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.

Based on observations collected with SPHERE mounted on the VLT at Paranal Observatory (ESO, Chile) under program 0103.C-0199(A) (PI: Rickman), and 105.20SZ.001 (PI: Rickman) as well as observations collected with the CORALIE spectrograph mounted on the 1.2 m Swiss telescope at La Silla Observatory.

The radial velocity measurements, reduced images, and additional data products discussed in this paper are available on the DACE web platform at https://dace.unige.ch/ and the links to individual targets are listed in Appendix A.