The AB Doradus system revisited: The dynamical mass of AB Dor A/C

¹ Departament d’Astronomia i Astrofísica, Universitat de València, C. Dr. Moliner 50, 46100 Burjassot, València, Spain
e-mail: Rebecca.Azulay@uv.es
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Observatori Astronòmic, Universitat de València, Parc Científic, C. Catedrático José Beltrán 2, 46980 Paterna, València, Spain
⁴ Onsala Space Observatory, Space Earth and Environment, Chalmers University of Technology, 43992 Onsala, Sweden
⁵ Department of Physics “E. Fermi”, University of Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
⁶ INFN, Section of Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
⁷ CSIRO Astronomy and Space Science, Australia Telescope National Facility, Epping, NSW 1710, Australia
⁸ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁹ Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC, 61 Av. de l’Observatoire, 75014 Paris, France

Received: 16 February 2017
Accepted: 11 August 2017

Abstract

Context. The study of pre-main-sequence (PMS) stars with model-independent measurements of their masses is essential to check the validity of theoretical models of stellar evolution. The well-known PMS binary AB Dor A/C is an important benchmark for this task, since it displays intense and compact radio emission, which makes possible the application of high-precision astrometric techniques to this system.

Aims. We aim to revisit the dynamical masses of the components of AB Dor A/C to refine earlier comparisons between the measurements of stellar parameters and the predictions of stellar models.

Methods. We observed in phase-reference mode the binary AB Dor A/C, 0.2′′ separation, with the Australian Long Baseline Array at 8.4 GHz. The astrometric information resulting from our observations was analyzed along with previously reported VLBI, optical (Hipparcos), and infrared measurements.

Results. The main star AB Dor A is clearly detected in all the VLBI observations, which allowed us to analyze the orbital motion of the system and to obtain model-independent dynamical masses of 0.90 ± 0.08 M_⊙ and 0.090 ± 0.008 M_⊙, for AB Dor A and AB Dor C, respectively. Comparisons with PMS stellar evolution models favor and age of 40−50 Myr for AB Dor A and of 25−120 Myr for AB Dor C.

Conclusions. We show that the orbital motion of the AB Dor A/C system is remarkably well determined, leading to precise estimates of the dynamical masses. Comparison of our results with the prediction of evolutionary models support the observational evidence that theoretical models tend to slightly underestimate the mass of the low-mass stars.