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Age as a Major Factor in the Onset of Multiple Populations in Stellar Clusters

Martocchia, S and Cabrera-Ziri, I and Lardo, C and Dalessandro, E and Bastian, N and Kozhurina-Platais, V and Usher, CG and Niederhofer, F and Cordero, M and Geisler, D and Hollyhead, K and Kacharov, N and Larsen, S and Li, C and Mackey, D and Hilker, M and Mucciarelli, A and Platais, I and Salaris, M Age as a Major Factor in the Onset of Multiple Populations in Stellar Clusters. Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711 (Accepted)

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Abstract

It is now well established that globular clusters (GCs) exhibit star-to-star light-element abundance variations (known as multiple stellar populations, MPs). Such chemical anomalies have been found in (nearly) all the ancient GCs (more than 10 Gyr old) of our Galaxy and its close companions, but so far no model for the origin of MPs is able to reproduce all the relevant observations. To gain new insights into this phenomenon, we have undertaken a photometric Hubble Space Telescope survey to study clusters with masses comparable to that of old GCs, where MPs have been identified, but with significantly younger ages. Nine clusters in the Magellanic Clouds with ages between $\sim$ 1.5-11 Gyr have been targeted in this survey. We confirm the presence of multiple populations in all clusters older than 6 Gyr and we add NGC 1978 to the group of clusters for which MPs have been identified. With an age of $\sim$ 2 Gyr, NGC 1978 is the youngest cluster known to host chemical abundance spreads found to date. We do not detect evident star-to-star variations for slightly younger massive clusters ($\sim$ 1.7 Gyr), thus pointing towards an unexpected age dependence for the onset of multiple populations. This discovery suggests that the formation of MPs is not restricted to the early Universe and that GCs and young massive clusters share common formation and evolutionary processes.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [insert complete citation information here] is available online at: xxxxxxx [insert URL that the author will receive upon publication here].
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: 24 Oct 2017 11:10
Last Modified: 24 Oct 2017 11:10
URI: http://researchonline.ljmu.ac.uk/id/eprint/7350

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