Lithium evolution in metal-poor stars: from Pre-Main Sequence to the Spite Plateau: an environmental solution to the cosmological lithium problem

Abstract

Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicts 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 Li 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<SUP> 7</SUP>Li could be significantly depleted by convective overshooting in the PMS 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 m<SUB>0 </SUB>= 0.62 - 0.80 M<SUB>☉ </SUB>and the Li decline branch for lower mass dwarfs e.g, m<SUB>0</SUB> = 0.57 - 0.60 M<SUB>☉</SUB> for a wide range of metallicities (Z=0.00001 to Z=0.0005) starting from an initial <SUP>7</SUP>Li abundance A(Li) = 2.72. This environmental Li evolution model offers the possibility to interpret the decreasing of Li abundance in extremely metal-poor stars, the Li disparities in spectroscopic binaries and low Li abundance in planet hosting stars.