The primordial lithium abundance

Lithium abundances in a selected sample of halo stars have been revised byusing 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 notrend with [Fe/H]. The trend with the Teff is fully consistent with thestandard Li isochrones of Deliyannis, Demarque & Kawaler (1990) implying aprimordial value for Li of A(Li) = 2.238 +/- 0.012 {1 sigma} +/- 0.05{sys}. Thepresent results argue against any kind of depletion predicted by diffusion,rotational mixing or stellar winds. Therefore the Li observed in Pop II starsprovides a direct and reliable estimate of the baryonic density that can rivalother baryonic indicators such as the deuterium in high redshift systems. Thepresent upwards revision of primordial Li in the framework of SBBN gives at 1sigma 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} .Comment: Tex, uses MN.tex, 18 .ps figures; accepted MNRA