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 to test models of mass-luminosity-age relations, as well as 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 combine long-period radial-velocity data from the CORALIE survey with relative astrometry from direct imaging with VLT/SPHERE, along 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 HD112863B and HD206505B, which are two new benchmark likely brown dwarfs that sit at the substellar-stellar boundary, with precise dynamical masses. We perform an orbital fit which yields dynamical masses for HD112863B and HD206505B to be $77.1^{+2.9}_{-2.8}~M_{\rm{Jup}}$ and $79.8\pm1.8~M_{\rm{Jup}}$ respectively. The orbital period for HD112863B is determined to be $21.59\pm0.05$ years and the orbital period of HD206505B is determined to be ${50.9}_{-1.5}^{+1.7}$ years. From the $H$ and $K$ band photometry from IRDIS data taken with VLT/SPHERE, we estimate the spectral types of both HD112863B and HD206505B to be early-mid L-types.