原行星盘中不均匀MRI生长对角速度的修正
Modification of Angular Velocity by Inhomogeneous MRI Growth in Protoplanetary Disks
摘要：
我们研究了具有径向非均匀磁场的原行星盘中磁旋转不稳定性（MRI）的演化，发现由于MRI湍流的非均匀增长，盘中气体以超开普勒速度旋转的区域出现。我们进行了二维电阻磁流体力学模拟与剪切盒模型。我们发现，如果空间平均磁雷诺数，这是由稳定和不稳定区域的宽度在初始条件和电阻率的值，是小于1，原来的开普勒剪切流转化为准定常流，使更平坦（刚性旋转在极端情况下）的速度分布出现局部和外部的轮廓往往是超开普勒。角动量和质量转移，由于暂时产生的MRI湍流在最初的不稳定区域是负责的转换。在局部超开普勒区域，由于气动气体阻力和潮汐与盘气体相互作用的迁移是反向的。模拟设置对应于磁盘中全局MRI死区的外边缘和内边缘附近的区域。因此，死区的外缘和内缘一样，都是一个有利于尘埃颗粒聚集形成星子和保留行星胚胎以防止I型迁移的地方。
英文摘要：
We have investigated evolution of magneto-rotational instability (MRI) in protoplanetary disks that have radially non-uniform magnetic field such that stable and unstable regions coexist initially, and found that a zone in which the disk gas rotates with a super-Keplerian velocity emerges as a result of the non-uniformly growing MRI turbulence. We have carried out two-dimensional resistive MHD simulations with a shearing box model. We found that if the spatially averaged magnetic Reynolds number, which is determined by widths of the stable and unstable regions in the initial conditions and values of the resistivity, is smaller than unity, the original Keplerian shear flow is transformed to the quasi-steady flow such that more flattened (rigid-rotation in extreme cases) velocity profile emerges locally and the outer part of the profile tends to be super-Keplerian. Angular momentum and mass transfer due to temporally generated MRI turbulence in the initially unstable region is responsible for the transformation. In the local super-Keplerian region, migrations due to aerodynamic gas drag and tidal interaction with disk gas are reversed. The simulation setting corresponds to the regions near the outer and inner edges of a global MRI dead zone in a disk. Therefore, the outer edge of dead zone, as well as the inner edge, would be a favorable site to accumulate dust particles to form planetesimals and retain planetary embryos against type I migration.
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