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Paper: Lithium in the Early Universe
Volume: 165, The Third Stromlo Symposium: The Galactic Halo
Page: 225
Authors: Ryan, Sean G.; Norris, John E.; Beers, Timothy C.
Abstract: To observe the products of nucleosynthesis created in the Big Bang and during the earliest episodes of star formation, it is necessary to turn to the oldest and least metal--enriched objects known. Contrary to common perceptions, these are not high redshift objects, but rather, are the most metal--poor stars of the Galactic halo. We have investigated whether the Li abundance in such stars is consistent with a single value, as is required if the Li is exclusively of primordial origin, or whether there is a range of Li, indicative of additional processing. Systematic and random errors were minimised through restrictive selection criteria and double--blind processing of high signal--to--noise data. High--resolution spectra of 22 stars, with [Fe/H] < -2.3 and lying within ~300K of the main--sequence turnoff, have been obtained. We find that, although three stars are depleted, 86% of the sample possess Li abundances consistent with no detectable spread in A(Li), with an estimated abundance dispersion of sigma <= 0.03~dex. This compelling evidence against a spread in the Spite Plateau leads to the conclusion that either the stars have all changed their surface Li abundances very uniformly, or else they exhibit the primordial abundance of cosmological significance. Although we cannot rule out uniform depletion, economy of hypothesis supports the latter interpretation.
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