Ice segregation toward massive protostars

Abstract

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.