Element segregation in low-metallicity stars and the primordial lithium abundance

Observational constraints on the primordial lithium abundance are important for the evaluation of the baryonic density of the universe. Its precise determination, however, suffers from uncertainties arising from the possible depletion of this element inside stars. Here we present and discuss new results for the lithium abundances in Population II stars obtained with the most recent stellar models including the best available physics. We show that it is possible to account for the general behavior of lithium observed in Population II stars without any free parameters. Macroscopic motions inside the stars are needed, but it is not necessary to specify their exact nature in order to interpret the observational data. This fact allows us to derive a parameter-free value for the primordial lithium abundance: log Li-p = 2.35 +/- 0.10 in the log H = 12 scale.