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Apparent Age Spreads in Clusters and the Role of Stellar Rotation

Apparent Age Spreads in Clusters and the Role of Stellar Rotation Thumbnail


Abstract

We use the Geneva Syclist isochrone models that include the effects of stellar rotation to investigate the role that rotation has on the resulting colour-magnitude diagram (CMD) of young and intermediate age clusters. We find that if a distribution of rotation velocities exists within the clusters, rotating stars will remain on the main sequence (MS) for longer, appearing to be younger than non-rotating stars within the same cluster. This results in an extended main sequence turn-off (eMSTO) that appears at young ages ($\sim30$~Myr) and lasts beyond 1~Gyr. If this eMSTO is interpreted as an age spread, the resulting age spread is proportional to the age of the cluster, i.e. young clusters ($<100$~Myr) appear to have small age spreads (10s of Myr) whereas older clusters ($\sim1$~Gyr) appear to have much larger spreads, up to a few hundred Myr. We compare the predicted spreads for a sample of rotation rates to observations of young and intermediate age clusters, and find a strong correlation between the measured 'age spread' and the age of the cluster, in good agreement with models of stellar rotation. This suggests that the 'age spreads' reported in the literature may simply be the result of a distribution of stellar rotation velocities within clusters.

Acceptance Date Jul 27, 2015
Publication Date Aug 25, 2015
Publicly Available Date Mar 29, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Publisher Oxford University Press
Pages 2070-2074
DOI https://doi.org/10.1093/mnras/stv1791
Keywords Hertzsprung–Russell and colour–magnitude diagrams, stars: rotation, galaxies: individual: LMC, galaxies: star clusters: general
Publisher URL https://doi.org/10.1093/mnras/stv1791

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