Physical properties and astrometry of radio-emitting brown dwarf TVLM513-46546 revisited

Abstract

We present multi-epoch astrometric observations of the M9 ultra-cool dwarf TVLM513-46546 that is placed at the brown dwarf boundary. The new observations have been performed with the European VLBI Network (EVN) at 6cm band. The target has been detected at 7~epochs spanning three years, with measured quiescent emission flux in the range 180-300 muJy. We identified four short-duration flaring events (0.5-2 mJy) with very high circular polarization (~75%-100%). Properties of the observed radio flares support the physical model of the source that is characterized by the electron cyclotron maser instability responsible for outbursts of radio emission. Combined with Very Long Baseline Array (VLBA) earlier data, our detections make it possible to refine the absolute parallax pi=93.27(+0.18,-0.17) mas. Our measurements rule out TVLM513-46546 companions more massive than Jupiter in orbits with periods longer than ~1 yr.