1998ApJ...500..398R

We have measured the Li abundances, or upper limits, of 26 metal-poor stars generally cooler than the Spite plateau, where Li destruction (in dwarfs) and dilution (in subgiants) is expected. These stars were targeted in order to study Li processing mechanisms that must be understood in order for the primordial Li abundances in warmer less-depleted halo stars to be inferred. Iron abundances have also been measured from the spectra. For the cool dwarfs, depletion of Li relative to hotter plateau stars (which may or may not be depleted) becomes significant at 5700 K. They show depletion of Li by ≃0.27 dex per 100 K over the interval 5000 K < T_eff < 5500 K. This trend is shallower than predicted by a subset of 16.5 Gyr Yale ``standard'' (nondiffusive, nonrotating, nonmagnetic, non-mass loss) models, but is in reasonable agreement at 5000 K. The overall depletion pattern appears to be generally independent of metallicity for halo stars. However, several stars of similar temperature and metallicity exhibit different degrees of depletion, and it is possible that metallicity plays a role in this more complex situation. Despite the shallower slope of the observations over this temperature range, depletion becomes a much steeper function of temperature cooler than ∼4900 K, consistent with these (and other) models. The subgiants conform to the dilution patterns previously revealed for this class, except for the high Li abundance of HD 89499. Another mechanism is believed to be responsible for this short-period binary, possibly the suppression by tidal forces of main-sequence rotationally induced mixing.