Optical colours and polarization of a model reflection nebula. III. Composite and mixture of grains in the nebula with the star in the rear

Abstract

The colour differences between the star and the associated reflection nebula and polarization caused by core mantle grains and mixture of grains have been given. They are based on homogeneous plane-parallel slab-model of the nebula with the star in the rear. The composite particles in the form of concentric spheres consist of homogeneous core of graphite, silicate or SiC and homogeneous mantle of ice. The effect of varying the core and mantle radii has been studied. The mixtures of grains composed of ice, silicate, graphite and SiC in various proportions have also been considered. Each of these grain species has been considered with exp(−a ³) type of size distribution function. The wavelength dependent indices of refraction have been used throughout.