A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite^*,**

II. Data analysis

¹ Onsala Space Observatory (OSO), Chalmers University of Technology, 43992 Onsala, Sweden e-mail: carina@oso.chalmers.se
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

Received: 2 February 2007
Accepted: 17 September 2007

Abstract

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.