Volume 607, November 2017
|Number of page(s)||16|
|Section||Galactic structure, stellar clusters and populations|
|Published online||08 November 2017|
Cluster mass and age in the multiple population context
1 INAF–Osservatorio Astronomico di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
2 INAF–Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
3 Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, Melbourne, VIC 3800, Australia
4 Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
Received: 7 July 2017
Accepted: 1 August 2017
To understand globular clusters (GCs) we need to comprehend how their formation process was able to produce their abundance distribution of light elements. In particular, we seek to figure out which stars imprinted the peculiar chemical signature of GCs. One of the best ways is to study the light-element anti-correlations in a large sample of GCs that are analysed homogeneously. As part of our spectroscopic survey of GCs with FLAMES, we present here the results of our study of about 30 red giant member stars in the low-mass, low-metallicity Milky Way cluster NGC 6535. We measured the metallicity (finding [Fe/H] =−1.95, rms = 0.04 dex in our homogeneous scale) and other elements of the cluster and, in particular, we concentrate here on O and Na abundances. These elements define the normal Na-O anti-correlation of classical GCs, making NGC 6535 perhaps the lowest mass cluster with a confirmed presence of multiple populations. We updated the census of Galactic and extragalactic GCs for which a statement on the presence or absence of multiple populations can be made on the basis of high-resolution spectroscopy preferentially, or photometry and low-resolution spectroscopy otherwise; we also discuss the importance of mass and age of the clusters as factors for multiple populations.
Key words: stars: abundances / stars: atmospheres / stars: Population II / open clusters and associations: individual: NGC 6535 / globular clusters: general
Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A44
© ESO, 2017
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