A SURVEY OF CN AND CH VARIATIONS IN GALACTIC GLOBULAR CLUSTERS FROM SLOAN DIGITAL SKY SURVEY SPECTROSCOPY

We present a homogeneous survey of the CN and CH band strengths in eight Galactic globular clusters observed during the course of the Sloan Extension for Galactic Understanding and Exploration sub-survey of the Sloan Digital Sky Survey. We confirm the existence of a bimodal CN distribution among red giant branch (RGB) stars in all of the clusters with metallicity greater than [Fe/H] = -1.7; the lowest metallicity cluster with an observed CN bimodality is M53, with [Fe/H] ≅ -2.1. There is also some evidence for individual CN groups on the subgiant branches of M92, M2, and M13, and on the RGBs of M92 and NGC 5053. Finally, we quantify the correlation between overall cluster metallicity and the slope of the CN band strength-luminosity plot as a means of further demonstrating the level of CN enrichment in cluster giants. Our results agree well with previous studies reported in the literature.