Potassium in globular cluster stars

Comparing normal clusters to the peculiar cluster NGC 2419

E. Carretta, R. G. Gratton, A. Bragaglia, V. D'Orazi, S. Lucatello, A. Sollima, C. Sneden

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Two independent studies recently uncovered two distinct populations among giants in the distant, massive globular cluster (GC) NGC 2419. One of these populations has normal magnesium (Mg) and potassium (K) abundances for halo stars: enhanced Mg and roughly solar K. The other population has extremely depleted Mg and very enhanced K. To better anchor the peculiar NGC 2419 chemical composition, we have investigated the behavior of K in a few red giant branch stars in NGC 6752, NGC 6121, NGC 1904, and ω Cen. To verify that the high K abundances are intrinsic and not due to some atmospheric features in giants, we also derived K abundances in less evolved turn-off and subgiant stars of clusters 47 Tuc, NGC 6752, NGC 6397, and NGC 7099. We normalized the K abundance as a function of the cluster metallicity using 21 field stars analyzed in a homogeneous manner. For all GCs of our sample, the stars lie in the K-Mg abundance plane on the same locus occupied by the Mg-normal population in NGC 2419 and by field stars. This holds for both giants and less-evolved stars. At present, NGC 2419 seems unique among GCs.

Original languageEnglish
Article number40
Pages (from-to)1-9
Number of pages9
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 20 May 2013

Bibliographical note

Copyright 2013 the American Astronomical Society. First published in the
Astrophysical journal, 769(1), 40, 2013, published by IOP Publishing. The
original publication is available at http://www.doi.org/10.1088/0004-637X/769/1/40. Version archived for private and non-commercial use with the
permission of the author/s and according to publisher conditions. For further
rights please contact the publisher.

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