BINARY AND MULTIPLE O-TYPE STARS IN THE CASSIOPEIA OB6 ASSOCIATION

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 doublelined systems is the eclipsing binarysystem DN Cas, and we present a preliminary light-curve analysis that yields the system inclination,masses, and radii. Wecompare thespectraof thesinglestarsand theindividual components ofthe binary stars with model synthetic spectra to estimate the stellar effective temperatures, gravities, and projected