Identifying Star Streams in the Milky Way Halo
  We develop statistical methods for identifying star streams in the halo of
the Milky Way galaxy that exploit observed spatial and radial velocity
distributions. Within a great circle, departures of the observed spatial
distribution from random provide a measure of the likelihood of a potential
star stream. Comparisons between the radial velocity distribution within a
great circle and the radial velocity distribution of the entire sample also
measure the statistical significance of potential streams. The radial
velocities enable construction of a more powerful joint statistical test for
identifying star streams in the Milky Way halo. Applying our method to halo
stars in the Hypervelocity Star (HVS) survey, we detect the Sagittarius stream
at high significance. Great circle counts and comparisons with theoretical
models suggest that the Sagittarius stream comprises 10% to 17% of the halo
stars in the HVS sample. The population of blue stragglers and blue horizontal
branch stars varies along the stream and is a potential probe of the
distribution of stellar populations in the Sagittarius dwarf galaxy prior to
disruption.
