Molecular oxygen in the rho Ophiuchi cloud

B. Larsson, R. Liseau, L. Pagani, P. Bergman, P. Bernath, N. Biver, J. H. Black, R. S. Booth, V. Buat, J. Crovisier, C. L. Curry, M. Dahlgren, P. J. Encrenaz, E. Falgarone, P. A. Feldman, M. Fich, H. G. Floren, M. Fredrixon, U. Frisk, G. F. GahmM. Gerin, M. Hagstrom, J. Harju, T. Hasegawa, A. Hjalmarson, L. E. B. Johansson, K. Justtanont, A. Klotz, E. Kyrola, S. Kwok, A. Lecacheux, T. Liljestrom, E. J. Llewellyn, S. Lundin, G. Megie, G. F. Mitchell, D. Murtagh, L. H. Nordh, L.-A. Nyman, M. Olberg, A. O. H. Olofsson, G. Olofsson, H. Olofsson, G. Persson, R. Plume, H. Rickman, I. Ristorcelli, G. Rydbeck, A. A. Sandqvist, F. V. Scheele, G. Serra, S. Torchinsky, N. F. Tothill, K. Volk, T. Wiklind, C. D. Wilson, A. Winnberg, G. Witt

Research output: Contribution to journalArticlepeer-review


Context. Molecular oxygen, O-2, 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 O-2 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 1.1m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O-2. Starting in 2002, the star forming molecular cloud core rho OphA was observed with Odin for 34 days during several observing runs.

Results. We detect a spectral line at v(LSR)= + 3.5 km s(-1) with = vFWHM = 1.5 km s(-1), parameters which are also common to other species associated with rho OphA. This feature is identified as the O-2 (N-J = 1(1)- 1(0)) transition at 118 750.343 MHz.

Conclusions. The abundance of molecular oxygen, relative to H-2, is 5 x 10(-8) averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.

Original languageEnglish
Pages (from-to)999-U158
Number of pages11
JournalAstronomy & Astrophysics
Issue number3
Publication statusPublished - May 2007


  • ISM : individual objects : rho OphA
  • ISM : clouds
  • ISM : molecules
  • ISM : abundances
  • stars : formation
  • radio lines : ISM
  • O-2
  • C-C2H4O

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