We propose to acquire high-resolution spectra of a set of metal-poor turn-off stars; there are very metal-poor field (EMP) stars selected in the DR12 SDSS survey and confirmed in DR17. Using a well-proven algorithm (Ludwig+08) the EMP stars have all estimated metallicities [Fe/H] ≤ -3.0 dex. These spectra will permit not only to confirm the very low metal content of these stars, but also to determine their detailed chemical abundances, and in particular the lithium abundance. As the stars are only TO stars, the abundances will not be affected by mixing, contrarily to other projects targetting mainly evolved EMP stars. The proposed observations will have an impact on our knowledge of the formation of most metal-poor stars, the chemical evolution, and the lithium content of the early Galaxy including merger events. Previous studies suggest a small departure from the Li Spite plateau for objects with [Fe/H]≤ -3 and significant depletion of Li in most metal-poor stars. Our sample will fill the critical zone of data points at very low metallicity. This proposal is a resubmission of an accepted proposal in S19B for which the observations were not feasible due to extremely bad weather.
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