Issue |
A&A
Volume 666, October 2022
|
|
---|---|---|
Article Number | A177 | |
Number of page(s) | 7 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/202244613 | |
Published online | 24 October 2022 |
Multiple stellar populations in the high-temperature regime: Potassium abundances in the globular cluster M 54 (NGC 6715)⋆
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
e-mail: eugenio.carretta@inaf.it
Received:
28
July
2022
Accepted:
5
September
2022
Among the multiple stellar populations in globular clusters (GCs) the very high-temperature H-burning regime, able to produce elements up to potassium, is still poorly explored. Here we present the first abundance analysis of K in 42 giants of NGC 6715 (M 54) with homogeneous abundances of light elements previously derived in our FLAMES survey. Owing to the large mass and low metallicity, a large excess of K could be expected in this GC, which is located in the nucleus of the Sagittarius dwarf galaxy. We actually found a spread in [K/Fe] spanning about 1 dex, with [K/Fe] presenting a significant anti-correlation with [O/Fe] ratios, regardless of the metallicity component in M 54. Evidence for a K–Mg anti-correlation also exists, but this is statistically marginal because of the lack of very Mg-poor stars in this GC. We found, however, a strong correlation between K and Ca. These observations clearly show that the K enhancement in M 54 is probably due to the same network of nuclear reactions generating the phenomenon of multiple stellar populations, at work in a regime of very high temperature. The comparison with recent results in ω Cen is hampered by an unexplained trend with the temperatures for K abundances from optical spectroscopy, and somewhat by a limited sample size for infrared APOGEE data. There are few doubts, however, that the two most massive GCs in the Milky Way host a K–Mg anti-correlation.
Key words: stars: abundances / stars: atmospheres / stars: Population II / globular clusters: general / globular clusters: individual: NGC 6715
© E. Carretta 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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