2019MNRAS.487.5520L

We performed new photometric and spectroscopic studies on four W UMa-type eclipsing binaries (V400 Lyr, V574 Lyr, V1033 Her and V1062 Her). The main aims were to determine the orbital parameters and period variations of these four systems. We classified V574 Lyr, V1033 Her and V1062 Her spectral types based on LAMOST spectra, and used a spectra subtraction technique to measure the properties of the Hα, Hβ and Ca II H&K lines. We updated the ephemerides of these four systems, and conducted analyses of period variation for three systems (V574 Lyr, V1033 Her and V1062 Her). The period of V400 Lyr shows a continuous decrease, while that of V1033 Her continuously increases. Meanwhile, V574 Lyr and V1062 Her show a cyclic variation, caused by the light-time effect via the third body or magnetic activity cycle. The orbital and star-spot parameters of these four systems were obtained using the Wilson-Devinney program. This is the first time that precise orbital parameters have been obtained for V574 Lyr and V1062. We also concluded that these four objects are shallow contact eclipsing binaries with a cool spot on the primary. We found star-spot variabilities of about one month for V574 Lyr, and on long (years) time-scales for V1033 Her and V1062 Her. There are also obvious variations in the differences of light-curve maxima between 0.25 and 0.75 phases.