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| Paper: |
Lithium Abundances in the Low Metallicity Hyades Analogue NGC 6633 |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
940 |
| Authors: |
Jeffries, R. D. |
| Abstract: |
NGC 6633 is a young open cluster with a similar age to the Hyades and Praesepe, but lower metallicity. Using photometric, proper motion and radial velocity information, a sample of late-type cluster members has been found and their projected rotation rates and lithium abundances measured. The projected rotation velocities in NGC 6633 are entirely consistent with rotation rates in the Hyades, as are the Li abundances of the F and G stars. However, the pattern of Li depletion among cooler stars is significantly different. In particular, three early K stars have log N(Li)>1.2, whereas only smaller upper limits are found in the Hyades. The differences can plausibly be explained by the lower metallicity and shallower convection zones of the NGC 6633 stars. Comparison with the Pleiades, which has a similar metallicity to NGC 6633, shows that Li depletion apparently occurs in G and K stars whilst they are on the main sequence. The data argue strongly against a modification to standard stellar evolution models involving ad hoc opacity increases and favour additional mixing mechanisms such as rotational turbulence. |
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