The Gaia -ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc

TL;DR

This study analyzes lithium enrichment in the Milky Way's thick and thin discs using Gaia-ESO data, revealing distinct enrichment histories and correlations with alpha and s-process elements, informing Galactic chemical evolution.

Contribution

It provides new observational evidence of lithium abundance patterns and their relation to Galactic disc evolution, highlighting differences in enrichment processes between thick and thin discs.

Findings

Li-[alpha/Fe] anticorrelation observed, independent of [Fe/H], Teff, log(g)

More Li produced during the thin disc phase than the thick disc

Li correlates with Ba and Y, decreasing above solar metallicity

Abstract

Lithium abundance in most of the warm metal-poor main sequence stars shows a constant plateau (A(Li)~2.2 dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium at the solar system formation time, show a lithium abundance A(Li)~3.26 dex. This pattern reflects the Li enrichment history of the interstellar medium during the Galaxy lifetime. After the initial Li production in Big Bang Nucleosynthesis, the sources of the enrichment include AGB stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia-ESO Survey iDR4 catalog and find a Li-[alpha/Fe] anticorrelation independent of [Fe/H], Teff, and log(g). Since in stellar evolution different {\alpha} enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models.