No abstract

We have secured and analyzed three-color light curves of V524 Monocerotis with the 2003 version of the Wilson–Devinney code. We confirmed that V524 Mon is a shallow W-type contact binary system with a mass ratio of $q$$=$ 2.099 and a degree of contact factor of $f$$=$ 7.7%. Based on the new eight times of the light minima and those published by previous investigators, we find that the orbital period of the binary shows a long-term decrease ($dp/dt$$=$$-$1.52 $\times$ 10$^{-10}$), while it undergoes a cyclic oscillation ($T_{3}$$=$ 23.93 yr, $A_{3}$$=$ 0.0082 d). The long-term period decrease can be explained by mass transfer from the primary to the secondary. The cyclic change, explained as the light-travel time effect, reveals the presence of a tertiary companion. The marginal contact configuration and the continuous period decrease both suggest that the system may be a newly formed contact binary.

Four sets of multi-color CCD photometric observations of the close binary BU Vul were carried out for four successive months in 2010. From our observations, there are obvious variations and asymmetry of light curves on the timescale of a month, indicating highlevel stellar spot activity on the surface of at least one component. The Wilson-Devinney (2010) program was used to determine the photometric solutions, which suggest that BU Vul is a semi-detached binary with the cool, less massive component filling with the critical Roche lobe. The solutions also reveal that the spots on the primary and the secondary have changed and drifted in 2010 July, August, and September. Based on analysis of the O − C curves of BU Vul, its orbital period shows a cyclic oscillation (T 3 = 22.4 yr, A 3 = 0.0029 d) superimposed on a secular increase. The continuous increase is possibly a result of mass transfer from the less massive component to the more massive one at a rate of dM/dt = −2.95 × 10 −9 M yr −1. The cyclic variation maybe be caused by the presence of a tertiary companion with extremely low luminosity. Combined with the distortions of the light curve on 2009 November 4, we infer that BU Vul has two additional companions in a quadruple system.