PERIOD CHANGES AND FOUR-COLOR LIGHT CURVES OF ACTIVE CONTACT BINARY VW BOOTIS

The secured four-color light curves of VW Boo were analyzed with the 2003 version of the Wilson-Devinney code. It is confirmed that VW Boo is a shallow W-type contact binary system with a degree of contact factor f = 10.8%(± 0.5%). Two dark spots were found on the massive cool component this time. They cause an unequal depth of the two maxima. A period investigation based on all available visual, photographic, CCD, and photoelectric data shows that the period of the system includes a long-term decrease (dP/dt = -1.454 x 10-7 days yr-1) and an oscillation (A3 = 0.0059 days; T3 = 25.96 years). These may be caused by mass transfer, angular momentum loss, and cyclic magnetic activity.