Self-Enrichment in Globular Clusters: Is There a Role for the Super-Asymptotic Giant Branch Stars?

Abstract

In four globular clusters (GCs) a non negligible fraction of stars can be interpreted only as a very helium rich population. The evidence comes from the presence of a "blue" main sequence in $\omega$ Cen and NGC 2808, and from the the very peculiar horizontal branch morphology in NGC 6441 and NGC 6388. Although a general consensus is emerging on the fact that self--enrichment is a common feature among GCs, the helium content required for these stars is Y$\simgt$0.35, and it is difficult to understand how it can be produced without any --or, for $\omega$ Cen, without a considerable--associated metal enhancement. We examine the possible role of super--AGB stars, and show that they may provide the required high helium. However, the ejecta of the most massive super--AGBs show a global CNO enrichment by a factor of $\simeq$4, due to the dredge--out process occurring at the second dredge up stage. If these clusters show no evidence for this CNO enrichment, we can rule out that at least the most massive super--AGBs evolve into O--Ne white dwarfs and take part in the formation of the second generation stars. This latter hypothesis may help to explain the high number of neutron stars present in GCs. The most massive super--AGBs would in fact evolve into electron--capture supernovae. Their envelopes would be easily ejected out of the cluster, but the remnant neutron stars remain into the clusters, thanks to their small supernova natal kicks.

version accepted for publication in The Astrophysical Journal Letters

References in corpus (17)

• A statistical study of 233 pulsar proper motions
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• A Triple Main Sequence in the Globular Cluster NGC 2808
• Metallicities on the Double Main Sequence of omega Centauri Imply Large Helium Enhancement
• A helium spread among the main sequence stars in NGC 2808
• Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
• Multi-Dimensional Simulations of the Accretion-Induced Collapse of White Dwarfs to Neutron Stars
• On the self-enrichment scenario of galactic globular clusters: Constraints on the IMF
• Abundances in a Large Sample of Stars in M3 and M13
• Full computation of massive AGB evolution. I. The large impact of convection on nucleosynthesis
• Na-O Anticorrelation And HB I. The Na-O anticorrelation in NGC 2808
• The origin of the double main sequence in Omega Centauri: Helium enrichment due to gas fueling from its ancient host galaxy ?
• NGC 6441: another indication for a very high helium content in Globular Cluster stars
• Modelling self-pollution of globular clusters from AGB stars
• The Chemical Evolution of Helium in Globular Clusters: Implications for the Self-Pollution Scenario
• The chemical evolution of Omega Centauri's progenitor system
• Double Neutron Stars: Evidence For Two Different Neutron-Star Formation Mechanisms

Cited by in corpus (26)

• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Quantifying the uncertainties of chemical evolution studies. II. Stellar yields
• Evolution of Thermally Pulsing Asymptotic Giant Branch Stars I. The COLIBRI Code
• The evolution of runaway stellar collision products
• Abundance patterns of multiple populations in Globular Clusters: a chemical evolution model based on yields from AGB ejecta
• Origin of multiple stellar populations in globular clusters and their helium enrichment
• A unique model for the variety of multiple populations formation(s) in globular clusters: a temporal sequence
• Super-AGB Stars and their role as Electron Capture Supernova progenitors
• A large C+N+O abundance spread in giant stars of the globular cluster NGC 1851
• Super and massive AGB stars - III. Nucleosynthesis in metal-poor and very metal-poor stars - Z=0.001 and 0.0001
• EC-SNe from super-AGB progenitors: theoretical models vs. observations
• The C+N+O abundances and the splitting of the subgiant branch in the Globular Cluster NGC 1851
• High Precision Differential Abundance Measurements in Globular Clusters: Chemical Inhomogeneities in NGC 6752
• Tracing the evolution of NGC6397 through the chemical composition of its stellar populations
• Super AGB and AGB evolution and the chemical inventory in NGC 2419
• The role of lithium production in massive AGB and super--AGB stars for the understanding of multiple populations in Globular Clusters
• The intermediate neutron capture process. III. The i-process in AGB stars of different masses and metallicities without overshoot
• A detailed study of the main sequence of the Globular Cluster NGC 6397: can we derive constraints on the existence of multiple population?
• The environment of formation as a second parameter for globular cluster classification
• Terzan 5: an alternative interpretation for the split horizontal branch
• On the internal pollution mechanisms in the globular cluster NGC 6121 (M4): heavy-element abundances and AGB models
• The evolutionary status of the blue hook stars in Omega Centauri
• On the origin of the helium-rich population in Omega Centauri
• Chemical evolution of star clusters
• Lithium factories in the Galaxy: novae and AGB stars