不透明度对原行星盘引力稳定性的影响
The effects of opacity on gravitational stability in protoplanetary discs
摘要：
在本文中，我们考虑的不透明度制度的稳定性的影响，自引力原行星盘破碎成绑定对象。使用自洽的1-D粘性盘模型，我们表明，局部冷却的比例动态时间尺度Ω *tcool有很强的依赖于当地的温度。我们调查的影响，温度依赖的冷却功能上的光盘的引力稳定性，通过控制数值实验，使用SPH代码。我们发现，这样的冷却功能提高磁盘的敏感性，通过温度扰动的影响-Ω *tcool的平均值增加，以防止当地的变化，导致崩溃的碎片。我们发现温度依赖性的影响是最显着的“不透明的差距”与尘埃升华，其中欧米茄 *tcool在碎片的平均值增加了超过一个数量级。然后，我们使用这个结果来预测原行星盘将在半径和吸积率方面分裂成束缚物体。我们发现，在没有温度依赖性的情况下，当半径小于10天文单位时，碎裂需要非常大的吸积速率~10^-3 Msun/yr，但在有温度依赖性的冷却条件下，这一速率降低到10^-4 Msun/yr。我们还发现，如果吸积速率小于~10^-7 Msun/yr、半径大于~ 50 AU的盘变得光学薄，那么较低的背景温度会增强盘的稳定性。
英文摘要：
In this paper we consider the effects of opacity regimes on the stability of self-gravitating protoplanetary discs to fragmentation into bound objects. Using a self-consistent 1-D viscous disc model, we show that the ratio of local cooling to dynamical timescales Omega*tcool has a strong dependence on the local temperature. We investigate the effects of temperature-dependent cooling functions on the disc's gravitational stability through controlled numerical experiments using an SPH code. We find that such cooling functions raise the susceptibility of discs to fragmentation through the influence of temperature perturbations - the average value of Omega*tcool has to increase to prevent local variability leading to collapse. We find the effects of temperature dependence to be most significant in the "opacity gap" associated with dust sublimation, where the average value of Omega*tcool at fragmentation is increased by over an order of magnitude. We then use this result to predict where protoplanetary discs will fragment into bound objects, in terms of radius and accretion rate. We find that without temperature dependence, for radii < ~10AU a very large accretion rate ~10^-3 Msun/yr is required for fragmentation, but that this is reduced to 10^-4 Msun/yr with temperature-dependent cooling. We also find that the stability of discs with accretion rates < ~10^-7 Msun/yr at radii > ~50AU is enhanced by a lower background temperature if the disc becomes optically thin.
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