Comparison between predicted and empirical ΔVHBbump in galactic globular clusters

We present observational estimates of Delta V-HB(bump) in a sample of 28 galactic globular clusters (GGCs) observed by the Hobble Space Telescope. The photometric accuracy and the sizable number of stars measured in each cluster allowed us to single out the red giant branch bump both in metal-poor and in metal-rich GGCs. Empirical values are compared with homogeneous theoretical predictions that account for both H- and He-burning phases over a wide range of metal abundances (0.0001 < Z < 0.02). We found that, within current observational uncertainties on both iron and alpha-element abundances, theory and observations are in very good agreement, provided that the metallicity scale by Carretta & Gratton as extended by Cohen et al. is adopted. Interestingly enough, we also found that both theoretical and observed values show a change in the slope of the Delta V-HB(bump)-[M/H] relation toward higher metal contents.