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

• Verfasst von: Hanke, Michael [VerfasserIn]
• Verfasst von: Koch-Hansen, Andreas [VerfasserIn]
• Titel: Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426
• Verf.angabe: M. Hanke, A. Koch, C.J. Hansen, A. McWilliam
• E-Jahr: 2017
• Jahr: 06 March 2017
• Umfang: 15 S.
• Fussnoten: Gesehen am 24.10.2017
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2017
• Band/Heft Quelle: 599(2017) Artikel-Nummer A97, 15 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201629650
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1564706265

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 <i>Magellan<i/>2/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 ± 0.05 dex (stat.) in accordance with previous studies. At a mean <i>α<i/>-abundance of [(Mg, Si, Ca)/3 Fe] = 0.39 ± 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 <i>α<i/>-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 have 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 points toward an enrichment history governed by the <i>r<i/>-process with little, if any, sign of <i>s<i/>-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317.