Infrared observations of hot gas and cold ice toward the low mass protostar Elias 29

We have obtained the full 1-200 mu m spectrum of the low luminosity (36 L-c ircle dot) Class I protostar Elias 29 in the rho Ophiuchi molecular cloud. It provides a unique opportunity to study the origin and evolution of inter stellar ice and the interrelationship of interstellar ice and hot core gase s around low mass protostars. We see abundant hot CO and H2O gas, as well a s the absorption bands of CO, CO2, H2O and "6.85 mu m" ices. We compare the abundances and physical conditions of the gas and ices toward Elias 29 wit h the conditions around several well studied luminous, high mass protostars . The high gas temperature and gas/solid ratios resemble those of relativel y evolved high mass objects (e.g. GL 2591). However, none of the ice band p rofiles shows evidence for significant thermal processing, and in this resp ect Elias 29 resembles the least evolved luminous protostars, such as NGC 7 538 : IRS9. Thus we conclude that the heating of the envelope of the low ma ss object Elias 29 is qualitatively different from that of high mass protos tars. This is possibly related to a different density gradient of the envel ope or shielding of the ices in a circumstellar disk. This result is import ant for our understanding of the evolution of interstellar ices, and their relation to cometary ices.