TOI-6508 b: A massive transiting brown dwarf orbiting a low-mass star

We report the discovery of a transiting brown dwarf orbiting a low-mass star, TOI-6508 b. Today, only ∼50 transiting brown dwarfs have been discovered. TOI-6508 b was first detected with data from the Transiting Exoplanet Survey Satellite ( TESS ) in Sectors 10, 37 and 63. Ground-based follow-up photometric data were collected with the SPECULOOS-South (Search for habitable Planets EClipsing ULtra-cOOl Stars) and LCOGT-1m telescopes, and RV measurements were obtained with the Near InfraRed Planet Searcher (NIRPS) spectrograph. We find that TOI-6508 b has a mass of M p = 72.5 −5.1 +7.6 M Jup and a radius of R p = 1.03 ± 0.03 R Jup . Our modeling shows that the data are consistent with an eccentric orbit of 19 day and an eccentricity of e = 0.28 −0.08 +0.09 . TOI-6508 b has a mass ratio of M BD / M ★ = 0.40, makes it the second highest mass ratio brown dwarf that transits a low-mass star. The host has a mass of M ★ = 0.174 ± 0.004 M ⊙ , a radius of R ★ = 0.205 ± 0.006 R ⊙ , an effective temperature of T eff = 2930 ± 70 K, and a metallicity of [ Fe/H ] = −0.22 ± 0.08. This makes TOI-6508 b an interesting discovery that has come to light in a region still sparsely populated.