2025PASP..137f4201Z

In this paper, photometric and spectroscopic data from ten contact binaries (CBs) are presented and analyzed. We found that CzeV710 was a totally eclipsing binary with a very low mass ratio (q ∼ 0.14), V401 Cam was a W-subtype totally eclipsing binary (f = 35.5%), the others were shallow CBs. Using O - C, we further discovered that five of them exhibit secular period changes, one show linear variations, and four show cyclic variations. For V1030 Cas, a long-term decrease superposed a cyclic variation was discovered. Except CzeV710, the light curves for the other nine targets show the O'Connell effect, and a cool star-spot on the active component can lead to a good fit of the asymmetric light curves. In addition, based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope low-resolution spectroscopic measurements, the equivalent width of the H_α emission line is used as a tracer of chromospheric activity. The analysis of the H_α emission line and the O'Connell effect suggested that our targets are active at present. After calculating the instability parameters, we also found that these ten targets are relatively stable now. By comparing the parameters of 360 short-period eclipsing binaries, we found that CBs have a minimum orbital angular momentum in close binaries, which indicates that they are at the end of the evolution chain of binaries. The evolution of CBs is very complex; the third body and angular momentum loss can help shallow CBs evolve into medium- and deep-ones.