Modeling of silicate emission features in circumstellar dust

Abstract

We present a composite grain model to explain the IR emission features at 10 and 18 µm from the circumstellar dust of stars. The IRAS-LRS data from about 700 stars have been analysed and fitted to a set of composite porous dust grains consisting silicate host and graphite/vacuum nclusions. The 10 µm silicate feature shifts with the inclusion volume fraction of graphite grains but not with the changes in porosity. Both 10 and 18 µm features do not broaden with the inclusions of graphite or vacuum. It is also noted that the axial ratio of the dust grain shapes change for various types of circumstellar dust observed in the IRAS data.The model uses a composite fluffy dust grain for ex-plaining most of the observed interstellar extinction curves and also polarization. Another parameter which needs to be constrained by the dust models is the in-terstellar abundances of Carbon and Silicon which is usually overestimated by the solid dust models but our model predicts closer match to the observed ISM abun-dances. Further, our composite dust model also ex-plains the IR emission from circumstellar dust.