Abstract

We calculate the absorption efficiency of the composite grain, made up of a host silicate spheroid and inclusions of ice/graphite/or voids, in the spectral region 1.0 - 30.0 ¹m. The absorption efficiencies of the composite spheroidal grains for three axial ratios are computed using the discrete dipole approximation (DDA). We study the absorption as a function of the volume fraction of the inclusions and porosity. In particular, we study the variation in the 10.0 μm and 18.0 μm absorption features with the volume fraction of the inclusions and porosity. We then calculate the infrared fluxes for these composite grains and compare the model curves with the average observed IRAS - LRS curve, obtained for circumstellar dust shells around several stars.