V1374 Tau: A Dwarf Eclipsing Binary with Starspots, a Superflare, and a Tertiary Companion

Abstract We present a comprehensive study of V1374 Tau, including starspot activity, a superflare, and the light-time effect. We acquired new ground-based photometry, LAMOST low-resolution spectra, and TESS time-series data. From the TESS data in Sectors 71 and 72, the differences between the two light maxima for each cycle are averaged to be Δ m max = −0.046 ± 0.005 mag during the 50 day interval. Using the Wilson–Devinney program, we derived two photometric solutions from LC HJD2461035 and LC BJD2460277 , in which spots migrate and evolve on the surfaces of two components. A superflare was found in TESS data (Sector 72), which was modelled by least-squares fitting and Markov Chain Monte Carlo (MCMC) methods. The flare energy emitted from the M dwarf secondary is estimated to be E flare = 3.2 5 − 0.35 + 0.36 × 1 0 36 erg . From the ( O − C ) analysis, the orbital period may be undergoing a secular decrease with a 5.28 yr cyclic variation. The former may result from mass transfer from the more massive component to the less one, while the latter may be attributed to the light-time effect via the presence of the third body. Mass transfer, tertiary angular momentum extraction, and flare mass loss jointly shrink the orbit, driving the system toward a contact configuration as predicted by the thermal relaxation oscillation theory.