HRD of UX Men. Full lines show the evolutionary track of the models with diffusion and an initial metallicity of [Fe/H] _i = 0.2 and Y_i = 0.29. Dashed lines show tracks of standard models with the same mass, but without diffusion and a composition of [Fe/H] = 0.04, and Y = 0.28. All tracks are indicated at 2.1 Gyr. The red and blue shaded areas show the observational errors (as explained in Sect. 3.3) of primary (left panel) and secondary (right panel), respectively.