date: 2012 March 14 (Wed) 16:30-17:00
room: CPS Conference Room
speaker: Ranjan Gupta (IUCAA)
organizer: Yoichi Itoh
title: NIR Silicate features and Statistics from IRAS data
abstract: We present a composite grain model to explain the IR emission features at 10 and 18 microns 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 inclusions. The 10 micron silicate feature shifts with the inclusion volume fraction of graphite grains but not with the changes in porosity. Both 10 and 18 micron 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 explaining most of the observed interstellar extinction curves and also polarization. Another parameter which needs to be constrained by the dust models is the interstellar abundances of Carbon and Silicon which is usually overestimated by the solid dust models but our model predicts closer match to the observed ISM abundances. Further, our composite dust model also explains the IR emission from circumstellar dust.
keywords: Dust, Extinction, Circumstellar Matter