2001PASP..113..754Q

Orbital period changes of eight neglected short-period close binaries, EP And, V724 Aql, SS Com, AM Eri, FZ Ori, BY Peg, EQ Tau, and NO Vul, are presented based on the analysis of their O-C observations. It is found that the periods of BY Peg and EQ Tau are decreasing at rates of dP/dt=-1.67x10^–7 and -1.72x10^–7 day.yr^–1, respectively, while the orbital periods of SS Com and AM Eri show secular increase at rates of dP/dt=+5.91x10^–7 and +4.39x10^–7 day.yr^–1. Weak evidence also indicates that the orbital period of EP And is increasing. For FZ Ori, the decrease rate of orbital period is revised. For the other two systems, V724 Aql and NO Vul, their O-C curve can be described by a sudden period decrease or a continuous period decrease; further investigation is needed. The period changes of the eight systems can be explained by mass transfer between the two components and/or mass and angular momentum loss from these binaries. A strong mass-radius relation for observed contact binaries is formed based on the parameters given by Maceroni & Van't Veer. It is shown that the parameters of SS Com and EQ Tau given by Brancewicz & Dworak do not agree with the mass-radius relation. This may suggest that the two systems are not yet in contact. In order to understand the physical properties of these binaries, complete photoelectric or CCD light curves and radial velocity observations are needed.