ICE SEGREGATION TOWARD MASSIVE PROTOSTARS

Recent ISO results allow new insights into the evolution of interstell ar ices in the vicinity of massive protostars. The presence of CO2 ice has recently been confirmed with the SWS (Short Wavelength Spectromet er) on-board ISO as a dominant ice component of interstellar grain man tles. The bending mode of CO2 ice, currently observed toward many mass ive 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 segreg ation process. The comparison of laboratory data and the ISO spectrum of RAFGL7009S indicates the presence of an ice layer with a compositio n of CO2, CH3OH and H2O in equal proportions. This paper shows evidenc e for ice segregation and thermal processing in the line-of-sight towa rd massive protostars.