Evolution of lithium abundance in the Sun and solar twins

TL;DR

This study investigates how lithium abundance in the Sun and solar twins evolves, emphasizing the significant depletion during the pre-main sequence stage and the minimal change during the main sequence, influenced by overshooting regions.

Contribution

It provides a detailed analysis of lithium burning stages, highlighting the role of overshooting regions and explaining lithium dispersion among solar twins.

Findings

Lithium is mainly burned during the pre-main sequence stage.

Overshooting regions influence lithium depletion but are limited during the main sequence.

Variations in early evolution conditions explain lithium abundance differences in solar twins.

Abstract

Evolution of the 7Li abundance in the convection zone of the Sun during different stages of its life time is considered to explain its low photospheric value in comparison with that of the solar system meteorites. Lithium is intensively and transiently burned in the early stages of evolution (pre-main sequence, pMS) when the radiative core arises, and then the Li abundance only slowly decreases during the main sequence (MS). We study the rates of lithium burning during these two stages. In a model of the Sun, computed ignoring pMS and without extra-convective mixing (overshooting) at the base of the convection zone, the lithium abundance does not decrease significantly during the MS life time of 4.6 Gyr. Analysis of helioseismic inversions together with post-model computations of chemical composition indicates the presence of the overshooting region and restricts its thickness. It is estimated to be approximately half of the local pressure scale height 0.5Hp) which corresponds to 3.8 % of the solar radius. Introducing this extra region does not noticeably deplete lithium during the MS stage. In contrast, at the pMS stage, an overshooting region with a value of approximately 0.18Hp is enough to produce the observed lithium depletion. If we conclude that the dominant lithium burning takes place during the pMS stage, the dispersion of the lithium abundance in solar twins is explained by different physical conditions, primarily during the early stage of evolution before the MS.