Context : AB Doradus is the main system of the AB Doradus moving group .
It is a quadruple system formed by two widely separated binaries of pre-main-sequence ( PMS ) stars : AB Dor A/C and AB Dor Ba/Bb .
The pair AB Dor A/C has been extensively studied and its dynamical masses have been determined with high precision , thus making of AB Dor C a benchmark for calibrating PMS stellar models .
If the orbit and dynamical masses of the pair AB Dor Ba/Bb can be determined , they could not only play a similar role to that of AB Dor C in calibrating PMS models , but would also help to better understand the dynamics of the whole AB Doradus system .

Aims : We aim to determine the individual masses of the pair AB Dor Ba/Bb using VLBI observations and archive infrared data , as part of a larger program directed to monitor binary systems in the AB Doradus moving group .

Methods : We observed the system AB Dor B between 2007 and 2013 with the Australian Long Baseline Array ( LBA ) , at a frequency of 8.4 GHz in phase-reference mode .

Results : We detected , for the first time , compact radio emission from both stars in the binary , AB Dor Ba and AB Dor Bb .
This result allowed us to determine the orbital parameters of both the relative and absolute orbits and , consequently , their individual dynamical masses : 0.28 \pm 0.05 M _ { \odot } and 0.25 \pm 0.05 M _ { \odot } , respectively .

Conclusions : Comparisons of the dynamical masses with the prediction of PMS evolutionary models show that the models underpredict the dynamical masses of the binary components Ba and Bb by 10–30 % and 10–40 % , respectively , although they all still agree at the 2- \sigma level .
Some of stellar models considered favour an age between 50 and 100 Myr for this system , meanwhile others predict older ages .
We also discuss the evolutionary status of AB Dor Ba/Bb in terms of an earlier double-double star scenario that might explain the strong radio emission detected in both components .