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Astron. Astrophys. 339, L17-L20 (1998)

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Letter to the Editor

Ice segregation toward massive protostars

P. Ehrenfreund 1, E. Dartois 2, K. Demyk 2 and L. d'Hendecourt 2

1 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
2 Institut d'Astrophysique Spatiale, Bat. 121, Campus d'Orsay, F-91405 Orsay Cedex, France

Received 11 August 1998 / Accepted 14 September 1998


Recent ISO results allow new insights into the evolution of interstellar ices in the vicinity of massive protostars. The presence of CO2 ice has recently been confirmed with the SWS (Short Wavelength Spectrometer) on-board ISO as a dominant ice component of interstellar grain mantles. The bending mode of CO2 ice, currently observed toward many massive protostars, shows a particular triple-peak structure. We report on recent laboratory results which identify the CO2 bending mode feature in dense clouds with molecular complexes formed between CO2 and CH3OH ice, which become spectroscopically discernible during the ice segregation process. The comparison of laboratory data and the ISO spectrum of RAFGL7009S indicates the presence of an ice layer with a composition of CO2, CH3OH and H2O in equal proportions. This paper shows evidence for ice segregation and thermal processing in the line-of-sight toward massive protostars.

Key words: ISM: molecules – dust – infrared: interstellar: lines – ISM: individual: RAFGL7009S

Send offprint requests to: P. Ehrenfreund

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© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998