Polarimetric studies of comet Hale-Bopp

In the present work, the non-spherical dust grain characteristics of comet Hale-Bopp are studied using the T-matrix method and the modified power law distribution function. It is found that the observed data fits very well with the power index (α) = −3. The best fit values of complex refractive index (n, k) and the aspect ratio (E) at α = −3 are calculated to be (1.382, 0.035, 0.936) and (1.379, 0.041, 0.936) at λ = 0.485μm and 0.684μm respectively. Kerola & Larson (K-L) analysed the same comet using the Tmatrix method and the power law distribution function (α = −3), and found that the prolate grains can explain the observed polarization in a more satisfactory manner as compared to the other shapes. But their analysis could not reproduce the negative polarization branch beyond scattering angle 157. However, the results obtained from the present work successfully generate the expected negative polarization curve beyond 157 and the fitting in this case is much better than K-L’s work. So it is concluded from the present study that the use of modified power law distribution function (with α = −3) can fit the observed data in a better way, as compared to the power law distribution function used by previous authors.