蓝超巨星Kappa Cas周围的天体层：其行星结构的可能解释
An astrosphere around the blue supergiant kappa Cas: possible explanation of its filamentary structure
摘要：
斯皮策太空望远镜进行的高分辨率中红外观测使人们能够解析许多天体层的精细结构。特别是，他们发现B0.7 Ia型恒星kappa Cas（HD 2905）周围的天体层具有清晰的弧形结构，其外部有许多卷云状细丝。从理论上证明了它们可能代表了星际尘埃粒子与星际磁场的相互作用所产生的非单调空间分布。在本文中，我们援引这一机制来解释围绕着Kappa Cas的天体层的结构。我们进行了三维磁流体动力学模拟的天体层的恒星风和空间速度的现实参数。在动力学模型的框架内计算了尘埃动力学和天体层中的密度分布。结果表明，星际介质中尘埃的经典MRN粒径分布模型的结果与观测结果不一致，只有当尘埃主要由大颗粒（微米级）组成时，观测到的天体层结构才能被再现。模型结果与观测结果的比较使我们能够估计周围星际介质的参数（数密度和磁场强度）。
英文摘要：
High-resolution mid-infrared observations carried out by the Spitzer Space Telescope allowed one to resolve the fine structure of many astrospheres. In particular, they showed that the astrosphere around the B0.7 Ia star kappa Cas (HD 2905) has a clear-cut arc structure with numerous cirrus-like filaments beyond it. Previously, we suggested a physical mechanism for the formation of such filamentary structures. Namely, we showed theoretically that they might represent the non-monotonic spatial distribution of the interstellar dust in astrospheres (viewed as filaments) caused by interaction of the dust grains with the interstellar magnetic field disturbed in the astrosphere due to colliding of the stellar and interstellar winds. In this paper, we invoke this mechanism to explain the structure of the astrosphere around kappa Cas. We performed 3D magnetohydrodynamic modelling of the astrosphere for realistic parameters of the stellar wind and space velocity. The dust dynamics and the density distribution in the astrosphere were calculated in the framework of a kinetic model. It is found that the model results with the classical MRN size distribution of dust in the interstellar medium do not match the observations, and that the observed filamentary structure of the astrosphere can be reproduced only if the dust is composed mainly of big (micron-sized) grains. Comparison of the model results with observations allowed us to estimate parameters (number density and magnetic field strength) of the surrounding interstellar medium.
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