TYPE I PLANET MIGRATION IN A MAGNETIZED DISK. II. EFFECT OF VERTICAL ANGULAR MOMENTUM TRANSPORT
TYPE I PLANET MIGRATION IN A MAGNETIZED DISK. II. EFFECT OF VERTICAL ANGULAR MOMENTUM TRANSPORT
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DOI：
10.1088/0004-637x/802/1/55
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发表时间：
2015-01
期刊：
影响因子：
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通讯作者：
A. Bans;A. Königl;A. Uribe
中科院分区：
文献类型：
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作者：
A. Bans;A. Königl;A. Uribe
在理想磁流体力学极限下，利用线性摄动分析研究了原行星盘中大尺度有序磁场对I型行星迁移的影响。我们关注风力驱动磁盘，其中磁转矩∝B 0 z∂B 0 /∂z ？>(其中B0z和b0 ？>是平衡垂直和方位场分量)诱导垂直角动量输运。导出了圆盘响应的控制微分方程，并确定了其共振点和拐点。对于含有轻度亚热纯b0z场的圆盘，总三维扭矩接近其在二维（2D）极限值，但仍低于流体动力扭矩。与二维纯b0 ？在Terquem考虑的>场模型中，当场振幅随半径减小时，向内偏移不减小。亚属b0的存在？>分量的振幅在z = 0时从零开始增加，单独作用时对转矩的影响很小，但与B0z分量一起作用时，它产生了一个强大的转矩，加速了向内迁移的速度，大约是原来的200倍。>。然而，在实际磁盘中，这个因素可以通过耗散和磁扩散效应来减小。与之前研究过的所有磁盘迁移模型不同，在b0z +∂b0 /∂z ？b>的情况下，主要贡献的扭矩，以相同的符号从行星的两侧相加。我们将这种行为归因于一种新的相互作用模式，即行星通过插入盘的潜在角动量传输机制向内移动。
We study the effects of a large-scale, ordered magnetic field in protoplanetary disks on Type I planet migration using a linear perturbation analysis in the ideal-magnetohydrodynamic limit. We focus on wind-driving disks, in which a magnetic torque ∝ B 0 z ∂ B 0 / ∂ z ?> (where B0z and B 0 ?> are the equilibrium vertical and azimuthal field components) induces vertical angular momentum transport. We derive the governing differential equation for the disk response and identify its resonances and turning points. For a disk containing a slightly subthermal, pure-B0z field, the total three-dimensional torque is close to its value in the two-dimensional (2D) limit, but remains lower than the hydrodynamic torque. In contrast with the 2D pure- B 0 ?> field model considered by Terquem, inward migration is not reduced when the field amplitude decreases with radius. The presence of a subdominant B 0 ?> component whose amplitude increases from zero at z = 0 has little effect on the torque when acting alone, but in conjunction with a B0z component it gives rise to a strong torque that speeds up the inward migration by a factor ≳ 200 ?> . This factor could, however, be reduced in a real disk by dissipation and magnetic diffusivity effects. Unlike all previously studied disk migration models, in the B 0 z + ∂ B 0 / ∂ z ?> case the dominant contributions to the torque add with the same sign from the two sides of the planet. We attribute this behavior to a new mode of interaction wherein a planet moves inward by plugging into the disk’s underlying angular momentum transport mechanism.