Photometry of long-period algol binaries. III. The accretion disk and mass transfer in RZ Ophiuchi

Five-color photometric observations of RZ Oph have been obtained from 1981 through 1986, in an effort to deduce the properties of the accretion disk in this long-period Algol. The partial eclipse of the disk by the cool star, and the partial occultation of the cool star by the disk, have both been observed in some detail. A simple gravitationally stratified model of the disk accounts very well for the emitted flux. The disk is viewed nearly edge-on, and is of moderate optical thickness. The principal extinction source in the disk is Rayleigh scattering from neutral hydrogen, and H(-) contributes to the thermal absorption. Disk temperatures run from about 5600 K to about 4400 K at the edge of the disk, and the disk appears to overflow the Roche lobe of the hot star. Most of the disk's luminosity is supplied by gravitational accretion, implying a mass-transfer rate of less than about 10 to the -6th solar mass/yr. Brightness fluctuations of the disk seem to account for small intrinsic scatter that is present in the observations at most phases. 27 references