期刊
ASTRONOMICAL JOURNAL
卷 162, 期 4, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.3847/1538-3881/ac0ce6
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资金
- National Research Foundation of Korea [2017R1A2B3002919]
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) [138713538-SFB 881]
- Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education [2018R1D1A1A02085433, 2020R1I1A1A01052358]
- National Research Foundation of Korea [2020R1I1A1A01052358, 2018R1D1A1A02085433] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
Low-resolution spectroscopy was conducted on red giant branch stars in the globular cluster NGC 2808, identifying four subpopulations and proposing a new method for analyzing abundance differences. High-resolution spectroscopy helped better separate the subpopulations and revealed chemical distinctions among them in this study.
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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