Stellar populations in $\omega$ Centauri: a multivariate analysis

TL;DR

This study uses multivariate statistical methods to analyze photometric and chemical data of stars in $$ Centauri, revealing complex population structures, chemical evolution, and star formation histories beyond simple metallicity distinctions.

Contribution

It introduces a multivariate analysis approach to classify and understand the multiple stellar populations in $$ Centauri, highlighting inhomogeneous chemical enrichment and evolutionary processes.

Findings

Seven distinct stellar groups identified with chemical, spatial, and kinematic differences.

Chemical evolution traced through group transitions, indicating inhomogeneous enrichment.

Metallicity alone does not distinguish different populations in $$ Centauri.

Abstract

We have performed multivariate statistical analyses of photometric and chemical abundance parameters of three large samples of stars in the globular cluster $\omega$ Centauri. The statistical analysis of a sample of 735 stars based on seven chemical abundances with the method of Maximum Parsimony (cladistics) yields the most promising results: seven groups are found, distributed along three branches with distinct chemical, spatial and kinematical properties. A progressive chemical evolution can be traced from one group to the next, but also within groups, suggestive of an inhomogeneous chemical enrichment of the initial interstellar matter. The adjustment of stellar evolution models shows that the groups with metallicities [Fe/H]\textgreater{}-1.5 are Helium-enriched, thus presumably of second generation. The spatial concentration of the groups increases with chemical evolution, except for two groups, which stand out in their other properties as well. The amplitude of rotation decreases with chemical evolution, except for two of the three metal-rich groups, which rotate fastest, as predicted by recent hydrodynamical simulations. The properties of the groups are interpreted in terms of star formation in gas clouds of different origins. In conclusion, our multivariate analysis has shown that metallicity alone cannot segregate the different populations of $\omega$ Centauri.