2001AJ....122.1561Q

The orbital periods of two Algol-type binaries, UU And and Z Per, are studied based on the analysis of the O-C data. It is discovered that the orbital period of UU And shows seven irregular jumps while it undergoes a secular decrease with rate of dP/dt=-4.76x10^–7 days yr^–1. For Z Per, seven irregular period jumps are also found superposed on a rapid period decrease (dP/dt=-1.54x10^–6 days yr^–1). Meanwhile, the orbital period changes of two other systems, BO Mon and Y Psc, studied in Paper II of this series, are reinvestigated by combining our previous data with earlier published times of light minimum. The secular period decrease rates of the two systems are revised, and apart from the sudden jumps proposed in Paper II, additional period jumps superposed on the secular period decrease are found. The period changes of these systems, both the decreases and the jumps, can be explained by secular mass and angular momentum loss via magnetic braking.