Suppression of lithium depletion in young low-mass stars from fast rotation

TL;DR

This study develops modified 1D stellar evolution models incorporating rotation effects inspired by 3D simulations, successfully explaining lithium depletion patterns in young low-mass stars.

Contribution

It introduces a new approach to modeling stellar convection by integrating the Solberg-H{ }iland criterion, improving the understanding of lithium depletion in fast-rotating stars.

Findings

Rapid rotation suppresses convection, reducing lithium depletion.

Modified models match observed lithium spread in young clusters.

Convection suppression explains the correlation between rotation and lithium abundance.

Abstract

We compute rotating 1D stellar evolution models that include a modified temperature gradient in convection zones and criterion for convective instability inspired by rotating 3D hydrodynamical simulations performed with the MUSIC code. In those 3D simulations we found that convective properties strongly depend on the Solberg-H{\o}iland criterion for stability. We therefore incorporated this into 1D stellar evolution models by replacing the usual Schwarzschild criterion for stability and also modifying the temperature gradient in convection zones. We computed a grid of 1D models between 0.55 and 1.2 stellar masses from the pre-main sequence to the end of main sequence in order to study the problem of lithium depletion in low-mass main sequence stars. This is an ideal test case because many of those stars are born as fast rotators and the rate of lithium depletion is very sensitive to the changes in the stellar structure. Additionally, observations show a correlation between slow rotation and lithium depletion, contrary to expectations from standard models of rotationally driven mixing. By suppressing convection, and therefore decreasing the temperature at the base of the convective envelope, lithium burning is strongly quenched in our rapidly rotating models to an extent sufficient to account for the lithium spread observed in young open clusters.