On the internal pollution mechanisms in the globular cluster NGC 6121 (M4): heavy-element abundances and AGB models

Abstract

Globular clusters display significant variations in their light-element content, pointing to the existence of a second stellar generation formed from the ejecta of an earlier generation. The nature of these internal polluters is still a matter of debate: the two most popular scenarios indicate intermediate-mass AGB stars and fast rotating massive stars. Abundances determination for some key elements can help distinguish between these competitor candidates. We present in this paper Y abundances for a sample of 103 red giant branch stars in NGC 6121. Within measurement errors, we find that the [Y/Fe] is constant in this cluster contrary to a recent suggestion. For a subsample of six stars we also find [Rb/Fe] to be constant, consistent with previous studies showing no variation in other s-process elements. We also present a new set of stellar yields for intermediate-mass AGB stellar models of 5 and 6 solar masses, including heavy element s-process abundances. The uncertainties on the mass-loss rate, the mixing-length parameter, and the nuclear reaction rates have a major impact on the stellar abundances. Within the IM-AGB pollution scenario, the constant abundance of heavy elements inside the cluster requires a marginal s-process efficiency in IM-AGB stars. Such a constrain could still be satisfied by the present models assuming a stronger mass-loss rate. The uncertainties mentioned above are limiting the predictive power of intermediate-mass AGB models. For these reasons, at the moment we are not able to clearly rule out their role as main polluters of the second population stars in globular clusters.

Accepted for publication in MNRAS, 18 pages, 21 figures

References in corpus (20)

• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• Origin of the abundance patterns in Galactic globular clusters: constraints on dynamical and chemical properties of globular clusters
• Origin of multiple stellar populations in globular clusters and their helium enrichment
• An abundance analysis of bright giants in the globular cluster NGC 1851
• Rubidium-Rich Asymptotic Giant Branch Stars
• s-Process Nucleosynthesis in Advanced Burning Phases of Massive Stars
• Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae
• Lithium and zirconium abundances in massive Galactic O-rich AGB stars
• Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way
• Heavy element abundances in giant stars of the globular clusters M4 and M5
• Comparing CN and CH Line Strengths in a Homogeneous Spectroscopic Sample of 8 Galactic Globular Clusters
• Low temperature Rosseland opacities with varied abundances of carbon and nitrogen
• Primordial r-process Dispersion in Metal-Poor Globular Clusters
• The evolution of two stellar populations in globular clusters I. The dynamical mixing timescale
• The Chemical Evolution of Helium in Globular Clusters: Implications for the Self-Pollution Scenario
• Rubidium and lead abundances in giant stars of the globular clusters M4 and M5
• Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning
• Heavy elements and chemical enrichment in globular clusters
• The AGB stars of the intermediate-age LMC cluster NGC 1846 Variability and age determination

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