Sodium-oxygen anticorrelation and neutron capture elements in Omega Centauri stellar populations

TL;DR

This study investigates the complex chemical enrichment history of Omega Centauri by analyzing stellar populations and their elemental abundances, revealing significant iron variation and distinct Na-O anticorrelation patterns across different metallicities.

Contribution

It provides detailed spectroscopic analysis of multiple stellar populations in Omega Centauri, highlighting the correlation and anticorrelation of key elements across metallicity ranges, which was not previously well characterized.

Findings

Omega Centauri shows large star-to-star iron variations from -2.0 to -0.7 dex.

Barium and lanthanum correlate with iron in metal-poor stars but plateau in metal-rich stars.

An extended Na-O anticorrelation exists for stars with [Fe/H] < -1.3, while more metal-rich stars are mostly Na-rich.

Abstract

Omega Centauri is no longer the only globular cluster known to contain multiple stellar populations, yet it remains the most puzzling. Due to the extreme way in which the multiple stellar population phenomenon manifests in this cluster, it has been suggested that it may be the remnant of a larger stellar system. In this work, we present a spectroscopic investigation of the stellar populations hosted in the globular cluster Omega Centauri to shed light on its, still puzzling, chemical enrichment history. With this aim we used FLAMES+GIRAFFE@VLT to observe 300 stars distributed along the multimodal red giant branch of this cluster, sampling with good statistics the stellar populations of different metallicities. We determined chemical abundances for Fe, Na, O, and n-capture elements Ba and La. We confirm that Omega Centauri exhibits large star-to-star variations in iron with [Fe/H] ranging from ~ -2.0 to ~ -0.7 dex. Barium and lanthanum abundances of metal poor stars are correlated with iron, up to [Fe/H] -1.5, while they are almost constant (or at least have only a moderate increase) in the more metal rich populations. There is an extended Na-O anticorrelation for stars with [Fe/H]<~ -1.3 while more metal rich stars are almost all Na-rich. Sodium was found to midly increase with iron over all the metallicity range.