Deriving the true mass of a Brown Dwarf companion by AO aided astrometry Available to Purchase

The true masses of non‐transiting substellar companions to stars are only known for a few objects so far and they have all been determined by astrometry with the HST fine guidence sensor [1, 2]. From radial velocity detections alone one does not get all orbital parameters needed to derive the true mass of a substellar companion to a star. Additional astrometric measurements are needed to calculate the inclination i and the longitude of the ascending node Ω. The parallax and proper motion of the star must also be considered. We aim to derive the true mass of a brown dwarf candidate companion to an early M dwarf with groundbased astrometry aided by adaptive optics. We found this unique brown dwarf desert object in our UVES precision radial velocity survey of M dwarfs, inferring a minimum companion mass of 27 Jupiter masses [3]. Combining the data with HIPPARCOS astrometry, we found a probability of only 2.9% that the companion is stellar. We are therefore observing the host star and a reference field within a monitoring program with NACO at the VLT to derive the true mass of the companion and establish its nature (BD vs. star).