At a distance of ∼ 2 pc, our nearest brown dwarf neighbor, Luhman 16 AB, has been extensively studied since its discovery 3 years ago, yet its most fundamental parameter -the masses of the individual dwarfs -has not been constrained with precision. In this work we present the full astrometric orbit and barycentric motion of Luhman 16 AB and the first precision measurements of the individual component masses. We draw upon archival observations spanning 31 years from the European Southern Observatory (ESO) Schmidt Telescope, the Deep Near-Infrared Survey of the Southern Sky (DENIS), public FORS2 data on the Very Large Telescope (VLT), and new astrometry from the Gemini South Multiconjugate Adaptive Optics System (GeMS). Finally, we include three radial velocity measurements of the two components from VLT/CRIRES, spanning one year. With this new data sampling a full period of the orbit, we use a Markov Chain Monte Carlo algorithm to fit a 16-parameter model incorporating mutual orbit and barycentric motion parameters and constrain the individual masses to be 27.9

Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main sequence (PMS) EBs are particularly valuable, both due to their rarity and the

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We determine the absolute dimensions of the eclipsing binary V578 Mon, a detached system of two early B-type stars (B0V + B1V, P=2.40848 d) in the star-forming region NGC 2244 of the Rosette Nebula. From the light curve analysis of 40 yr of photometry and the analysis of hermes spectra, we find radii of 5.41 ± 0.04 Rsun and 4.29±0.05 Rsun, and temperatures of 30000±500 K and 25750±435 K respectively. We find that our disentangled component spectra for V578 Mon agree well previous spectral disentangling from the literature. We also reconfirm the previous spectroscopic orbit of V578 Mon finding that masses of 14.54 ± 0.08 Msun and 10.29 ± 0.06 Msun are fully compatible with the new analysis. We compare the absolute dimensions to the rotating models of the Geneva and Utrecht groups and the models of Granada group. We find all three sets of models marginally reproduce the absolute dimensions of both stars with a common age within uncertainty for gravity-effective temperature isochrones. Howeverthere are some apparent age discrepancies for the corresponding mass-radius isochrones. Models with larger convective overshoot > 0.35 worked best. Combined with our previously determined apsidal motion of 0.07089 +0.00021 −0.00013 deg cycle −1 , we compute the internal structure constants (tidal Love number) for the newtonian and general relativistic contribution to the apsidal motion, log k 2 = −1.975 ± 0.017 and log k 2 = −3.412 ± 0.018 respectively. We find the relativistic contribution to the apsidal motion of be small < 4%. We find that the prediction of log k 2,theo = −2.005 ± 0.025 of the Granada models fully agrees with our observed log k 2 .