Abundance analysis of a sample of evolved stars in the outskirts of Omega Centauri

TL;DR

This study investigates the chemical abundance patterns of evolved stars in the outskirts of Omega Centauri to determine if the cluster's population and chemical trends are consistent throughout, revealing no clear radial gradients.

Contribution

It provides the first detailed chemical abundance analysis of stars in the outer regions of Omega Centauri, comparing them with inner regions to assess population homogeneity.

Findings

Outer regions have similar population mix to inner regions.

No significant radial abundance gradients detected.

Data suggests the need for larger samples for definitive conclusions.

Abstract

The globular cluster $\omega$ Centauri (NGC 5139) is a puzzling stellar system harboring several distinct stellar populations whose origin still represents a unique astrophysical challenge. Current scenarios range from primordial chemical inhomogeneities in the mother cloud to merging of different sub-units and/or subsequent generations of enriched stars - with a variety of different pollution sources- within the same potential well. In this paper we study the chemical abundance pattern in the outskirts of Omega Centauri, half-way to the tidal radius (covering the range of 20-30 arcmin from the cluster center), and compare it with chemical trends in the inner cluster regions, in an attempt to explore whether the same population mix and chemical compositions trends routinely found in the more central regions is also present in the cluster periphery.We extract abundances of many elements from FLAMES/UVES spectra of 48 RGB stars using the equivalent width method and then analyze the metallicity distribution function and abundance ratios of the observed stars. We find, within the uncertainties of small number statistics and slightly different evolutionary phases, that the population mix in the outer regions cannot be distinguished from the more central regions, although it is clear that more data are necessary to obtain a firmer description of the situation. From the abundance analysis, we did not find obvious radial gradients in any of the measured elements.