Jr. Sowell et al., Period changes in four short-period spotted binaries: UV Piscium, YY Geminorum, CG Cygni, and XY Ursae Majoris, ASTRONOM J, 122(4), 2001, pp. 1965-1973
Recently acquired times of minimum for three RS CVn systems and one BY Drac
onis 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. Thes
e 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 sho
wed 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.