再论Be星的粘性跨音速衰变
Revisiting Viscous Transonic Decretion Disks of Be Stars
摘要：
在Be星的背景下，我们重新研究了Be星的粘性跨音速衰减盘模型。该模型是由辐射力驱动的，由于考虑到Shakura Sunyaev处方的光学细线和粘度的合奏。非线性运动方程给出了一个奇点（音速点）和一个本征值，这也是恒星表面的初始条件。然后，为了获得这个特征值，我们将其设置为径向量并进行详细的拓扑分析。此后，我们描述了一个数值方法求解节点和鞍跨音速的解决方案。粘度的值，"alpha"，几乎不能确定声波点的位置，但它决定了解决方案的拓扑结构。我们发现了两个节点的解决方案，这是几乎无法区分它们之间。鞍形解的"alpha"值低于节点解的要求。此外，旋转速度在速度（和密度）分布中并不起决定性作用，因为粘性效应使所有解在恒星表面上方的一个小区域内几乎都是唯一的。线力参数和/或磁盘温度的适当组合，给出低于50恒星半径的音速点的位置，描述了一个截断的磁盘。这可以解释在Be星中观察到的SED翻转，而不需要一个双伴星。
英文摘要：
In the context of Be stars, we restudied the viscous transonic decretion disk model of these stars. This model is driven by a radiative force due to an ensemble of optically-thin lines and viscosity considering the Shakura Sunyaev prescription. The non-linear equation of motion presents a singularity (sonic point) and an eigenvalue, which is also the initial condition at the stellar surface. Then, to obtain this eigenvalue, we set it as a radial quantity and perform a detailed topological analysis. Thereafter, we describe a numerical method for solving either Nodal and Saddle transonic solutions. The value of the viscosity,"alpha", barely determine the location of the sonic point, but it determines the topology of the solution. We found two Nodal solutions, which are almost indistinguishable between them. Saddle solutions are founded for lower values of "alpha" than the required of the Nodal solutions. In addition, rotational velocity do not play a determine role in the velocity (and density) profile, because viscosity effects collapse all the solutions to almost a unique one in a small region above the stellar surface. A suitable combination of line force parameters and/or disk temperature, give location of the sonic point lower than 50 stellar radii, describing a truncated disk. This could explain the SED turndown observed in Be stars without needing a binary companion.
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