Iron and s-elements abundance variations in NGC 5286: comparison with `anomalous' globular clusters and Milky Way satellites

Journal
Date Issued
2015
Author(s)
•
Milone, A. P.
•
Karakas, A. I.
•
Casagrande, L.
•
Yong, D.
•
Shingles, L.
•
Da Costa, G.
•
Norris, J. E.
•
Stetson, P. B.
•
Lind, K.
•
Asplund, M.
•
Collet, R.
•
Jerjen, H.
•
Sbordone, L.
•
Aparicio, A.
•
DOI
Description
This research has been supported in part by the Australian Research Council through grants FL110100012, DP120100991, and DP120101237. APM acknowledges support by the Australian Research Council through Discovery Early Career Researcher Award DE150101816.
Abstract
We present a high-resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster (GC) NGC 5286. We have determined abundances of representative light proton-capture, α, Fe-peak and neutron-capture element groups, and combined them with photometry of multiple sequences observed along the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal distribution in s-process element abundance ratios, with two main groups, the s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the s-rich stars having higher Fe, e.g. < [Fe/H]> _{s-rich}} - < [Fe/H]> _{s-poor}} ̃ 0.2 dex; and (iii) the presence of O-Na-Al (anti)correlations in both stellar groups. We have defined a new photometric index, cBVI = (B - V) - (V - I), to maximize the separation in the colour-magnitude diagram between the two stellar groups with different Fe and s-element content, and this index is not significantly affected by variations in light elements (such as the O-Na anticorrelation). The variations in the overall metallicity present in NGC 5286 add this object to the class of anomalous GCs. Furthermore, the chemical abundance pattern of NGC 5286 resembles that observed in some of the anomalous GCs, e.g. M 22, NGC 1851, M 2, and the more extreme ω Centauri, that also show internal variations in s-elements, and in light elements within stars with different Fe and s-elements content. In view of the common variations in s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class of objects. The similarities in chemical abundance ratios between these objects strongly suggest similar formation and evolution histories, possibly associated with an origin in tidally disrupted dwarf satellites.
Volume
450
Issue
1
Start page
815
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.450..815M
Rights
open.access
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