Testing the AGB Scenario as the Origin of the Extreme-Helium Population in omega Centauri
arXiv:0804.1598 · doi:10.1111/j.1365-2966.2008.13178.x
Abstract
The most massive Galactic globular cluster, Omega centauri, appears to have multiple populations. Its bluest main sequence and extended horizontal branch stars are suggested to have the common origin, that is, an extremely high helium abundance of Y ~ 0.4. The high helium abundance is most often attributed to asymptotic giant branch (AGB) stars. In this study we test the AGB hypothesis. We simulate the maximum-AGB models where the impact of AGB stars is maximised by assuming that supernova explosions do not affect the chemical evolution of the proto cloud. We compare the enrichment history of helium, metals, carbon and nitrogen to the observed values. Even under the most generous condition, the maximum-AGB models fail to reproduce the large values of helium Y ~ 0.4 and helium enrichment parameter Delta Y / Delta Z ~ 70 which were deduced from the colour-magnitude diagram fits. They also fail to reproduce the C and N contents of the blue population spectroscopically determined. We conclude that the AGB scenario with the canonical stellar evolution theory cannot explain the observational constraints and that the self chemical enrichment does not provide a viable solution. Alternative processes are desperately called for.
6 pages, 5 figures, Accepted by MNRAS
References in corpus (13)
- Deep FORS1 observations of the double Main Sequence of omega Centauri
- Kinematic Decoupling of Globular Clusters with Extended Horizontal-Branch
- Origin of Abundance Inhomogeneity in Globular Clusters
- The Chemical Evolution of Helium in Globular Clusters: Implications for the Self-Pollution Scenario
- Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning
- UV Bright Globular Clusters in M87: More Evidence for Super-helium-rich Stellar Populations?
- A spectral atlas of post-main-sequence stars in omega Centauri: kinematics, evolution, enrichment and interstellar medium
- The chemical evolution of Omega Centauri's progenitor system
- Medium resolution spectroscopy in Omega Centauri: abundances of 400 subgiant and turn-off region
- Abundances on the Main Sequence of Omega Centauri
- Observational consequences of the hypothesized helium rich stellar population in Omega Centauri
- First stars as a possible origin for the helium-rich population in omega Centauri
- Surface pollution of main-sequence stars through encounters with AGB ejecta in omega Centauri