The discovery of two new benchmark brown dwarfs with precise dynamical masses at the stellar-substellar boundary

Aims. Measuring dynamical masses of substellar companions is a powerful tool for testing models of mass-luminosity-age relations as well as for determining observational features that constrain the boundary between stellar and substellar companions. In order to dynamically constrain the mass of such companions, we use multiple exoplanet measurement techniques to remove degeneracies in the orbital fits of these objects and place tight constraints on their model-independent masses. Methods. We combined long-period radial velocity data from the CORALIE survey with relative astrometry from direct imaging with VLT/SPHERE as well as with astrometric accelerations from HIPPARCOS-Gaia eDR3 to perform a combined orbital fit and measure precise dynamical masses of two newly discovered benchmark brown dwarfs. Results. We report the discovery of HD 112863 B and HD 206505 B, which are two new benchmark likely brown dwarfs that sit at the substellar-stellar boundary, with precise dynamical masses. We performed an orbital fit that yielded the dynamical masses of 77.1(-2.8)(+2.9) M-Jup and 79.8 +/- 1.8 M-Jup for HD 112863 B and HD 206505 B, respectively. We determined the orbital period of HD 112863 B to be 21.59 +/- 0.05 yr and the orbital period of HD 206505 B to be 50.9(-1.5)(+1.7) yr. From the H and K band photometry from IRDIS data taken with VLT/SPHERE, we estimate the spectral types of both HD 112863 B and HD 206505 B to be early-mid L-types.