We determine the absolute dimensions of the eclipsing binary V578Â Mon , a detached system of two early B-type stars ( B0V + B1V , P = 2.40848 d ) in the star-forming region NGCÂ 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 \pm 0.04  Rsun and 4.29 \pm 0.05  Rsun , and temperatures of 30000 \pm 500  K and 25750 \pm 435  K respectively .
We find that our disentangled component spectra for V578Â 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 \pm 0.08  Msun and 10.29 \pm 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 .
However - there 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 \pm 0.017 and \log { k _ { 2 } } = -3.412 \pm 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 \pm 0.025 of the Granada models fully agrees with our observed \log { k _ { 2 } } .