Vol. 671
1. Letters to the Editor

Direct discovery of the inner exoplanet in the HD206893 system. Evidence for deuterium burning in a planetary-mass companion

The HD206893 F5V star is orbited by both a debris disk and a known brown dwarf in an ~10 AU orbit, and residuals in its radial velocity and proper motion measurements strongly suggest an additional inner companion. Guided by orbital fits to those residuals, Hinkley et al. used the GRAVITY instrument of the VLTI interferometer to detect the additional companion with a 1.5 10^-4 contrast within just 100 milliarcseconds of the primary star, extract 50-100 microarcsecond relative astrometry, and obtain an R=500 resolution spectrum. Orbital fits provide dynamical masses of 13 and 28 Jupiter masses with 10% and 5% precision for the two components. A comparison of the mass and bolometric luminosity of the inner b companion to evolutionary models provides tight age constraints for the system and shows that b straddles the deuterium burning limit. This makes the system an essential benchmark of evolution and structure at the transition between planets and brown dwarfs.