low-mass young stellar objects. A total of 25 out of 52 ice sources in the “Cores to Disks” (c2d) Legacy program have an absorption feature at 7.7 μm, attributed to the bending mode of solid CH4. The solid CH4/H2O abundances are 2%–8%, except for three sources with abundances as high as 11%–13%. The latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H2O column densities above cm−2, the CH4 abundances (20 out of 25) are nearly constant at . Correlation plots with solid H2O, CH3OH, CO2, and CO column densities and abundances relative to H2O reveal a closer relationship of solid CH4 with CO2 and H2O than with solid CO and CH3OH. The inferred solid CH4 abundances are consistent with models where CH4 is formed through sequential hydrogenation of C on grain surfaces. Finally, the equal or higher abundances toward low-mass young stellar objects compared with high-mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH3OH and formation in gas phase with subsequent freezeout.

Item Type:Article
Related URLs:
URLURL TypeDescription
Öberg, Karin I.0000-0001-8798-1347
Pontoppidan, Klaus M.0000-0001-7552-1562
Blake, Geoffrey A.0000-0003-0787-1610
Evans, Neal J., II0000-0001-5175-1777
van Dishoeck, Ewine F.0000-0001-7591-1907
Additional Information:© 2008. The American Astronomical Society. Received 2007 October 15; accepted 2008 January 7. We thank Claudia Knez and the Spitzer c2d IRS team for useful comments on the manuscript. Funding for K.I.Ö. and E.F.v.D. was provided by NOVA, the Netherlands Research School for Astronomy, a grant from the European Early Stage Training Network (MEST-CT-2004-504604), and an NWO Spinoza grant. Support for K. M. P. was provided by NASA through Hubble Fellowship grant 1201.01 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.
Funding AgencyGrant Number
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
European Early Stage Training NetworkMEST-CT-2004-504604
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
NASA Hubble Fellowship1201.01
NASANAS 5-26555
Space Telescope Science InstituteUNSPECIFIED
Association of Universities for Research in Astronomy (AURA)UNSPECIFIED
Subject Keywords:astrochemistry; methane; interstellar medium; star formation
Issue or Number:2
Record Number:CaltechAUTHORS:OBEapj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11397
Deposited By: Archive Administrator
Deposited On:12 Aug 2008 17:08
Last Modified:08 Nov 2021 21:58

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