加热和冷却原恒星
Heating and Cooling Protostellar Disks
摘要：
我们研究加热和冷却的原恒星盘使用3-D辐射MHD计算补丁的太阳星云在1 AU，采用剪切盒和通量限制辐射扩散近似。盘状大气被恒星X射线电离，与磁场耦合良好，并维持着由磁旋转不稳定性驱动的湍流吸积流，而内部是电阻性的和磁死的。湍流层通过吸收来自中心恒星的光和耗散磁场来加热。它们对于自身的辐射来说是光学薄的，并且冷却效率低。相比之下，光学厚度的内部只有微弱的加热，来自大气的再辐射。内部比经典的粘性模型更冷，并且是等温的。磁场支持扩展大气层，吸收的星光比流体静力粘性模型高1.5倍。因此，磁盘厚度测量的不是内部温度，而是磁场强度。磁场的波动使吸收星光的表面上下移动。在几个轨道的时间尺度上，高度范围在半径的13%到24%之间，这对红外变化有影响。磁场是浮力的，因此大气中的吸积加热发生在比应力更高的地方。加热是本地化的电流片周围，造成磁旋转不稳定性在较低的海拔和帕克不稳定性在较高的海拔。气体片被加热到恒星的辐射温度以上，即使吸积是远远低于辐射功率时，体积平均。热的光学薄电流片可以通过它们的线发射来检测。
英文摘要：
We examine heating and cooling in protostellar disks using 3-D radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well-coupled to magnetic fields, and sustains a turbulent accretion flow driven by magneto-rotational instability, while the interior is resistive and magnetically dead. The turbulent layers heat by absorbing the light from the central star and by dissipating the magnetic fields. They are optically-thin to their own radiation and cool inefficiently. The optically-thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model, and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations in the fields move the starlight-absorbing surface up and down. The height ranges between 13% and 24% of the radius over timescales of several orbits, with implications for infrared variability. The fields are buoyant, so the accretion heating occurs higher in the atmosphere than the stresses. The heating is localized around current sheets, caused by magneto-rotational instability at lower elevations and by Parker instability at higher elevations. Gas in the sheets is heated above the stellar irradiation temperature, even though accretion is much less than irradiation power when volume-averaged. The hot optically-thin current sheets might be detectable through their line emission.
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