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We present abundances of Fe, Na, and O for 1409 red giant stars in 15galactic globular clusters, derived from the homogeneous analysis of highresolution FLAMES/GIRAFFE spectra. Combining the present data with previousresults, we obtained a total sample of 1958 stars in 19 clusters, the largestand most homogeneous database of this kind to date. Our GCs have [Fe/H] from-2.4 to -0.4, with a wide variety of global parameters (morphology of thehorizontal branch, mass, concentration, etc). For all clusters we find the Na-Oanticorrelation, the classical signature of proton-capture reactions inH-burning at high temperature in a previous generation of more massive stars,now extinct. Using quantitative criteria (from the morphology and extension ofthe Na-O anticorrelation), we can define 3 components of the stellar populationin GCs: a primordial component (P) of first-generation stars, and 2 componentsof second-generation stars (intermediate I and extreme E populations from theirdifferent chemical composition). The P component is present in all GCs, and itsfraction is almost constant at about one third. The I component represents thebulk of the cluster population. The E component is not present in all GCs, andit is more conspicuous in some (but not in all) of the most massive ones. Wediscuss the fractions and spatial distributions of these components in oursample and in two additional clusters (M3 and M13) from the literature. We alsofind that the slope of the anti-correlation (defined by the minimum O andmaximum Na abundances) changes from cluster-to-cluster, a change that isrepresented well by a bilinear relation on cluster metallicity and luminosity.This second dependence suggests a correlation between average mass of pollutersand cluster mass.

Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra