Optically thin dust models for IRAS point sources

A simple optically thin model is derived to explain the range of infrared spectra of the IRAS point sources. It is found that a model with a stellar source at the center of a small (less than 1-2 pc in radius) dust cloud, where the average temperature of the cloud is varied, can account for the range of IRAS spectral shapes. In this model, a power-law dependence on radius is assumed for both temperature and dust density. Models have been produced for clouds with gas densities of n(H2) about 100-1,000,000/cu cm and masses of about 100-10,000 solar masses. Also, a variety of different types of dust were used to determine their importance. The results are in agreement with Natta and Panagia (1976), that the model is sensitive to the dust type. The model predicts that most of the IRAS sources with a rising spectrum from 12 to 100 microns are O or B type stars. 31 refs.