The dependence of convective core overshooting on stellar mass: semi-empirical determination using the diffusive approach with two different element mixtures

TL;DR

This study investigates how convective core overshooting depends on stellar mass by analyzing binary star data and comparing it with stellar evolution models, revealing a sharp increase in overshooting with mass up to 2 solar masses.

Contribution

It provides the first semi-empirical determination of the overshooting parameter's dependence on stellar mass using a sample of well-studied eclipsing binaries.

Findings

Overshooting parameter f(ov) increases sharply from zero between 1.2 and 2.0 solar masses.

The trend is consistent across different element mixtures.

A relationship between overshooting parameters alpha(ov) and f(ov) is established.

Abstract

Convective core overshooting has a strong influence on the evolution of stars of moderate and high mass. Studies of double-lined eclipsing binaries and stellar oscillations have renewed interest in the possible dependence of overshooting on stellar mass, which has been poorly constrained by observations so far. Here we have used a sample of 29 well-studied double-lined eclipsing binaries in key locations of the H-R diagram to establish the explicit dependence of f(ov) on mass, where f(ov) is the free parameter in the diffusive approximation to overshooting. Measurements of the masses, radii, and temperatures of the binary components were compared against stellar evolution calculations based on the MESA code to infer semi-empirical values of f(ov) for each component. We find a clear mass dependence such that f(ov) rises sharply from zero in the range 1.2--2.0 solar masses, and levels off thereafter up to the 4.4 solar mass limit of our sample. Tests with two different element mixtures indicate the trend is the same, and we find it is also qualitatively similar to the one established in our previous study with the classical step-function implementation of overshooting characterized by the free parameter alpha(ov). Based on these measurements we infer an approximate relationship between the two overshooting parameters of alpha(ov)/f(ov) = 11.36 +/- 0.22, with a possible dependence on stellar properties.