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Astron. Astrophys. 342, L32-L35 (1999)


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Letter to the Editor

Methanol: The second most abundant ice species towards the high-mass protostars RAFGL7009S and W 33A *

E. Dartois 1, W. Schutte 2, T.R. Geballe 3, K. Demyk 1, P. Ehrenfreund 2 and L. d'Hendecourt 1

1 Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, F-91405 Orsay Cedex, France
2 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
3 Joint Astronomy Centre, Hawaii Headquarters, 660 N. A'ohoku Place, Hilo, HI 96720, USA

Received 17 November 1998 / Accepted 15 December 1998

Abstract

We present ground-based L-band spectra of the high-mass protostars RAFGL7009S and W 33A. Absorption bands at 3.54, 3.84 and 3.94 [FORMULA]m arise in both lines of sight. We attribute these bands to the methanol [FORMULA] CH3 symmetric stretch and combination modes. The [FORMULA] abundance relative to water ice is about 30% for RAFGL7009S and 5-22% for W 33A, making [FORMULA] the most abundant solid state molecule after [FORMULA] toward these two sources. The profiles of the absorption features toward these objects are very similar, showing that the methanol is located in similar ice environments. Detailed spectral comparison with laboratory data implies that the methanol is not mixed uniformly with the water ice. The similarities in the spectra of these two protostars are discussed within the context of chemical differences along other lines of sight. Methanol appears to be more efficiently produced on grain mantles in the vicinity of high-mass protostars than in other locations.

Key words: ISM: abundances – ISM: dust, extinction – ISM: H ii regions – ISM: individual objects: – infrared: ISM: continuum – infrared: ISM: lines and bands

* Based on observations with the United Kingdom Infrared Telescope, operated by the Joint Astronomy Centre on behalf of the U.K. Particle Physics and Astronomy Research Council

Send offprint requests to: E. Dartois (dartois@ias.fr)

© European Southern Observatory (ESO) 1999

Online publication: February 22, 1999

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