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Martocchia, S, Kamann, S, Saracino, S, Usher, CG, Bastian, N, Rejkuba, M, Latour, M, Lardo, C, Cabrera-Ziri, I, Dreizler, S, Kacharov, N, Kozhurina-Platais, V, Larsen, S, Mancino, S, Platais, I and Salaris, M (2020) Leveraging HST with MUSE: II. Na-abundance variations in intermediate age star clusters. Monthly Notices of the Royal Astronomical Society, 499 (1). pp. 1200-1211. ISSN 0035-8711
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Abstract
Ancient ($>$10 Gyr) globular clusters (GCs) show chemical abundance variations in the form of patterns among certain elements, e.g. N correlates with Na and anti-correlates with O. Recently, N abundance spreads have also been observed in massive star clusters that are significantly younger than old GCs, down to an age of $\sim$2 Gyr. However, so far N has been the only element found to vary in such young objects. We report here the presence of Na abundance variations in the intermediate age massive star clusters NGC 416 ($\sim$6.5 Gyr old) and Lindsay 1 ($\sim$7.5 Gyr old) in the Small Magellanic Cloud, by combining HST and ESO-VLT MUSE observations. Using HST photometry we were able to construct ''chromosome maps'' and separate sub-populations with different N content, in the red giant branch of each cluster. MUSE spectra of individual stars belonging to each population were combined, resulting in high signal-to-noise spectra representative of each population, which were compared to search for mean differences in Na. We find a mean abundance variation of $\Delta$[Na/Fe]$=0.18\pm0.04$ dex for NGC 416 and $\Delta$[Na/Fe]$=0.24\pm0.05$ dex for Lindsay 1. In both clusters we find that the population that is enhanced in N is also enhanced in Na, which is the same pattern to the one observed in ancient GCs. Furthermore, we detect a bimodal distribution of core-helium burning Red Clump (RC) giants in the UV colour magnitude diagram of NGC 416. A comparison of the stacked MUSE spectra of the two RCs shows the same mean Na abundance difference between the two populations. The results reported in this work are a crucial hint that star clusters of a large age range share the same origin: they are the same types of objects, but only separated in age.
| Item Type: | Article |
|---|---|
| Additional Information: | This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
| Uncontrolled Keywords: | astro-ph.SR; astro-ph.SR; astro-ph.GA |
| Subjects: | Q Science > QB Astronomy Q Science > QC Physics |
| Divisions: | Astrophysics Research Institute |
| Publisher: | Oxford University Press |
| Related URLs: | |
| Date of acceptance: | 18 September 2020 |
| Date of first compliant Open Access: | 25 September 2020 |
| Date Deposited: | 25 Sep 2020 12:07 |
| Last Modified: | 04 Sep 2021 06:37 |
| DOI or ID number: | 10.1093/mnras/staa2929 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/13718 |
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