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Multi-line detection of O_2 toward ρ Ophiuchi A
- Source :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, EDP Sciences, 2012, 541, pp.A73. ⟨10.1051/0004-6361/201118575⟩, Astronomy & astrophysics, 541:A73. EDP Sciences, Astronomy and Astrophysics-A&A, 2012, 541, pp.A73. ⟨10.1051/0004-6361/201118575⟩
- Publication Year :
- 2012
- Publisher :
- EDP Sciences, 2012.
-
Abstract
- 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.
- Subjects :
- Aperture
DARK-CLOUD
Astrophysics
MAIN CLOUD
PHOTODISSOCIATION REGIONS
010402 general chemistry
OPH CLOUD
7. Clean energy
01 natural sciences
ISM: clouds
Spectral line
ISM: abundances
law.invention
Telescope
Far infrared
law
0103 physical sciences
010303 astronomy & astrophysics
ISM: individual objects: rho Oph A SM1
ComputingMilieux_MISCELLANEOUS
Line (formation)
Physics
[PHYS]Physics [physics]
DUST GRAINS
stars: formation
Molecular cloud
Astronomy and Astrophysics
ISM: molecules
0104 chemical sciences
ISM: lines and bands
INTERSTELLAR HYDROGEN-PEROXIDE
C-I EMISSION
Interstellar medium
ODIN SATELLITE
SUBMILLIMETER OBSERVATIONS
13. Climate action
Space and Planetary Science
MOLECULAR CLOUDS
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Water vapor
Subjects
Details
- Language :
- English
- ISSN :
- 00046361
- Database :
- OpenAIRE
- Journal :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, EDP Sciences, 2012, 541, pp.A73. ⟨10.1051/0004-6361/201118575⟩, Astronomy & astrophysics, 541:A73. EDP Sciences, Astronomy and Astrophysics-A&A, 2012, 541, pp.A73. ⟨10.1051/0004-6361/201118575⟩
- Accession number :
- edsair.doi.dedup.....8bcfb61e8e98f8374a098bb80b8e02ac