THE INFLUENCE OF ICE-COATED GRAINS ON PROTOSTELLAR SPECTRA

Information about protostellar sources obtained by fit calculations co ntain a number of uncertainties due to our poor knowledge of the prope rties of dust grains in dense clouds. From the results of recent obser vational and theoretical studies of dust in dense regions we construct a new dust model that consists of amorphous carbon grains and ice-coa ted silicate grains. The model is based on new refractive indices of a morphous carbon and ice-coated silicate grains. Our model of the ''dir ty ice'' assumes a mixture of H2O and NH3 ice with inclusions of amorp hous carbon. The optical constants are calculated using effective-medi um theory. We determine the opacities of core-mantle-particles with va rying mantle thickness and pollution by spherical Mie calculations and investigate the effects on the spectrum of a embedded source. The dif ferent models for the core-mantle-particles are used to fit the observ ed spectra of two protostellar sources and to determine the envelopes masses of these objects. We find considerable differences in the masse s obtained from different dust models.