New results on the two low-mass-ratio overcontact binaries V1309 Herculis and AS Coronae Borealis.

This article focuses on the photometric and orbital period analyses of two W UMa-type contact binary star systems, V1309 Herculis (V1309 Her) and AS Coronae Borealis (AS CrB), based on new multi-color light curves obtained with the 60 cm telescope at Maidanak Astronomical Observatory and atmospheric parameters from the Large-Sky-Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Both systems are identified as low-mass-ratio overcontact binaries (V1309 Her: q ≈ 0.21; AS CrB: q ≈ 0.16), with AS CrB exhibiting a higher fill-out factor indicative of a more advanced evolutionary stage. Orbital period variations reveal periodic oscillations in their O − C (observed minus calculated) diagrams, attributed primarily to the light travel-time effect caused by third bodies, supported by detected third light contributions in the photometric solutions. Additionally, AS CrB shows a long-term period increase consistent with mass transfer from the less massive to the more massive component, suggesting it may eventually merge into a rapidly rotating single star. The study notes that while magnetic activity cycles could also explain the periodic variations, the presence of third bodies is the more likely cause, warranting further long-term observations.