On the intrinsic width of the giant branch in the globular cluster Omega Centauri

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Abstract
The range in heavy-element abundance is found to be insufficient to explain the range in color index observed on the giant branch of Omega Cen. The red stars, which include both mixed and unmixed stars, appear to be too cool for their metallicity as judged against CM diagrams and mean color–metallicity relations for other clusters. For those stars which have mixed CN-cycle products into their atmospheres and have high [N/C], the most likely explanation is that they have a reduced value of the convective element mixing length. A possible link is suggested between this anomaly and stellar rotation, with angular momentum increasing with metallicity. The colors of the unmixed red stars are similar to those of giants in NGC 6171, and possibly other metal-rich clusters.

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