  We present the results of time-resolved spectroscopy of 13 O-type stars in
the Cas OB6 stellar association. We conducted a survey for radial velocity
variability in search of binary systems, which are expected to be plentiful in
young OB associations. Here we report the discovery of two new single-lined
binaries, and we present new orbital elements for three double-lined binaries
(including one in the multiple star system HD 17505). One of the double-lined
systems is the eclipsing binary system DN Cas, and we present a preliminary
light curve analysis that yields the system inclination, masses, and radii. We
compare the spectra of the single stars and the individual components of the
binary stars with model synthetic spectra to estimate the stellar effective
temperatures, gravities, and projected rotational velocities. We also make fits
of the spectral energy distributions to derive E(B-V), R=A_V/E(B-V), and
angular diameter. A distance of 1.9 kpc yields radii that are consistent with
evolutionary models. We find that 7 of 14 systems with spectroscopic data are
probable binaries, consistent with the high binary frequency found for other
massive stars in clusters and associations.
