Dust models for cometary grains to explain optical polarization
A. K. Sen* and H. S. Das
- Department of Physics, Assam University, Silchar 788011, India.
The observed optical polarizations for comets have been explained in the past by assuming the cometary grains to be compact spheres, such that Mie theory could be applied to simulate the observed polarizations. However, from a realistic point of view, recently other shapes like spheroids and aggregates of monomers have been considered for cometary grains. For this purpose, T-matrix or DDA based light scattering techniques have mostly been used to simulate the observed polarizations. Such polarizations, as observed by the authors for comets Halley and Austin, have been explained earlier using Mie theory to understand the composition and size distribution of cometary grains. Recently, the authors have used T-matrix technique and aggregate grain model to explain the polarizations of comets like Hale-Bopp, Levy, and Hyakutake. The simulated polarization values, with the aggregate model, were found to match the observed values much better as compared to compact spherical or spheroidal models. However, difficulties have been noted in a simple aggregate model of grains and some possibilities are discussed here.
- * Corresponding author