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On the Nitrogen variation in ~2 Gyr old massive star clusters in the Large Magellanic Cloud

Martocchia, S, Lardo, C, Rejkuba, M, Kamann, S, Bastian, N, Larsen, S, Cabrera-Ziri, I, Chantereau, W, Dalessandro, E, Kacharov, N and Salaris, M (2021) On the Nitrogen variation in ~2 Gyr old massive star clusters in the Large Magellanic Cloud. Monthly Notices of the Royal Astronomical Society, 505 (4). pp. 5389-5402. ISSN 0035-8711

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We present ESO/VLT FORS2 low resolution spectroscopy of red giant branch stars in three massive, intermediate age ($\sim 1.7-2.3$ Gyr) star clusters in the Large Magellanic Cloud. We measure CH and CN index bands at 4300A, and 3883A, as well as [C/Fe] and [N/Fe] abundance ratios for 24, 21 and 12 member stars of NGC 1978, NGC 1651, NGC 1783, respectively. We find a significant intrinsic spread in CN in NGC 1978 and NGC 1651, a signal of multiple stellar populations (MPs) within the clusters. On the contrary, we report a null CN spread in NGC 1783 within our measurement precision. For NGC 1978, we separated the two populations in the CN distribution and we translated the CN spread into an internal N variation $\Delta$[N/Fe]$=0.63\pm0.49$ dex. For NGC 1651 and NGC 1783, we put upper limits on the N abundance variations of $\Delta$[N/Fe]$\leq 0.2, 0.4$ dex, respectively. The spectroscopic analysis confirms previous results from HST photometry, where NGC 1978 was found to host MPs in the form of N spreads, while slightly younger clusters (e.g. NGC 1783, $<$ 2 Gyr old) were not, within the limits of the uncertainties. It also confirms that intermediate age massive clusters show lower N abundance variations with respect to the ancient globular clusters, although this is in part due to the effect of the first dredge up at these stellar masses, as recently reported in the literature. We stress the importance of future studies to estimate the initial N abundance variations, free of stellar evolutionary mixing processes, by observing unevolved stars in young clusters.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: astro-ph.GA; astro-ph.GA; astro-ph.SR
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 17 Jun 2021 10:00
Last Modified: 10 Sep 2021 09:15
DOI or ID number: 10.1093/mnras/stab1590
URI: https://researchonline.ljmu.ac.uk/id/eprint/15141
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