The vertical Na-O relation in the bulge globular cluster NGC 6553
  In this article, we present a detailed chemical analysis of seven red giant
members of NGC 6553 using high-resolution spectroscopy from VLT FLAMES. We
obtained the stellar parameters (Teff, Log(g), vt, [Fe/H]) of these stars from
the spectra, and we measured the chemical abundance for 20 elements, including
light elements, iron-peak elements, alpha-elements and neutron-capture
elements. The metallicities in our sample stars are consistent with a
homogeneous distribution. We found a mean of [Fe/H]=-0.14+/-0.07 dex, in
agreement with other studies. Using the alpha-elements Mg, Si, Ca and Ti we
obtain the mean of [alpha/Fe]=0.11+/-0.05. We found a vertical relation between
Na and O, characterized by a significant spread in Na and an almost
non-existent spread in O. In fact, Na and Al are the only two light elements
with a large intrinsic spread, which demonstrates the presence of Multiple
Populations (MPs). An intrinsic spread in Mg is not detected in this study. The
alpha, iron-peak and neutron capture elements show good agreement with the
trend of the bulge field stars, indicating similar origin and evolution, in
concordance with our previous studies for two other bulge GCs (NGC 6440 and NGC
6528).
