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Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites | | A. F. Marino
; A. P. Milone
; A. I. Karakas
; L. Casagrande
; D. Yong
; L. Shingles
; G. Da Costa
; J. E. Norris
; P.B. Stetson
; K. Lind
; M. Asplund
; R. Collet
; H. Jerjen
; L. Sbordone
; A. Aparicio
; S. Cassisi
; | | Date: |
26 Feb 2015 | | Abstract: | We present a high resolution spectroscopic analysis of 62 red giants in the
Milky Way globular cluster NGC5286. We have determined abundances of
representative light proton-capture, alpha, 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, c_{BVI}=(B-V)-(V-I), to
maximise 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 NGC5286
add this object to the class of "anomalous" GCs. Furthermore, the chemical
abundance pattern of NGC5286 resembles that observed in some of the anomalous
GCs, e.g. M22, NGC1851, M2, and the more extreme Omega 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. | | Source: | arXiv, 1502.7438 | | Services: | Forum | Review | PDF | Favorites | |
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