LITHIUM IN A SHORT-PERIOD TIDALLY LOCKED BINARY OF M67 - IMPLICATIONSFOR STELLAR EVOLUTION, GALACTIC LITHIUM EVOLUTION, AND COSMOLOGY

In open clusters, late-F stars exhibit a Li maximum (the Li ''peak'' r egion) at lower abundance with age, which could be due either to stell ar depletion or Galactic Li enrichment (or some other cause). We have observed a short-period tidally locked binary (SPTLB) on the Li peak r egion in the old cluster M67 to distinguish between alternatives. SPTL Bs which synchronized in the early pre-main sequence would avoid the r otational mixing which, according to Yale models, may be responsible f or depleting Li with age in open cluster dwarfs. We find that both com ponents of the M67 SPTLB have a Li abundance lying about a factor of 2 or more above any other M67 single star and about a factor of 3 or mo re above the mean Li peak region abundance in M67. Our results suggest that the initial Li abundance in M67 is at least as high as approxima tely 3.0 = 12 + log (N(Li)/N(H)). Our high M67 SPTLB Li abundance and those in other clusters support the combination of Zahn's tidal circul arization and the Yale rotational mixing theories and may indicate tha t the halo Li plateau (analogous to the cluster Li peak region) abunda nce has been depleted from a higher primordial value. Implications are discussed.