2025MNRAS.537.2258L

This paper presents the photometric and spectroscopic analysis of a long-period totally eclipsing contact binary (HAT 307-0007476) for the first time. This system is a low mass ratio ($q\sim 0.114$) and medium contact binary ($f\sim 37.1~{{\ \rm per\ cent}}$). Two flare events were detected in multiple bands observations in December 2022. The interval between the two flare events is 4 d. The average duration of these two flares is about 2289 s. Both the two flares achieve the energy levels of superflares. The excess emission of the H$_\alpha$ line in the LAMOST spectra of this object was analysed, indicating its chromospheric activity. The O-C diagram showed a long-term orbital period increase, which is due to the mass transfer between the two component stars. We conclude that HAT 307-0007476 is currently in a stable region based on both J_spin/J_orb and the comparison between the instability parameters and its current values.