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Solid CH4 toward low-mass protostars: How much is there to build complex organics?

Published online by Cambridge University Press:  01 February 2008

Karin I. Öberg ,
A. C. Adwin Boogert ,
Klaus M. Pontoppidan ,
Geoffrey A. Blake ,
Neal J. Evans ,
Fred Lahuis  and
Ewine F. van Dishoeck
Karin I. Öberg
Affiliation:
Leiden Observatory, Leiden University, P.O. Box 9513, NL–2300 RA Leiden, the Netherlands email: oberg@strw.leidenuniv.nl
A. C. Adwin Boogert
Affiliation:
IPAC, NASA Herschel Science Center, Mail Code100-22, California Institute of Technology, Pasadena, CA 91125, USA email: aboogert@ipac.caltech.edu
Klaus M. Pontoppidan
Affiliation:
Division of Geological and Planetary Sciences, California Institute of Technology Pasadena, CA 91125, USA email: pontoppi@gps.caltech.edu
Geoffrey A. Blake
Affiliation:
Division of Geological and Planetary Sciences, California Institute of Technology Pasadena, CA 91125, USA email: pontoppi@gps.caltech.edu
Neal J. Evans
Affiliation:
Department of Astronomy, University of Texas at Austin, Austin, TX 78712-0259, USA email: nje@bubba.as.utexas.edu
Fred Lahuis
Affiliation:
SRON, PO Box 800, NL–9700 AV Groningen, The Netherlands email: F.Lahuis@sron.nl
Ewine F. van Dishoeck
Affiliation:
Leiden Observatory, Leiden University, P.O. Box 9513, NL–2300 RA Leiden, the Netherlands email: oberg@strw.leidenuniv.nl
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Abstract

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We use Spitzer IRS spectra to determine the solid CH4 abundance toward a large sample (52 sources) of low mass protostars. 50% of the sources have an absorption feature at 7.7 μm, attributed to solid CH4. The solid CH4/H2O abundances are 2–13%, but toward sources with H2O column densities above 2 × 1018 cm−2, the CH4 abundances (20 out of 25) are nearly constant at 4.7 ± 1.6%. Correlations with CO2 and H2O together with the inferred abundances are consistent with CH4 formation through sequential hydrogenation of C on grain surfaces, but not with formation from CH3OH and formation in gas phase with subsequent freeze-out.

Keywords

Astrochemistrymolecular processescircumstellar matterISM: abundancesinfrared: ISM

Information

Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S251: Organic Matter in Space , February 2008 , pp. 127 - 128
Copyright
Copyright © International Astronomical Union 2008

References

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