The AMBRE project: a study of Li evolution in the Galactic thin and thick discs

TL;DR

This study models lithium evolution in the Milky Way's thin and thick discs, revealing that observed double-branch behavior depends on stellar source longevity and primordial lithium levels, with implications for stellar depletion processes.

Contribution

It introduces a semi-analytical model incorporating updated yields and radial migration to explain lithium evolution and the double-branch behavior in Galactic discs.

Findings

Long-lived stellar sources reproduce the observed Li/H double-branch.

Li depletion in stellar envelopes affects observed Li/H trends.

Primordial Li levels influence the Li evolution patterns.

Abstract

Recent observations suggest a "double-branch" behaviour of Li/H versus metallicity in the local thick and thin discs. This is reminiscent of the corresponding O/Fe versus Fe/H behaviour, which has been explained as resulting from radial migration in the Milky Way disc. We use a semi-analytical model of disc evolution with updated chemical yields and parameterised radial migration. We explore the cases of long-lived (red giants of a few Gy lifetime) and shorter-lived (Asymptotic Giant Branch stars of several 10$^8$ yr) stellar sources of Li, as well as those of low and high primordial Li. We show that both factors play a key role in the overall Li evolution. We find that the observed "two-branch" Li behaviour is only directly obtained in the case of long-lived stellar Li sources and low primordial Li. In all other cases, the data imply systematic Li depletion in stellar envelopes, thus no simple picture of the Li evolution can be obtained. This concerns also the reported Li/H decrease at supersolar metallicities.