A chemical confirmation of the faint Bootes II dwarf Spheroidal Galaxy
  We present a chemical abundance study of the brightest confirmed member star
of the ultrafaint dwarf galaxy Bootes II from Keck/HIRES high-resolution
spectroscopy at moderate signal-to-noise ratios. At [Fe/H] = -2.93 +/- 0.03
(stat.) +/- 0.17 (sys.) this star chemically resembles metal-poor halo field
stars and the signatures of other faint dwarf spheroidal galaxies at the same
metallicities in that it shows enhanced [alpha/Fe] ratios, Solar Fe-peak
element abundances, and low upper limits on the neutron-capture element Ba.
Moreover, this star shows no chemical peculiarities in any of the eight
elements we were able to measure. This implies that the chemical outliers found
in other systems remain outliers pertaining to the unusual enrichment histories
of the respective environments, while Bootes II appears to have experienced an
enrichment history typical of its very low mass. We also re-calibrated previous
measurements of the galaxy's metallicity from the calcium triplet (CaT) and
find a much lower value than reported before. The resulting broad metallicity
spread, in excess of one dex, the very metal poor mean, and the chemical
abundance patterns of the present star imply that Bootes II is a low-mass, old,
metal poor dwarf galaxy and not an overdensity associated with the Sagittarius
Stream as has been previously suggested based on its sky position and
kinematics. The low, mean CaT metallicity of -2.7 dex falls right on the
luminosity-metallicity relation delineated over four orders of magnitude from
the more luminous to the faintest galaxies. Thus Bootes II's chemical
enrichment appears representative of the galaxy's original mass, while tidal
stripping and other mass loss mechanisms were probably not significant as for
other low-mass satellites.
