Lithium abundances for 185 main-sequence stars - Galactic evolution and stellar depletion of lithium

We present a survey of lithium abundances in 185 main- sequence field stars with Teff between 5600 and 6600 K and [Fe/H] from -1.4 to +0.2 based on high-resolution spectra of 130 stars and a reanalysis of data from Lambert et al. (1991). The survey takes advantage of improved ways of determining effective temperature, metallicity, mass and age, offering an opportunity to investigate the behaviour of Li as a function of these parameters. An interesting result is the presence of a large gap in the Li-Teff plane, which distinguishes `Hyades-like, Li-dip' stars from other stars. These Li-dip stars have a well-defined mass, which decreases with metallicity. Stars above the gap, when divided into four metallicity groups, may show a correlation between Li abundance and stellar mass, but with a large dispersion that cannot be explained by observational errors or differences in metallicity and age, which ranges from 1.5 to 15 Gyr. This suggests that Li depletion occurs early in stellar life and that other parameters, e.g. initial rotation velocity and/or the rate of angular momentum loss, affect the degree of depletion. A comparison of the distribution of stars in the Li-[Fe/H] plane with evolutionary models of Romano et al. (1999) suggests that novae are a major source for the Li production in the Galactic disk.