MULTICOLOR ECLIPSE STUDIES OF UU-AQUARII .1. OBSERVATIONS AND SYSTEM PARAMETERS

A study of the eclipses in UU Aqr from multicolor high-speed photometry is presented. A revised ephemeris for the times of minimum and an upper limit for orbital period variations are obtained. We use measurements of contact phases in the eclipse light curve to derive the binary geometry and to estimate masses and relevant dimensions. We find a mass ratio of q = 0.30 +/- 0.07 and an inclination of i = 78-degrees + 2-degrees. The masses of the component stars are M1 = 0.67 +/- 0.14 M. and M. = 0.20 +/- 0.07 M.. Our photometric model predicts K1 = 84 +/- 26 km s-1, which is approximately 30% smaller than the velocity amplitude obtained from the emission lines. From the white dwarf fluxes we estimate T(wd) congruent-to 34,000 K and a distance of d = 270 +/- 50 pc if the inner disk is opaque. UU Aqr has long-term brightness variations of almost-equal-to 0.3m on timescales of approximately 4 yr. The system was in a ''high'' state in 1989 and 1990 and in a '' low '' state in 1988 and 1992. The high state results from an increase in the brightness of the outer and cooler parts of the disk, mainly due to the appearance of a bright spot at disk rim. Based on the smooth and gradual eclipse shape and on the absence of a prominent hump in the light curve we suggest that UU Aqr is a high mass-transfer nova-like system with a relatively bright and optically thick accretion disk. We find no perceptible eclipse in the Halpha emission line. The fluxes at mid-eclipse can be fitted by a composition of a late-type spectrum plus an optically thin hydrogen emission-line spectrum. These evidences suggest that the emission lines are formed in an extended region only partially occulted during eclipse.