LITHIUM IN THE BINARY HALO STAR HD-89499

We report the finding of an unusually large lithium abundance in the tidally locked binary halo star HD 89499. The effective temperature of this star has been determined to be 4900 + 150 K from photometric and spectroscopic analyses. Its metallicity has been determined to be [Fe/H] = -2.08 +/- 0.07 from 26 Fe I lines and its rotational velocity is estimated to be 22 +/- 4 km s-1. If the star is a dwarf, its lithium abundance log epsilon(Li) = 1.35 which is a factor of 10-30 above that for other halo dwarfs of the same temperature. In this case, the lithium depletion may have been arrested when the rotational period of the star tidally synchronized with the binary orbital period. We discuss applicable models. The rotational velocity is not consistent with a tidally locked dwarf in an ancient 6 day binary system, so either the orbital period is incorrect or the star is evolved. We discuss the difficulties in assigning HD 89499 such an evolved status, but note it is marginally possible, in which case its lithium abundance is still a factor of 3 higher than comparable temperature halo subgiants.