Approximate contour maps of the likelihood ℒ as a function of the stellar masses and ages. Values within 1, 2, and 3 of each term of Eq. (11) appear in red, yellow, and blue, respectively. Considering a flat prior (which is reasonable), these maps show the joint PDF of M_⋆ and the age. The best fit old and young (if any) solutions are represented by crosses. The solid horizontal line in the case of HD 75732 corresponds to an independent estimate of the mass, and the dashed horizontal lines correspond to the errobars on M_⋆ (see Sect. 4.3).