磁离心恒星风引起的行星迁移和盘破坏
Planet Migration and Disk Destruction due to Magneto-Centrifugal Stellar Winds
摘要：
本文研究了快速旋转的强磁化金牛座T星的磁离心驱动或简单的磁风对近距离巨行星向内或向外迁移的影响。如果恒星的自转周期$P_*$小于行星的轨道周期$P_p$，作用在行星上的磁化风的方位角冲压压力会增加行星的角动量，并导致向外迁移。在相反的情况下，$P_* > P_p$，行星向内移动。因此，在距离大于（小于）$0.06 {\rm AU}(P_*/5{\rm d})^{2/3}$的轨道上运行的行星往往会被向外（向内）推，其中$P_*$是假设有太阳质量的恒星的自转周期。磁风很可能发生在金牛座T星，那里靠近恒星的气体热速度很小，恒星的磁场很强，恒星旋转很快。这颗行星可观测到的径向运动的时间尺度估计为$\sim 2 - 20$ Myr。一个足够大的行星可能会导致潮汐锁定，一旦发生这种情况，由于磁风的径向迁移就会停止。在多极磁场而不是偶极磁场的情况下，磁风预计对行星迁移很重要，因为在偶极磁场中，风的方向远离赤道面，形成磁层空腔。分析了磁风对吸积盘的侵蚀和最终破坏作用。湍流风/盘边界层的动量积分，这是用来估计磁盘侵蚀的时间尺度为$\sim 1-10^2$ MYR，较低的值的青睐。
英文摘要：
This paper investigates the influence of magneto-centrifugally driven or simply magnetic winds of rapidly-rotating, strongly-magnetized T Tauri stars in causing the inward or outward migration of close-in giant planets. The azimuthal ram pressure of the magnetized wind acting on the planet tends to increase the planet's angular momentum and cause outward migration if the star's rotation period $P_*$ is less than the planet's orbital period $P_p$. In the opposite case, $P_* > P_p$, the planet migrates inward. Thus, planets orbiting at distances larger (smaller) than $0.06 {\rm AU}(P_*/5{\rm d})^{2/3}$ tend to be pushed outward (inward), where $P_*$ is the rotation period of the star assumed to have the mass of the sun. The magnetic winds are likely to occur in T Tauri stars where the thermal speed of the gas close to the star is small, where the star's magnetic field is strong, and where the star rotates rapidly. The time-scale for appreciable radial motion of the planet is estimated as $\sim 2 - 20$ Myr. A sufficiently massive close-in planet may cause tidal locking and once this happens the radial migration due to the magnetic wind ceases. The magnetic winds are expected to be important for planet migration for the case of a multipolar magnetic field rather than a dipole field where the wind is directed away from the equatorial plane and where a magnetospheric cavity forms. The influence of the magnetic wind in eroding and eventually destroying the accretion disk is analyzed. A momentum integral is derived for the turbulent wind/disk boundary layer and this is used to estimate the disk erosion time-scale as $\sim 1-10^2$ Myr, with the lower value favored.
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