Lithium abundances in extremely metal-poor turn-off stars

TL;DR

This paper reviews lithium abundances in extremely metal-poor turn-off stars, highlighting the disruption of the Spite plateau at very low metallicities and presenting new data on 44 such stars.

Contribution

It provides an updated analysis of lithium abundances in EMP stars, emphasizing the plateau's meltdown and including new measurements for a significant sample.

Findings

Evidence of Spite plateau disruption at [Fe/H] < -2.8

Li depletion observed in ultra-metal poor star SDSS J102915+172927

Li abundances show broader distribution at lower metallicities

Abstract

We discuss the current status of the sample of Lithium abundances in extremely metal poor (EMP) turn-off (TO) stars collected by our group, and compare it with the available literature results. In the last years, evidences have accumulated of a progressive disruption of the Spite plateau in stars of extremely low metallicity. What appears to be a flat, thin plateau above [Fe/H]\sim-2.8 turns, at lower metallicities, into a broader distribution for which the plateau level constitutes the upper limit, but more and more stars show lower Li abundances. The sample we have collected currently counts abundances or upper limits for 44 EMP TO stars between [Fe/H]=-2.5 and -3.5, plus the ultra-metal poor star SDSS J102915+172927 at [Fe/H]=-4.9. The "meltdown" of the Spite plateau is quite evident and, at the current status of the sample, does not appear to be restricted to the cool end of the effective temperature distribution. SDSS J102915+172927 displays an extreme Li depletion that contrasts with its otherwise quite ordinary set of [X/Fe] ratios.