The vertical Na-O relation in the bulge globular cluster NGC 6553

TL;DR

This study provides a detailed chemical analysis of NGC 6553, revealing a Na-O relation and evidence of multiple populations, with chemical abundances consistent with bulge field stars, enhancing understanding of globular cluster evolution.

Contribution

First detailed high-resolution spectroscopic analysis of NGC 6553 revealing chemical abundance patterns and multiple populations in this bulge globular cluster.

Findings

Detected a Na-O anti-correlation with significant Na spread and minimal O spread.

Identified multiple populations through large Na and Al spreads.

Chemical abundances align with bulge field star trends.

Abstract

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).