Transformation to the observational plane

The theoretical parameters of the isochrones have been transformed to the observational plane (colours and magnitudes) by using relations inferred on the basis of extensive empirical photometric stellar libraries. We use the metallicity-dependent empirical relations of Alonso, Arribas & Martinez-Roger (1996, 1999), for dwarfs and giants respectively. The empirical (not the theoretical) compilation of Lejeune, Cuisinier & Buser (1997, 1998; and references therein) are used for the coolest dwarfs (Teff < 4000 K) and giants (Teff < 3500 K), respectively, for solar metallicity. A semi-empirical approach was applied to other metallicities on the basis of these relations and the model atmospheres of Bessell et al. (1989, 1991) and the library of Fluks et al. (1994). The empirical compilation of Lejeune et al. was also used for stars with temperatures above ~ 8000 K.

Metal-dependent bolometric correction given by Alonso, Arribas & Martinez-Roger (1995, 1999) for dwarfs and giants have been applied respectively. For the Sun, a bolometric correction BC_sun=-0.12 and a bolometric magnitude of 4.70 has been used according to these authors.

Ages and metallicities of the "best" CMD fits for different sets of isochrones

We have carried out a "by eye" fitting procedure, trying to fit (1) the top main sequence plus the turn-off; (2) the subgiant and red giant branches (the later specially at low magnitudes, as the redder part of the RGB is not very well constrained); and (3) the magnitude of the horizontal branch base. Reddening effects have not been considered; instead, apropriate offsets in both axis have been applied to the isochrones to match the observational CMD.