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