Comparison of the parameters of W_DEB (stars), W36 (circles) and W13 (squares) with evolutionary tracks (solid lines) for stars with 5−60   M_⊙ and isochrones (dotted lines) for single rotating stars at solar metallicity from Ekström et al. (2012). Isochrones, from the bottom up, correspond to 3 − 6, 8 and 10 Myr. Single star isochrones are not compatible with the measured parameters for W36 and W13, indicating mass transfer.