Lithium depletion in solar-like stars: effect of overshooting based on realistic multi-dimensional simulations

TL;DR

This paper introduces a new physically motivated model for lithium depletion in solar-like stars, based on multi-dimensional simulations and statistical analysis of convective mixing, explaining observed lithium abundances across stellar ages.

Contribution

It develops a novel diffusion coefficient from 3D hydrodynamic simulations and integrates it into stellar models to explain lithium depletion.

Findings

The model reproduces observed lithium trends in stars from 50 Myr to 4 Gyr.

Rotation influences mixing efficiency, affecting lithium depletion.

A threshold in stellar rotation rate determines the extent of convective penetration.

Abstract

We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from $\sim$ 50 Myr to $\sim$ 4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long standing problem of lithium depletion in pre-main sequence and main sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.