Magnetic turbulence and thermodynamics in the inner region of protoplanetary discs
Magnetic turbulence and thermodynamics in the inner region of protoplanetary discs
复制标题
原行星盘内部区域的磁湍流和热力学
DOI：
10.1093/mnras/stv203
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发表时间：
2015
影响因子：
4.8
通讯作者：
Shigenobu
中科院分区：
文献类型：
--
作者：
Hirose;Shigenobu
使用辐射磁流体力学模拟与现实的不透明度和状态方程，零净磁通量，我们已经探讨了热力学的内部原行星盘的磁湍流是预期的。热平衡曲线由上、下、中支组成。上（下）分支分别对应于热（冷）和光学上非常（中等）厚的圆盘，而中间分支的特征是中平面附近的对流能量传输。对流也是上分支低面密度端附近主要的能量输送过程。在那里，对流运动是快速的，马赫数达到10.01，并增强了磁湍流和冷却，提高了垂直积分剪切应力的比例垂直积分压力的几个因素。这种对流增强的比率似乎是一个强大的功能，在吸积盘电离过渡。我们还研究了S形热平衡曲线的原因，以及平衡溶液的热稳定性。最后，我们将我们的结果与用于解释FU Ori爆发的盘不稳定模型进行了比较。虽然在我们的研究结果中的热平衡曲线也表现出双稳态，表面密度对比度的双稳态是一个数量级较小，和应力-压力比在上，下分支是两个数量级以上，比在磁盘不稳定模型的青睐。因此，FU Ori爆发似乎不仅仅是由于局部磁湍流驱动的吸积引起的热粘性极限环。
Using radiation magnetohydrodynamics simulations with realistic opacities and equation of state, and zero net magnetic flux, we have explored thermodynamics in the inner part of protoplanetary discs where magnetic turbulence is expected. The thermal equilibrium curve consists of the upper, lower, and middle branches. The upper (lower) branch corresponds to hot (cool) and optically very (moderately) thick discs, respectively, while the middle branch is characterized by convective energy transport near the mid-plane. Convection is also the major energy transport process near the low surface density end of the upper branch. There, convective motion is fast with Mach numbers reaching ≳ 0.01, and enhances both magnetic turbulence and cooling, raising the ratio of vertically-integrated shear stress to vertically-integrated pressure by a factor of several. This convectively enhanced ratio seems a robust feature in accretion discs having an ionization transition. We have also examined causes of the S-shaped thermal equilibrium curve, as well as the thermal stability of the equilibrium solutions. Finally, we compared our results with the disc instability models used to explain FU Ori outbursts. Although the thermal equilibrium curve in our results also exhibits bistability, the surface density contrast across the bistability is an order of magnitude smaller, and the stress-to-pressure ratios in both upper and lower branches are two orders of magnitude greater, than those favoured in the disc instability models. It therefore appears likely that FU Ori outbursts are not due solely to a thermal-viscous limit cycle resulting from accretion driven by local magnetic turbulence.