X-Shooter GTO: evidence for a population of extremely metal-poor,
  alpha-poor stars
  The extremely metal-poor stars are the direct descendants of the first
generation stars. They carry the chemical signature of the pristine Universe at
the time they formed, shortly after the Big Bang. We aim to derive information
about extremely metal-poor stars from their observed spectra. Four extremely
metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and
observed during the guaranteed observing time of X-Shooter. The X-Shooter
spectra were analysed using an automatic code, MyGIsFOS, which is based on a
traditional analysis method. It makes use of a synthetic grid computed from
one-dimensional, plane-parallel, hydrostatic model atmospheres. The low
metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars
are found. Two stars are confirmed to be extremely metal-poor, with no evidence
of any enhancement in carbon. The two other stars are strongly enhanced in
carbon. We could not derive iron abundance for one of them, while [Ca/H] is
below -4.5. Two of the stars are members of the rare population of extremely
metal-poor stars low in alpha elements.
