Molecular oxygen in the ρ  Ophiuchi cloud ^*,**

¹ Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm, Sweden; e-mail: name@astro.su.se
² LERMA & UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
³ Onsala Space Observatory, 439 92 Onsala, Sweden
⁴ APEX team, ESO, Santiago, Casilla 19001, Santiago 19, Chile
⁵ Department of Physics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
⁶ LESIA, Observatoire de Paris, Section de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁷ Laboratoire d'Astronomie Spatiale, BP 8, 13376 Marseille Cedex 12, France
⁸ LERMA & UMR 8112 du CNRS, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
⁹ Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
¹⁰ Swedish Space Corporation, PO Box 4207, 171 04 Solna, Sweden
¹¹ Observatory, PO Box 14, University of Helsinki, 00014 Helsinki, Finland
¹² Department of Physics and Astronomy, University of Calgary, Calgary, ABT 2N 1N4, Canada
¹³ CESR, 9 avenue du Colonel Roche, BP 4346, 31029 Toulouse, France
¹⁴ Finnish Meteorological Institute, PO Box 503, 00101 Helsinki, Finland
¹⁵ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 106, Taiwan
¹⁶ Metsähovi Radio Observatory, Helsinki University of Technology, Otakaari 5A, 02150 Espoo, Finland
¹⁷ Department of Physics and Engineering Physics, 116 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
¹⁸ Institut Pierre Simon Laplace, CNRS-Université Paris 6, 4 place Jussieu, 75252 Paris Cedex 05, France
¹⁹ Department of Astronomy and Physics, Saint Mary's University, Halifax, NS, B3H 3C3, Canada
²⁰ Global Environmental Measurements Group, Chalmers University of Technology, 412 96 Göteborg, Sweden
²¹ Swedish National Space Board, Box 4006, 171 04 Solna, Sweden
²² Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
²³ Canadian Space Agency, St-Hubert, J3Y 8Y9, Québec, Canada
²⁴ ESA Space Telescope Division, STScI, 3700 San Martin Drive Baltimore, MD 21218, USA
²⁵ Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada
²⁶ Department of Meteorology, Stockholm University, 106 91 Stockholm, Sweden

Received: 26 April 2006
Accepted: 15 February 2007

Abstract

Context.Molecular oxygen, O₂, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O₂ emission.

Aims.The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium.

Methods.The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O₂. Starting in 2002, the star forming molecular cloud core  was observed with Odin for 34 days during several observing runs.

Results.We detect a spectral line at v_LSR  km s^-1 with  km s^-1, parameters which are also common to other species associated with . This feature is identified as the O₂ () transition at 118 750.343 MHz.

Conclusions.The abundance of molecular oxygen, relative to H₂ , is averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.