Two Intermediate-mass Transiting Brown Dwarfs from the TESS Mission

We report the discovery of two intermediate-mass transiting brown dwarfs (BDs), TOI-569b and TOI-1406b, from NASA's Transiting Exoplanet Survey Satellite mission. TOI-569b has an orbital period of P = 6.55604 ± 0.00016 days, a mass of M_b = 64.1 ± 1.9 ${M}_{{\rm{J}}}$ , and a radius of R_b = 0.75 ± 0.02 ${R}_{{\rm{J}}}$ . Its host star, TOI-569, has a mass of M_⋆ = 1.21 ± 0.05 $\,{M}_{\odot }$ , a radius of R_⋆ = 1.47 ± 0.03 $\,{R}_{\odot }$ , $[\mathrm{Fe}/{\rm{H}}]=+0.29\pm 0.09$ dex, and an effective temperature of T_eff = 5768 ± 110 K. TOI-1406b has an orbital period of P = 10.57415 ± 0.00063 days, a mass of M_b = 46.0 ± 2.7 ${M}_{{\rm{J}}}$ , and a radius of R_b = 0.86 ± 0.03 ${R}_{{\rm{J}}}$ . The host star for this BD has a mass of M_⋆ = 1.18 ± 0.09 $\,{M}_{\odot }$ , a radius of R_⋆ = 1.35 ± 0.03 $\,{R}_{\odot }$ , $[\mathrm{Fe}/{\rm{H}}]=-0.08\pm 0.09$ dex, and an effective temperature of T_eff = 6290 ± 100 K. Both BDs are in circular orbits around their host stars and are older than 3 Gyr based on stellar isochrone models of the stars. TOI-569 is one of two slightly evolved stars known to host a transiting BD (the other being KOI-415). TOI-1406b is one of three known transiting BDs to occupy the mass range of 40-50 ${M}_{{\rm{J}}}$ and one of two to have a circular orbit at a period near 10 days (with the first being KOI-205b). Both BDs have reliable ages from stellar isochrones, in addition to their well-constrained masses and radii, making them particularly valuable as tests for substellar isochrones in the BD mass-radius diagram.