Binary and Multiple O‐Type Stars in the Cassiopeia OB6 Association

We present the results of time-resolved spectroscopy of 13 O-type stars inthe Cas OB6 stellar association. We conducted a survey for radial velocityvariability in search of binary systems, which are expected to be plentiful inyoung OB associations. Here we report the discovery of two new single-linedbinaries, and we present new orbital elements for three double-lined binaries(including one in the multiple star system HD 17505). One of the double-linedsystems is the eclipsing binary system DN Cas, and we present a preliminarylight curve analysis that yields the system inclination, masses, and radii. Wecompare the spectra of the single stars and the individual components of thebinary stars with model synthetic spectra to estimate the stellar effectivetemperatures, gravities, and projected rotational velocities. We also make fitsof the spectral energy distributions to derive E(B-V), R=A_V/E(B-V), andangular diameter. A distance of 1.9 kpc yields radii that are consistent withevolutionary models. We find that 7 of 14 systems with spectroscopic data areprobable binaries, consistent with the high binary frequency found for othermassive stars in clusters and associations.Comment: 40 pages, ApJ, in pres