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Spectroscopy and photometry of the least-massive Type-II globular clusters: NGC1261 AND NGC6934

Journal
Date Issued
2021
Author(s)
•
Milone, A. P.
•
Renzini, A.
•
Yong, D.
•
Asplund, M.
•
Da Costa, G. S.
•
Jerjen, H.
•
Cordoni, G.
•
Carlos,M.
•
Dondoglio, E.
•
Lagioia, E. P.
•
Jang, S.
•
Tailo, M.
DOI
Abstract
Recent work has revealed two classes of Globular Clusters (GCs), dubbed Type-I and Type-II. Type-II GCs are characterized by a blue- and a red- red giant branch composed of stars with different metallicities, often coupled with distinct abundances in the slow-neutron capture elements (s-elements). Here we continue the chemical tagging of Type-II GCs by adding the two least-massive clusters of this class, NGC1261 and NGC6934. Based on both spectroscopy and photometry, we find that red stars in NGC1261 are slightly enhanced in [Fe/H] by ~0.1 dex and confirm that red stars of NGC 6934 are enhanced in iron by ~0.2 dex. Neither NGC1261 nor NGC6934 show internal variations in the s-elements, which suggests a GC mass threshold for the occurrence of s-process enrichment. We found a significant correlation between the additional Fe locked in the red stars of Type-II GCs and the present-day mass of the cluster. Nevertheless, most Type II GCs retained a small fraction of Fe produced by SNe II, lower than the 2%; NGC6273, M54 and omega Centauri are remarkable exceptions. In the appendix, we infer for the first time chemical abundances of Lanthanum, assumed as representative of the s-elements, in M54, the GC located in the nucleus of the Sagittarius dwarf galaxy. Red-sequence stars are marginally enhanced in [La/Fe] by 0.10\pm0.06 dex, in contrast with the large [La/Fe] spread of most Type II GCs. We suggest that different processes are responsible for the enrichment in iron and s-elements in Type-II GCs.
Volume
923
Issue
1
Start page
22
Uri
Url
Issn Identifier
0004-637X
Rights
open.access
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