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

Journal article, 2017

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 ABDorA/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 ABDorA/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 DorA/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 ABDorA 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 circle dot and 0.090 +/- 0.008 M circle dot, for ABDorA and ABDor C, respectively. Comparisons with PMS stellar evolution models favor and age of 40 50 Myr for ABDorA and of 25-120 Myr for ABDor C. Conclusions. We show that the orbital motion of the ABDorA/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.