Stellar Convective Penetration: Parameterized Theory and Dynamical Simulations
Stellar Convective Penetration: Parameterized Theory and Dynamical Simulations
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DOI：
10.3847/1538-4357/ac408d
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发表时间：
2022-02-01
影响因子：
4.9
通讯作者：
Brown, Benjamin P.
中科院分区：
文献类型：
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作者：
Anders, Evan H.;Jermyn, Adam S.;Brown, Benjamin P.
大多数恒星都有对流区，其中热量通过流体运动直接传递，但对流边界的行为尚未得到很好的理解。在这里，我们展示了三维数值模拟，展示了穿透区：整个亮度可以由辐射携带的区域，但温度梯度近似为绝热并且存在对流。为了将这种效应参数化，我们定义了“穿透参数”P，它比较了史瓦西对流边界两侧的辐射梯度偏离绝热梯度的距离。在Roxburgh和Zahn的基础上，我们构建了一个基于能量的理论模型，其中P控制渗透程度。我们使用3D数值模拟来验证这一理论，该模拟采用了简化的Boussinesq恒星对流模型。对流是由内部加热驱动的，我们使用与高度相关的辐射电导率。这允许我们单独指定。还有刚度。辐射-对流边界。我们在所有模拟中都发现了显著的对流穿透。我们的简单理论很好地描述了模拟。穿透层的形成可能需要数千次的翻转，因此需要长时间的模拟或加速进化技术。在恒星中，我们预计P近似于1，在这种情况下，我们的结果表明对流区可能会延伸到史瓦西边界之外，最多可达混合长度的20%-30%。我们提出了一个MESA太阳恒星模型，该模型采用对流穿透的参数化作为概念的证明。最后，我们讨论了将这些结果扩展到更现实的恒星背景的前景。
Most stars host convection zones in which heat is transported directly by fluid motion, but the behavior of convective boundaries is not well-understood. Here, we present 3D numerical simulations that exhibit penetration zones: regions where the entire luminosity could be carried by radiation, but where the temperature gradient is approximately adiabatic and convection is present. To parameterize this effect, we define the "penetration parameter" P, which compares how far the radiative gradient deviates from the adiabatic gradient on either side of the Schwarzschild convective boundary. Following Roxburgh and Zahn, we construct an energy-based theoretical model in which P controls the extent of penetration. We test this theory using 3D numerical simulations that employ a simplified Boussinesq model of stellar convection. The convection is driven by internal heating, and we use a height-dependent radiative conductivity. This allows us to separately specify . and the stiffness. of the radiative-convective boundary. We find significant convective penetration in all simulations. Our simple theory describes the simulations well. Penetration zones can take thousands of overturn times to develop, so long simulations or accelerated evolutionary techniques are required. In stars, we expect P approximate to 1, and in this regime, our results suggest that convection zones may extend beyond the Schwarzschild boundary by up to similar to 20%-30% of a mixing length. We present a MESA stellar model of the Sun that employs our parameterization of convective penetration as a proof of concept. Finally, we discuss prospects for extending these results to more realistic stellar contexts.