Multi-line detection of O2 toward rho Ophiuchi A
Artikel i vetenskaplig tidskrift, 2012
Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O-2, and water, H2O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O-2 in the dense star-forming interstellar medium. Aims. Only toward rho OphA did Odin detect a very weak line of O-2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O-2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O-2 spectra toward selected positions in the rho Oph A core. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. Results. The N-J = 3(3)-1(2) line at 487.2 GHz is clearly detected toward all three observed positions in the rho Oph A core. In addition, an oversampled map of the 5(4)-3(4) transition at 773.8 GHz reveals the detection of the line in only half of the observed area. On the basis of their ratios, the temperature of the O-2 emitting gas appears to vary quite substantially, with warm gas (greater than or similar to 50 K) being adjacent to a much colder region, of temperatures lower than 30 K. Conclusions. The exploited models predict that the O-2 column densities are sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these models, the observationally determined O-2 column densities do not seem to depend strongly on the derived gas temperatures, but fall into the range N(O-2) = 3 to greater than or similar to 6 x 10(15) cm(-2). Beam-averaged O-2 abundances are about 5 x 10(-8) relative to H-2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz in the range of 4 to 5 arcmin, encompassing the entire rho Oph A core. We speculate that one of the reasons for the generally very low detection rate of O-2 is the short period of time during which O-2 molecules are reasonably abundant in molecular clouds.
submillimeter observations
dark-cloud
dust grains
c-i emission
interstellar hydrogen-peroxide
ISM: lines and bands
photodissociation regions
clouds
odin
ISM: clouds
ISM: individual objects: rho Oph
main cloud
ISM: molecules
ISM: abundances
satellite
oph cloud
molecular
Författare
René Liseau
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
P. F. Goldsmith
California Institute of Technology (Caltech)
B. Larsson
Stockholms universitet
L. Pagani
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
Per Bergman
Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium
J. Le Bourlot
LUTH - Laboratoire de l'Univers et de ses Theories
T. A. Bell
Centro de Astrobiologia (CAB)
A. O. Benz
Eidgenössische Technische Hochschule Zürich (ETH)
E. A. Bergin
University of Michigan
Per Bjerkeli
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
John H Black
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
S. Bruderer
Max-Planck-Gesellschaft
Eidgenössische Technische Hochschule Zürich (ETH)
P. Caselli
University of Leeds
E. Caux
Université de Toulouse
Jo-Hsin Chen
California Institute of Technology (Caltech)
M. de Luca
LUTH - Laboratoire de l'Univers et de ses Theories
P. Encrenaz
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
E. Falgarone
Centre national de la recherche scientifique (CNRS)
M. Gerin
Centre national de la recherche scientifique (CNRS)
J. R. Goicoechea
Centro de Astrobiologia (CAB)
Åke Hjalmarson
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
D. J. Hollenbach
SETI Institute
Kay Justtanont
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
M. J. Kaufman
San Jose State University
F. Le Petit
LUTH - Laboratoire de l'Univers et de ses Theories
D. Li
Chinese Academy of Sciences
California Institute of Technology (Caltech)
D. C. Lis
California Institute of Technology (Caltech)
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
Z. Nagy
Rijksuniversiteit Groningen
Netherlands Institute for Space Research (SRON)
Henrik Olofsson
Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium
G. Olofsson
Stockholms universitet
E. Roueff
LUTH - Laboratoire de l'Univers et de ses Theories
A. Sandqvist
Stockholms universitet
R. L. Snell
University of Massachusetts
F. F. S. van der Tak
Rijksuniversiteit Groningen
Netherlands Institute for Space Research (SRON)
E. F. van Dishoeck
Universiteit Leiden
Max-Planck-Gesellschaft
C. Vastel
Centre national de la recherche scientifique (CNRS)
Université de Toulouse
S. Viti
University College London (UCL)
U. A. Yildiz
Universiteit Leiden
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 541 A73Ämneskategorier (SSIF 2011)
Astronomi, astrofysik och kosmologi
DOI
10.1051/0004-6361/201118575