As Fig. 3 but only for the AC objects. The fundamental mode (solid line) and first overtone (dashed line) blue and red edge of the IS of AC are indicated (Fiorentino et al. 2006). Tracks from the BaSTI database (Pietrinferni et al. 2004) are plotted in light blue (Z = 0.0001), magenta (Z = 0.0003), yellow (Z = 0.0006), brown (Z = 0.001), green (Z = 0.002) for stars of 1.1 M_⊙ (1 model, bluest extension near log L ~ 1.9), 1.5 M_⊙ (2 models, bluest extension near log L ~ 2.1), 1.9 M_⊙ (1 model, bluest extension near log L ~ 2.2), and 2.3 M_⊙ (3 models, bluest extension between log L = 2.25–2.45). A point is plotted for every 1 Myr of evolution.