摘要

Orbital period changes of the solar-type contact binary V700 Cyg were investigated based on one new eclipse time combined with the others collected from the literature. A cyclic oscillation, with a period of 39.1 yr and an amplitude of 0.(d)0197, was found to be superimposed on a secular period increase at a rate of dP/dt = 2.8 x 10(-8) d yr(-1). Weak evidence indicates that there exists another small-amplitude period oscillation. The long-term period increase is in agreement with the conclusion that high-mass ratio W-type overcontact binaries usually show period increasing. This suggests that it may be in the stage controlled by thermal relaxation oscillations. Cyclic period oscillation can be explained as being the result of a light-travel time effect via the presence of an additional body. On the other hand, since both components of V700 Cyg are late-type stars, the period oscillation may be evidence of magnetic activity cycles of the two component stars.