INTERSTELLAR EXTINCTION MODELLING BY AGGREGATE DUST

Extinction generally ours whenever electromagnetic radiation propagates through a medium containing small particles. The spectral dependence of extinction, or extinction curve, is a function of the composition, structure and size distribution of the particles. The study of interstellar extinction is important because they provide essential information for understanding the properties of the dust. In this work we have considered the aggregate dust model to interpret the extinction efficiency (Qext) of interstellar dust in the wavelength range 0.11µm to 3.4µm. Using Superposition T-matrix code with Ballistic Cluster-Cluster Aggregate (BCCA) aggregate having 64 number of monomers with graphite, astronomical silicates and amorphous carbon, the normalized extinction efficiency has been calculated for a well designed size distribution within a size range 0.001 to 0.077 micron of extinction near wavelength 0.2175µm. It is seen that for large grain size distribution the well pronounced UV-bump almost disappear. Moreover the nature of variation of extinction curve with increasing size of          the grain has also been shown.