  We have completed a Monte-Carlo simulation to estimate the effect of binary
star orbits on the measured velocity dispersion in dwarf spheroidal galaxies.
This paper analyses previous attempts at this calculation, and explains the
simulations which were performed with mass, period and ellipticity
distributions similar to that measured for the solar neighbourhood. The
conclusion is that with functions such as these, the contribution of binary
stars to the velocity dispersion is small. The distributions are consistent
with the percentage of binaries detected by observations, although this is
quite dependent on the measuring errors and on the number of years over which
measurements have been taken. For binaries to be making a significant
contribution to the dispersion measured in dSph galaxies, the distributions of
the orbital parameters would need to be very different from those of stars in
the solar neighbourhood. In particular more smaller period orbits with higher
mass secondaries would be required. The shape of the velocity distribution may
help to resolve this issue when more data becomes available. In general, the
scenarios producing a larger apparent dispersion have a velocity distribution
which deviates more clearly from Gaussian.
