磁旋转驱动湍流盘II中的尘埃沉降：流动不稳定性的普遍性及其后果
Dust Settling in Magnetorotationally-Driven Turbulent Discs II: The Pervasiveness of the Streaming Instability and its Consequences
摘要：
我们提出了一系列的模拟湍流分层的原恒星盘的目标，在整个最小质量的太阳星云的尘埃沉降的特征。我们比较了两个紧凑的球形颗粒的演变，以及高度分形颗粒。我们的模拟使用剪切盒配方来研究尘埃颗粒的演变，在光盘本地，和集体我们的模拟跨越一个典型的吸积盘的整个范围。尘埃被经历MRI驱动的湍流的气体搅动。这建立了粉尘的稳态标度高度，其对于不同尺寸的粉尘是不同的。这种尘埃的沉积是行星形成的重要的第一步，我们预测ALMA应该能够通过观测证实它的存在。当发生显著的沉降时，尘埃将参与流动不稳定性，从而显著提高尘埃密度。我们表明，流的不稳定性是普遍的外光盘。我们的特点的规模高度的灰尘，其大小范围从几微米到几厘米。我们发现，对于球形晶粒，幂律关系的发展规模的高度与晶粒尺寸，与一个斜率是稍微陡于-1/2。沉积作用在外盘最强，大颗粒的沉积作用增强。这里给出的结果表明，直接测量颗粒沉降可以由ALMA，我们提出了有利的条件，可观测性。流不稳定性也应该是直接可观察的，我们提供了直接观察它的条件，我们计算了碰撞率和增长率的尘埃颗粒在我们的模拟不同大小的碰撞与其他颗粒，并发现这些速率显着提高，通过密度增强所产生的流不稳定性。
英文摘要：
We present a series of simulations of turbulent stratified protostellar discs with the goal of characterizing the settling of dust throughout a minimum-mass solar nebula. We compare the evolution of both compact spherical grains, as well as highly fractal grains. Our simulations use a shearing-box formulation to study the evolution of dust grains locally within the disc, and collectively our simulations span the entire extent of a typical accretion disc. The dust is stirred by gas that undergoes MRI-driven turbulence. This establishes a steady state scale height for the dust that is different for dust of different sizes. This sedimentation of dust is an important first step in planet formation and we predict that ALMA should be able to observationally verify its existence. When significant sedimentation occurs, the dust will participate in a streaming instability that significantly enhances the dust density. We show that the streaming instability is pervasive in the outer disc. We characterize the scale heights of dust whose size ranges from a few microns to a few centimeters. We find that for spherical grains, a power-law relationship develops for the scale height with grain size, with a slope that is slightly steeper than -1/2. The sedimentation is strongest in the outer disc and increases for large grains. The results presented here show that direct measurements of grain settling can be made by ALMA and we present favorable conditions for observability. The streaming instability should also be directly observable and we provide conditions for directly observing it. We calculate collision rates and growth rates for the dust grains in our simulations of various sizes colliding with other grains, and find that these rates are significantly enhanced through the density enhancement arising from the streaming instability.
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