Quantifying mixing by shear instabilities in stellar interiors

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

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.