The Chromospherically Active Contact Binary CE Leonis

Abstract

We present complete VRI light curves of the contact binary CE Leo and provide detailed photometric solutions, as well as an analysis of its period variation. A total of 73 times of minima over 50 years, including our observations, were used for the period study. The complex period variation can be sorted into a linear period improvement, a period of P = 0.30342771 days, a secular period increase at the rate of /P = +3.05 × 10-7 days yr-1, and a 22.6 ± 0.5 yr periodic component. The ∼22.6 yr periodic variation in the O-C residuals most likely arises from the light-travel time effect from a low-mass (m3 ∼ 0.3M⊙ sin i) dM tertiary companion moving in an eccentric (e' = 0.61 ± 0.04) orbit. However, it is also possible that this periodic variation arises from the effects of a magnetic activity cycle, known as the Applegate mechanism. The light curves show asymmetries in the two different maxima. The 1998 light curves show that primary maximunm was 0.042, 0.038, and 0.038 mag brighter than secondary maximum in V, R, and I, respectively. The durations of totality for three epochs were 18.3 minutes in 1989, 19.7 minutes in 1998, and 18.8 minutes in 2001. The relative depth of primary minimum was found to vary between 1.20 and 1.32 mag. We have analyzed the light curves from the three epochs using the 1993 version of the Wilson-Devinney differential corrections computer code to find a unique solution for CE Leo. The corresponding spectral type of the secondary star from the colors and effective temperature is ∼dK2. The asymmetric light curves can be explained by the effects of starspots. We find that the light curves are best fitted by employing a cool spot on the cooler, larger component of the system. The spot-effect parameter SE = 0.05 found for CE Leo is relatively large for W UMa binaries.