RX GEMINORUM: PHOTOMETRIC SOLUTIONS, (NEARLY UNIFORM) GAINER ROTATION, DONOR RADIAL VELOCITY SOLUTION, NON-LTE ACCRETION DISK MODELS OF H α EMISSION PROFILES, AND SECULAR LIGHT CURVE CHANGES IN THE 20TH CENTURY

We obtained full-orbit Iybvu intermediate-band photometry and CCD spectroscopy of the long-period Algol eclipsing binary RX Geminorum. Photometric solutions using the Wilson-Devinney code give a gainer rotation (hotter, mass-accreting component) about 15 times the synchronous rate. We describe a simple technique to detect departures from uniform rotation of the hotter component. These binaries radiate double-peaked Ha emission from a low-mass accretion disk around the gainer. We used an approximate non-LTE disk code to predict models in fair agreement with observations, except in the far wings of the emission profile, where the star-inner disk boundary layer emits extra radiation. Variations in Ha emission derive from modulations in the transfer rate. A study of times of minima during the 20th century suggests that a perturbing third body is present near RX Gem.