On the dynamics of the AB Doradus system

¹ Departamento de Astronomía y Astrofísica, Universidad de Valencia, 46100 Burjassot, Valencia, Spain e-mail: jose.c.guirado@uv.es
² Steward Observatory, University of Arizona, Tucson, Arizona 85721, USA
³ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Observatoire de Paris/LERMA, Rue de l'Observatoire 61, 75014 Paris, France
⁵ Australian Telescope National Facility, P.O. Box 76, Epping, NSW 2121, Australia
⁶ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA

Received: 4 July 2005
Accepted: 21 September 2005

Abstract

We present an astrometric analysis of the binary systems AB Dor A /AB Dor C and AB Dor Ba /AB Dor Bb. These two systems of well-known late-type stars are gravitationally associated and they constitute the quadruple AB Doradus system. From the astrometric data available at different wavelengths, we report: (i) a determination of the orbit of AB Dor C, the very low mass companion to AB Dor A, which confirms the mass estimate of 0.090  reported in previous works; (ii) a measurement of the parallax of AB Dor Ba, which unambiguously confirms the long-suspected physical association between this star and AB Dor A; and (iii) evidence of orbital motion of AB Dor Ba  around AB Dor A, which places an upper bound of 0.4  on the mass of the pair AB Dor Ba /AB Dor Bb  (50% probability). Further astrometric monitoring of the system at all possible wavelengths would determine with extraordinary precision the dynamical mass of its four components.