Dynamical masses of M-dwarf binaries in young moving groups; I - The case of TWA~22 and GJ~2060

TWA 22 and GJ 2060 are two young (120-150 Myr) tight pairs of M dwarfs resolved through high-angular resolution techniques. Their short periods allow for dynamical mass determination within a few years, which make them precious benchmarks for the pre-main sequence (PMS) evolutionary models. We present new resolved images of both systems (VLT/SPHERE, VLT/NaCo, Keck/NIRC2, NTT/AstraLux), integral field spectra of GJ~2060 A and B, and radial velocity measurements of GJ~2060 AB (VLT/SINFONI, FEROS, ESO/HARPS). We used these new measurements to derive revised and robust constraints on the orbital parameters and dynamical masses of both binaries via dedicated MCMC orbital fitting. We used SINFONI data to study the spectrophotometric properties of GJ~2060 AB and derive luminosities and temperatures of the individual components. TWA 22, a member of the Beta Pictoris moving group whose age is particularly well constrained, displays a perfect agreement between dynamical mass determination and models predictions. Moreover, our orbital fit is fully consistent with previous estimates. On the other hand, GJ 2060 is a bona fide member of the ABDor moving group whose age constraint is loose. For the first time, we are able to derive a robust orbital determination that reveals a highly eccentric (e∼0.9) but clearly bound orbit. Models fail to give a total mass estimate consistent with the dynamical mass that we derive. In light of these case studies, we will discuss the precision of the models for PMS stars, and the possibility of hidden companions in those systems.