Accurate dynamical mass and orbit determination of the M dwarf binary DG CVn using astrometric very long baseline interferometry

Abstract

Complex periodic variable (CPV) stars are a small subset of young M dwarfs that exhibit puzzling periodic variations in their optical light curve. Astrometry through very long baseline interferometry (VLBI) allows the monitoring of radio-loud stars and the detection of any reflex motion due to stellar or substellar companions. We observe the radio emission and motion of the nearby CPV M dwarf binary (GJ,3789, G,165--8) to determine the composition of the system. DG,CVn The system was monitored using VLBI with observations that spanned 18 years and reached sub-milliarcsecond accuracy. Orbital parameters were fitted to these results and compared with the historical optical relative astrometric record. In our recent observations, we reliably detected both binary components. A unique and accurate determination of the 1647.647,±,0.027 day orbit, with a parallax distance of 18.1851,±,0.0033,pc, is presented. The dynamical masses were estimated with a precision of 0.16% from the sampled posteriors. The value of combining archival and recent VLBI astrometric observations has been demonstrated. It resulted in a highly accurate determination of the system composition, orbit, position, and distance. We present the first dynamical mass measurement of a binary containing a CPV star.