UC Santa Cruz

Minor mixing processes—any fluid processes that mix material or transport heat other than convection or other large-scale flows—play a critical role in stellar evolution. These processes have been invoked through phenomenological models in order to explain away many issues in stellar evolution, such as the blue-red supergiant ratio problem and the progenitor problem of SN 1987A. We discuss our incompressible numerical simulations of one such process, thermohaline convection. We developed a semi-analytic formulation of the thermal and compositional transport of this process, which has been tested by other groups and implemented into MESA and the Toulouse–Geneva Evolution code. We also discuss compressible simulations of overshooting convection by Brummell et al. (2002) and the incompressible simulations of semi- convection by Wood et al. (2013), from which we developed one-dimensional models. We present some recent results of the effects of these models on a 15 solar mass star using the stellar evolution code KEPLER. These simulations put stricter limits on the extent of overshooting convection and the efficiency of semi-convection.