Temperatures vs. gravities. Y² isochrones representing different ages and metallicities are shown. The lines connecting an open and a filled circle depict changes in temperature and gravity of HD 94374 and HD 182572 to achieve excitation equilibrium (see text). The open circles indicate photometric temperatures obtained as described in Sect. 5.1; the filled circles correspond to the excitation-equilibrium values, which were adopted for these two stars.