Correcting velocity dispersions of dwarf spheroidal galaxies for binary
  orbital motion
  We show that measured velocity dispersions of dwarf spheroidal galaxies from
about 4 to 10 km/s are unlikely to be inflated by more than 20% due to the
orbital motion of binary stars, and demonstrate that the intrinsic velocity
dispersions can be determined to within a few percent accuracy using two-epoch
observations with 1-2 years as the optimal time interval. The crucial
observable is the threshold fraction--the fraction of stars that show velocity
changes larger than a given threshold between measurements. The threshold
fraction is tightly correlated with the dispersion introduced by binaries,
independent of the underlying binary fraction and distribution of orbital
parameters. We outline a simple procedure to correct the velocity dispersion to
within a few percent accuracy by using the threshold fraction and provide
fitting functions for this method. We also develop a methodology for
constraining properties of binary populations from both single- and two-epoch
velocity measurements by including the binary velocity distribution in a
Bayesian analysis.
