Kinematics and Metallicities in the Bootes III Stellar Overdensity: a
  Disrupted Dwarf Galaxy?
  We report the results of a spectroscopic study of the Bootes III (BooIII)
stellar overdensity carried out with the Hectospec multifiber spectrograph on
the MMT telescope. Radial velocities have been measured for 193 BooIII
candidate stars selected to have magnitudes and colors consistent with its
upper main sequence and lower red giant branch, as well as a number of
horizontal branch candidates. From 20 identified candidate BooIII members, we
measure a systemic velocity of V_sun=197.5+-3.8 km/s and a velocity dispersion
of sigma_o=14.0+-3.2 km/s. We use the somewhat large velocity dispersion and
the implied highly radial orbit, along with morphological evidence from
Grillmair (2009) and stellar abundances, to argue that BooIII is likely the
first known object observed in a transitional state between being a bound dwarf
galaxy and a completely unbound tidal stream.
