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Omega Cen is composed of several stellar populations. Their history mightallow us to reconstruct the evolution of this complex object. We performed astatistical cluster analysis on the large data set provided by Johnson andPilachowski (2010). Stars in Omega Cen divide into three main groups. Themetal-poor group includes about a third of the total. It shows a moderate O-Naanticorrelation, and similarly to other clusters, the O-poor second generationstars are more centrally concentrated than the O-rich first generation ones.This whole population is La-poor, with a pattern of abundances for n-captureelements which is very close to a scaled r-process one. The metal-intermediategroup includes the majority of the cluster stars. This is a much more complexpopulation, with an internal spread in the abundances of most elements. Itshows an extreme O-Na anticorrelation, with a very numerous population ofextremely O-poor and He-rich second generation stars. This second generation isvery centrally concentrated. This whole population is La-rich, with a patternof the abundances of n-capture elements that shows a strong contribution by thes-process. The spread in metallicity within this metal-intermediate populationis not very large, and we might attribute it either to non uniformities of anoriginally very extended star forming region, or to some ability to retain afraction of the ejecta of the core collapse SNe that exploded first, or both.As previously noticed, the metal-rich group has an Na-O correlation, ratherthan anticorrelation. There is evidence for the contribution of both massivestars ending their life as core-collapse SNe, and intermediate/low mass stars,producing the s-capture elements. Kinematics of this population suggests thatit formed within the cluster rather than being accreted.

Multiple populations in Omega Centauri: a cluster analysis of spectroscopic data