2020MNRAS.491.6065Z

We performed photometric and spectroscopic studies on four W Ursae Majoris eclipsing binaries (V384 Ser, AQ Psc, V480 Gem and 2MASS J07095549+3643564). The binaries were observed from 2015 to 2018. The orbital period of V384 Ser showed an interesting cyclic variation overlaying a decreasing period, which may be caused by the light-time effect (LITE) of approximately 2.84 ± 0.01 yr or the magnetic activity cycle of 2.83 ± 0.01 yr. For AQ Psc, we found cyclic variations in its period caused by the LITE either as a result of a tertiary companion or because of a magnetic activity cycle. We derived the cycle of the tertiary component of AQ Psc as 23.87 (±0.14) yr or a magnetic cycle of 44.08 (±1.15) yr. We revised the linear ephemeris of eclipsing binaries V480 Gem and 2MASS J07095549+3643564. We also determined their orbital parameters and star-spot parameters by fitting the light curves. In addition, we found weak excess emissions in the LAMOST spectra of V384 Ser, AQ Psc, V480 Gem and 2MASS J07095549+3643564 in the Hα line, which indicates weak chromospheric activities.