Disappearance of the extended main sequence turn-off in intermediate age clusters as a consequence of magnetic braking

Abstract

Extended MS turn-offs are features commonly found in the colour-magnitude diagrams of young and intermediate age (less than about 2 Gyr) massive star clusters, where the MS turn-off is broader than can be explained by photometric uncertainties, crowding, or binarity. Rotation is suspected to be the cause of this feature, by accumulating fast rotating stars, strongly affected by gravity darkening and rotation-induced mixing, near the MS turn-off. This scenario successfully reproduces the tight relation between the age and the actual extent in luminosity of the extended MS turn-off of observed clusters. Below a given mass (dependent on the metallicity), stars are efficiently braked early on the MS due to the interaction of stellar winds and the surface magnetic field, making their tracks converge towards those of non-rotating tracks in the HRD. When these stars are located at the turn-off of a cluster, their slow rotation causes the extended MS turn-off feature to disappear. We investigate the maximal mass for which this braking occurs at different metallicities, and determine the age above which no extended MS turn-off is expected in clusters. Our models predict that the extended MS turn-off phenomenon disappears at ages older than about 2 Gyr. There is a trend with the metallicity, the age at which the disappearance occurs becoming older at higher metallicity. These results are robust between the two codes used in this work, despite some differences in the input physics and in particular in the detailed description of rotation-induced internal processes and of angular momentum extraction by stellar winds. Comparing our results with clusters in the LMC and Galaxy shows a very good fit to the observations. This strengthens the rotation scenario to explain the cause of the extended MS turn-off phenomenon.

7 pages, 4 figures, accepted for publication in A&A

References in corpus (14)

• The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
• A double main sequence turn-off in the rich star cluster NGC 1846 in the Large Magellanic Cloud
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• Diagnoses to unravel secular hydrodynamical processes in rotating main sequence stars
• Populations of rotating stars III. SYCLIST, the new Geneva Population Synthesis code
• Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
• Rotating Stellar Models Can Account for the Extended Main Sequence Turnoffs in Intermediate Age Clusters
• NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
• No Evidence for Significant Age Spreads in Young Massive LMC Clusters
• Multiple stellar populations in Magellanic Cloud clusters. V. The split main sequence of the young cluster NGC1866
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: Stellar Rotation diminishes, but does not eliminate, Age Spreads
• New Clues to the Cause of Extended Main Sequence Turn-Offs in Intermediate-Age Star Clusters in the Magellanic Clouds
• On the Interpretation of Sub-Giant Branch Morphologies of Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs
• The effects of the overshooting of the convective core on main-sequence turnoffs of young- and intermediate-age star clusters

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