Light curve variation and period changes of VW Cep

PhotometricUBV-observations of VW Cep, a W UMa-type eclipsing binary, were made in 1971 and 1978–79. The (O-C)-diagram, with the newly determined times of minima extended, shows sudden increases and decreases in the period of VW Cep. The difference light curves (the observed light curves compared with a reference light curve) show some correlations with the sudden change of the period. In particular, the difference between the two light curves from 1971 and 1978 is also presented. The system may be in marginal contact, and as such is possibly unstable with respect to mass exchange between its components. In accordance with the variation of (O-C)-values the mass transfer between the both components is discussed. The difference between the depths of the two minima shows irregular changes, while that between the heights of the two maxima shows a long term variation on which irregular fluctuations are superimposed.