47 Tuc and M 5

In this Section, we compare our model predictions to data for two of the best studied Galactic globular clusters, 47 Tuc and M 5. It is very interesting to test our models in the region of stellar population parameter space occupied by metal-poor to mildly metal-rich old globular clusters, in view of the on-going efforts to constrain the history of merging/star-formation of external galaxies through the determination of the spectroscopic ages and metallicities of their globular clusters (e.g., Cohen et al. 1998, Cohen, Blakeslee & Côté 2003, Larsen et al. 2003, Burstein et al. 2004, Beasley et al. 2005, Puzia et al. 2005, Brodie & Strader 2006, and references therein).

The data for these two clusters are compared to the models in Figures 22a through 22f. The abundance patterns of 47 Tuc and M 5 are $\alpha$-enhanced (Table 25), in particular with [O/Fe] = +0.5 and +0.3, respectively. We recall from Section 4.3.1 that the $\alpha$-enhanced Padova isochrones were computed assuming [O/Fe]=+0.5. However, they do not extend to low enough metallicities for a comparison with M 5 data. Moreover, Weiss et al. (2006) showed that the Padova $\alpha$-enhanced isochrones need to be revised (see discussion in Section 4.3.1) so that we choose to compare the data with models generated using the solar-scaled Padova isochrones (models 1-5 in Table 24). This set of theoretical isochrones does not match the oxygen abundances of the two clusters. However, based on our discussion in Section 4.3.1, the evolutionary $\alpha$-enhancement effects are well-understood, so that we can use models based on solar-scaled isochrones, while keeping in mind the effect of that inconsistency. In particular, we expect to predict slightly too old ages, regardless of the Balmer line used.