TOMOGRAPHIC SEPARATION OF COMPOSITE SPECTRA .4. THE PHYSICAL-PROPERTIES OF THE MASSIVE CLOSE BINARY DH CEPHEI

We present the results of a Doppler tomographic reconstruction of the UV spectra of the double-lined, O binary DH Cephei based on observatio ns made with the International Ultraviolet Explorer. We describe cross -correlation methods we use to obtain precise radial velocities, and w e present a radial velocity curve based on combined optical and UV mea surements. We also show how we use fits of the cross-correlation funct ions to estimate the UV flux ratio and projected rotational velocities . The individual component spectra are classified as O6 V + O7 V using UV criteria defined by Penny, Gies, & Bagnuolo. We place the individu al components in the theoretical Hertzsprung-Russell diagram using the distance modulus and reddening estimated for its home cluster, NGC 73 80, and we find that the stars are larger than estimates from prior st udies of the ''ellipsoidal'' light variations. We reconsider the ellip soidal light curve and show that there is a range in acceptable stella r radii (as a function of orbital inclination). We discuss the constra ints on inclination and system masses based on cluster distance modulu s, presumed synchronous rotation, and on consistency with masses deriv ed from evolutionary tracks (which involves the issue of the temperatu re calibration of O stars). We find that primary and secondary masses of 39-50 M. and 35-45 M., respectively, satisfy all the constraints fr om spectroscopy, photometry, distance modulus, and single-star evoluti onary tracks.