First 3DMHD simulation of a massive-star magnetosphere with application to Hα emission from θ1 Ori C
First 3DMHD simulation of a massive-star magnetosphere with application to Hα emission from θ1 Ori C
复制标题
首次对大质量恒星磁层进行 3DMHD 模拟，并将其应用于 θ1 Ori C 的 Hα 发射
DOI：
10.1093/mnras/sts246
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发表时间：
2012
影响因子：
4.8
通讯作者：
R. Townsend
中科院分区：
文献类型：
--
作者：
A. ud;J. Sundqvist;S. Owocki;V. Petit;R. Townsend
我们提出了第一个完整的三维磁流体动力学（MHD）模拟磁沟道和约束的辐射驱动，恒星风。选择特定的参数来代表典型的缓慢旋转的磁性O星星θ 1 Ori C，对于它，离心和其他旋转动力学效应可以忽略不计。计算出的纬度和半径的全球结构与以前的二维模拟中发现的相似，在磁极附近沿着沿着开放磁力线无阻碍的外流，以及一个复杂的内风赤道带被恒星表面附近的闭合环路捕获，让位于阿尔夫夫恩半径以上的外流。与之前的2D工作相比，这里描述的3D模拟现在还显示了这个复杂结构如何在方位角上破碎，在Alfv 'en半径内形成不同的闭合环落块，在外部风中过渡到密度增强的径向辐条，其特征方位角间隔为15 °-20 °。将这些结果应用于线辐射传输的3D程序中，我们发现来自相关3D“动态磁层”的辐射与观测到的来自θ 1 Ori C的Hα辐射很好地匹配，既拟合了其在旋转相位上的动态谱，又拟合了观测到的周期到周期的随机变化水平。与以前开发的2D模型的动态磁层的巴尔末发射的比较一般证实，时间平均超过2D快照可以是一个很好的代理空间平均超过3D的方位角风结构。尽管如此，仍然需要全三维模拟来模拟具有非偶极场分量的磁层的发射，例如θ 1 Ori C的Hα等效宽度曲线中的不对称特征。
We present the first fully 3D magnetohydrodynamic (MHD) simulation for magnetic channelling and confinement of a radiatively driven, massive-star wind. The specific parameters are chosen to represent the prototypical slowly rotating magnetic O star θ 1 Ori C, for which centrifugal and other dynamical effects of rotation are negligible. The computed global structure in latitude and radius resembles that found in previous 2D simulations, with unimpeded outflow along open field lines near the magnetic poles, and a complex equatorial belt of inner wind trapping by closed loops near the stellar surface, giving way to outflow above the Alfv´ en radius. In contrast to this previous 2D work, the 3D simulation described here now also shows how this complex structure fragments in azimuth, forming distinct clumps of closed loop infall within the Alfv´ en radius, transitioning in the outer wind to radial spokes of enhanced density with characteristic azimuthal separation of 15 ◦ –20 ◦ . Applying these results in a 3D code for line radiative transfer, we show that emission from the associated 3D ‘dynamical magnetosphere’ matches well the observed Hα emission seen from θ 1 Ori C, fitting both its dynamic spectrum over rotational phase and the observed level of cycle-to-cycle stochastic variation. Comparison with previously developed 2D models for the Balmer emission from a dynamical magnetosphere generally confirms that time averaging over 2D snapshots can be a good proxy for the spatial averaging over 3D azimuthal wind structure. Nevertheless, fully 3D simulations will still be needed to model the emission from magnetospheres with non-dipole field components, such as suggested by asymmetric features seen in the Hα equivalent-width curve of θ 1 Ori C.