Quantifying mixing by shear instabilities in stellar interiors

这个项目将数学研究与计算机建模相结合，以更好地理解恒星内部的物质是如何混合的。这些详细的计算模拟结果将被转化为一种适合指导计算机模型的形式，这些模型被天文学团体广泛使用，以了解恒星的整个生命周期。该项目将构成博士论文的基础，并为UCSC本科生提供获得有价值的研究训练的机会。与此同时，PI和她的学生将参与下一届国际夏季天体物理学建模研究所，这是一个为期6周的项目，旨在解决天体物理学领域的突出问题。该项目旨在通过丰富的研究经验培养某一特定领域的研究生，并通过对一名学生的共同指导，促进更多资深研究人员之间的长期合作。这一提议是关于在旋转恒星的稳定分层区域中获得由流体动力剪切不稳定性引起的混合（热、动量、角动量和化学物质）的鲁棒定量估计。对于给定的输入强迫、旋转速率和给定的流体参数，将运行数值模拟来测量全局结果，例如(1)在平衡状态下产生的剪切剖面和分层剖面(2)湍流雷诺应力和热和化学物质的湍流通量。结果将用于验证或取消现有的混合处方，并在必要时创建新的处方。最后，该模型将被实现到恒星演化代码（如MESA）中，并应用于最近的星震观测提出的一些选择动力学问题（特别是红巨星的旋转剖面）。

This program combines mathematical studies with computer modeling to better understand how material gets mixed inside of stars. The results of these detailed computational simulations will be translated into a form suitable to guide computer models that are widely used by the astronomical community to understand the entire life cycle of stars. This program will form the basis of a PhD thesis and provide opportunities for UCSC undergraduates to gain valuable research training. In conjunction with this effort, the PI and her students will be involved with the next International Summer-Institute for Modeling in Astrophysics, a 6-week long program to solve topical outstanding problems in astrophysics. The program aims to train graduate students in a particular field through intense research experience, and to catalyze long-lasting collaborations between more senior researchers through shared mentorship of a student. This proposal is concerned with obtaining robust quantitative estimates for mixing (of heat, momentum, angular momentum and chemical species) induced by hydrodynamic shear instabilities in stably stratified regions of rotating stars. Numerical simulations will be run to measure, for given input forcing, rotation rate, and given fluid parameters, global outcomes such as (1) the resulting shear profile and stratification profile at equilibrium (2) the turbulent Reynolds stresses and turbulent fluxes of heat and chemical species. The results will be used to validate or invalidate existing mixing prescription and to create new prescriptions as necessary. Finally, the model will be implemented into stellar evolution codes (such as MESA), and applied to a few choice dynamical problems (notably, the rotation profiles of red giants) raised by recent asteroseismic observations.