Spin-up/spin-down of magnetized stars with accretion discs and outflows
Spin-up/spin-down of magnetized stars with accretion discs and outflows
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DOI：
10.1093/mnras/275.2.244
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发表时间：
1994-12
影响因子：
4.8
通讯作者：
R. Lovelace;M. Romanova;G. Bisnovatyi-Kogan
中科院分区：
文献类型：
--
作者：
R. Lovelace;M. Romanova;G. Bisnovatyi-Kogan
一项研究是对具有对齐偶极子磁场的旋转恒星上的物质盘吸积进行的研究。这项工作的一个新方面是，当恒星和圆盘的角速度显着不同时，我们认为连接恒星和圆盘的 $\bf B$ 场会迅速膨胀，从而给出从恒星的极帽和圆盘延伸的开放场线区域。盘的开场线区域导致磁力驱动流出的可能性。假设盘的“$\ap$”湍流粘度模型和与该粘度相当的磁扩散率，对流出物及其对盘结构的反向影响进行了分析。发现流出物在径向距离范围内向内延伸到接近$r_{to}$的距离，这是盘的角旋转速率最大值的距离。我们发现$r_{to}$取决于恒星的磁矩，当 $r_{to}$ 超过恒星的共转半径 $r_{cr} = (GM/\om_*^2)^{1\ov 3}$ 时，流出区域通常伴随着恒星的自转速率，我们认为不会出现流出解，而是由于场线扭曲而导致恒星的“磁制动”发生在附近。 $r_{cr}$。磁制动解决方案可以使恒星自转向上或向下旋转（或不改变自转），这主要取决于恒星的磁矩和质量吸积率。对于 $r_{to}$ 与 $r_{cr}$ 相当的系统，当外部扰动导致系统在自旋向上和向下自旋之间翻转时，双峰行为是可能的。
An investigation is made of disk accretion of matter onto a rotating star with an aligned dipole magnetic field. A new aspect of this work is that when the angular velocity of the star and disk differ substantially we argue that the $\bf B$ field linking the star and disk rapidly inflates to give regions of open field lines extending from the polar caps of the star and from the disk. The open field line region of the disk leads to the possibility of magnetically driven outflows. An analysis is made of the outflows and their back affect on the disk structure assuming an ``$\ap$" turbulent viscosity model for the disk and a magnetic diffusivity comparable to this viscosity. The outflows are found to extend over a range of radial distances inward to a distance close to $r_{to}$, which is the distance of the maximum of the angular rotation rate of the disk. We find that $r_{to}$ depends on the star's magnetic moment, the accretion rate, and the disk's magnetic diffusivity. The outflow regime is accompanied in general by a spin-up of the rotation rate of the star. When $r_{to}$ exceeds the star's corotation radius $r_{cr} = (GM/\om_*^2)^{1\ov 3}$, we argue that outflow solutions do not occur, but instead that ``magnetic braking" of the star by the disk due to field-line twisting occurs in the vicinity of $r_{cr}$. The magnetic braking solutions can give spin-up or spin-down (or no spin change) of the star depending mainly on the star's magnetic moment and the mass accretion rate. For a system with $r_{to}$ comparable to $r_{cr}$, bimodal behavior is possible where extraneous perturbations cause the system to flip between spin-up and spin-down.