2003A&A...400..649Q

A detailed orbital period investigation of the short-period (P=0.37d) W UMa type star, V417 Aql, is presented based on the analysis of its O-C data. It is shown that the period change of the binary system is continuous. A periodic variation, with a period of 42.4years and an amplitude of 0.0130d, is found superimposed on a long-term period decrease (dP/dt=-5.50x10^–8days/year). The period oscillation can be explained either by the light-time effect via the presence of an unseen third body or by magnetic activity cycles of the components. V417 Aql is a W-type overcontact binary system with a low mass ratio of q=0.36. The long-term period variation is in agreement with the conclusion of Qian (2001MNRAS.328..635Q) that a low-mass ratio W-type system usually shows a secular period decrease. This suggests that V417 Aql is on the AML-controlled stage of the evolutionary scheme proposed by Qian (2001MNRAS.328..635Q). Meanwhile, the light-curve paradox encountered by TRO theory is discussed.