NGC 6441: another indication for a very high helium content in Globular Cluster stars

Abstract

The metal-rich bulge globular cluster NGC 6441 shows a well developed blue horizontal branch (Rich et al.), together with a strong slope upward from the red clump to the blue of the RR Lyrae region. Both features, the former corresponding to the well-known second parameter problem, are not explained by conventional evolutionary models. Helium self-enrichment is proposed as a possible solution to both questions, a mechanism already invoked for the interpretation of the peculiarities in NGC 2808 and M13. We make use of horizontal branch simulations, covering a wide range in main sequence helium abundance, to investigate whether the main features of NGC 6441 horizontal branch population, including the RR Lyrae variables period, can be reproduced. To describe the horizontal branch of NGC 6441, the helium content Y in the red clump must reach at least 0.35; values up to Y~0.37 are necessary to populate the RR Lyr region, reproducing also the observed mean long periods; depending on the dispersion in mass loss assumed in the simulations, values up to Y~0.38--0.40 are necessary to populate the blue HB. The total self--enriched population amounts to ~60% of the whole stellar content. Self-enrichment and multiple star formation episodes in the early evolution of globular clusters appear more and more able to account for many of the chemical and population peculiarities observed in these systems. The very large helium abundances (Y>0.35) required for ~14% of the horizontal branch population pose some problem on the enrichment mechanisms.

arXiv comment9 pages, 10 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (23)

• Abundances for Globular Cluster Giants: I. Homogeneous Metallicities for 24 Clusters
• The O-Na and Mg-Al Anticorrelations in Turn-Off and early Subgiants in Globular Clusters
• Metallicities on the Double Main Sequence of omega Centauri Imply Large Helium Enhancement
• Predictions for self-pollution in globular cluster stars
• A helium spread among the main sequence stars in NGC 2808
• Helium variation due to self-pollution among Globular Cluster stars: consequences on the horizontal branch morphology
• HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands
• The early evolution of Globular Clusters: the case of NGC 2808
• Discovery of Extended Blue Horizontal Branches in Two Metal-Rich Globular Clusters
• 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 Second-Parameter Effect in Metal-Rich Globular Clusters
• Abundances in Stars from the Red Giant Branch Tip to Near the Main Sequence Turn Off in M5
• The Initial Helium Abundance of the Galactic Globular Cluster System
• The Variable Stars and Blue Horizontal Branch of the Metal-Rich Globular Cluster NGC 6441
• HST Snaphot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441
• RR Lyrae Stars in NGC 6388 and NGC 6441: A New Oosterhoff Group?
• Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6441
• Towards a working model for the abundance variations within Globular Clusters stars
• Horizontal-Branch Models and the Second-Parameter Effect. IV. The Case of M3 and Palomar 3
• On the observational properties of He-burning stars: some clues on the tilt of the HB in metal rich clusters
• Metal abundances of RR Lyrae stars in the metal rich globular cluster NGC 6441

