Young, active radio stars in the AB Doradus moving group
1 Departament d’Astronomia i Astrofísica, Universitat de València, C. Dr. Moliner 50, 46100 Burjassot, València, Spain
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, 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 Max-Planck-Institut für Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany
8 Instituto de Astrofísica de Andalucía (IAA-CSIC), Apt 3004, 1808 Granada, Spain
Received: 14 October 2016
Accepted: 14 March 2017
Context. Precise determination of stellar masses is necessary to test the validity of pre-main-sequence (PMS) stellar evolutionary models, whose predictions are in disagreement with measurements for masses below 1.2 M⊙. To improve such a test, and based on our previous studies, we selected the AB Doradus moving group (AB Dor-MG) as the best-suited association on which to apply radio-based high-precision astrometric techniques to study binary systems.
Aims. We seek to determine precise estimates of the masses of a set of stars belonging to the AB Dor-MG using radio and infrared observations.
Methods. We observed in phase-reference mode with the Very Large Array (VLA) at 5 GHz and with the European VLBI Network (EVN) at 8.4 GHz the stars HD 160934, EK Dra, PW And, and LO Peg. We also observed some of these stars with the near-infrared CCD AstraLux camera at the Calar Alto observatory to complement the radio observations.
Results. We determine model-independent dynamical masses of both components of the star HD 160934, A and c, which are 0.70 ± 0.07 M⊙ and 0.45 ± 0.04 M⊙, respectively. We revised the orbital parameters of EK Dra and we determine a sum of the masses of the system of 1.38 ± 0.08 M⊙. We also explored the binarity of the stars LO Peg and PW And.
Conclusions. We found observational evidence that PMS evolutionary models underpredict the mass of PMS stars by 10%−40%, as previously reported by other authors. We also inferred that the origin of the radio emission must be similar in all observed stars, that is, extreme magnetic activity of the stellar corona that triggers gyrosynchrotron emission from non-thermal, accelerated electrons.
Key words: binaries: general / stars: pre-main sequence / radio continuum: general / astrometry
© ESO, 2017