Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426

Abstract

We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H] = -2.34$\pm$0.05 dex (stat.) in accordance with previous studies. At a mean $\alpha$-abundance of [(Mg,Si,Ca)/3 Fe] = 0.39$\pm$0.03 dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter $\alpha$-elements as well as the enhanced ratio [Zn/Fe] = 0.39 dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn point towards an enrichment history governed by the r-process with only little -if any- sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317.

arXiv comment14 pages, 12 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (47)

• The chemical composition of the Sun
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• 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
• An absolutely calibrated effective temperature scale from the InfraRed Flux Method
• Optimal Techniques in Two-dimensional Spectroscopy: Background Subtraction for the 21st Century
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Galactic Evolution of Sr, Y, Zr: A Multiplicity of Nucleosynthetic Processes
• 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
• Nucleosynthesis of Zinc and Iron-Peak Elements in Pop III Type II Supernovae : Comparison with abundances of Very Metal-Poor Halo Stars
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Non-LTE calculations for neutral Na in late-type stars using improved atomic data
• The Rise of the s-Process in the Galaxy
• NLTE line formation of Fe for late-type stars. I. Standard stars with 1D and <3D> model atmospheres
• NLTE line formation of Fe in late-type stars II: 1D spectroscopic stellar parameters
• Gaia FGK Benchmark Stars - Metallicity
• A Globular Cluster Metallicity Scale Based on the Abundance of Fe II
• Variations in the Abundance Pattern of Extremely Metal-poor Stars and Nucleosynthesis in Population III Supernovae
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• Gaia FGK Benchmark Stars: Effective temperatures and surface gravities
• A Comparison of Elemental Abundance Ratios in Globular Clusters, Field Stars, and Dwarf Spheroidal Galaxies
• A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars
• Homogeneous age dating of 55 Galactic globular clusters. Clues to the Galaxy formation mechanisms
• Analysis and calibration of CaII triplet spectroscopy of Red Giant Branch stars from VLT/FLAMES observations
• Non-standard s process in low metallicity massive rotating stars
• Abundances of Baade's Window Giants from Keck/HIRES Spectra: I. Stellar Parameters and [Fe/H] Values
• Globular clusters in the outer Galactic halo: new HST/ACS imaging of 6 globular clusters and the Galactic globular cluster age-metallicity relation
• Silver and palladium help unveil the nature of a second r-process
• New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars
• NLTE analysis of Sr lines in spectra of late-type stars with new R-matrix atomic data
• A new abundance scale for the globular cluster 47 Tuc
• Tracing the evolution of NGC6397 through the chemical composition of its stellar populations
• Metal-poor stars towards the Galactic bulge - a population potpourri
• A New Reddening Law for M4
• Formation of Multiple Populations in Globular Clusters: constraints on the dilution by pristine gas
• Bolometric correction and spectral energy distribution of cool stars in Galactic clusters
• First stars XIII. Two extremely metal-poor RR Lyrae stars?
• Detailed Chemical Abundances in NGC 5824: Another Metal-Poor Globular Cluster with Internal Heavy Element Abundance Variations
• All quiet in the outer halo: chemical abundances in the globular cluster Pal 3
• The chemical composition of a regular halo globular cluster: NGC 5897
• Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf Spheroidal galaxy?
• A spectroscopic study of the Globular Cluster NGC 4147
• Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833
• FORS2/VLT survey of Milky Way globular clusters I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8
• Potassium Abundances in Red Giants of Mildly to Very Metal-Poor Globular Clusters
• Microturbulent velocity from stellar spectra: a comparison between different approaches (Research Note)

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