2006A&A...446..733G

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 0.090M_☉ 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 0.4M_☉ 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.