In search of massive single{population Globular Clusters

ABSTRACT The vast majority of globular clusters so far examined shows the chemical signaturesof hosting (at least) two stellar populations. According to recent ideas, this featurerequires a two{step process, in which the nuclearly processed matter from a \ rstgeneration" (FG) of stars gives birth to a \second generation" (SG) bearing the n-gerprint of a fully CNO{cycled matter. Since, as observed, the present population ofmost globular clusters is made up largely of SG stars, a substantial fraction of theFG ( ˘ > 90%) must be lost. Nevertheless, two types of clusters dominated by a sim-ple stellar population (FG clusters) should exist: either clusters initally too small tobe able to retain a cooling ow and form a second generation (FG{only clusters), ormassive clusters that could retain the CNO processed ejecta and form a SG, but wereunable to lose a signi cant fraction of their FG (mainly{FG clusters). Identi cationof mainly{FG clusters may provide an estimate of the fraction of the initial massinvolved in the formation of the SG.We attempt a rst classi cation of FG clusters, based on the morphology of theirhorizontal branches (HBs), as displayed in the published catalogues of photometricdata for 106 clusters. We select, as FG candidates, the clusters in which the HB canbe reproduced by the evolution of an almost unique mass. We nd that less than 20%of clusters with [Fe/H] 30% of SGstars, and its present dynamical status bears less information on its formation processthan the analysis of the chemical abundances of its stars and of its HB morphology.Key words: globular clusters:general; globular clusters:individual: NGC 2419; M 53;Pal 3; stars:abundances