Simultaneous light and velocity curve solution and probable starspot activities for the W Uma system U Pegasi

Abstract

In view of the fair agreement between the photometric qptm by Zhai et al. (1984) and the spectroscopic mass ratio qsp by Lu (1985), a simultaneous light and velocity curve solution was carried out for U Peg with the Wilson-Devinney Program. For purpose of comparison, we performed separate light and velocity curve solutions and then the simultaneous photometric-spectroscopic solution. The improved absolute d-imensions turned out to be M1 = 0.387 ±0.004 M⊙, M2 = 1.167 ±0.015 Mo, R1 = 0.754 ±0.007 Ro and R2 = 1.236 +-0.004 Ro. Based on the simultaneous solution, a thorough analysis was made for total B and v light curves of U Peg obtained from 1950 to 1984. It was found that: 1. the complexities on light curves in 1958, 1961 and 1970 can be re-produced by spot model and there may be spot cycle with the period at least larger than 28 years; 2. the common envelope of the contact binary U Peg appears to be oscillation instability with the over-contact degree varied by a large percentage.