论文标题
发电机场对帕克风的影响
The effect of a dynamo-generated field on the Parker wind
论文作者
论文摘要
恒星风是基础发电机的组成部分，这是恒星活动的电动机。风控制恒星的角动量损失，这取决于磁场几何形状，该几何形状在时间和纬度上差异很大。在这里，我们研究了一个自洽模型的基本特性，该模型在球形外壳中包括全局恒星发电机的简单表示，以及风加速并变为超音速的外部。我们使用等温状态方程来为诱导，动量和连续性方程求解轴对称平均场模型。该模型允许同时生成平均磁场和帕克风的发展。所得流量是临界点的跨音速，我们安排在模型的内部和外部半径之间。假定边界条件使磁场对赤道（即偶极）是反对称的。以太阳旋转速率，发电机是振荡性的，为$α^2 $类型。在大多数域中，磁场对应于分裂单极的磁场。磁能通量在恒星表面和临界点之间最大。角动量通量在时间上是高度变化的，并且可以达到负值，尤其是在中间值时。在太阳值高达50倍的快速旋转时，大多数磁场沿模型内部切向圆柱体内的轴丢失。该模型揭示了旨在重现太阳风的模型通常不会预期的意外特征：即使仅在恒星中的$α^2 $ dynamo中，高度可变的角动量通量也是如此。我们的等温模型的主要警告是，具有发电机产生的磁场的磁场很难达到足够小的等离子ββ，而发电机本身在恒星内变得不切实际。
Stellar winds are an integral part of the underlying dynamo, the motor of stellar activity. The wind controls the star's angular momentum loss, which depends on the magnetic field geometry which varies significantly in time and latitude. Here we study basic properties of a self-consistent model that includes simple representations of both the global stellar dynamo in a spherical shell and the exterior in which the wind accelerates and becomes supersonic. We numerically solve an axisymmetric mean-field model for the induction, momentum, and continuity equations using an isothermal equation of state. The model allows for the simultaneous generation of a mean magnetic field and the development of a Parker wind. The resulting flow is transonic at the critical point, which we arrange to be between the inner and outer radii of the model. The boundary conditions are assumed to be such that the magnetic field is antisymmetric about the equator, i.e., dipolar. At the solar rotation rate, the dynamo is oscillatory and of $α^2$ type. In most of the domain, the magnetic field corresponds to that of a split monopole. The magnetic energy flux is largest between the stellar surface and the critical point. The angular momentum flux is highly variable in time and can reach negative values, especially at midlatitudes. At rapid rotation of up to 50 times the solar value, most of the magnetic field is lost along the axis within the inner tangential cylinder of the model. The model reveals unexpected features that are not generally anticipated from models that are designed to reproduce the solar wind: highly variable angular momentum fluxes even from just an $α^2$ dynamo in the star. A major caveat of our isothermal models with a magnetic field produced by a dynamo is the difficulty to reach small enough plasma betas without the dynamo itself becoming unrealistically strong inside the star.
