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High contrast imaging enables the determination of orbital parameters forsubstellar companions (planets, brown dwarfs) from the observed relativeastrometry and the estimation of model and age-dependent masses from theirobserved magnitudes or spectra. Combining astrometric positions with radialvelocity gives direct constraints on the orbit and on the dynamical masses ofcompanions. A brown dwarf was discovered with the VLT/SPHERE instrument in2017, which orbits at $\sim$ 11 au around HD 206893. Its mass was estimatedbetween 12 and 50 $M_{Jup}$ from evolutionary models and its photometry.However, given the significant uncertainty on the age of the system and thepeculiar spectrophotometric properties of the companion, this mass is not wellconstrained. We aim at constraining the orbit and dynamical mass of HD 206893B. We combined radial velocity data obtained with HARPS spectra and astrometricdata obtained with the high contrast imaging VLT/SPHERE and VLT/NaCoinstruments, with a time baseline less than three years. We then combined thosedata with astrometry data obtained by Hipparcos and Gaia with a time baselineof 24 years. We used a MCMC approach to estimate the orbital parameters anddynamical mass of the brown dwarf from those data. We infer a period between 21and 33{\deg} and an inclination in the range 20-41{\deg} from pole-on from HD206893 B relative astrometry. The RV data show a significant RV drift over 1.6yrs. We show that HD 206893 B cannot be the source of this observed RV drift asit would lead to a dynamical mass inconsistent with its photometry and spectraand with Hipparcos and Gaia data. An additional inner (semimajor axis in therange 1.4-2.6 au) and massive ($\sim$ 15 $M_{Jup}$) companion is needed toexplain the RV drift, which is compatible with the available astrometric dataof the star, as well as with the VLT/SPHERE and VLT/NaCo nondetection.

Constraining the properties of HD 206893 B. A combination of radial velocity, direct imaging, and astrometry data