%AWay, Zachary%AJayasinghe, T%AKochanek, C%AStanek, K%AVallely, Patrick%AThompson, Todd%AHoloien, Thomas%AShappee, Benjamin%BJournal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 514; Journal Issue: 1 %D2022%I %JJournal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 514; Journal Issue: 1 %K %MOSTI ID: 10342146 %PMedium: X %TDiscovery of a highly eccentric, chromospherically active binary: ASASSN-V J192114.84+624950.8 %XABSTRACT As part of an All-Sky Automated Survey for SuperNovae (ASAS-SN) search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source ASASSN-V J192114.84+624950.8 rapidly decreased in flux by $\sim 55{{\ \rm per\ cent}}$ (∼0.9 mag) in the g band. The Transiting Exoplanet Survey Satellite light curve revealed that the source is a highly eccentric, eclipsing binary. Fits to the light curve using phoebe find the binary orbit to have e = 0.79, Porb = 18.462 d, and i = 88.6°, and the ratios of the stellar radii and temperatures to be R2/R1 = 0.71 and Te,2/Te,1 = 0.82. Both stars are chromospherically active, allowing us to determine their rotational periods of P1 = 1.52 d and P2 = 1.79 d, respectively. A Large Binocular Telescope/Multi-Object Double Spectrograph spectrum shows that the primary is a late-G- or early-K-type dwarf. Fits to the spectral energy distribution show that the luminosities and temperatures of the two stars are L1 = 0.48 L⊙, $T_1= 5050\, \mathrm{K}$, L2 = 0.12 L⊙, and $T_{2} = 4190\, \mathrm{K}$. We conclude that ASASSN-V J192114.84+624950.8 consists of two chromospherically active, rotational variable stars in a highly elliptical eclipsing orbit. %0Journal Article