辐射加热，原行星盘与死区。I. M星周围星盘的尘埃沉降和热结构
Radiatively heated, protoplanetary discs with dead zones. I. Dust settling and thermal structure of discs around M stars
摘要：
中心恒星对原行星盘的照射是盘的主要加热机制，导致其呈喇叭状几何结构。在一系列论文中，我们研究了2D自洽盘结构和行星迁移之间的深层联系，特别是在M星周围。在这第一篇论文中，我们分析了光盘的热结构，由一个M星通过求解辐射转移方程的Monte Carlo代码。我们对辐射流体静力盘的模拟是现实的和自洽的，因为它们包括具有多种粒度（N=15）的尘埃沉降，盘上嵌入行星的引力，以及死亡区的存在我们表明，尘埃沉降驱动的温度中平面从$r^{-3/5}$分布（良好混合的灰尘模型）朝向$r^{-3/4}$。同时，死区在其外边缘处留下灰尘壁，因为与较大圆盘半径处的主动湍流圆盘相比，在该区域中的灰尘沉降增强。由该辐射壁产生的盘加热在壁前面的死区中提供正的温度梯度区域。这对于减缓行星迁移至关重要，因为林德布拉德扭矩与盘温度成反比。此外，我们表明，低湍流的死区是自洽引起的灰尘沉降，导致开尔文-亥姆霍兹不稳定性（KHI）。我们表明，在死区中由KHI引起的湍流强度为$α=10^{-5}$。
英文摘要：
The irradiation of protoplanetary discs by central stars is the main heating mechanism for discs, resulting in their flared geometric structure. In a series of papers, we investigate the deep links between 2D self-consistent disc structure and planetary migration in irradiated discs, focusing particularly on those around M stars. In this first paper, we analyse the thermal structure of discs that are irradiated by an M star by solving the radiative transfer equation by means of a Monte Carlo code. Our simulations of irradiated hydrostatic discs are realistic and self-consistent in that they include dust settling with multiple grain sizes (N=15), the gravitational force of an embedded planet on the disc, and the presence of a dead zone (a region with very low levels of turbulence) within it. We show that dust settling drives the temperature of the mid-plane from an $r^{-3/5}$ distribution (well mixed dust models) toward an $r^{-3/4}$. The dead zone, meanwhile, leaves a dusty wall at its outer edge because dust settling in this region is enhanced compared to the active turbulent disc at larger disc radii. The disc heating produced by this irradiated wall provides a positive gradient region of the temperature in the dead zone in front of the wall. This is crucially important for slowing planetary migration because Lindblad torques are inversely proportional to the disc temperature. Furthermore, we show that low turbulence of the dead zone is self-consistently induced by dust settling, resulting in the Kelvin-Helmholtz instability (KHI). We show that the strength of turbulence arising from the KHI in the dead zone is $α=10^{-5}$.
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