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arXiv · 2106.12583

New sub-grouping of multiple stellar populations in NGC 2808 based on low-resolution spectroscopy

Seungsoo Hong·Dongwook Lim·Chul Chung·Jaeyeon Kim·Sang-Il Han·Young-Wook Lee
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Abstract

We performed low-resolution spectroscopy for the red giant branch stars in an intriguing globular cluster (GC) NGC 2808, which hosts subpopulations with extreme helium and light-element abundances. In order to trace N, C, and Ca abundance differences among subpopulations, we measured CN, CH, and Ca II H&K spectral indices, respectively. We identified four subpopulations (G1, G2, G3, and G4) from CN and CH strength, with CN-weak/CH-strong G1, CN-intermediate/CH-strong G2, CN-strong/CH-intermediate G3, and CN-strong/CH-weak G4. Compared to [Na/O] from high-resolution spectroscopy, we show that CN index can more clearly separate G1 and G2. Since CN traces N abundance in a GC, it implies that G1 and G2 would show a larger difference in [N/Fe] compared to [Na/Fe], as predicted by chemical evolution models. Later generation stars G3 and G4, however, are better separated with high-resolution spectroscopy. We also found that G4 shows a stronger Ca II H&K line strength compared to that of G1, but we suspect this to be a result of unusually strong He enhancement and/or Mg depletion in G4 of this GC. This work illustrates that combining low- and high-resolution spectroscopic studies can improve the separation of subpopulations in GCs.

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Seungsoo Hong, Dongwook Lim, Chul Chung, Jaeyeon Kim, Sang-Il Han, Young-Wook Lee. 2021-06-23. New sub-grouping of multiple stellar populations in NGC 2808 based on low-resolution spectroscopy. https://doi.org/10.3847/1538-3881/ac0ce6

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