Detailed abundances in a sample of very metal poor stars
  Unevolved metal poor stars are the witness of the early evolution of the
Galaxy. The determination of their detailed chemical composition is an
important tool to understand the chemical history of our Galaxy. The study of
their chemical composition can also be used to constrain the nucleosynthesis of
the first generation of supernovae that enriched the interstellar medium. The
aim is to observe a sample of extremely metal poor stars (EMP stars) candidates
selected from SDSS DR12 release and determine their chemical composition.
  We obtained high resolution spectra of a sample of five stars using HDS on
Subaru telescope and used standard 1D models to compute the abundances. The
stars we analysed have a metallicity [Fe/H] between -3.50 dex and -4.25 dex .
  We confirm that the five metal poor candidates selected from low resolution
spectra are very metal poor.
  We present, the discovery of a new ultra metal-poor star (UMP star) with a
metallicity of [Fe/H]= -4.25 dex (SDSS~J1050032.34$-$241009.7). We measured in
this star an upper limit of lithium ( log(Li/H) <= 2.0. We found that the 4
most metal poor stars of our sample have a lower lithium abundance than the
Spite plateau lithium value. We obtain upper limits for carbon in the sample of
stars. None of them belong to the high carbon band. We measured abundances of
Mg and Ca in most of the stars and found three new alpha-poor stars.
