Abstract

The Transiting Exoplanet Survey Satellite (TESS) produces a large number of single-transit event candidates, since the mission monitors most stars for only similar to 27 d. Such candidates correspond to long-period planets or eclipsing binaries. Using the TESS Sector 1 full-frame images, we identified a 7750 ppm single-transit event with a duration of 7 h around the moderately evolved F-dwarf star TIC-238855958 (T-mag = 10.23, T-eff = 6280 +/- 85 K). Using archival WASP photometry we constrained the true orbital period to one of three possible values. We detected a subsequent transit-event with NGTS, which revealed the orbital period to be 38.20 d. Radial velocity measurements from the CORALIE Spectrograph show the secondary object has a mass of M-2 = 0.148 +/- 0.003M(circle dot), indicating this system is an F-M eclipsing binary. The radius of the M-dwarf companion is R-2 = 0.171 +/- 0.003 R-circle dot, making this one of the most well characterized stars in this mass regime. We find that its radius is 2.3 sigma lower than expected from stellar evolution models.