Discovery of a cyclic period change in the contact binary system V1128 Tau

We obtained several epochs of light minima and a complete R light curve of the W-type contact binary V1128 Tau in 2009. Two cool spots on the massive component are used to model the photometric light curve. Using all available data we find evidence for a long-term period variation with an amplitude of 0.0050±0.0012 days and a period of 16.7±0.9 years. Using parameters derived from a photometric model of the 2009 light curve we show that this period change could be explained by the Applegate mechanism on one of the components.