Direct infrared observations of the very low mass object Gliese 623B

A low-mass, probably stellar, companion to the nearby star Gliese 623 has been detected interferometrically at 1.25, 1.65, and 2.2 microns, and its motion has been monitored over more than one full revolution cycle. Detection of this companion confirms a low-amplitude perturbation of the photocenter indicated previously by extensive astrometric observations. The interferometry, together with available astrometric and radial velocity measurements, yields improved orbital elements and the first photometric measurements and mass determinations of the component stars. The indicated luminosity and mass of G1 623B appear inconsistent with stellar models which predict a rapid decline of luminosity with decreasing mass for stars of age 2 Gyr and greater. 21 references.