Reappraising the Spite Lithium Plateau: Extremely Thin and Marginally Consistent with WMAP

The lithium abundance in 62 halo dwarfs is determined from accurate equivalent widths reported in the literature and an improved infrared flux method (IRFM) temperature scale. The Li abundance of 41 plateau stars (those with Teff > 6000 K) is found to be independent of temperature and metallicity, with a star-to-star scatter of only 0.06 dex over a broad range of temperatures (6000 K < Teff < 6800 K) and metallicities (-3.4 < [Fe/H] < -1), thus imposing stringent constraints on depletion by mixing and production by Galactic chemical evolution. We find a mean Li plateau abundance of A(Li) = 2.37 dex (7Li/H = 2.34 X 10^{-10}), which, considering errors of the order of 0.1 dex in the absolute abundance scale, is just in borderline agreement with the constraints imposed by the theory of primordial nucleosynthesis and WMAP data (2.51 < A(Li)[WMAP] < 2.66 dex).