Variations of the light levels at the primary minimum and both maxima are found. Uniform solutions of four sets of photometric data were derived by using the Wilson-Devinney method. The solutions suggest that AD Cancri is a shallow W-type contact binary ( f ¼ 8:3% AE 1:3%) with a high mass ratio of 1/q ¼ 0:770 AE 0:002. The long-term variation of the light curve is explained by variable dark-spot models of the more massive component star with a possible 17 yr cycle. Our 13 times of light minimum over 5 years, including others collected from the literature, have been used for the period study. The complex period changes can be sorted into a long-term period increase at rate of dP/dt ¼ þ(4:94 AE 0:16) ; 10 À7 days yr À1 , a 16.2 yr periodic component (A 3 ¼ 0:0155 days), and a very small amplitude period oscillation (A 4 ¼ 0:0051 days, P 4 ¼ 6:6 yr). The existence of third light may indicate that there is a tertiary component in the binary system. Solving the four-band light curves of Samec & Bookmyer, it is found that the contribution of the tertiary component to the total light of the triple system increases with wavelength, which suggests that it is very cool and may be a very red main-sequence star. The small-amplitude period oscillation may be caused by the light-time effect of the cool tertiary component (M 3 $ 0:41 M ). The 16.2 yr periodic component in the orbital period and the 17 yr cyclic activity of the dark spot on the more massive component both may reveal that the more massive component displays solar-type magnetic activity with a cycle length of about 16 yr.

Abstract. -New complete BV light curves of BL Eri are presented. Light-curve variability and asymmetry are seen in both B and V bands, and the observed times of light minimum indicate period changes. The light curves have been analyzed by using the light-curve-synthesis method. Our photometric solution reveals that BL Eri is a contact binary with a common convective envelope. An examination of the available photometric and spectroscopic data indicates that the light-curve variability may be due to changes of the component radii and the light-curve asymmetry may be consistent with starspot activity on one or both components.

Abstract. New times of light minimum of the short-period (P = 0 d .26) close binary system, VZ Psc, are presented. A period investigation of the binary star, by combining the three new eclipse times with the others collected from the literatures, shows that the variation of the period might be in an alternate way. Under the hypothesis that the variation of the orbital period is cyclic, a period of 25 years and an amplitude of 0.d 0030 for the cyclic change are determined. If this periodic variation is caused by the presence of a third body, the mass of the third body (m3) should be no less than 0.081 M . Since both components of VZ Psc are strong chromospherically active and the level of activity of the secondary component is higher than that of the primary one, the period may be more plausibly explained by cyclic magnetic activity of the less massive component.

NARIT) has joined the BIMA Project as the main partner. This project aims to build an open-database of eclipsing binary minima and to establish the orbital period of each system and its variations. The project is conducted on the basis of multisite monitoring observations of eclipsing binaries with magnitudes less than 19 mag. Differential photometry methods have been applied throughout the observations. Data reduction was performed using IRAF. The observations were carried out in BVRI bands using three different small telescopes situated in Indonesia, Thailand, and Chile. Computer programs have been developed for calculating the time of minima. To date, more than 140 eclipsing binaries have been observed. From them 71 minima have been determined. We present and discuss the O-C diagrams for some eclipsing binary systems.

The photometric solutions of the ultrashort period close binary V0644 Ser based on our new complete BVRI light curves are derived by the W-D code. The results show that V0644 Ser is a W-type shallow contact binary, and the third light was found in R and I bands. Compared with the light curves in 2011, the amplitude variation of the secondary maximum can be explained by the temperature change from hot to cold in the local region of the star surface caused by magnetic activity or convective instability. Combined with the GAIA parallax, the absolute parameters of this system are obtained: M1 = 0.29(4) M⊙, M2 = 0.56(9) M⊙, R1 = 0.48(3) R⊙, R2 = 0.65(3) R⊙, L1 = 0.11(2) L⊙, L2 = 0.16(2) L⊙. To study the period variation, we fitted the SuperWASP, CSS, ASAS-SN and ZTF survey timing data to obtain light minima times spanning 14 years. Through O-C analysis, we find that the orbital period of this system has a long-term period decrease and periodic oscillation. The long-term period decrease can be explained by the mass transfer from more-massive component to less one and angular momentum loss (AML) via magnetic stellar wind. With the period decrease, this system is evolving from the present shallow contact phase to a relatively deeper stage predicted by the thermal relaxation oscillation (TRO) theory. Periodic oscillation can be explained by the light-time effect of the cool third body. This third body may play an important role in the early formation and evolution of the binary system by removing angular momentum.