A comprehensive photometric study of the marginal-contact binary BE Cephei

New photometry for the eclipsing binary BE Cephei was performed from 2008 to 2011. The light-curve synthesis indicates that it is a marginal-contact binary with a mass ratio of q = 2.340(±0.009) and a degree of contact of f = 6.9%(±2.3%). From the O − C curve, it is discovered that the orbital period changes show a sinusoidal curve superimposed on a downward parabola. The period and semi-amplitude of the cyclic variation are Pmod = 59.26(±0.52) yr and A = 0.d0067(±0.d0010), which may be possibly attributed to light-time effect via the presence of an unseen third body. The long-term period decreases at a rate of dP/dt = −4.84(±0.31) × 10−8 d yr−1, which may result from mass transfer from the more massive component to the less massive one, accompanied by angular momentum loss. With the period decreasing, the degree of contact will increase. Finally, the marginal-contact binary BE Cep may be evolving into a deep-contact configuration.

► We present the results of the photometric observations of BE Cep.
► Our photometric model describes BE Cep as a marginal-contact binary.
► We found that the orbital period may be secularly increasing, with a small oscillation.
► The secular period decrease rate of −4.8∗10(−8) d yr.
► The period of 59.2 yr and amplitude of 0.0069 day for the cyclic variation.