EVOLUTIONARY MODELS OF HALO STARS WITH ROTATION .2. EFFECTS OF METALLICITY ON LITHIUM DEPLETION, AND POSSIBLE IMPLICATIONS FOR THE PRIMORDIAL LITHIUM ABUNDANCE

We have computed models of metal-poor stars with rotation and compared their lithium depletion with observations of halo stars. The models that have turn-off ages compatible with the observations have a nearly flat Li-T(eff) relationship in the region of the Spite lithium "plateau." Depending on the initial angular momentum, the models have a depletion factor ranging between a factor of 5 and a factor of 10 at fixed T(eff), implying a maximum initial lithium abundance of 3.1. Both the dispersion and the overall depletion factor are much smaller for metal-poor models than for solar metallicity ones. The factors that deter-mine lithium depletion in rotational models are discussed, and the different depletion patterns in solar metallicity and metal-poor models are traced to differences in their structure and evolution. The dependence of the lithium depletion on age, mass, initial angular momentum, and metallicity is also discussed. The dispersion predicted from our models is not inconsistent with the observations.