Lithium abundance in cluster giants: constraints on meridional circulation transport on the main sequence

The observed Li abundances in giants are used here to constrain meridional circulation transport on the main sequence. It is shown how meridional circulation, operating over the main-sequence lifetime, can lead to Li depletion in the upper radiative envelope and eventually to extreme Li underabundance in first-ascent giants, following convective dilution on the lower giant branch. In the mass range 1.2-2.0 solar, stars with equatorial rotational velocities greater than 30-35 km/s on the ZAMS should destroy most of their Li. These result are compared to recent Li abundance determination in three moderately old clusters, NGC 7789, NGC 752, and M67. Reasonably good agreement is found with data on M67 and NGC 752, but surprising disagreement with data on NGC 7789 is found. Possible explanations are considered. 60 refs.