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

TL;DR

This study combines radial velocity, absolute, and relative astrometry data to accurately determine the true masses and orbital inclinations of long-period companions, refining their classification as planets or stars.

Contribution

It introduces a Markov Chain Monte Carlo method to integrate multiple data types, lifting the sin(i) ambiguity for several long-period companions.

Findings

True masses of companions in planetary range for several systems.

Refined orbital parameters for multiple long-period companions.

Improved mass estimates using Gaia and Hipparcos data.

Abstract

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.