  Context. Thanks to more than 20 years of monitoring, the radial velocity (RV)
method has detected long-period companions (P > 10yr) around several dozens of
stars. Yet, the true nature of these companions remains unclear because of the
uncertainty as to the inclination of the companion orbital plane. Aims. We wish
to constrain the orbital inclination and the true mass of long-period single
companions. Methods. We used a Markov Chain Monte Carlo (MCMC) fitting
algorithm to combine RV measurements with absolute astrometry and, when
available, relative astrometry data. Results. We have lifted the sin(i)
indetermination for 7 seven long-period companions. We find true masses in the
planetary mass range for the candidate planets detected in the following
systems: Epsilon Indi A, HD 13931, HD 115954, and HD 222155. The mass of HD
219077 b is close to the deuterium-burning limit and its nature is uncertain
because of the imprecise mass of the host star. Using additional RV
measurements, we refine the orbital parameters of HIP 70849 b and find a mass
in the planetary range. By combining RV data with absolute and relative
astrometry, we significantly improve the characterization of HD 211847 B and
properly determine its mass, which appears to be in the low-mass star range.
This work illustrates how Gaia and Hipparcos allow for the orbital properties
and masses of long-period RV companions to be further constrained.
