Improved age constraints for the AB Doradus quadruple system ^*

The binary nature of AB Doradus B

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: [janson;brandner;lenzen;henning]@mpia.de
² UCLA, Div. of Astronomy, 475 Portola Plaza, Los Angeles, 90095-1547, USA e-mail: brandner@astro.ucla.edu
³ Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ-85721-0065, USA e-mail: [lclose;enielsen]@as.arizona.edu
⁴ European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile e-mail: mhartung@eso.org
⁵ Astronomy Dpt. of UC Berkeley, 601 Campbell Hall, Berkeley, 94720-3411, USA e-mail: hbouy@astro.berkeley.edu

Received: 8 August 2006
Accepted: 12 November 2006

Abstract

We present resolved NACO photometry of the close binary AB Dor B in H- and Ks-band. AB Dor B is itself known to be a wide binary companion to AB Dor A, which in turn has a very low-mass close companion named AB Dor C. These four known components make up the young and dynamically interesting system AB Dor, which will likely become a benchmark system for calibrating theoretical pre-main sequence evolutionary mass tracks for low-mass stars. However, for this purpose the actual age has to be known, and this subject has been a matter of discussion in the recent scientific literature. We compare our resolved photometry of AB Dor Ba and Bb with theoretical and empirical isochrones in order to constrain the age of the system. This leads to an age estimate of about 50 to 100 Myr. We discuss the implications of such an age range for the case of AB Dor C, and compare with other results in the literature.