Manganese evolution in Omega Centauri: a clue to the cluster formation mechanisms?

TL;DR

This study models manganese evolution in Omega Centauri, comparing predictions with observations, and suggests inhomogeneous chemical evolution might explain the observed abundance spread, highlighting the need for more data.

Contribution

It introduces a chemical evolution model tailored to Omega Centauri and discusses the potential role of inhomogeneous evolution in explaining manganese abundance variations.

Findings

Standard models cannot explain high [Mn/Fe] in some stars.

Inhomogeneous chemical evolution may account for observed abundance spread.

More Mn measurements are needed for conclusive insights.

Abstract

We model the evolution of manganese relative to iron in the progenitor system of the globular cluster Omega Centauri by means of a self-consistent chemical evolution model. We use stellar yields that already reproduce the measurements of [Mn/Fe] versus [Fe/H] in Galactic field disc and halo stars, in Galactic bulge stars and in the Sagittarius dwarf spheroidal galaxy. We compare our model predictions to the Mn abundances measured in a sample of 10 red giant members and 6 subgiant members of Omega Cen. The low values of [Mn/Fe] observed in a few, metal-rich stars of the sample cannot be explained in the framework of our standard, homogeneous chemical evolution model. Introducing cooling flows that selectively bring to the cluster core only the ejecta from specific categories of stars does not help to heal the disagreement with the observations. The capture of field stars does not offer a viable explanation either. The observed spread in the data and the lowest [Mn/Fe] values could, in principle, be understood if the system experienced inhomogeneous chemical evolution. Such an eventuality is qualitatively discussed in the present paper. However, more measurements of Mn in Omega Cen stars are needed to settle the issue of Mn evolution in this cluster.