Spectroscopy of the three distant Andromedan satellites Cassiopeia III,
  Lacerta I, and Perseus I
  We present Keck II/DEIMOS spectroscopy of the three distant dwarf galaxies of
M31 Lacerta I, Cassiopeia III, and Perseus I, recently discovered within the
Pan-STARRS1 3\pi imaging survey. The systemic velocities of the three systems
(v_{r,helio} = -198.4 +/- 1.1 km/s, -371.6 +/- 0.7 km/s, and -326 +/- 3 km/s,
respectively) confirm that they are satellites of M31. In the case of Lacerta I
and Cassiopeia III, the high quality of the data obtained for 126 and 212
member stars, respectively, yields reliable constraints on their global
velocity dispersions (\sigma_{vr} = 10.3 +/- 0.9 km/s and 8.4 +/- 0.6 km/s,
respectively), leading to dynamical-mass estimates for both of ~4x10^7 Msun
within their half-light radius. These translate to V-band mass-to-light ratios
of 15^{+12}_{-9} and 8^{+9}_{-5} in solar units. We also use our spectroscopic
data to determine the average metallicity of the 3 dwarf galaxies ([Fe/H] =
-2.0 +/- 0.1, -1.7 +/- 0.1, and -2.0 +/- 0.2, respectively). All these
properties are typical of dwarf galaxy satellites of Andromeda with their
luminosity and size.
