Updated characterization of long-period single companion by combining radial velocity, relative astrometry, and absolute astrometry

Abstract

Context. Thanks to more than 20 yr of monitoring, the radial velocity (RV) method has detected long-period companions (P > 10 yr) 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 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.