V524 Monoceroits: A Marginal Contact Binary with a Cyclic Period Variation

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 × 10^-10), while it undergoes a cyclic oscillation (T₃ = 23.93 yr, A₃ = 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.