Volume 476, Number 2, December III 2007
|Page(s)||807 - 827|
|Section||Interstellar and circumstellar matter|
|Published online||24 September 2007|
II. Data analysis
Onsala Space Observatory (OSO), Chalmers University of Technology, 43992 Onsala, Sweden e-mail: email@example.com
2 LERMA, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
3 Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada
4 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
5 Department of Chemistry, University of Waterloo, Waterloo, ON N2L 3G1, Canada
6 Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA
7 Department of Chemistry, University of York, Heslington, York YO10 5DD, UK
8 Swedish Space Corporation, PO Box 4207, 17104 Solna, Sweden
9 Molecular Physics Division, Department of Physics, Stockholm University AlbaNova, 10691 Stockholm, Sweden
10 Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 106, Taiwan, R.O.C.
11 Department of Physics, University of Hong Kong, Hong Kong, PR China
12 Stockholm Observatory, AlbaNova University Center, 10691 Stockholm, Sweden
13 LESIA, Observatoire de Paris, Section de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
14 Computer science and engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
Accepted: 17 September 2007
Aims.We investigate the physical and chemical conditions in a typical star forming region, including an unbiased search for new molecules in a spectral region previously unobserved.
Methods.Due to its proximity, the Orion KL region offers a unique laboratory of molecular astrophysics in a chemically rich, massive star forming region. Several ground-based spectral line surveys have been made, but due to the absorption by water and oxygen, the terrestrial atmosphere is completely opaque at frequencies around 487 and 557 GHz. To cover these frequencies we used the Odin satellite to perform a spectral line survey in the frequency ranges 486-492 GHz and 541-577 GHz, filling the gaps between previous spectral scans. Odin's high main beam efficiency, = 0.9, and observations performed outside the atmosphere make our intensity scale very well determined.
Results.We observed 280 spectral lines from 38 molecules including isotopologues, and, in addition, 64 unidentified lines. A few U-lines have interesting frequency coincidences such as ND and the anion SH-. The beam-averaged emission is dominated by CO, H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are CH3OH, (CHO, SO2, 13CH3OH, CH3CN and NO. Six water lines are detected including the ground state rotational transition 1–1 of o-H2O, its isotopologues o-HO and o-HO, the Hot Core tracing p-H2O transition 6–7, and the 2–1 transition of HDO. Other lines of special interest are the 10–0 transition of NH3 and its isotopologue 15NH3. Isotopologue abundance ratios of D/H, 12C/13C, 32S/34S, 34S/33S, and 18O/17O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of H2O, NH3, SO2, SO, NO, and CH3OH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules.
Key words: ISM: abundances / ISM: individual objects: Orion KL / ISM: molecules / line: formation / line: identification / submillimeter
Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Etudes Spatiales (CNES). The Swedish Space Corporation was the prime contractor and also is responsible for the satellite operation.
© ESO, 2007
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