Horizontal-branch morphology and multiple stellar populations in the anomalous globular cluster M22
Abstract
M22 is an anomalous globular cluster that hosts two groups of stars with different metallicity and s-element abundance. The star-to-star light-element variations in both groups, with the presence of individual Na-O and C-N anticorrelations, demonstrates that this Milky-Way satellite has experienced a complex star-formation history. We have analysed FLAMES/UVES spectra for seven stars covering a small color interval, on the reddest horizontal-branch (HB) portion of this cluster and investigated possible relations between the chemical composition of a star and its location along the HB. Our chemical abundance analysis takes into account effects introduced by deviations from the local-thermodynamic equilibrium (NLTE effects), that are significant for the measured spectral lines in the atmospheric parameters range spanned by our stars. We find that all the analysed stars are barium-poor and sodium-poor, thus supporting the idea that the position of a star along the HB is strictly related to the chemical composition, and that the HB-morphology is influenced by the presence of different stellar populations.
Keywords
Cite
@article{arxiv.1302.5870,
title = {Horizontal-branch morphology and multiple stellar populations in the anomalous globular cluster M22},
author = {A. F. Marino and A. P. Milone and K. Lind},
journal= {arXiv preprint arXiv:1302.5870},
year = {2015}
}
Comments
21 pages, 3 figures, accepted for publication in ApJ