Lithium evolution in metal-poor stars: from Pre-Main Sequence to the Spite plateau

TL;DR

This paper models lithium evolution in metal-poor stars, incorporating convective overshooting and residual accretion, to explain observed Li abundances and the Spite plateau, addressing the longstanding lithium problem.

Contribution

It introduces a comprehensive stellar Li evolution model that accounts for overshooting and accretion effects, successfully reproducing observed Li patterns across different stellar masses and metallicities.

Findings

Convective overshooting significantly depletes Li in pre-main sequence stars.

Residual accretion can partially restore Li in stellar atmospheres.

The model reproduces the Spite plateau and Li decline in low-mass stars.

Abstract

Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicted by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred as the lithium problem. We here reconsider the stellar Li evolution from the pre-main sequence to the end of the main sequence phase by introducing the effects of convective overshooting and residual mass accretion. We show that $^7$Li could be significantly depleted by convective overshooting in the pre-main sequence phase and then partially restored in the stellar atmosphere by a tail of matter accretion which follows the Li depletion phase and that could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and microscopic diffusion along the main sequence we can reproduce the Spite plateau for stars with initial mass $m_0=0.62 - 0.80 M_{\odot}$, and the Li declining branch for lower mass dwarfs, e.g, $m_0=0.57 - 0.60 M_{\odot}$, for a wide range of metallicities (Z=0.00001 to Z=0.0005), starting from an initial Li abundance $A({\rm Li}) =2.72$. This environmental Li evolution model also offers the possibility to interpret the decrease of Li abundance in extremely metal-poor stars, the Li disparities in spectroscopic binaries and the low Li abundance in planet hosting stars.