Article
Evidence of globular cluster abundance anomalies in the SMC intermediate-age cluster Kron 3
Registro en:
0035-8711
1365-2966
Autor
Salgado, C.
Da Costa, G. S.
Yong, D.
Salinas, R.
Norris, J. E.
Mackey, A. D.
Marino, A. F.
Milone, A. P.
Resumen
Artículo de publicación WOS - SCOPUS Using spectra obtained with the VLT/FORS2 and Gemini-S/GMOS-S instruments, we have investigated carbon, nitrogen, and
sodium abundances in a sample of red giant members of the Small Magellanic Cloud star cluster Kron 3. The metallicity and
luminosity of the cluster are comparable to those of Galactic globular clusters but it is notably younger (age ≈ 6.5 Gyr). We
have measured the strengths of the CN and CH molecular bands, finding a bimodal CN band-strength distribution and a CH/CN
anticorrelation. Application of spectrum synthesis techniques reveals that the difference in the mean [N/Fe] and [C/Fe] values
for the CN-strong and CN-weak stars are <[N/Fe]> = 0.63 ± 0.16 dex and <[C/Fe]> = −0.01 ± 0.07 dex after applying
correctionsfor evolutionary mixing. We have also measured sodium abundances from the Na D lines finding an observed range in
[Na/Fe] of ∼0.6 dex that correlates positively with the [N/Fe] values and a <[Na/Fe]> = 0.12 ± 0.12 dex. While the statistical
significance of the sodium abundance difference is not high, the observed correlation between the Na and N abundances supports
its existence. The outcome represents the first star-by-star demonstration of correlated abundance variations involving sodium in
an intermediate-age star cluster. The results add to existing photometric and spectroscopic indications of the presence of multiple
populations in intermediate-age clusters with masses in excess of ∼105 M . It confirms that the mechanism(s) responsible for
the multiple populations in ancient globular clusters cannot solely be an early cosmological effect applying only in old clusters.