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• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• A Triple Main Sequence in the Globular Cluster NGC 2808
• Multiple Stellar Populations in Globular Clusters
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• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• The ACS Survey of Galactic Globular Clusters. VII. Relative Ages
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• The second and third parameters of the Horizontal Branch in Globular Clusters
• Abundance patterns of multiple populations in Globular Clusters: a chemical evolution model based on yields from AGB ejecta
• Origin of the abundance patterns in Galactic globular clusters: constraints on dynamical and chemical properties of globular clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XVI. The helium abundance of multiple populations
• Massive AGB models of low metallicity: the implications for the self-enrichment scenario in metal poor Globular Clusters
• The fraction of second generation stars in Globular Clusters from the analysis of the Horizontal Branch
• The Luminosities and Distance Scales of Type II Cepheid and RR Lyrae variables
• Mass loss on the red giant branch: the value and metallicity dependence of Reimers' η in globular clusters
• The Helium abundance and Delta Y / Delta Z in Lower Main Sequence stars
• The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations
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• Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?
• The Presence of Two Distinct Red Giant Branches in the Globular Cluster NGC 1851
• Another Non-segregated Blue Straggler Population in a Globular Cluster: the Case of NGC 2419
• Red Giant Branch Bump Brightness and Number Counts in 72 Galactic Globular Clusters Observed with the Hubble Space Telescope
• Space Velocities of Southern Globular Clusters. V. A Low Galactic Latitude Sample
• Constraining stellar population models - I. Age, metallicity, and abundance pattern compilation for Galactic globular clusters
• Evolution of two stellar populations in globular clusters II. Effects of primordial gas expulsion
• The evolution of two stellar populations in globular clusters I. The dynamical mixing timescale
• The intriguing stellar populations in the globular clusters NGC 6388 and NGC 6441
• The formation of multiple populations in the globular cluster 47 Tuc
• The ACS Fornax Cluster Survey. IX. The Color-Magnitude Relation of Globular Cluster Systems
• MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields
• NGC 2419: a large and extreme second generation in a currently undisturbed cluster
• The treatment of mixing in core helium burning models -- II. Constraints from cluster star counts
• Revisiting nucleosynthesis in globular clusters: the case of NGC 2808 and the role of He and K
• Variable stars in the VVV globular clusters. I. 2MASS-GC02 and Terzan10
• Are Globular Clusters the Remnant Nuclei of Progenitor Disk Galaxies?
• Constraints on Helium Enhancement in the Globular Cluster M3 (NGC 5272): The Horizontal Branch Test
• RR Lyrae stars in Galactic globular clusters. VI. The Period-Amplitude relation
• UV Bright Globular Clusters in M87: More Evidence for Super-helium-rich Stellar Populations?
• Prospects for asteroseismic inference on the envelope helium abundance in red giant stars
• On the Origin of Bimodal Horizontal-Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441
• Is mass loss along the red giant branch of globular clusters sharply peaked? The case of M3
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. VII. Implications from the Nearly Universal Nature of Horizontal Branch Discontinuities
• Rapidly rotating second-generation progenitors for the blue hook stars of ω Cen
• Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in Omega Centauri
• RR Lyrae From Binary Evolution: Abundant, Young and Metal-Rich
• Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441
• A view of the H-band light-element chemical patterns in Globular Clusters under the AGB self-enrichment scenario
• Self-Enrichment in Globular Clusters: Is There a Role for the Super-Asymptotic Giant Branch Stars?
• New insight on the origin of the double red clump in the Milky Way bulge
• Evolution of long-lived globular cluster stars I. Grid of stellar models with helium enhancement at [Fe/H] = -1.75
• Multiple populations in massive star clusters under the magnifying glass of photometry: Theory and tools
• Terzan 5: an alternative interpretation for the split horizontal branch
• The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars
• The Optical Colors of Giant Elliptical Galaxies and their Metal-Rich Globular Clusters Indicate a Bottom-Heavy Initial Mass Function
• Explaining the multiple populations in globular clusters by multiple episodes of star formation and enrichment without gas expulsion from massive star feedback
• Helium enrichment in intermediate-age Magellanic Clouds clusters: towards an ubiquity of multiple stellar populations?
• Double Horizontal Branches in NGC 6440 and NGC 6569 unveiled by the VVV Survey
• Hubble Space Telescope analysis of stellar populations within the globular cluster G1 (Mayall II) in M31
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters -- XI. The horizontal branch in NGC\,6388 and NGC\,6441
• Period Change Similarities among the RR Lyrae Variables in Oosterhoff I and Oosterhoff II Globular Systems
• A Semi-Empirical Study of the Mass Distribution of Horizontal Branch Stars in M3 (NGC 5272)
• Massive stars and globular cluster formation
• On the origin of the helium-rich population in Omega Centauri
• Common Origin of Two RR Lyrae Populations and the Double Red Clump in the Milky Way Bulge
• Evolved Stars in the Core of the Massive Globular Cluster NGC 2419
• Dissolved Massive Metal-Rich Globular Clusters Can Cause the Range of UV Upturn Strengths Found among Early-type Galaxies
• Globular clusters in the far-ultraviolet: evidence for He-enriched second populations in extra-galactic globular clusters?
• The peculiar properties of horizontal branch stars in omega Centauri
• On the nature of the brightest globular cluster in M81
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• The horizontal branch morphology of M31 globular clusters. Extreme second parameter effect in outer halo clusters
• Overluminous Blue Horizontal Branch Stars Formed by Low Mass Companions
• Physics of rotation in stellar models
• Nonlinear Color-Metallicity Relations of Globular Clusters. IV. Testing the Nonlinearity Scenario for Color Bimodality via HST/WFC3 u-band Photometry of M84 (NGC 4374)
• A stellar population synthesis approach to the Oosterhoff dichotomy
• Stellar populations in $\omega$ Centauri: a multivariate analysis
• Revisiting Delta Y/Delta Z from multiple main sequences in Globular Clusters: insight from nearby stars
• Near-infrared observations of RR Lyrae and Type II Cepheid variables in the metal-rich bulge globular cluster NGC 6441
• Radial velocities of RR Lyrae stars in and around NGC 6441
• Stellar Populations in Globular Cluster Cores: Evidence for a Peculiar Trend Among Red Giant Branch Stars
• Chemical evolution of star clusters
• The ages of Galactic globular clusters in the context of self-enrichment
• A Universal Transition in Atmospheric Diffusion for Hot Subdwarfs Near 18,000 K
• Evolution of Massive Stars along the Cosmic History
• The Ages of Stars: The Horizontal Branch
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