YZ-PHOENICIS - PHOTOMETRIC-STUDY OF A W-UMA BINARY NEAR THE SHORT-PERIOD LIMIT

An analysis of BVRI photometry of the high galactic southern latitude W UMa variable, YZ Phe, is reported. The photometry was done in Novemb er 1989 at Cerro Tololo Inter-American Observatory. Four new precision epochs of minimum light were determined and improved linear ephemerid es were computed from all available epochs. The period study indicates that its period has probably remained constant at 0(d).23472 over the 30-yr interval it has been observed. A large O'Connell effect is pres ent in the light curves with the maximum following Min II similar to 0 .1 mag brighter in B than the maximum following Min I. A brief similar to 15-min interval of constant light is discernible in the primary ec lipse, indicating that the more-massive component is the cooler. A fou r-color simultaneous computation including a second-order reflection e ffect strongly favored the presence of a large 54 degrees radius super luminous region instead of the usual dark spot on the cooler component with a temperature factor of only 1.03. Further, we find that the sys tem consists of two early K spectral-type dwarfs in marginal contact w ith similar to 2% fill out, and a mass ratio of similar to 0.40.