supported partly by funds of project RD 08-244 of Scientific Foundation of Shumen University;the AAVSO Photometric All-Sky Survey(APASS),funded by the Robert Martin Ayers Sciences Fund
Photometric observations in Sloan 9' and i' bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7+385531 and VSX J062624.4+570907, are presented. The light curve solutions reveal that all targets hav...