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Astron. Astrophys. 315, L349-L352 (1996)

A search for interstellar gas-phase CO2*

Gas: solid state abundance ratios

E.F. van Dishoeck1, F.P. Helmich1, Th. de Graauw2,4, J.H. Black3, A.C.A. Boogert4, P. Ehrenfreund1, P.A. Gerakines5, J.H. Lacy6, T.J. Millar7, W.A. Schutte1, A.G.G.M. Tielens8, D.C.B. Whittet5, D.R. Boxhoorn2,9, D.J.M. Kester2, K. Leech9, P.R. Roelfsema2,9, A. Salama9, and B. Vandenbussche9,10

1 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
2 SRON, P.O. Box 800, 9700 AV Groningen, The Netherlands
3 Onsala Space Observatory, Chalmers University of Technology, S-43992 Onsala, Sweden
4 Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands
5 Department of Physics, Applied Physics & Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
6 Department of Astronomy, University of Texas at Austin, Austin, TX 78712-1083, USA
7 Department of Physics, UMIST, P.O. Box 88, Manchester M60 1QD, UK
8 NASA-Ames Research Center, MS 245-3, Moffett Field, CA 94035, USA
9 ISO Science Operation Center, Astrophysics Dvision of ESA, P.O. Box 50727, E-28080 Villafranca/Madrid, Spain
10 Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200B, B-3001 Heverlee, Belgium

Received 1 July 1996 / Accepted 21 August 1996

Abstract. We present searches for gas-phase CO2 features in the ISO-SWS infrared spectra of four deeply embedded massive young stars, which all show strong solid CO2 absorption. The abundance of gas-phase CO2 is at most img3.gif with respect to H2, and is less than 5% of that in the solid phase. This is in strong contrast to CO, which is a factor of 10-100 more abundant in the gas than in solid form in these objects. The gas/solid state ratios of CO2, CO and H2O are discussed in terms of the physical and chemical state of the clouds.

Key words: ISM: abundances; ISM: molecules; ISM: individual: AFGL 2591, AFGL 4176, AFGL 2136, NGC 7538 IRS9

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

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Last change: December 16, 1996
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