The Metal-Poor End Of The Spite Plateau

We present the largest sample available to date of lithium abundances in extremely metal poor (EMP) Halo dwarfs. Four T-eff estimators are used, including HUM and H alpha wings fitting against 3D hydrodynamical synthetic profiles. Lithium abundances are computed by means of 1D and 3D-hydrodynamical NLTE computations. Below [Fe/H]similar to-3, a strong positive correlation of A(Li) with [Fe/H] appears, not influenced by the choice of the Teff estimator. A linear fit finds a. slope of about 0.30 dex in A(Li) per dex in [Fe/H], significant to 2-3 sigma, and consistent within 1 sigma among all the T-eff estimators. The scatter in A(Li) increases significantly below [Fe/H]similar to-3. Above, the plateau lies at < A(Li)(3D,NLTE)> = 2.199 +/- 0.086. If the primordial A (Li) is the one derived from standard Big Bang Nucleosynthesis (BBN), it appears difficult to envision a single depletion phenomenon producing a thin, metallicity independent plateau above [Fe/H] = -2.8, and a highly scattered, metallicity dependent distribution below.