Quantifying mixing by shear instabilities in stellar interiors: differential rotation

要了解恒星内部的细节及其随时间的演化，需要结合仔细的观测和复杂的理论模型。 加州大学圣克鲁斯分校的这个研究小组将提供改进的、经过数值验证的定量计算机模型，用于恒星内部气体和能量的运输和混合。 这项研究将带来近30年前得出的最新处方，这些处方从未经过严格测试。 这项工作对于恒星内部自转的科学研究具有根本的重要性。这一点在今天尤其重要，因为恒星内部正在用星震学观测进行探测。 首席研究员将继续为各级青年研究人员提供咨询。她参与了两个国际研究生培训项目的执行级别，即伍兹霍尔地球物理流体动力学（GFD）项目和天体物理学的Kavli夏季项目。她帮助运行这些项目，并通过它们为学生提供建议。 下一个GFD计划将集中在类似于这个研究项目的主题上。PI和她的团队将获得旋转恒星稳定分层区域中流体动力学剪切不稳定性引起的混合（热，动量，角动量和化学物质）的可靠定量估计。数值模拟将运行在旋转笛卡尔域位于不同纬度的星星使用剪切盒形式主义。模拟将用于测量，对于给定的剪切速率，旋转速率和流体参数，全球的结果，如湍流雷诺应力，湍流热通量，和化学物种。将探讨两种制度，其中一种是热扩散的影响是重要的（低Peclet数限制）和一个在其中他们不是。后者是标准的剪切不稳定性问题，而前者已被调用作为一种替代机制，称为长期剪切不稳定性。结果将用于验证或无效现有的混合处方，并在必要时创建新的处方。这个奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding the details of the interiors of stars and of their evolution with time requires a combination of careful observations and sophisticated theoretical models. This research team at the University of California-Santa Cruz will provide improved, numerically-validated quantitative computer models for the transport and mixing of gases and energy within stellar interiors. The research will bring up to date prescriptions derived nearly 30 years ago that have never strictly been tested. The work is of fundamental importance for scientific investigations into the internal rotation of stars. This is particularly relevant today, when stellar interiors are being probed with asteroseismology observations. The principal investigator will continue to advise young researchers at all levels. She is involved at the executive level in two international graduate training programs, the Woods Hole Geophysical Fluid Dynamics (GFD) program, and the Kavli Summer Program in Astrophysics. She helps run the programs and advises students through them. The next GFD program will be focused on topics similar to this research project.The PI and her team will obtain 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 in rotating Cartesian domains located at various latitudes in the star using the shearing-box formalism. The simulations will be used to measure, for given shearing rate, rotation rate, and fluid parameters, global outcomes such as the turbulent Reynolds stresses, turbulent fluxes of heat, and the chemical species. Two regimes will be explored, one in which the effects of thermal diffusion are important (the low Peclet number limit) and one in which they are not. The latter is the standard shear instability problem, while the former has been invoked as an alternative mechanism called secular shear instability. The results will be used to validate or invalidate existing mixing prescriptions, and create new prescriptions as necessary. The team also plans to look at both baroclinically stable and unstable cases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.