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Paper: The Case of the Missing Cyanogen-rich AGB Stars in Galactic Globular Clusters
Volume: 458, Galactic Archaeology: Near-Field Cosmology and the Formation of the Milky Way
Page: 205
Authors: Campbell, S. W.; Yong, D.; Wylie-de Boer, E. C.; Stancliffe, R. J.; Lattanzio, J. C.; Angelou, G. C.; Grundahl, F.; Sneden, C.
Abstract: The handful of available observations of AGB stars in Galactic Globular Clusters suggest that the GC AGB populations are dominated by cyanogen-weak stars (eg. Norris et al. 1981; Sneden et al. 2000). This contrasts strongly with the distributions on the RGB (and other) populations, which generally show a 50:50 bimodality in CN band strength. If this is a real difference then it presents a serious problem for low metallicity stellar evolution theory — since such a surface abundance change going from the RGB to AGB is not predicted by stellar models. However this is only a tentative conclusion, since it is based on very small AGB sample sizes. To test whether this problem really exists we have carried out an observational campaign targeting AGB stars in GCs. Our preliminary results indicate there is indeed a lack of CN-strong AGB stars.
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