Lithium Abundances of Extremely Metal-Poor Turn-off Stars

TL;DR

This study measures lithium abundances in eleven extremely metal-poor turn-off stars, revealing some with low Li levels and exploring their properties to understand early universe stellar chemistry.

Contribution

First LTE-based Li abundance measurements for four extremely metal-poor stars, expanding knowledge of Li behavior at very low metallicities.

Findings

Some stars have Li abundances below the Spite Plateau.

Average Li abundance for [Fe/H]<-3 stars is lower than for more metal-rich stars.

No clear correlation between Li abundance and other stellar properties.

Abstract

We have determined Li abundances for eleven metal-poor turn-off stars, among which eight have [Fe/H]<-3, based on LTE analyses of high-resolution spectra obtained with the HDS on the Subaru telescope. The Li abundances for four of these eight stars are determined for the first time by this study. Effective temperatures are determined by a profile analysis of H-alpha and H-beta. While seven stars have Li abundances as high as the Spite Plateau value, the remaining four objects with [Fe/H] <-3 have A(Li)=log(Li/H)+12 ~< 2.0, confirming the existence of extremely metal-poor turn-off stars having low Li abundances, as reported by previous work. The average of the Li abundances for stars with [Fe/H]<-3 is lower by 0.2 dex than that of the stars with higher metallicity. No clear constraint on the metallicity dependence or scatter of the Li abundances is derived from our measurements for the stars with [Fe/H]<-3. Correlations of the Li abundance with effective temperatures, with abundances of Na, Mg and Sr, and with the kinematical properties are investigated, but no clear correlation is seen in the extremely metal-poor star sample.