CN variations among asymptotic giant branch and horizontal branch stars in the intermediate metallicity globular clusters M5, M4, and NGC 6752

Abstract

The distribution of λ3883 CN band strengths has been investigated among stars in the asymptotic giant branch phase of evolution in the globular clusters M5 and NGC 6752, as well as among red horizontal branch stars in M4. Differences in the strength of the CN band have been identified among the asymptotic giant branch stars in both M5 and NGC 6752. Synthetic spectrum computations reveal that the differences in the strength of this band between the CN-strongest stars found on the red giant and asymptotic giant branches of M5 can be accounted for entirely by their differences in effective temperature and gravity, without having to invoke differences in the surface abundances of carbon and nitrogen