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Astron. Astrophys. 327, L17-L20 (1997)

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Letter to the Editor

New upper limits on the interstellar O2 abundance

F. Combes 1, T. Wiklind 2 and N. Nakai 3

1 Observatoire de Paris, DEMIRM, 61 av. de l'Observatoire, F-75014 Paris, France
2 Onsala Space Observatory, S-43992 Onsala, Sweden
3 Nobeyama Radio Observatory, Minamimaki-mura, Minamisaku-gun, Nagano 384-13, Japan

Received 7 July 1997 / Accepted 22 August 1997


We report new observations of molecular oxygen in absorption at [FORMULA] in front of the radio source B0218+357. The lines at 56.3 and 118.7 GHz have been observed, redshifted to 33.4 and 70.5 GHz respectively, with the 12m at Kitt Peak, 43m at Green Bank telescopes, and the 45m Nobeyama radio telescope. Deriving the surface filling factor of the absorbing dark cloud with other lines detected at nearby frequencies, we deduce from the upper limits on the O2 lines a relative abundance of molecular oxygen with respect to carbon monoxyde of O2 /CO [FORMULA] 2 10-3 at 1 [FORMULA], seven times lower than the previous limit. The consequences of this result are discussed.

Key words: ISM: abundances, general, molecules – Quasars: absorption lines – Radio lines: ISM

Send offprint requests to: F. Combes (e-mail: bottaro@obspm.fr)

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998