DETAILED ABUNDANCES OF RED GIANTS IN THE GLOBULAR CLUSTER NGC 1851: C+N+O AND THE ORIGIN OF MULTIPLE POPULATIONS

We present chemical abundance analysis of a sample of 15 red giant branch (RGB) stars of the globular cluster NGC 1851 distributed along the two RGBs of the (v, v-y) color-magnitude diagram. We determined abundances for C+N+O, Na, alpha, iron-peak, and s-elements. We found that the two RGB populations significantly differ in their light (N, O, Na) and s-element content. On the other hand, they do not show any significant difference in their alpha and iron-peak element content. More importantly, the two RGB populations do not show any significant difference in their total C+N+O content. Our results do not support previous hypotheses suggesting that the origins of the two RGBs and the two subgiant branches of the cluster are related to different content of either alpha (including Ca) or iron-peak elements, or C+N+O abundance, due to a second generation polluted by Type II supernovae.