Polarimetric studies of comet Halley
In the present work, the non-spherical grain characteristics of comet Halley are analysed using the T-matrix method at $\lambda = 0.365, 0.485$ and $0.684\mu m$ respectively. In order to analyse the polarisation data of comet Halley, the dust size distribution function derived by Das et al. (2004) for comet Halley is used in the present work. The size range of the grains is taken to be 0.01$\mu m \le$ s $\le 3\mu m$. Using the T-matrix method, the best fit values of complex refractive indices $(n, k)$ and aspect ratio ($E$) are determined at three different wavelengths $ 0.365, 0.485$ and $0.684\mu m$ and the corresponding values are given by $(1.380, 0.043, 0.962), (1.378, 0.049, 0.962)$ and $(1.377, 0.058,0.962)$ respectively. After comparing the above result with Mie theory result, it is found that prolate grains give the best fit to the observed polarisation data of comet Halley. Also the negative polarisation behaviour of comet Halley is discussed thereafter.