Evolutionary modelling of subdwarf B stars using MESA with the predictive mixing and convective premixing schemes

TL;DR

This study employs new algorithms in the MESA code to model core and near-core mixing in subdwarf B stars, addressing longstanding issues in core mass determination and convective boundary treatment.

Contribution

It introduces and compares the predictive mixing and convective premixing schemes for evolutionary modeling of subdwarf B stars, highlighting their advantages over traditional methods.

Findings

Convective premixing scheme is preferable.

Core masses are higher with new schemes but still below seismic estimates.

Both algorithms effectively address core boundary and breathing pulse issues.

Abstract

Results of evolutionary modelling of subdwarf B stars are presented. For the first time, we explore the core and near-core mixing in the subdwarf B stars using new algorithms available in the MESA code: the predictive mixing scheme and the convective premixing scheme. We show how both methods handle the problems with determination of convective boundary, discrepancy between core masses obtained from asteroseismology and evolutionary models, and long-standing problems related to the core-helium-burning phase such as splitting of the convective core and the occurrence of breathing pulses. We find that the convective premixing scheme is the preferable algorithm. The masses of the convective core in case of the predictive mixing and the combined convective and semiconvective regions in case of the convective premixing scheme are higher than in the models with only the Ledoux criterion, but they are still lower than the seismic-derived values. Both algorithms are promising and alternative methods of studying models of subdwarf B stars.