5 Ages

The magnitude difference between the HB and the TO is a good age indicator (Iben 1974; Sandage 1986 and references therein), and is particularly suitable for reddened globular clusters (Ortolani et al. 1995). Recently Chaboyer et al. (1996) gathered this parameter for a series of globular clusters, most of them in the halo. Chaboyer et al. report the following clusters with -1.0 < [Fe/H] < -0.5 and the corresponding $\Delta V^{\rm TO}_{\rm HB}$: 47 Tuc (3.61), NGC 6171 (3.75), NGC 6352 (3.67), M 71 (3.56) and NGC 6652 (3.35). Kinematical arguments would make distinction as to whether some of them belong to halo or bulge, but we shall leave aside this point.

For Terzan 3, using the NTT CMD, we obtain $\Delta V\rm ^{TO}_{HB}$ $\approx$ 3.35 $\pm$ 0.15 and for IC 1276 $\Delta V\rm ^{TO}_{HB}$ $\approx$ 3.45 $\pm$ 0.20. In metallicity terms they are similar to Chaboyer et al.'s clusters above, although spatially they are more internal in the bulge.

We point out that recently some additional metal-rich clusters have photometry down to the MS region. In Rich et al. (1997) a HST CMD for NGC 5927 was presented, where we measure $\Delta V\rm ^{TO}_{HB}$ = 3.50 $\pm$ 0.10. Tonantzintla 2 was studied in Bica et al. 1996; we measure $\Delta V\rm ^{TO}_{HB}$ = 3.15 $\pm$ 0.20. Finally, in Ortolani et al. (1995) we obtained $\Delta V\rm ^{TO}_{HB}$ $\approx$ 3.7 $\pm$ 0.15 for the nearly solar metallicity bulge clusters NGC 6528 and NGC 6553.

These numbers indicate that the 47 Tuc-like -1.0 < [Fe/H] < -0.5 clusters are old or in some cases possibly slightly younger than the halo of $\Delta V\rm ^{TO}_{HB}$ = 3.55 (Buonanno et al. 1989). On the other hand the nearly solar ones have a value comparable to that of the halo. In conclusion, metal-rich globular clusters, at least as can be deduced from available measurements of $\Delta V\rm ^{TO}_{HB}$, appear to be typically old, and not intermediate age, as has been sometimes suggested for the field bulge population (e.g. Holtzman et al. 1993; Kiraga et al. 1997).