Properties of stellar generations in globular clusters and relations with global parameters

摘要

We revise the scenario of the formation of Galactic globular clusters(GCs) byadding the observed detailed chemical composition of their differentstellargenerations to the set of their global parameters. We exploit theunprecedented set of homogeneous abundances of more than1200red giants in 19clusters, as well as additionaldata from literature, to give a new definition of bona fideGCs, as the stellar aggregates showing the Na-O anticorrelation. Wepropose a classification of GCs according to theirkinematics and location in the Galaxy in three populations: disk/bulge,innerhalo, and outer halo. We find that the luminosity function of GCsis fairly independent of their population, suggesting that it isimprinted bythe formation mechanism only marginally affected by the ensuingevolution.We show that a large fraction of the primordial population should havebeenlost by the proto-GCs. The extremely low Al abundances found for theprimordial population of massive GCs indicate a very fast enrichmentprocess before the formation of the primordial population. We suggest ascenario for the formation of GCs that includes at least three mainphases: i)the formation of a precursor population (likely dueto the interaction of cosmological structures similar to those that ledto the formation of dwarf spheroidals, but residing at smallerGalactocentric distances, with the early Galaxy or with otherstructures); ii)the triggering of a long episode of starformation (the primordial population) from the precursor population;and iii)the formation of the current GC, mainly within acooling flow formed by the slow winds of a fraction of the primordialpopulation. The precursor population is very effective in raising themetal content in massive and/or metal-poor (mainly halo) clusters,while its r?le is minor in small and/or metal-rich (mainly disk) ones.Finally, we use principal component analysis and multivariate relationsto study the phase of metal enrichment from first to second generation.We conclude that most of the chemical signatures of GCs may be ascribedto a few parameters, the most important being metallicity, mass, andcluster age. Location within the Galaxy (as described by thekinematics) also plays some r?le, while additional parameters arerequired to describe their dynamical status.Key words: stars: abundances - stars:atmospheres - stars: PopulationII - globular clusters:general