Search for brown-dwarf companions of stars

TL;DR

This study reports the discovery and characterization of brown-dwarf companions around stars, including new candidates and refined mass estimates, and assesses their frequency around Sun-like stars using radial velocity and astrometric data.

Contribution

The paper introduces new brown-dwarf candidates, refines orbital parameters with Hipparcos data, and provides an updated frequency estimate of brown-dwarf companions around Sun-like stars.

Findings

9 new brown-dwarf candidates discovered

Masses of some companions confirmed as brown dwarfs or stellar

Upper limit of 0.6% for brown-dwarf companion frequency

Abstract

The discovery of 9 new brown-dwarf candidates orbiting stars in the CORALIE and HARPS radial-velocity surveys is reported. New CORALIE radial velocities yielding accurate orbits of 6 previously-known hosts of potential brown-dwarf companions are presented. Including targets selected from the literature, 33 hosts of potential brown-dwarf companions are examined. Employing innovative methods, we use the new reduction of the Hipparcos data to fully characterise the astrometric orbits of 6 objects, revealing M-dwarf companions with masses between 90 M_Jup and 0.52 M_Sun. Additionally, the masses of two companions can be restricted to the stellar domain. The companion to HD 137510 is found to be a brown dwarf. At 95 % confidence, the companion of HD 190228 is also a brown dwarf. The remaining 23 companions persist as brown-dwarf candidates. Based on the CORALIE planet-search sample, we obtain an upper limit of 0.6 % for the frequency of brown-dwarf companions around Sun-like stars. We find that the companion-mass distribution function is rising at the lower end of the brown-dwarf mass range, suggesting that in fact we are detecting the high-mass tail of the planetary distribution.