Abstract

We report the disco v ery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Surv e y data, with supporting observations found in TESS sectors 11 and 38. We confirmed the disco v ery with follow- up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of ∼1.25 d, a mass of 69 . 0 + 5 . 3 -4 . 8 M J , close to the hydrogen burning limit, and a radius of 0.95 ±0.05 R J . We determine the age to be > 0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important disco v ery within this scarcely populated region.