基于三方程非定域理论的超调恒星演化模型I。耗散率的物理基础及计算
Stellar evolution models with overshooting based on 3-equation non-local theories I. Physical basis and the computation of the dissipation rate
摘要：
上下文对流过冲混合长期以来一直被认为对恒星对流核心中可用于核燃烧的氢量起着重要作用。模拟这种效应的最佳方法仍在争论中。目标。我们提出了一种改进的湍流动能耗散率计算模型，该模型可用于恒星对流的非局域模型，并且可以很容易地实现并自洽地用于一维恒星演化计算。方法.本文综述了恒星天体物理学中计算湍流动能耗散率ε的各种模型的物理基础，特别是在局部和非局部对流模型中。不同的贡献的耗散率和它们的依赖本地分层和非本地运输进行了分析，并提出了一种新的方法来考虑至少一些这些物理机制。结果我们展示了新的方法如何影响中等质量主序星的恒星模型的预测，以及这些变化如何不同于其他修改的非本地对流模型，专注于水平与垂直（湍流）动能的比例。结论.新的模型允许在物理上更完整的描述对流超冲和大质量恒星的混合。浮力波耗散被认为是一个关键的成分，必须占湍流对流的非本地模型。
英文摘要：
Context. Mixing by convective overshooting has long been suggested to play an important role for the amount of hydrogen available to nuclear burning in convective cores of stars. The best way to model this effect is still debated. Aims. We suggest an improved model for the computation of the dissipation rate of turbulent kinetic energy which can be used in non-local models of stellar convection and can readily be implemented and self-consistently used in 1D stellar evolution calculations. Methods. We review the physics underlying various models to compute the dissipation rate of turbulent kinetic energy, ε, in local and particularly in non-local models of convection in stellar astrophysics. The different contributions to the dissipation rate and their dependence on local stratification and on non-local transport are analysed and a new method to account for at least some of these physical mechanisms is suggested. Results. We show how the new approach influences predictions of stellar models of intermediate-mass main-sequence stars and how these changes differ from other modifications of the non-local convection model that focus on the ratio of horizontal to vertical (turbulent) kinetic energy. Conclusions. The new model is shown to allow for a physically more complete description of convective overshooting and mixing in massive stars. Dissipation by buoyancy waves is found to be a key ingredient which has to be accounted for in non-local models of turbulent convection.
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