Galactic Evolution of ⁷Li: Observational Clues for Models

Abstract

Different stellar sources may have contributed to the ⁷Li enrichment of the Galaxy: type-II supernovae, novae, and AGB stars. In the latter case, the interplay between the Hot Bottom Burning (HBB) process (via the Cameron-Fowler mechanism) and a very high mass-loss rate before the evolution off the AGB (the so-called ‘superwind’ phase), can lead to a significant production of ⁷Li from low- and intermediate-mass AGB stars (Travaglio et al., 2001). We have now undertaken an observational campaign aimed at constraining our stellar and Galactic models, with a twofold goal: (i)to assemble a compilation of high-resolution spectra of Galactic, unevolved (i.e. dwarfs), warm (spectral type F) stars, in a selected metallicity range (−1.0 ≤ [Fe/H] ≤ −0.3), using the ESO 1.5m telescope and the FEROS spectrograph; (ii) to carry out a Li survey among a sample of selected AGB stars, to investigate the possible correlation between ⁷Li abundance (when detected) and mass-loss rate.