# Mixing by overshooting and rotation in intermediate mass stars

## TL;DR

This study reanalyzed eclipsing binary data with models including overshooting and rotational mixing, suggesting that rotational velocity variations explain the observed dispersion in stellar mixing efficiency.

## Contribution

It introduces a combined model of overshooting and rotational mixing to better interpret stellar data, highlighting the role of rotational velocity variations.

## Key findings

- Good agreement with models using fixed overshooting and variable rotation rates.
- Rotational velocities of observed stars match model predictions.
- Large dispersion in overshooting parameter can be explained by rotational mixing.

## Abstract

Double-line eclipsing binaries (DLEBs) have been recently used to constrain the amount of central mixing as a function of stellar mass, with contrasting results. In this work, we reanalyze the DLEB sample by Claret & Torres, using a Bayesian method and new PARSEC tracks that account for both convective core overshooting and rotational mixing. Using overshooting alone we obtain that, for masses larger than about 1.9 M$_{\odot}$, the distribution of the overshooting parameter, $\lambda_\mathrm{ov}$, has a wide dispersion between 0.3 and 0.8, with essentially no values below $\lambda_\mathrm{ov}=$ 0.3 - 0.4. While the lower limit supports a mild convective overshooting efficiency, the large dispersion derived is difficult to explain in the framework of current models of that process, which leave little room for large randomness. We suggest that a simple interpretation of our results can be rotational mixing: different initial rotational velocities, in addition to a fixed amount of overshooting, could reproduce the high dispersion derived for intermediate-mass stars. After a reanalysis of the data, we find good agreement with models computed with fixed overshooting parameter, $\lambda_\mathrm{ov}=0.4$, and initial rotational rates, $\omega$, uniformly distributed in a wide range between $0$ and $0.8$ times the break-up value, at varying initial mass. We also find that our best-fitting models for the components of $\alpha$ Aurigae and TZ Fornacis, agree with their observed rotational velocities, thus providing independent support to our hypothesis. We conclude that a constant efficiency of overshooting in concurrence with a star-to-star variation in the rotational mixing, might be crucial in the interpretation of such data.