The Giant, Horizontal, and Asymptotic Branches of Galactic Globular Clusters. I. The Catalog, Photometric Observables, and Features

Abstract

A catalog including a set of the most recent color-magnitude diagrams (CMDs) is presented for a sample of 61 Galactic globular clusters (GGCs). We used this database to perform a homogeneous systematic analysis of the evolved sequences (namely, the red giant branch [RGB], horizontal branch [HB], and asymptotic giant branch [AGB]). Based on this analysis, we present (1) a new procedure to measure the level of the zero-age horizontal branch (VZAHB) and a homogeneous set of distance moduli obtained by adopting the HB as standard candle; (2) an independent estimate for RGB metallicity indicators and new calibrations of these parameters in terms of both spectroscopic ([Fe/H]CG97) and global metallicity ([M/H], including also the α-element enhancement), such that the set of equations presented can be used to simultaneously derive a photometric estimate of the metal abundance and the reddening from the morphology and the location of the RGB in the (V, B - V) CMD; and (3) the location of the RGB bump (in 47 GGCs) and the AGB bump (in nine GGCs). The dependence of these features on metallicity is discussed. We find that by using the latest theoretical models and the new metallicity scales, the earlier discrepancy between theory and observations ( ∼ 0.4 mag) completely disappears.