| Abstract |
We present a composite grain model to explain the IRemission features at 10 and 18 microns from thecircumstellar dust of stars. The IRAS-LRS data from about700 stars have been analysed and fitted to a set ofcomposite porous dust grains consisting silicate host andgraphite/vacuum inclusions. The 10 micron silicate featureshifts with the inclusion volume fraction of graphite grainsbut not with the changes in porosity. Both 10 and 18 micronfeatures do not broaden with the inclusions of graphite orvacuum. It is also noted that the axial ratio of the dustgrain shapes change for various types of circumstellar dustobserved in the IRAS data.The model uses a composite fluffy dust grain for explainingmost of the observed interstellar extinction curves and alsopolarization. Another parameter which needs to beconstrained by the dust models is the interstellarabundances of Carbon and Silicon which is usuallyoverestimated by the solid dust models but our modelpredicts closer match to the observed ISM abundances.Further, our composite dust model also explains the IRemission from circumstellar dust. |
