From First Stars to the Spite Plateau: A Possible Reconciliation of Halo Stars Observations with Predictions from Big Bang Nucleosynthesis

Since the pioneering observations of Spite & Spite in 1982, the constantlithium abundance of metal-poor ([Fe/H]<-1.3) halo stars near the turnoff hasbeen attributed a cosmological origin. Closer analysis revealed that theobserved abundance lies at $\Delta$ Li~0.4 dex below the predictions of BigBang Nucleosynthesis. The measurements of deuterium abundances on the lines ofsight toward quasars and the recent data from the Wilkinson MicrowaveAnisotropy Probe independently confirmed this gap. We suggest here that part ofthe discrepancy is explained by the first generation of stars that efficientlydepleted lithium. Assuming that the models for lithium evolution in the haloturnoff stars and $\Delta$ Li estimates are correct, we infer that between 1/3and 1/2 of the baryonic matter of the early halo (~10^9 Mo) was processedthrough Population III stars. This new paradigm proposes a very economicalsolution to the lingering difficulty of understanding the properties of theSpite Plateau and its lack of star-to-star scatter down to [Fe/H]=-2.5. It ismoreover in agreement both with the absence of lithium detection in the mostmetal-poor star presently known (HE 1327-2326), and also with new trends of thePlateau suggesting its low metallicity edge may be reached around [Fe/H]=-2.5.We discuss the turbulent mixing associated with enhanced supernovae explosionsin the early interstellar medium in this picture. Finally we show that otherchemical properties of the extremely metal-poor stars are in agreement with asignificant Population III processing in the halo, provided these modelsinclude mass-loss and rotationally-induced mixing.Comment: 27 pages, 6 figures accepted to the Astrophysical Journa