A Photometric Method for estimating CNO Abundances in Globular Clusters

Stromgren indices v and b are combined with broad-band index I, and a new index p, the short wavelength half of the v band, to estimate CN 4215A molecular absorption in a sample of stars in M22. The results have been used to estimate carbon and nitrogen abundances and suggest groups of stars within this cluster, each with a characteristic nitrogen abundance, but with a range of carbon abundances. The results suggest the possibility of stars consisting of material which has undergone CNO recycling two or three times. The method can be subsequently used for other globular clusters.