Statistical Properties of Blue Horizontal Branch Stars in the Spheroid:
  Detection of a Moving Group approximately 50 kpc from the Sun
  A new moving group comprising at least four Blue Horizontal Branch (BHB)
stars is identified at (l,b) = (65 deg, 48 deg). The horizontal branch at
g0=18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric
radial velocity is RV = -157 +/- 4 km/s, corresponding to V(gsr) = -10 km/s;
the dispersion in line-of-sight velocity is consistent with the instrumental
errors for these stars. The mean metallicity of the moving group is [Fe/H]
approximately -2.4, which is significantly more metal poor than the stellar
spheroid. We estimate that the BHB stars in the outer halo have a mean
metallicity of [Fe/H] = -2.0, with a wide scatter and a distribution that does
not change much as a function of distance from the Sun. We explore the
systematics of SDSS DR7 surface gravity metallicity determinations for faint
BHB stars, and present a technique for estimating the significance of clumps
discovered in multidimensional data. This moving group cannot be distinguished
in density, and highlights the need to collect many more spectra of Galactic
stars to unravel the merger history of the Galaxy.
