Search for Extremely Metal-poor Stars with Gemini-N/Graces. I. Chemical-abundance Analysis
Abstract
We present stellar parameters and abundances of 13 elements for 18 very metal-poor (VMP; [Fe/H] < –2.0) stars, selected as extremely metal-poor (EMP; [Fe/H] < –3.0) candidates from the Sloan Digital Sky Survey and Large sky Area Multi-Object Fiber Spectroscopic Telescope survey. High-resolution spectroscopic observations were performed using GEMINI-N/GRACES. We find 10 EMP stars among our candidates, and we newly identify three carbon-enhanced metal-poor stars with [Ba/Fe] < 0. Although chemical abundances of our VMP/EMP stars generally follow the overall trend of other Galactic halo stars, there are a few exceptions. One Na-rich star ([Na/Fe] = +1.14) with low [Mg/Fe] suggests a possible chemical connection with second-generation stars in a globular cluster. The progenitor of an extremely Na-poor star ([Na/Fe] = –1.02) with high K- and Ni-abundance ratios may have undergone a distinct nucleosynthesis episode, associated with core-collapse supernovae (SNe) having a high explosion energy. We have also found a Mg-rich star ([Mg/Fe] = +0.73) with slightly enhanced Na and extremely low [Ba/Fe], indicating that its origin is not associated with neutron-capture events. On the other hand, the origin of the lowest Mg abundance ([Mg/Fe] = –0.61) star could be explained by accretion from a dwarf galaxy, or formation in a gas cloud largely polluted by SNe Ia. We have also explored the progenitor masses of our EMP stars by comparing their chemical-abundance patterns with those predicted by Population III SNe models, and find a mass range of 10–26 M ⊙, suggesting that such stars were primarily responsible for the chemical enrichment of the early Milky Way.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2023
- DOI:
- 10.3847/1538-4357/acc58a
- arXiv:
- arXiv:2301.06236
- Bibcode:
- 2023ApJ...948...38J
- Keywords:
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- Chemical abundances;
- Galaxy chemical evolution;
- Milky Way Galaxy;
- Interstellar abundances;
- Galaxy stellar content;
- 224;
- 580;
- 1054;
- 832;
- 621;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 29 pages, 11 figures, 8 tables, submitted to ApJ