CNO enrichment by rotating AGB stars in globular clusters
  AGB stars have long been held responsible for the important star-to-star
variations in light elements observed in Galactic globular clusters. We analyse
the main impacts of a first generation of rotating intermediate-mass stars on
the chemical properties of second-generation globular cluster stars. The
rotating models were computed without magnetic fields and without the effects
of internal gravity waves. They account for the transports by meridional
currents and turbulence. We computed the evolution of both standard and
rotating stellar models with initial masses between 2.5 and 8 Msun within the
metallicity range covered by Galactic globular clusters. During central
He-burning, rotational mixing transports fresh CO-rich material from the core
towards the hydrogen-burning shell, leading to the production of primary 14N.
In stars more massive than M > 4 Msun, the convective envelope reaches this
reservoir during the second dredge-up episode, resulting in a large increase in
the total C+N+O content at the stellar surface and in the stellar wind. The
corresponding pollution depends on the initial metallicity. At low- and
intermediate-metallicity, it is at odds with the constancy of C+N+O observed
among globular cluster low-mass stars. With the given input physics, our models
suggest that massive rotating AGB stars have not shaped the abundance patterns
observed in low- and intermediate-metallicity globular clusters. Our
non-rotating models, on the other hands, do not predict surface C+N+O
enhancements, hence are in a better position as sources of the chemical
anomalies in globular clusters showing the constancy of the C+N+O. However at
the moment, there is no reason to think that intermediate mass stars were not
rotating.
