Collaborative Research: Multidimensional Hydrodynamic Studies of Convection and Mixing in Stars, Novae, and Supernovae

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This project builds upon a recent breakthrough in the simulation of fully three-dimensional compressible, multifluid, turbulent convection. The convection is nearly adiabatic (high Peclet number), typical of almost all convection in stars (except near the stellar surface), and is calculated until it settles into a quasi-static turbulent steady state. This allows theoretical analysis which shows how to improve the conventional approach to modeling convection (mixing-length theory). It also shows how mixing-length theory could have worked well enough to survive for a half-century. The new results are applicable to almost all stages of stellar evolution. A new feature is turbulent entrainment, which is well known in meteorology, oceanography, and terrestrial experiments, but has not been previously applied to the evolution of stars. The three-dimensional simulations point to a simpler formulation of the stellar convection physics which is being incorporated into stellar evolutionary codes. Here, three specific projects will be undertaken by Drs. Arnett and Starrfield: (1) a recalculation of stellar evolution, from stellar birth to death with the formation of a supernova or a white dwarf, including entrainment and rotation, (2) an extension of the 3D simulations to test these new ideas in different physical conditions, including the effect of rotation, and (3) use of the extensive observational data on classical novae as a theoretical test bed for convective and shear mixing. Extension to classical novae involves both the mixing prior to the thermonuclear runaway and the mixing during the runaway itself. Several outstanding problems will be addressed using the new methods, including the solar abundance problem and helioseismology, mixing in classical novae, isotopic yields from massive stars, mixing in the first stars and its effect on yields, nonspherical behavior in supernova progenitors, and the effect of compositional gradients on solar simulations. The software for stellar evolution developed here and the input data, will be freely available on a website for use by advanced students, teachers, and other scientists, as will a set of multidimensional progenitor models for simulation of core collapse and thermonuclear supernova explosions, and novae. In addition, sample evolutionary sequences (from 0.7 to 200 Solar masses) and isotopic yields will be available for use in galactic evolutionary modeling and for meteoritic studies. Simulations of the bottom of the solar convection zone are proposed which should aid the extension of anelastic methods to deal with nonhomogeneous fluids. Target design for laser experiments at the National Ignition Facility will use simulations from this project to test mixing models for Supernova 1987A.