EDP Sciences
Free access
Issue
A&A
Volume 402, Number 3, May II 2003
First Science with the ODIN satellite
Page(s) L77 - L81
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20030344


A&A 402, L77-L81 (2003)
DOI: 10.1051/0004-6361:20030344

Letter

Low upper limits on the O $\mathsf{_2}$ abundance from the Odin satellite

L. Pagani1, A. O. H. Olofsson2, P. Bergman2, P. Bernath3, J. H. Black2, R. S. Booth2, V. Buat4, J. Crovisier5, C. L. Curry3, P. J. Encrenaz1, E. Falgarone6, P. A. Feldman7, M. Fich3, H. G. Floren8, U. Frisk9, M. Gerin6, E. M. Gregersen10, J. Harju11, T. Hasegawa12, Å. Hjalmarson2, L. E. B. Johansson2, S. Kwok12, B. Larsson8, A. Lecacheux5, T. Liljeström13, M. Lindqvist2, R. Liseau8, K. Mattila11, G. F. Mitchell14, L. H. Nordh15, M. Olberg2, G. Olofsson8, I. Ristorcelli16, Aa. Sandqvist8, F. von Scheele9, G. Serra16, N. F. Tothill14, K. Volk12, T. Wiklind2 and C. D. Wilson10

1  LERMA & FRE 2460 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75140 Paris, France
2  Onsala Space Observatory, 439 92 Onsala, Sweden
3  Department of Physics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
4  Laboratoire d'Astronomie Spatiale, BP 8, 13376 Marseille Cedex 12, France
5  LESIA, Observatoire de Paris, Section de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
6  LERMA & FRE 2460 du CNRS, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
7  Herzberg Institute of Astrophysics, NRC of Canada, 5071 W. Saanich Rd, Victoria, BC V9E 2E7, Canada
8  Stockholm Observatory, SCFAB, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
9  Swedish Space Corporation, PO Box 4207, 171 04 Solna, Sweden
10  Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
11  Observatory, PO Box 14, University of Helsinki, 00014 Helsinki, Finland
12  Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada
13  Metsähovi Radio Observatory, Helsinki University of Technology, Otakaari 5A, 02150 Espoo, Finland
14  Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scottia B3H 3C3, Canada
15  Swedish National Space Board, PO Box 4006, 171 04 Solna, Sweden
16  CESR, 9 avenue du Colonel Roche, BP 4346, 31029 Toulouse, France

(Received 2 December 2002 / Accepted 25 January 2003)

Abstract
For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O 2, using the Odin satellite. Equipped with a sensitive 3 mm receiver ( $T_{\rm sys}({\rm SSB}) = 600$ K), Odin has reached unprecedented upper limits on the abundance of O 2, especially in cold dark clouds where the excited state levels involved in the 487 GHz transition are not expected to be significantly populated. Here we report upper limits for a dozen sources. In cold dark clouds we improve upon the published SWAS upper limits by more than an order of magnitude, reaching N(O 2)/ N(H $_2) \leq 10^{-7}$ in half of the sources. While standard chemical models are definitively ruled out by these new limits, our results are compatible with several recent studies that derive lower O 2 abundances. Goldsmith et al. (2002) recently reported a SWAS tentative detection of the 487 GHz transition of O 2 in an outflow wing towards $\rho$ Oph A in a combination of 7 beams covering approximately $10\arcmin \times 14\arcmin$. In a brief (1.3 hour integration time) and partial covering of the SWAS region ( $\approx$65% if we exclude their central position), we did not detect the corresponding 119 GHz line. Our 3 sigma upper limit on the O 2 column density is  $7.3\times 10^{15}$ cm -2. We presently cannot exclude the possibility that the SWAS signal lies mostly outside of the 9´ Odin beam and has escaped our sensitive detector.


Key words: radio lines: ISM -- ISM: molecules -- Galaxy: abundances

Offprint request: L. Pagani, laurent.pagani@obspm.fr

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