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

I. The observational data

¹ Onsala Space Observatory (OSO), 43992 Onsala, Sweden e-mail: henrik@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 Arizona, Tucson, AZ 85721, USA
⁶ Department of Chemistry, University of Waterloo, Waterloo, ON N2L 3G1, Canada
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: 30 August 2007

Abstract

Aims.Spectral line surveys are useful since they allow identification of new molecules and new lines in uniformly calibrated data sets. The subsequent multi-transition analysis will provide improved knowledge of molecular abundances, cloud temperatures and densities, and may also reveal previously unsuspected blends of molecular lines, which otherwise may lead to erroneous conclusions. Nonetheless, large portions of the sub-millimetre spectral regime remain unexplored due to severe absorptions by H₂O and O₂ in the terrestrial atmosphere. The purpose of the measurements presented here is to cover wavelength regions at and around 0.55 mm – regions largely unobservable from the ground.

Methods.Using the Odin astronomy/aeronomy satellite, we performed the first spectral survey of the Orion KL molecular cloud core in the bands 486–492 and 541–576 GHz with rather uniform sensitivity (22–25 mK baseline noise). Odin's 1.1 m size telescope, equipped with four cryo-cooled tuneable mixers connected to broad band spectrometers, was used in a satellite position-switching mode. Two mixers simultaneously observed different 1.1 GHz bands using frequency steps of 0.5 GHz (25 h each). An on-source integration time of 20 h was achieved for most bands. The entire campaign consumed ~1100 orbits, each containing one hour of serviceable astro-observation.

Results.We identified 280 spectral lines from 38 known interstellar molecules (including isotopologues) having intensities in the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart from the ground state rotational 1–1 transitions of ortho-H₂O, HO and HO, the high energy 6–7 line of para-H₂O ( K) and the HDO(2–1) line have been observed, as well as the 1₀–0₁ lines from NH₃ and its rare isotopologue ¹⁵NH₃. We suggest assignments for some unidentified features, notably the new interstellar molecules ND and SH^-. Severe blends have been detected in the line wings of the HO, HO and ¹³CO lines changing the true linewidths of the outflow emission.