Rotation and stellar ages

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Rotation and stellar ages

Post by Lazarus on 20th January 2015, 3:37 pm

Not directly related to exoplanets, but may have some significant implications and Kappa Andromedae is one of the test stars...

Brandt & Huang "Bayesian Ages for Early-Type Stars from Isochrones Including Rotation, and a Possible Old Age for the Hyades"
http://arxiv.org/abs/1501.04404

Using stellar evolution models with rotation to work out stellar ages. Interestingly the Hyades comes out substantially older than previous estimates (950±100 Myr versus 625±50 Myr), which would have significant implications as the age of the Hyades is one of the values used to calibrate stellar age estimations.

The older age we derive for the Hyades turnoff stars raises questions about either the cluster’s age, stellar modeling, or both. Including stellar modeling uncertainties could imply a much larger error for the cluster age, perhaps 800 ± 200 Myr, which would propagate into secondary age indicators calibrated on clusters like the Hyades. Resolving these modeling uncertainties will likely require independent age indicators, perhaps asteroseismology of F and G type Hyades stars.
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Re: Rotation and stellar ages

Post by Shellface on 3rd April 2015, 3:46 pm

From the same authors:

The Age and Age Spread of the Praesepe and Hyades Clusters: a Consistent, ~800 Myr Picture from Rotating Stellar Models

We fit the upper main sequence of the Praesepe and Hyades open clusters using stellar models with and without rotation. When neglecting rotation, we find that no single isochrone can fit the entire upper main sequence at the clusters' spectroscopic metallicity: more massive stars appear, at high significance, to be younger than less massive stars. This discrepancy is consistent with earlier studies, but vanishes when including stellar rotation. The entire upper main sequence of both clusters is very well-fit by a distribution of 800 Myr-old stars with the spectroscopically measured [Fe/H]=0.12. The increase over the consensus age of ~600-650 Myr is due both to the revised Solar metallicity (from Z⊙≈0.02 to Z⊙≈0.014) and to the lengthening of main sequence lifetimes and increase in luminosities with rapid rotation. Our results show that rotation can remove the need for large age spreads in intermediate age clusters, and that these clusters may be significantly older than is commonly accepted. A Hyades/Praesepe age of ~800 Myr would also require a recalibration of rotation/activity age indicators.
The effects of rotation on stellar evolution are, as the introduction makes clear, not perfectly understood, but the results presented here are rather convincing. As said previously, though, independent age estimates are probably necessary to be certain of such a sensitive result.

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