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Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs

Asa'd, Randa S., Vazdekis, Alexandre, Cerviño, Miguel, Noel, Noelia, Beasley, Michael A. and Kassab, Mahmoud (2017) Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs Monthly Notices of the Royal Astronomical Society, 471 (3). pp. 3599-3614.

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The optical integrated spectra of three Large Magellanic Cloud young stellar clusters (NGC 1984, NGC 1994 and NGC 2011) exhibit concave continua and prominent molecular bands which deviate significantly from the predictions of single stellar population (SSP) models. In order to understand the appearance of these spectra, we create a set of young stellar population (MILES) models, which we make available to the community. We use archival International Ultraviolet Explorer integrated UV spectra to independently constrain the cluster masses and extinction, and rule out strong stochastic effects in the optical spectra. In addition, we also analyse deep colour–magnitude diagrams of the clusters to provide independent age determinations based on isochrone fitting. We explore hypotheses, including age spreads in the clusters, a top-heavy initial mass function, different SSP models and the role of red supergiant stars (RSG). We find that the strong molecular features in the optical spectra can be only reproduced by modelling an increased fraction of about ∼20 per cent by luminosity of RSG above what is predicted by canonical stellar evolution models. Given the uncertainties in stellar evolution at Myr ages, we cannot presently rule out the presence of Myr age spreads in these clusters. Our work combines different wavelengths as well as different approaches (resolved data as well as integrated spectra for the same sample) in order to reveal the complete picture. We show that each approach provides important information but in combination we can better understand the cluster stellar populations.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Asa'd, Randa S.
Vazdekis, Alexandre
Cerviño, Miguel
Beasley, Michael A.
Kassab, Mahmoud
Date : 20 July 2017
DOI : 10.1093/mnras/stx1824
Copyright Disclaimer : This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords : Stars: massive. Galaxies: star clusters: general.
Depositing User : Clive Harris
Date Deposited : 13 Nov 2017 16:19
Last Modified : 16 Jan 2019 19:04

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