Exploring Mixing Thresholds in Asteroseismic Stellar Evolution Models

Abstract

Inferences from observations clearly show that mixing in stars extends beyond the convective boundaries defined by mixing length theory. This triggered the proposal of a variety of prescriptions to include additional mixing in stellar models. These prescriptions typically introduce free parameters to set the extent of the additional mixing and may also introduce numerical parameters. In the case of exponential overshooting, one must decide the threshold at which the exponential decay of the mixing coefficient can be treated as zero. Using the MESA stellar evolution code, I explore the effect of varying this parameter on asteroseismic models of main-sequence stars with growing convective cores. From this, I conclude that overshoot_D_min should be set to $10^{-2}$ cm$^2$/s or lower for these stars. The default value in MESA is four orders of magnitude higher than this recommendation, which results in discontinuous evolution.