Turbulent Mixing and the Dead Zone in Protostellar Disks
Turbulent Mixing and the Dead Zone in Protostellar Disks
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DOI：
10.1086/512007
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发表时间：
2006-12
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影响因子：
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通讯作者：
N. J. Turner;Takayoshi Sano;N. Dziourkevitch
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文献类型：
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作者：
N. J. Turner;Takayoshi Sano;N. Dziourkevitch
我们调查的条件下，在原恒星磁盘使用三维剪切盒MHD计算，包括垂直分层，欧姆电阻率和随时间变化的电离化学的磁不活跃的死区的存在。由磁旋转不稳定性驱动的活动充满了整个厚度的磁盘在5 Au，提供宇宙射线电离是存在的，小颗粒是缺席的，气相金属丰度足够高。在1 Au处，1700 g cm-2的较大柱密度意味着即使在所考虑的最有利的条件下，中平面也被电离粒子屏蔽并且保持磁旋转稳定。然而，有效地消除了死区。湍流将自由电荷混合到内部，因为它们重新组合，导致中平面气体与磁场的轻微耦合。弱的、大尺度的径向场扩散到中平面，在那里它们被剪切掉以产生更强的方位场。平均而言，由此产生的中平面吸积应力仅比表面层小几倍。
We investigate the conditions for the presence of a magnetically inactive dead zone in protostellar disks using three-dimensional shearing-box MHD calculations, including vertical stratification, ohmic resistivity, and time-dependent ionization chemistry. Activity driven by the magneto-rotational instability fills the whole thickness of the disk at 5 AU, provided cosmic-ray ionization is present, small grains are absent, and the gas-phase metal abundance is sufficiently high. At 1 AU, the larger column density of 1700 g cm-2 means the midplane is shielded from ionizing particles and remains magneto-rotationally stable, even under the most favorable conditions considered. Nevertheless, the dead zone is effectively eliminated. Turbulence mixes free charges into the interior as they recombine, leading to a slight coupling of the midplane gas to the magnetic fields. Weak, large-scale radial fields diffuse to the midplane, where they are sheared out to produce stronger azimuthal fields. On average, the resulting midplane accretion stresses are just a few times less than in the surface layers.