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Astron. Astrophys. 339, L81-L84 (1998)

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Letter to the Editor

Low interstellar abundance of O2 confirmed by the PIROG 8 balloon experiment

G. Olofsson 1, L. Pagani 2, J. Tauber 3, P. Febvre 4, A. Deschamps 2, P. Encrenaz 2, H.-G. Florén 1, S. George 2, B. Lecomte 2, B. Ljung 5, L. Nordh 1, J.R. Pardo 2, 7, I. Peron 2, M. Sjökvist 5, K. Stegner 5, L. Stenmark 6 and C. Ullberg 6

1 Stockholm Observatory, SE-133 36 Saltsjöbaden, Sweden
2 DEMIRM, Observatoire de Paris, F-75014 Paris, France
3 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
4 LAHC, Université de Savoie, F-73376 Le Bourget du Lac Cedex, France
5 Swedish Space Corporation, Box 4207, SE-171 04 Solna, Sweden
6 ACR Electronic AB, Box 99, SE-61 922 Trosa, Sweden
7 Presently at NASA-Goddard Institute for Space Studies, 2880 Broadway, New York, USA

Received 10 September 1998 / Accepted 7 October 1998


Using a balloon-borne 60 cm telescope equipped with an SIS receiver we have searched for the 425 GHz molecular oxygen line in the NGC7538 and the W51 regions. The experiment was technically successful (confirmed by the detection of the 13CO (4-3) line at 440 GHz), but we failed to detect emission from molecular oxygen. The inferred upper limits of the O2/CO ratio are 0.04 and 0.05 (3 [FORMULA]) for the two regions, which are the lowest upper limits so far determined for Galactic clouds.

Key words: interstellar medium: abundances – interstellar medium: clouds – interstellar medium: molecules – interstellar medium: individual objects: NGC7538, W51 – radio lines: interstellar medium

Send offprint requests to: G. Olofsson
Correspondence to: olofsson@astro.su.se

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© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998