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The tight subgiant branch of the intermediate-age star cluster NGC 411 implies a single-aged stellar population

Li, C and de Grijs, R and Bastian, N and Deng, L and Niederhofer, F and Zhang, C (2016) The tight subgiant branch of the intermediate-age star cluster NGC 411 implies a single-aged stellar population. Monthly Notices of the Royal Astronomical Society, 461 (3). pp. 3212-3221. ISSN 0035-8711

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Open Access URL: https://arxiv.org/pdf/1606.05394.pdf (Accepted version)

Abstract

The presence of extended main-sequence turn-off (eMSTO) regions in intermediate-age star clusters in the Large and Small Magellanic Clouds is often interpreted as resulting from extended star formation histories (SFHs), lasting ≥300 Myr. This strongly conflicts with the traditional view of the dominant star formation mode in stellar clusters, which are thought of as single-aged stellar populations. Here we present a test of this interpretation by exploring the morphology of the subgiant branch (SGB) of NGC 411, which hosts possibly the most extended eMSTO among all known intermediate-age star clusters. We show that the width of the NGC 411 SGB favours the single-aged stellar population interpretation and rules out an extended SFH. In addition, when considering the red clump (RC) morphology and adopting the unproven premise that the widths of all features in the colour–magnitude diagram are determined by an underlying range in ages, we find that the SFH implied is still very close to that resulting from a single-aged stellar population, with a minor fraction of stars scattering to younger ages compared with the bulk of the population. The SFHs derived from the SGB and RC are both inconsistent with the SFH derived from the eMSTO region. NGC 411 has a very low escape velocity and it has unlikely undergone significant mass-loss at an early stage, thus indicating that it may lack the capacity to capture most of its initial, expelled gas from stellar evolutionary processes, a condition often required for extended SFHs to take root.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 07 Apr 2017 11:59
Last Modified: 07 Apr 2017 11:59
DOI or Identification number: 10.1093/mnras/stw1491
URI: http://researchonline.ljmu.ac.uk/id/eprint/6226

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