The primordial lithium abundance

Abstract

Lithium abundances in a selected sample of halo stars have been revised by using the new accurate IRFM effective temperatures by Alonso, Arribas & Martinez-Roger (1996a). From 41 plateau stars (Teff > 5700 and [Fe/H] <= -1.5) we found no evidence for intrinsic dispersion, a tiny trend with Teff and no trend with [Fe/H]. The trend with the Teff is fully consistent with the standard Li isochrones of Deliyannis, Demarque & Kawaler (1990) implying a primordial value for Li of A(Li) = 2.238 +/- 0.012 {1 sigma} +/- 0.05{sys}. The present results argue against any kind of depletion predicted by diffusion, rotational mixing or stellar winds. Therefore the Li observed in Pop II stars provides a direct and reliable estimate of the baryonic density that can rival other baryonic indicators such as the deuterium in high redshift systems. The present upwards revision of primordial Li in the framework of SBBN gives at 1 sigma two solutions for the baryonic density: Omega_{B}h^2 = 0.0062 {+0.0018,-0.0011} or Omega_{B}h^2 = 0.0146 {+0.0029,-0.0033} .