2001AJ....122.1965S

Recently acquired times of minimum for three RS CVn systems and one BY Draconis binary, all with periods under a day, are presented. Times of minimum for UV Psc, YY Gem, CG Cyg, and XY UMa have been measured for decades. These observations have been collected, and the O-C curves for each system have been examined for period changes. The O-C curves for UV Psc and YY Gem showed a linear deviation, and improved periods have been computed. CG Cyg and XY UMa, though, appear to have experienced true changes in their periods. An additional 11.0 yr periodic variation has been found in the O-C data of XY UMa. The mechanism for the period variations remains uncertain.