Aggregate dust model to study the polarization properties of comet C/1996 B2 Hyakutake

摘要

In our present study, the observed linear polarization data of cometHyakutake are studied at wavelengths $\lambda=0.365\mu m$, $\lambda=0.485\mu m$and 0.684$\mu m$ through simulations using Ballistic Particle-Cluster Aggregateand Ballistic Cluster-Cluster Aggregate aggregates of 128 spherical monomers.We first investigated that the size parameter of the monomer, $x$ $\sim$ 1.56-- 1.70, turned out to be most suitable which provides the best fits to theobserved dust scattering properties at three wavelengths $\lambda = 0.365$$\mum$, 0.485$\mu m$ and 0.684$\mu m$. Thus the effective radius of the aggregate(r) lies in the range $0.45 \mu m \le r \le 0.49 \mu m$ at $\lambda =0.365$$\mu m$; $ 0.60 \mu m \le r \le 0.66 \mu m$ at $\lambda = 0.485$$\mu m$and $0.88 \mu m \le r \le 0.94 \mu m$ at $\lambda = 0.684$$\mu m$. Now usingsuperposition \textsc{t-matrix} code and the power-law size distribution, $n(r)\sim r^{-3}$, the best-fitting values of complex refractive indices arecalculated which can best fit the observed polarization data at the above threewavelengths. The best-fitting complex refractive indices $(n,k)$ are found tobe (1.745, 0.095) at $\lambda = 0.365 $ $\mu m$, (1.743, 0.100) at $\lambda =0.485 $ $\mu m$ and (1.695, 0.100) at $\lambda = 0.684$ $\mu m$. The refractiveindices coming out from the present analysis correspond to mixture of bothsilicates and organics, which are in good agreement with the \textit{in situ}measurement of comets by different spacecraft.