Chemical abundances of giant stars in the Crater stellar system
  We obtained spectra for two giants of Crater (Crater J113613-105227 and
Crater J113615-105244) using X-Shooter at the VLT. The spectra have been
analysed with the MyGIsFoS code using a grid of synthetic spectra computed from
one dimensional, Local Thermodynamic Equilibrium (LTE) model atmospheres.
Effective temperature and surface gravity have been derived from photometry
measured from images obtained by the Dark Energy Survey. The radial velocities
are 144.3+-4.0 km/s for Crater J113613-105227 and and 134.1+-4.0 km/s for
Crater J113615-105244. The metallicities are [Fe/H]=-1.73 and [Fe/H]=-1.67,
respectively. Beside the iron abundance we could determine abundances for nine
elements: Na, Mg, Ca, Ti, V, Cr, Mn, Ni and Ba. For Na and Ba we took into
account deviations from LTE, since the corrections are significant. The
abundance ratios are similar in the two stars and resemble those of Galactic
stars of the same metallicity. On the deep photometric images we could detect
several stars that lie to the blue of the turn-off. conclusions heading
(optional), leave it empty if necessary The radial velocities imply that both
stars are members of the Crater stellar system. The difference in velocity
between the two taken at face value, implies a velocity dispersion > 3.7 km/s
at 95% confidence level. Our spectroscopic metallicities are in excellent
agreement with that determined by previous investigations using photometry. Our
deep photometry and the spectroscopic metallicity imply an age of 7 Gyr for the
main population of the system. The stars to the blue of the turn-off can be
interpreted as a younger population, of the same metallicity and an age of 2.2
Gyr. Finally, spatial and kinematical parameters support the idea that this
system is associated to the galaxies Leo~IV and Leo~V. All the observations
favour the interpretation of Crater as a dwarf galaxy. (Abridged).
