The Gaia-ESO Survey: Galactic evolution of lithium from iDR6

Context. After more than 50 years, astronomical research still struggles to reconstruct the history of lithium enrichment in the Galaxy and to establish the relative importance of the various Li-7 sources in enriching the interstellar medium (ISM) with this fragile element. Aims. To better trace the evolution of lithium in the Milky Way discs, we exploit the unique characteristics of a sample of open clusters (OCs) and field stars for which high-precision Li-7 abundances and stellar parameters are homogeneously derived by the Gaia-ESO Survey (GES). Methods. We derive possibly un-depleted Li-7 abundances for 26 OCs and star forming regions with ages from young (similar to 3 Myr) to old (similar to 4.5 Gyr), spanning a large range of galactocentric distances, 5 < R-GC/kpc < 15, which allows us to reconstruct the local late Galactic evolution of lithium as well as its current abundance gradient along the disc. Field stars are added to look further back in time and to constrain Li-7 evolution in other Galactic components. The data are then compared to theoretical tracks from chemical evolution models that implement different Li-7 forges. Results. Thanks to the homogeneity of the GES analysis, we can combine the maximum average Li-7 abundances derived for the clusters with Li-7 measurements in field stars. We find that the upper envelope of the Li-7 abundances measured in field stars of nearly solar metallicities (-0.3 < [Fe/H]/dex < +0.3) traces very well the level of lithium enrichment attained by the ISM as inferred from observations of cluster stars in the same metallicity range. We confirm previous findings that the abundance of Li-7 in the solar neighbourhood does not decrease at super-solar metallicity. The comparison of the data with the chemical evolution model predictions favours a scenario in which the majority of the Li-7 abundance in meteorites comes from novae. Current data also seem to suggest that the nova rate flattens out at later times. This requirement might have implications for the masses of the white dwarf nova progenitors and deserves further investigation. Neutrino-induced reactions taking place in core-collapse supernovae also produce some fresh lithium. This likely makes a negligible contribution to the meteoritic abundance, but could be responsible for a mild increase in the Li-7 abundance in the ISM of low-metallicity systems that would counterbalance the astration processes.

Automated summary

By studying open clusters and field stars, we can gain insights into the evolution and distribution of lithium in the Milky Way galaxy. This research helps us understand the origins and enrichment processes of Li-7 in different regions of the Galaxy over time.