Discrepancies in the ages of young star clusters; evidence for mergers?
AffiliationUniv Arizona, Steward Observ
MetadataShow full item record
PublisherOXFORD UNIV PRESS
CitationEmma R Beasor, Ben Davies, Nathan Smith, Nate Bastian, Discrepancies in the ages of young star clusters; evidence for mergers?, Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 1, June 2019, Pages 266–273, https://doi.org/10.1093/mnras/stz732
Rights© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
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AbstractThere is growing evidence that star clusters can no longer be considered simple stellar populations. Intermediate- and old-age clusters are often found to have extended main-sequence turn-offs (eMSTOs) which are difficult to explain with single-age isochrones, an effect attributed to rotation. In this paper, we provide the first characterization of this effect in young (<20 Myr) clusters. We determine ages for four young massive clusters (2 Large Magellanic Cloud and 2 Galactic) by three different methods: using the brightest single turn-off (TO) star; using the luminosity function (LF) of the TO; and by using the lowest L-bol red supergiant (RSG). The age found using the cluster TO is consistently younger than the age found using the lowest RSG L-bol. Under the assumption that the lowest luminosity RSG age is the 'true' age, we argue that the eMSTOs of these clusters cannot be explained solely by rotation or unresolved binaries. We speculate that the most luminous stars above the TO are massive blue straggler stars formed via binary interaction, either as mass gainers or merger products. Therefore, using the cluster TO method to infer ages and initial masses of post-MS stars, such as Wolf-Rayet stars, luminous blue variables, and RSGs, will result in ages inferred being too young and masses too high.
VersionFinal published version
SponsorsSTFC doctoral studentship; Royal Society (University Research Fellowship); European Research Council [ERC-CoG-646928-Multi-Pop]