FIG. 6-Color-absolute magnitude diagram for the halo stars. Three groups are indicated by separate symbols as presented in Fig. 3. We have overplotted 16 Gyr isochrones taken from Bergbusch & Vandenberg (1992), from left to right, [Fe/H] = -1.78, -1.66, -1.48, -1.26, -1.03, and -0.78, respectively