Astrometric detection of a very low-mass companion orbiting a late-type radio star

From the combination of VLBI (Very Long Baseline Interferometry) phase-referenced observations and Hipparcos satellite data, we have found evidence of a very low-mass object orbiting the late-type star AB Doradus. The mass of the companion inferred from the observed orbital motion places this object on the boundary between a brown dwarf and a very low-mass star. If accurate photometry of the companion can be obtained, our mass determination will allow the AB Dor companion to serve as an accurate calibration point for the different theoretical evolutionary models of very low-mass objects. This represents the first detection of a low-mass stellar companion using the VLBI technique, which could become an important tool in future searches for planets and brown dwarfs orbiting other stars.