Light-curve and period changes in the W UMa-type system TY Bootis

摘要

A detailed study of the period and the light curve of the eclipsing binary TY Bootis is presented. Based on a study of the (O - C) curve, we have found that two periodical variations superimpose on a continuous increase (d P/dt = 6.283 x 10(-8) d yr(-1)) in its period. We compared light curves obtained by other groups, and found that the light curve of the system has changed considerably. We analyzed the physical mechanisms that underlie the variation in the period and light curve of the system, and obtained some new conclusions. The continuous increase of its orbital period is probably caused by mass transfer from the secondary to the primary, rather than an expansion of the primary due to its dynamical instability. Also, the two periodical components are probably caused by two different physical mechanisms, i.e., the light-time effect is one of the possible mechanisms, which might cause a periodical component with a longer timescale (31.5 yr), and the magnetic activity cycle is the other one, which might underlie the other periodical component with a shorter timescale (11.76 yr). The long-term variation in the light curve of the system is likely to be caused by a decrease in the light level of the primary due to starspot(s) on the primary or an expansion of the primary. Finally, the trends in the evolution of the system are discussed according to a theory of W UMa systems.