Combining observational techniques to constrain convection in evolved massive star models

TL;DR

This paper investigates how different convection modeling techniques affect the surface abundance predictions of evolved massive stars, using observational data from blue supergiants to constrain stellar interior physics.

Contribution

It demonstrates that the choice of convection criterion, specifically Ledoux versus Schwarzschild, significantly influences the surface abundance predictions in massive star models.

Findings

Ledoux criterion provides a better fit to observed surface abundances.

Surface abundances are highly sensitive to the location of the intermediate convective shell.

Convection physics constraints improve understanding of massive star evolution.

Abstract

Recent stellar evolution computations indicate that massive stars in the range ~ 20 - 30 Msun are located in the blue supergiant (BSG) region of the Hertzsprung-Russell diagram at two different stages of their life: immediately after the main sequence (MS, group 1) and during a blueward evolution after the red supergiant phase (group 2). From the observation of the pulsationnal properties of a subgroup of variable BSGs (alpha Cyg variables), one can deduce that these stars belongs to group 2. It is however difficult to simultaneously fit the observed surface abundances and gravity for these stars, and this allows to constrain the physical processes of chemical species transport in massive stars. We will show here that the surface abundances are extremely sensitive to the physics of convection, particularly the location of the intermediate convective shell that appears at the ignition of the hydrogen shell burning after the MS. Our results show that the use of the Ledoux criterion to determine the convective regions in the stellar models leads to a better fit of the surface abundances for alpha Cyg variables than the Schwarzschild one.