WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. I. SUPPRESSION OF THE MAGNETOROTATIONAL INSTABILITY AND LAUNCHING OF THE MAGNETOCENTRIFUGAL WIND
WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. I. SUPPRESSION OF THE MAGNETOROTATIONAL INSTABILITY AND LAUNCHING OF THE MAGNETOCENTRIFUGAL WIND
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DOI：
10.1088/0004-637x/769/1/76
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发表时间：
2013-05-20
影响因子：
4.9
通讯作者：
Stone, James M.
中科院分区：
文献类型：
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作者：
Bai, Xue-Ning;Stone, James M.
我们进行本地，垂直分层剪切盒MHD模拟的原行星盘（PPD）的基准半径为1 Au，考虑到欧姆电阻率和双极扩散（AD）的影响。的磁扩散系数进行评估自洽从一个查找表的基础上平衡化学。我们首先表明，列入AD显着改变了传统的分层吸积的图片。没有净垂直磁场，系统演变成一个环向场占主导地位的配置与极弱的湍流在远紫外电离层，这是太低效，以驱动快速吸积。在存在弱的净垂直场（等离子体β类似于10（5）在中平面），我们发现，磁旋转不稳定性（MRI）被完全抑制，导致在整个垂直范围的磁盘完全层流。一个强大的磁离心风发射，有效地带走磁盘角动量，很容易占所观察到的吸积率在PPD。此外，在物理盘风的几何形状，所有的吸积流的收益，通过一个强电流层的厚度类似于0.3H，是从磁盘中平面偏移的径向速度高达0.4倍的声速。欧姆电阻率和AD对于抑制MRI和风发射都是必不可少的。风传输效率随着净垂直磁通量和FUV电离穿透深度的增加而增加。我们的层流风解对行星形成和全球PPD演化具有重要意义。
We perform local, vertically stratified shearing-box MHD simulations of protoplanetary disks (PPDs) at a fiducial radius of 1 AU that take into account the effects of both Ohmic resistivity and ambipolar diffusion (AD). The magnetic diffusion coefficients are evaluated self-consistently from a look-up table based on equilibrium chemistry. We first show that the inclusion of AD dramatically changes the conventional picture of layered accretion. Without net vertical magnetic field, the system evolves into a toroidal field dominated configuration with extremely weak turbulence in the far-UV ionization layer that is far too inefficient to drive rapid accretion. In the presence of a weak net vertical field (plasma beta similar to 10(5) at midplane), we find that the magnetorotational instability (MRI) is completely suppressed, resulting in a fully laminar flow throughout the vertical extent of the disk. A strong magnetocentrifugal wind is launched that efficiently carries away disk angular momentum and easily accounts for the observed accretion rate in PPDs. Moreover, under a physical disk wind geometry, all the accretion flow proceeds through a strong current layer with a thickness of similar to 0.3H that is offset from disk midplane with radial velocity of up to 0.4 times the sound speed. Both Ohmic resistivity and AD are essential for the suppression of the MRI and wind launching. The efficiency of wind transport increases with increasing net vertical magnetic flux and the penetration depth of the FUV ionization. Our laminar wind solution has important implications on planet formation and global evolution of PPDs.