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| Paper: |
Rotation, Activity, and Lithium in NGC 6475 |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
1269 |
| Authors: |
Jeffries, R. D.; James, D. J. |
| Abstract: |
We present rotational velocities, magnetic activity indices and lithium abundances for an X-ray selected sample of cool stars in the 220 Myr age open cluster, NGC 6475. The rapid spin down and convergence of rotation rates experienced by stars as they reach the ZAMS is incomplete in NGC 6475. Both G and K stars are found with v sin i >10 km s{-1}. Peak rotation rates for G stars are 12-14 km s^{-1}, whereas two mid-K stars are found with v sin i ~25 km s^{-1}. We compare our rotation data and the fastest rotators in other open clusters, with simple rotational evolution models. These suggest an increase in the nominal Pleiades age to 100 Myr and a mass-dependent dynamo saturation rotation rate. All the cool stars exhibit Li 1 6708 AA absorption features and the cluster metallicity has been measured as [M/H]=+0.110+/-0.034. When compared to Li in the Pleiades and Hyades, it is evident that G and K stars experience significant main sequence Li depletion between 220 and 600 Myr and probably at earlier times as well. Interpretation is confused by the X-ray selection bias and we are unable to decide whether the dispersion of Li abundances seen in the Pleiades K stars is reduced in NGC 6475. |
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