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 $M_J$, and a radius of R _b = 0.75 ± 0.02 $R_J$. Its host star, TOI-569, has a mass of M _⋆ = 1.21 ± 0.05 $M_{\odot }$, a radius of R _⋆ = 1.47 ± 0.03 $R_{\odot }$, $\left[Fe/H\right]=+0.29\pm 0.09$ 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 $M_J$, and a radius of R _b = 0.86 ± 0.03 $R_J$. 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 $R_{\odot }$, $\left[Fe/H\right]=-0.08\pm 0.09$ 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 $M_J$ 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.