由可变磁盘风和雪崩吸积流产生的环和隙：I。轴对称电阻性MHD模拟
Rings and gaps produced by variable magnetic disk winds and avalanche accretion streams: I. Axisymmetric resistive MHD simulations
摘要：
在年轻恒星周围越来越多的圆盘中观察到环和间隙。我们说明了这样的径向结构的形成，通过理想化的，二维（轴对称）的电阻MHD模拟耦合盘风系统线程由一个相对较弱的极向磁场（等离子体- $β\sim 10^3$）。我们发现两种不同的吸积模式取决于电阻率和场强。小的电阻率或高的场强促进了在垂直延伸的盘包层中快速下落的“雪崩吸积流”的发展，这种包层主导着系统的动力学，特别是质量吸积。在模拟中，流被抑制在较大的折射率或较低的场强下，其中大部分吸积而是通过层流盘发生的。在这些模拟中，磁盘吸积主要是由一个缓慢的风，通常是加速的压力梯度从一个占主导地位的环形磁场。以风为主的吸积和以流为主的吸积模式在盘的表面密度分布中产生突出的特征，包括环和间隙，具有相对于质量的磁通量的强烈空间变化。质量流量比低的区域会快速地吸积，导致间隙的发展，而质量流量比高的区域往往吸积得更慢，从而使物质积累并形成致密的环。在某些情况下，雪崩吸积流被观察到直接通过连续馈送产生致密环。我们讨论了由风和水流驱动的环和间隙形成对晶粒生长和行星形成的影响。
英文摘要：
Rings and gaps are being observed in an increasing number of disks around young stellar objects. We illustrate the formation of such radial structures through idealized, 2D (axisymmetric) resistive MHD simulations of coupled disk-wind systems threaded by a relatively weak poloidal magnetic field (plasma-$β\sim 10^3$). We find two distinct modes of accretion depending on the resistivity and field strength. A small resistivity or high field strength promotes the development of rapidly infalling `avalanche accretion streams' in a vertically extended disk envelope that dominates the dynamics of the system, especially the mass accretion. The streams are suppressed in simulations with larger resistivities or lower field strengths, where most of the accretion instead occurs through a laminar disk. In these simulations, the disk accretion is driven mainly by a slow wind that is typically accelerated by the pressure gradient from a predominantly toroidal magnetic field. Both wind-dominated and stream-dominated modes of accretion create prominent features in the surface density distribution of the disk, including rings and gaps, with a strong spatial variation of the magnetic flux relative to the mass. Regions with low mass-to-flux ratios accrete quickly, leading to the development of gaps, whereas regions with higher mass-to-flux ratios tend to accrete more slowly, allowing matter to accumulate and form dense rings. In some cases, avalanche accretion streams are observed to produce dense rings directly through continuous feeding. We discuss the implications of ring and gap formation driven by winds and streams on grain growth and planet formation.
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