Run of the parameter Fe, which represents the average intensity of 17 Fe I lines in our spectra, against effective temperature. Symbols are as in Fig. 3. We overimpose three curves, representing the results obtained from a similar analysis of synthetic spectra computed with Fe abundances of [Fe/H] = −0.9, −1.1, and −1.3 (dashed, solid, and dotted lines, respectively). We note that the gravity and microturbulence of the models used for these synthetic spectra do not coincide with those appropriate for the individual stars, hence abundances cannot be derived by a simple interpolation in this plot.