A study of the chromospherically active, short-period binary VZ piscium

The short-period binary VZ Piscium is unusual in that it has a high space velocity, indicating that it is old, and a high mass ratio, suggesting that it is presently evolving into contact with little mass exchange having occurred between the components. In this study, we obtained IUE and visible spectra to investigate Mg II h + k and Ca II H and K emission strengths. Both features are found to be strong and variable. From the visible spectra, radial velocities were measured, and a new mass ratio of q = 0.80 was deter-mined. This mass ratio was used in a new light-curve analysis, and the system was found to be in marginal contact, with the secondary component slightly detached. A model with bright (hot) regions on the inner hemisphere of the slightly detached, less massive component was found to fit well with the variety of spectroscopic and photometric observations of the system. The masses determined for the components are compatible with normal K dwarfs.