Abundances of red giants in 15 globular clusters

The program clusters cover a range in metallicity from [Fe/H]=-2.4dex to [Fe/H]=-0.4dex, with a wide variety of global parameters (morphology of the horizontal branch, mass, concentration, etc.). For all clusters we find the Na-O anticorrelation, classical signature of the operation of proton-capture reactions in H burning at high temperature in a previous generation of more massive stars now extinct.

Using quantitative criteria (from the morphology and extension of the Na-O anticorrelation), we can define three different components of the stellar population in GCs.