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.
|Number of pages||12|
|Journal||The Astrophysical Journal: an international review of astronomy and astronomical physics|
|Publication status||Published - 1 Aug 2017|
Bibliographical noteCopyright 2017 The American Astronomical Society. First published in the Astrophysical journal, 844(2), 119, 2017, published by IOP Publishing. The original publication is available at http://www.doi.org/10.3847/1538-4357/aa7b36. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.
- globular clusters: individual (NGC 330, NGC 1805, NGC 1818, NGC 2164)
- Hertzsprung-Russell and C-M diagrams
- Magellanic Clouds
- globular clusters: Individual (NGC 330, NGC 1805, NGC 1818, NGC 2164)