A photometric study of the detached binary WY Hydrae with twin components

Abstract

We present a multicolor photometry for the eclipsing binary WY Hydrae, observed on four nights of 2008 December. From our new observations and Carr’s data, the photometric solutions were deduced by using the updated W–D program. The results show that WY Hya is a detached binary with a mass ratio of q = 0.970(±0.005). By analyzing the O– C curve, it is found that there exists either a continuous period increase or a cyclic variation. From Eq. (2), the orbital period of WY Hya secularly increases at a rate of dP/ dt = +3.56(±0.37) × 10 −7 days/yr, which may be interpreted by some mass transfer for the near-contact configuration or tidal dissipation. From Eq. (3), the period and semi-amplitude of the periodic oscillation are P 3 = 95.4(±4.2) yr and A = 0 d .0087(±0 d .0003), respectively. This may be likely attributed by light-time effect via the presence of the assumed third body. Assumed in the coplanar orbit with the binary, the mass of the third body should be M 3 = 0.18 M ⊙. If the unseen additional companion exists, it will extract angular momentum from the binary system. Finally, WY Hya with high fill-out factors (i.e., f 1,2 > 80%), may evolve into a semi-detached configuration.