The chemical composition of a regular halo globular cluster: NGC 5897

• Verfasst von: Koch-Hansen, Andreas [VerfasserIn]
• Verfasst von: McWilliam, Andrew [VerfasserIn]
• Titel: The chemical composition of a regular halo globular cluster: NGC 5897
• Verf.angabe: Andreas Koch and Andrew McWilliam
• E-Jahr: 2014
• Jahr: 28 April 2014
• Umfang: 13 S.
• Fussnoten: Gesehen am 25.08.2020
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2014
• Band/Heft Quelle: 565(2014) Artikel-Nummer A23, 13 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201323119
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1727770765

Abstract

We report for the first time on the chemical composition of the halo cluster NGC 5897 (<i>R<i/><sub>⊙<sub/> = 12.5 kpc), based on chemical abundance ratios for 27 <i>α<i/>-, iron-peak, and neutron-capture elements in seven red giants. From our high-resolution, high signal-to-noise spectra obtained with the <i>Magellan<i/>/MIKE spectrograph, we find a mean iron abundance from the neutral species of [Fe/H] = − 2.04 ± 0.01 (stat.) ± 0.15 (sys.), which is more metal-poor than implied by previous photometric and low-resolution spectroscopic studies. The cluster NGC 5897 is <i>α<i/>-enhanced (to 0.34 ± 0.01 dex) and shows Fe-peak element ratios typical of other (metal-poor) halo globular clusters (GCs) with no overall, significant abundance spreads in iron or in any other heavy element. Like other GCs, NGC 5897 shows a clear Na-O anti-correlation, where we find a prominent primordial population of stars with enhanced O abundances and approximately solar Na/Fe ratios, while two stars are Na-rich, providing chemical proof of the presence of multiple populations in this cluster. Comparison of the heavy element abundances with the solar-scaled values and the metal-poor GC M15 from the literature confirms that NGC 5897 has experienced little contribution from s-process nucleosynthesis. One star of the first generation stands out in that it shows very low La and Eu abundances. Overall, NGC 5897 is a well behaved GC showing archetypical correlations and element-patterns, with little room for surprises in our data. We suggest that its lower metallicity could explain the unusually long periods of RR Lyr that were found in NGC 5897.