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