2023RAA....23d5010W

Two sets of CCD photometric observations for contact binary TU Boo were obtained in 2020 and 2021. Different from its asymmetric light curves published from the literature, our BVR_cI_c-band curves show that the heights of maximum are almost equal. These distortions of light curves possibly indicate that the components were active in past 25 yr, but they were stable in the last two years. For total-eclipse binary TU Boo, due to some star-spots on the surface of the components, the physical structure obtained by many investigators are different. Therefore, the symmetric multi-color light curves in 2020, 2021 are important for understanding configuration and evolution of this system. By using the Wilson-Devinney program, it is confirmed that TU Boo is an A-type shallow-contact binary with the temperature difference of ΔT = 152 K and fill-out of f = 14.67%. In the O-C diagram of orbital period analysis, a cyclic oscillation superimposed on a continuous decrease was determined. The long-term decreasing is often explained by the mass transfer from the more massive star to less massive one, this system will evolve into a deeper contact binary with time. The cyclic oscillations computed from much more CCD times of light minimum maybe result from the light-travel time effect via the presence of a third body. These characters of structure, evolution and ternary belong to typical A-type W UMa binaries with spectral G.