Exploring the Chemical Composition and Double Horizontal Branch of the Bulge Globular Cluster NGC 6569

Abstract

Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of -48.8 km/s (sigma = 5.3 km/s; 148 stars) and a mean [Fe/H] =-0.87 dex (19 stars), but the cluster's 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti)correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster's low mean [La/Eu] = -0.11 dex indicates significant pollution with r-process material. We confirm that both HBs contain cluster members, but metallicity and light-element variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as delta Y ~ 0.02 cannot be ruled out and may be sufficient to reproduce the double HB.

72 pages, 14 figures, 8 tables; published in The Astronomical Journal; electronic versions of all tables are available in the published version

References in corpus (43)

• The Dartmouth Stellar Evolution Database
• A new implementation of the infrared flux method using the 2MASS catalogue
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• The nucleus of the Sagittarius dSph galaxy and M54: a window on the process of galaxy nucleation
• Origin of the abundance patterns in Galactic globular clusters: constraints on dynamical and chemical properties of globular clusters
• Analysis and calibration of CaII triplet spectroscopy of Red Giant Branch stars from VLT/FLAMES observations
• Chemical similarities between Galactic bulge and local thick disk red giant stars
• Line lists for the A2PI-X2Sigma+ (red) and {B2Sigma+-X2Sigma} (violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra
• Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
• Light nuclei in galactic globular clusters : constraints on the self-enrichment scenario from nucleosynthesis
• Light, Alpha, and Fe-Peak Element Abundances in the Galactic Bulge
• A model for the Globular Cluster extreme anomalies
• Ceci n'est pas a globular cluster: the metallicity distribution of the stellar system Terzan 5
• APOGEE Chemical Abundances of Globular Cluster Giants in the Inner Galaxy
• The Infrared Ca II triplet as metallicity indicator
• The age of the young bulge-like population in the stellar system Terzan5: linking the Galactic bulge to the high-z Universe
• Na-O Anticorrelation and HB. VI. The chemical composition of the peculiar bulge globular cluster NGC 6388
• The Gaia-ESO Survey: the most metal-poor stars in the Galactic bulge
• Primordial r-process Dispersion in Metal-Poor Globular Clusters
• High-resolution abundance analysis of red giants in the globular cluster NGC 6522
• Na-O Anticorrelation And HB. III. The abundances of NGC 6441 from FLAMES-UVES spectra
• High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters
• Heavy elements and chemical enrichment in globular clusters
• The Chemical Composition of the Galactic Bulge and Implications for its Evolution
• AGB Sodium Abundances in the Globular Cluster 47 Tucanae (NGC 104)
• Multiple Stellar Populations of Globular Clusters from Homogenous Ca by Photometry I. M22 (NGC 6656)
• Two Groups of Red Giants with Distinct Chemical Abundances in the Bulge Globular Cluster NGC 6553 Through the Eyes of APOGEE
• High resolution reddening map in the direction of the stellar system Terzan 5
• On the Origin of Bimodal Horizontal-Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441
• The link between chemical anomalies along the red giant branch and the horizontal branch extension in globular clusters
• A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19)
• VLT-UVES abundance analysis of four giants in NGC 6553
• A spectroscopic study of the Globular Cluster M28 (NGC~6626)
• The Na-O anticorrelation in horizontal branch stars. V. NGC 6723
• Stellar abundances and ages for metal-rich Milky Way globular clusters - Stellar parameters and elemental abundances for 9 HB stars in NGC6352
• Chemical Complexity in the Eu-enhanced Monometallic Globular Cluster NGC 5986
• NGC 6522: A typical globular cluster in the Galactic bulge without signatures of rapidly rotating Population III stars
• Light and Heavy Element Abundance Variations in the Outer Halo Globular Cluster NGC 6229
• Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. IV. Oxygen diagnostics in extremely metal-poor red giants with infrared OH lines
• The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366
• High-resolution CRIRES spectra of Terzan1: a metal-poor globular cluster toward the inner bulge
• High Resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681
• Abundances of disk and bulge giants from hi-res optical spectra: I. O, Mg, Ca, and Ti in the Solar neighborhood and Kepler field samples

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• What is a globular cluster? An observational perspective
• The Relationship Between Globular Cluster Mass, Metallicity, and Light Element Abundance Variations
• A panchromatic view of the bulge globular cluster NGC 6569
• Blanco DECam Bulge Survey (BDBS) II: Project Performance, Data Analysis, and Early Science Results
• First evidence of multi-iron sub-populations in the Bulge Fossil Fragment candidate Liller 1
• Excess of Ca (and Sc) produced in globular cluster multiple populations: a first census in 77 Galactic globular clusters
• Light Element Discontinuities Suggest an Early Termination of Star Formation in the Globular Cluster NGC 6402 (M14)
• Relative Ages of Nine Inner Milky Way Globular Clusters from Proper Motion Cleaned Color-Magnitude Diagrams
• CAPOS: The bulge Cluster APOgee Survey III. Spectroscopic Tomography of Tonantzintla 2
• Internal kinematics and structure of the bulge globular cluster NGC 6569
• Chemical analysis of the Bulge Globular Cluster NGC 6553
• Infrared photometry and CaT spectroscopy of globular cluster M 28 (NGC 6626)
• CAPOS: The bulge Cluster APOGEE Survey VI. Characterizing multiple stellar populations and chemical abundances in the bulge globular cluster NGC 6569
• CAPOS: The bulge Cluster APOgee Survey VIII. Final ASPCAP results for all clusters
• Variable stars in the VVV globular clusters. II. NGC6441, NGC6569, NGC6626 (M28), NGC6656 (M22), 2MASS-GC02, and Terzan10
• Globular Cluster Intrinsic Iron Abundance Spreads: I. Catalog