From the CMD of Omega Centauri and (super-)AGB stellar models to a Galactic plane passage gas purging chemical evolution scenario

Abstract

[Abbreviated] We have investigated the color-magnitude diagram of Omega Centauri and find that the blue main sequence (bMS) can be reproduced only by models that have a of helium abundance in the range Y=0.35-$\mathrm{0.40.}Toexplainthefaintsubgiantbranchofthereddeststars("MS-a/RG-a"sequence),isochronesfortheobservedmetallicity([Fe/H]\approx 0.7)appeartorequirebothahighage(13Gyr)andenhancedCNOabundances([CNO/Fe]\approx 0.9$). Y~0.35 must also be assumed in order to counteract the effects of high CNO on turnoff colors, and thereby to obtain a good fit to the relatively blue turnoff of this stellar population. This suggest a short chemical evolution period of time (<1Gyr) for Omega Cen. Our intermediate-mass (super-)AGB models are able to reproduce the high helium abundances, along with [N/Fe]~2 and substantial O depletions if uncertainties in the treatment of convection are fully taken into account. These abundance features distinguish the bMS stars from the dominant [Fe/H] $\approx 1.7$ population. The most massive super-AGB stellar models (M_zams>=6.8M_sun, M_He,core>=1.245M_sun) predict too large N-enhancements, which limits their role in contributing to the extreme populations. We show quantitatively that highly He- and N-enriched AGB ejecta have particularly efficient cooling properties. Based on these results and on the reconstruction of the orbit of Omega Cen with respect to the Milky Way we propose the galactic plane passage gas purging scenario for the chemical evolution of this cluster. Our model addresses the formation and properties of the bMS population (including their central location in the cluster). We follow our model descriptively through four passage events, which could explain not only some key properties of the bMS, but also of the MS-a/RGB-a and the s-enriched stars.

Accepted for publication in ApJ. 10 figures, 5 tables, 21 pages

References in corpus (22)

• Modules for Experiments in Stellar Astrophysics (MESA)
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The Tidal Evolution of Local Group Dwarf Spheroidals
• Effects of Supernova Feedback on the Formation of Galaxy Disks
• The double Subgiant Branch of NGC 1851: the role of the CNO abundance
• The fraction of second generation stars in Globular Clusters from the analysis of the Horizontal Branch
• Deep FORS1 observations of the double Main Sequence of omega Centauri
• First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars
• The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations
• Hubble Space Telescope Observations of an Outer Field in Omega Centauri: A Definitive Helium Abundance
• Fe and Al Abundances for 180 Red Giants in the Globular Cluster Omega Centauri (NGC 5139)
• Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning
• Are Globular Clusters the Remnant Nuclei of Progenitor Disk Galaxies?
• 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
• Modeling the chemical evolution of Omega Centauri using three-dimensional hydrodynamical simulations
• Medium resolution spectroscopy in Omega Centauri: abundances of 400 subgiant and turn-off region
• Abundances on the Main Sequence of Omega Centauri
• The Mass Function of omega Centauri down to 0.15 M_s
• About the Chemical Evolution of dSphs (and the peculiar Globular Cluster Omega Cen)

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• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• The Ages of 55 Globular Clusters as Determined Using an Improved delta V_TO^HB Method Along with Color-Magnitude Diagram Constraints, and Their Implications for Broader Issues
• Super-Massive Stars as a Source of Abundance Anomalies of Proton-Capture Elements in Globular Clusters
• Super and massive AGB stars - IV. Final fates - Initial to final mass relation
• Super and Massive AGB Stars: II - Nucleosynthesis and Yields - Z=0.02, 0.008 and 0.004
• Super-AGB Stars and their role as Electron Capture Supernova progenitors
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• Super and massive AGB stars - III. Nucleosynthesis in metal-poor and very metal-poor stars - Z=0.001 and 0.0001
• H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis
• Remnants and ejecta of thermonuclear electron-capture supernovae: Constraining oxygen-neon deflagrations in high-density white dwarfs
• Gas depletion in primordial globular clusters due to accretion onto stellar-mass black holes
• Convective H-He Interactions in Massive Population III Stellar Evolution Models
• Generation of massive stellar black holes by rapid gas accretion in primordial dense clusters
• Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in Omega Centauri
• Light and Heavy Element Abundance Variations in the Outer Halo Globular Cluster NGC 6229
• Spectral matching for abundances and clustering analysis of stars on the giant branches of ω Centauri
• Light Element Discontinuities Suggest an Early Termination of Star Formation in the Globular Cluster NGC 6402 (M14)
• Binary black hole growth by gas accretion in stellar clusters
• Spectral matching for abundances of 848 stars of the giant branches of the globular cluster ω Centauri
• Models of Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. I. Bolometric Corrections Derived from New MARCS Synthetic Spectra and Their Implications for Observed Colour-Magnitude Diagrams
• The Predicted Properties of Helium-Enriched Globular Cluster Progenitors at High Redshift