海尔-波普彗星的偏振研究
Polarimetric studies of comet Hale-Bopp
摘要：
本文用T矩阵方法和修正的幂律分布函数研究了海尔-波普彗星的非球形尘埃颗粒特征。发现观测数据与幂指数（$α) = - 3$ .计算了复折射率$(n, k)$和$α= - 3$处的纵横比（E）的最佳拟合值分别为$λ= 0.485 μm$和$0.684μm$处的$(1.382, 0.035, 0.936)$和$(1.379, 0.041,0.936)$。Kerola & Larson（K-L）使用T矩阵方法和幂律分布函数（$α= -3$）分析了同一颗彗星，发现与其他形状相比，扁长颗粒可以更令人满意的方式解释观察到的偏振。但他们的分析不能再现散射角$157^0$以外的负偏振分支。然而，从目前的工作中获得的结果成功地产生了预期的负极化曲线超过$157^0$和拟合在这种情况下是远远优于K-L的工作。因此，从本研究中得出的结论是，使用修改的幂律分布函数（与$α= - 3$）可以更好地拟合观测数据，与以前的作者使用的幂律分布函数相比。
英文摘要：
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 $λ= 0.485 μm$ and $0.684μm$ respectively. Kerola & Larson (K-L) analysed the same comet using the T-matrix 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 $157^0$. However, the results obtained from the present work successfully generate the expected negative polarization curve beyond $157^0$ 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.
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