YZ Phoenicis : photometric study of a W UMa binary near the short-period limit.
SAMEC R.G. and TERRELL D.
Abstract (from CDS):
An analysis of BVRI photometry of the high galactic southern latitutde W UMa variable, YZ Phe, is reported. The photometry was done in November 1989 at Cerro Tololo InterAmerican Observatory. Four new precision epochs of minimum light were determined and improved linear ephemerides were computed from all available epochs. The period study indicates that its period has probably remained constant at 0.23472d over the 30 year interval it has been observed. A large O'Connell effect is present in the light curves with the maximum following Min II ∼0.1m brighter in B than the maximum following Min I. A brief ∼15 minute interval of constant light is discernible in the primary eclipse, indicating that the more massive component is the cooler. A four-color simultaneous computation including a second-order reflection effect strongly favored the presence of a large 54 degree radius super liminous region instead of the usual dark spot on teh cooler component with a temperature factor of only 1.03. Further, we find that the system consists of two early K spectral type dwarfs in marginal contact with ∼20% fill-out, and a mass ratio of 0.40.