辐照后碎片的产生和存活：一个综合的冷却准则
Fragment Production and Survival in Irradiated Disks: A Comprehensive Cooling Criterion
摘要：
引力不稳定的吸积盘会碎裂成恒星或亚恒星伴星。这些碎片的形成和存活取决于自重力、内部压力、潮汐剪切和旋转之间的不稳定平衡。盘的碎裂取决于两个关键因素：（1）盘是否能到达Q=1的碎裂边界;（2）碎片是否能存活许多轨道周期。先前的工作表明，要达到Q=1，并使碎片存活下来，盘必须在轨道时间尺度上冷却。在这里，我们表明，主要由外部照射加热的磁盘总是满足标准的冷却时间准则。因此，即使辐射加热磁盘，使他们更稳定的一般，一旦他们达到碎裂边界，他们更容易碎裂。我们推导出一个新的冷却标准，确定碎片的生存，并计算压力修改希尔半径，它设置的压力支持的对象在开普勒磁盘的最大尺寸。我们的结论是，在原恒星磁盘碎片可能会发生在比以前认为的半径略小，并建议测试未来的模拟，将更好地预测在真实磁盘碎片的结果。
英文摘要：
Accretion disks that become gravitationally unstable can fragment into stellar or sub-stellar companions. The formation and survival of these fragments depends on the precarious balance between self-gravity, internal pressure, tidal shearing, and rotation. Disk fragmentation depends on two key factors (1) whether the disk can get to the fragmentation boundary of Q=1, and (2) whether fragments can survive for many orbital periods. Previous work suggests that to reach Q=1, and have fragments survive, a disk must cool on an orbital timescale. Here we show that disks heated primarily by external irradiation always satisfy the standard cooling time criterion. Thus even though irradiation heats disks, and makes them more stable in general, once they reach the fragmentation boundary, they fragment more easily. We derive a new cooling criterion that determines fragment survival, and calculate a pressure modified Hill radius, which sets the maximum size of pressure-supported objects in a Keplerian disk. We conclude that fragmentation in protostellar disks might occur at slightly smaller radii than previously thought, and recommend tests for future simulations that will better predict the outcome of fragmentation in real disks.
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