High-resolution spectroscopy of extremely metal-poor stars in the least
  evolved galaxies: Bootes II
  We present high-resolution Magellan/MIKE spectra of the four brightest
confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II).
These stars all inhabit the metal-poor tail of the Boo II metallicity
distribution function. The chemical abundance pattern of all detectable
elements in these stars is consistent with that of the Galactic halo. However,
all four stars have undetectable amounts of neutron-capture elements Sr and Ba,
with upper limits comparable to the lowest ever detected in the halo or in
other dwarf galaxies. One star exhibits significant radial velocity variations
over time, suggesting it to be in a binary system. Its variable velocity has
likely increased past determinations of the Boo II velocity dispersion. Our
four stars span a limited metallicity range, but their enhanced
{\alpha}-abundances and low neutron-capture abundances are consistent with the
interpretation that Boo II has been enriched by very few generations of stars.
The chemical abundance pattern in Boo II confirms the emerging trend that the
faintest dwarf galaxies have neutron-capture abundances distinct from the halo,
suggesting the dominant source of neutron-capture elements in halo stars may be
different than in ultra-faint dwarfs.
