The Na-O anticorrelation in horizontal branch stars. V. NGC 6723

Abstract

We used FLAMES+GIRAFFE (Medusa mode) at the VLT to obtain moderately high resolution spectra for 30 red horizontal branch (RHB) stars, 4 RR Lyrae variables, and 17 blue horizontal branch (BHB) stars in the low-concentration, moderately metal-rich globular cluster NGC6723 ([Fe/H]=-1.22+/-0.08 from our present sample). The spectra were optimized to derive O and Na abundances. In addition, we obtained abundances for other elements, including N, Fe, Mg, Ca, Ni, and Ba. We used these data to discuss the evidence of a connection between the distribution of stars along the horizontal branch (HB) and the multiple populations that are typically present in globular clusters. We found that all RHB and most (13 out of 17) BHB stars are O-rich, Na-poor, and N-poor; these stars probably belong to the first stellar generation in this cluster. Only the four warmest observed stars are (moderately) O-poor, Na-rich, and N-rich, and they probably belong to the second generation. While our sample is not fully representative of the whole HB population in NGC6723, our data suggest that in this cluster only HB stars warmer than ~9000 K, that is one fourth of the total, belong to the second generation, if at all. Since in many other clusters this fraction is about two thirds, we conclude that the fraction of first/second generation in globular clusters may be strongly variable. In addition, the wide range in colour of chemically homogeneous first-generation HB stars requires a considerable spread in mass loss (>0.10 Mo). The reason for this spread is yet to be understood. Finally, we found a high Ba abundance, with a statistically significant radial abundance gradient.

arXiv commentAstronomy and Astrophysics, in press; 15 pages; 11 figures

References in corpus (66)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries
• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Abundances for Globular Cluster Giants: I. Homogeneous Metallicities for 24 Clusters
• Na-O Anticorrelation and HB. VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra
• Neutron-Capture Elements in the Early Galaxy: Insights from a Large Sample of Metal-Poor Giants
• Omega Centauri: The Population Puzzle Goes Deeper
• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• The ACS Survey of Galactic Globular Clusters. VII. Relative Ages
• 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
• The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon
• Metallicities on the Double Main Sequence of omega Centauri Imply Large Helium Enhancement
• Predictions for self-pollution in globular cluster stars
• Neutron star mergers versus core-collapse supernovae as dominant r-process sites in the early Galaxy
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• A helium spread among the main sequence stars in NGC 2808
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• Primordial Nucleosynthesis for the New Cosmology: Determining Uncertainties and Examining Concordance
• Early Disc Accretion as the Origin of Abundance Anomalies in Globular Clusters
• 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
• Multiple stellar populations in 47 Tucanae
• The second and third parameters of the Horizontal Branch in Globular Clusters
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• A non-LTE study of neutral and singly-ionized calcium in late-type stars
• The Ubiquity of the Rapid Neutron-Capture Process
• The double Subgiant Branch of NGC 1851: the role of the CNO abundance
• The fraction of binary systems in the core of thirteen low-density Galactic globular clusters
• Galactic Globular Cluster Metallicity Scale from the Ca II Triplet. I. Catalog
• Chemical Abundances and Rotation Velocities of Blue Horizontal-Branch Stars in Six Globular Clusters
• A large stellar evolution database for population synthesis studies. V. Stellar models and isochrones with CNONa abundance anticorrelations
• Sodium-Oxygen anticorrelation among Horizontal Branch Stars in the Globular Cluster M4
• Constraints on mass loss and self-enrichment scenarios for the globular clusters of the Fornax dSph
• Mass loss rates and the mass evolution of star clusters
• Rotations and Abundances of Blue Horizontal-Branch Stars in Globular Cluster M15
• Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13
• Global and non-global parameters of horizontal branch morphology of globular clusters
• Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
• The Helium content of Globular Clusters: light element abundance correlations and HB morphology. I. NGC6752
• A New Spin on the Problem of HB Gaps: Stellar Rotation along the Blue Horizontal Branch of Globular Cluster M13
• Bimodality and Gaps on Globular Cluster Horizontal Branches. II. The Cases of NGC 6229, NGC 1851 and NGC 2808
• The peculiar Horizontal Branch of NGC 2808
• The Na-O anticorrelation in horizontal branch stars. III. 47 Tuc and M 5
• Nucleosynthesis in Magnetically Driven Jets from Collapsars
• Ba stars and other binaries in first and second generation stars in globular clusters
• Hot Horizontal Branch Stars: Predictions for Mass Loss
• The helium content of globular clusters: NGC6121 (M4)
• Calcium and light-elements abundance variations from high resolution spectroscopy in globular clusters
• Space Velocities of Southern Globular Clusters. IV. First Results for Inner-Galaxy Clusters
• The Na-O anticorrelation in horizontal branch stars. I. NGC 2808
• The self-enrichment scenario in intermediate metallicity globular clusters
• The Na-O anticorrelation in horizontal branch stars. II. NGC1851
• The Chemical Compositions of Non-Variable Red and Blue Field Horizontal Branch Stars
• Chemical and kinematical properties of BSSs and HB stars in NGC 6397
• Constraints on Helium Enhancement in the Globular Cluster M3 (NGC 5272): The Horizontal Branch Test
• The Horizontal Branch of NGC 1851: Constraints on the Cluster Subpopulations
• In search of massive single-population Globular Clusters
• Rotation velocities of hot horizontal branch stars in the globular clusters NGC 1904, NGC 2808, NGC 6093, and NGC 7078: the database
• Horizontal-branch morphology and multiple stellar populations in the anomalous globular cluster M22
• The Na-O anticorrelation in horizontal branch stars. IV. M22
• Towards a better understanding of the distance scale from RR Lyrae variable stars: A case study for the inner halo globular cluster NGC 6723

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