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Astron. Astrophys. 346, L57-L60 (1999)

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Letter to the Editor

Constraints on the abundance of solid O2 in dense clouds from ISO-SWS and ground-based observations *

B. Vandenbussche 1, P. Ehrenfreund 2, A.C.A. Boogert 4, E.F. van Dishoeck 2,3, W.A. Schutte 2, P.A. Gerakines 5, J. Chiar 7, A.G.G.M. Tielens 4, J. Keane 4, D.C.B. Whittet 5, M. Breitfellner 6 and M. Burgdorf 6

1 Instituut voor Sterrenkunde, K.U.Leuven, Celestijnenlaan 200B, B-3001 Heverlee, Belgium
2 Raymond and Beverly Sackler Laboratory for Astrophysics at Leiden Observatory, 2300 RA Leiden, The Netherlands
3 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
4 Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands
5 Rensselaer Polytechnic Institute, Dept of Physics, Applied Physics & Astronomy, Troy, NY 12180, USA
6 ISO Data Centre, Astrophysics Division, Space Science Department of ESA, Villafranca, P.O. Box 50727, E-28080 Madrid, Spain
7 NASA-Ames Research Center, Mail Stop 245-3, Moffet Field, CA 94035, USA

Received 22 March 1999 / Accepted 19 May 1999


The Short Wavelength Spectrometer (SWS) on-board the Infrared Space Observatory (ISO) has been used to search for solid O2 in cold dense clouds at 6.45 µm. Additional constraints on the O2 abundance are obtained from analysis of the 4.67 µm solid CO absorption profile observed from the ground. We derive upper limits of 50% and 100% of solid O2 relative to solid CO toward the protostellar sources R CrA IRS2 and NGC 7538 IRS9 respectively, corresponding to abundances of [FORMULA] and [FORMULA] relative to nH. These results indicate that the abundance of solid O2 in dense clouds accounts for less than 6% of the total oxygen budget in the interstellar medium. The reservoirs of oxygen in dense clouds are discussed, taking into account recent measurements of oxygen-bearing species.

Key words: ISM: abundances – ISM: molecules – ISM: dust, extinction – infrared: ISM: lines and bands

* 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.

Send offprint requests to: B. Vandenbussche

© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999