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

In our present study, the observed linear polarization data of comet Hyakutake are studied at wavelengths $λ=0.365μm$, $λ=0.485μm$ and 0.684$μm$ through simulations using Ballistic Particle-Cluster Aggregate and 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 the observed dust scattering properties at three wavelengths $λ= 0.365$$μm$, 0.485$μm$ and 0.684$μm$. Thus the effective radius of the aggregate (r) lies in the range $0.45 μm \le r \le 0.49 μm$ at $λ= 0.365$$μm$; $0.60 μm \le r \le 0.66 μm$ at $λ= 0.485$$μm$ and $0.88 μm \le r \le 0.94 μm$ at $λ= 0.684$$μm$. Now using superposition \textsc{t-matrix} code and the power-law size distribution, $n(r) \sim r^{-3}$, the best-fitting values of complex refractive indices are calculated which can best fit the observed polarization data at the above three wavelengths. The best-fitting complex refractive indices $(n,k)$ are found to be (1.745, 0.095) at $λ= 0.365$ $μm$, (1.743, 0.100) at $λ= 0.485$ $μm$ and (1.695, 0.100) at $λ= 0.684$ $μm$. The refractive indices coming out from the present analysis correspond to mixture of both silicates and organics, which are in good agreement with the \textit{in situ} measurement of comets by different spacecraft.

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