Detailed abundances of Red Giants in the Globular Cluster NGC~1851: C+N+O and the Origin of Multiple Populations

TL;DR

This study analyzes the chemical compositions of red giant stars in NGC 1851, revealing differences in light and s-elements between populations but no significant difference in total C+N+O or alpha/iron-peak elements, challenging previous pollution hypotheses.

Contribution

It provides detailed chemical abundance measurements of two RGB populations, showing that their differences are not due to total C+N+O or alpha/iron-peak element variations, refining understanding of multiple populations.

Findings

Two RGB populations differ in N, O, Na, and s-elements.

No significant difference in total C+N+O content.

Results challenge previous pollution-based formation scenarios.

Abstract

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) CMD. 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 origin of the two RGBs and the two subgiant branches of the cluster is related to a different content of either $\alpha$ (including Ca) or iron-peak elements, or C+N+O abundance, due to a second generation polluted by SNeII.