A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite: II. Data analysis

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, HO, SO, SO, CO and CHOH. Species with the largest number of lines are CHOH, (CHO, SO, CHOH, CHCN and NO. Six water lines are detected including the ground state rotational transition 1-1 of -HO, its isotopologues -HO and -HO, the Hot Core tracing -HO transition 6-7, and the 2-1 transition of HDO. Other lines of special interest are the 1-0 transition of NH and its isotopologue NH. Isotopologue abundance ratios of D/H, C/C, S/S, S/S, and O/O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of HO, NH, SO, SO, NO, and CHOH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules.. © 2007 ESO.