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Title: Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds

Abstract

An increasing number of young massive clusters (YMCs) in the Magellanic Clouds have been found to exhibit bimodal or extended main sequences (MSs) in their color–magnitude diagrams (CMDs). These features are usually interpreted in terms of a coeval stellar population with different stellar rotational rates, where the blue and red MS stars are populated by non- (or slowly) and rapidly rotating stellar populations, respectively. However, some studies have shown that an age spread of several million years is required to reproduce the observed wide turnoff regions in some YMCs. Here we present the ultraviolet–visual CMDs of four Large and Small Magellanic Cloud YMCs, NGC 330, NGC 1805, NGC 1818, and NGC 2164, based on high-precision Hubble Space Telescope photometry. We show that they all exhibit extended main-sequence turnoffs (MSTOs). The importance of age spreads and stellar rotation in reproducing the observations is investigated. The observed extended MSTOs cannot be explained by stellar rotation alone. Adopting an age spread of 35–50 Myr can alleviate this difficulty. We conclude that stars in these clusters are characterized by ranges in both their ages and rotation properties, but the origin of the age spread in these clusters remains unknown.

Authors:
 [1];  [2];  [3];  [4]
  1. Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia)
  2. Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China)
  3. Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)
  4. Research School of Astronomy and Astrophysics, Australian National University, Mt. Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
Publication Date:
OSTI Identifier:
22663328
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 844; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; MAGELLANIC CLOUDS; PHOTOMETRY; ROTATION; SPACE; STAR CLUSTERS; STARS; TELESCOPES; ULTRAVIOLET RADIATION

Citation Formats

Li, Chengyuan, De Grijs, Richard, Deng, Licai, and Milone, Antonino P. Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA7B36.
Li, Chengyuan, De Grijs, Richard, Deng, Licai, & Milone, Antonino P. Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds. United States. doi:10.3847/1538-4357/AA7B36.
Li, Chengyuan, De Grijs, Richard, Deng, Licai, and Milone, Antonino P. Tue . "Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds". United States. doi:10.3847/1538-4357/AA7B36.
@article{osti_22663328,
title = {Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds},
author = {Li, Chengyuan and De Grijs, Richard and Deng, Licai and Milone, Antonino P.},
abstractNote = {An increasing number of young massive clusters (YMCs) in the Magellanic Clouds have been found to exhibit bimodal or extended main sequences (MSs) in their color–magnitude diagrams (CMDs). These features are usually interpreted in terms of a coeval stellar population with different stellar rotational rates, where the blue and red MS stars are populated by non- (or slowly) and rapidly rotating stellar populations, respectively. However, some studies have shown that an age spread of several million years is required to reproduce the observed wide turnoff regions in some YMCs. Here we present the ultraviolet–visual CMDs of four Large and Small Magellanic Cloud YMCs, NGC 330, NGC 1805, NGC 1818, and NGC 2164, based on high-precision Hubble Space Telescope photometry. We show that they all exhibit extended main-sequence turnoffs (MSTOs). The importance of age spreads and stellar rotation in reproducing the observations is investigated. The observed extended MSTOs cannot be explained by stellar rotation alone. Adopting an age spread of 35–50 Myr can alleviate this difficulty. We conclude that stars in these clusters are characterized by ranges in both their ages and rotation properties, but the origin of the age spread in these clusters remains unknown.},
doi = {10.3847/1538-4357/AA7B36},
journal = {Astrophysical Journal},
number = 2,
volume = 844,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 2017},
month = {Tue Aug 01 00:00:00 EDT 2017}
}