VLT-FLAMES Analysis of 8 giants in the Bulge Metal-poor Globular Cluster NGC 6522: Oldest Cluster in the Galaxy?

Abstract

NGC 6522 has been the first metal-poor globular cluster identified in the bulge by W. Baade. Despite its importance, very few high resolution abundance analyses of stars in this cluster are available in the literature. The bulge metal-poor clusters may be important tracers of the early chemical enrichment of the Galaxy. The main purpose of this study is the determination of metallicity and elemental ratios in individual stars of NGC 6522. High resolution spectra of 8 giants of the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with the FLAMES+GIRAFFE spectrograph. Multiband V,I,J,Ks} photometry was used to derive effective temperatures as reference values. Spectroscopic parameters are derived from FeI and FeII lines, and adopted for the derivation of abundance ratios. The present analysis provides a metallicity [Fe/H] = -1.0+-0.2. The alpha-elements Oxygen, Magnesium and Silicon show [O/Fe]=+0.4, [Mg/Fe]=[Si/Fe]= +0.25, whereas Calcium and Titanium show shallower ratios of [Ca/Fe]=[Ti/Fe]=+0.15. The neutron-capture r-process element Europium appears to be overabundant by [Eu/Fe]=+0.4. The neutron-capture s-elements La and Ba are enhanced by [La/Fe]=+0.35 and [Ba/Fe]=+0.5. The large internal errors, indicating the large star-to-star variationin the Ba and Eu abundances, are also discussed. The moderate metallicity combined to a blue Horizontal Branch (BHB), are characteristics similar to those of HP~1 and NGC 6558, pointing to a population of very old globular clusters in the Galactic bulge. Also, the abundance ratios in NGC 6522 resemble those in HP 1 and NGC 6558. The ultimate conclusion is that the bulge is old, and went through an early prompt chemical enrichment.

18 pages, 16 figures. Astronomy & Astrophysics, accepted

References in corpus (12)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The ACS Survey of Galactic Globular Clusters. VII. Relative Ages
• The Metal Content of Bulge Field Stars from FLAMES-GIRAFFE Spectra. I. Stellar parameters and Iron Abundances
• DAOSPEC: an automatic code for measuring equivalent widths in high-resolution stellar spectra
• Oxygen, Sodium, Magnesium and Aluminium as tracers of the Galactic Bulge Formation
• Both accurate and precise gf-values for FeII lines
• Kinematic Decoupling of Globular Clusters with Extended Horizontal-Branch
• A new abundance scale for the globular cluster 47 Tuc
• Heavy element abundances in giant stars of the globular clusters M4 and M5
• Distances of the bulge globular clusters Terzan 5, Liller 1, UKS 1 and Terzan 4 based on HST NICMOS photometry
• VLT-UVES abundance analysis of four giants in NGC 6553
• AL 3 (BH 261): a new globular cluster in the Galaxy

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