Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample
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arXiv
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| Natura: | Preprint |
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2025
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| author | Xie, Renjing Li, Haining Zhang, Ruizhi Wu, Yin Xue, Xiang-Xiang Zhao, Gang Zhang, Shi-Lin Xie, Xiao-Jin |
| author_facet | Xie, Renjing Li, Haining Zhang, Ruizhi Wu, Yin Xue, Xiang-Xiang Zhao, Gang Zhang, Shi-Lin Xie, Xiao-Jin |
| contents | The main-sequence turnoff (MSTO) stars well preserve the chemical properties where they were born, making them ideal tracers for studying the stellar population. We perform a detailed chemo-dynamical analysis on moderately metal-poor ($-2.0<\mathrm{[Fe/H]}<-1.0$) MSTO stars to explore the early accretion history of the Milky Way. Our sample includes four stars observed with high-resolution spectroscopy using CFHT/ESPaDOnS and 163 nearby MSTO stars selected from the SAGA database with high-resolution results. Within the action-angle spaces, we identified Gaia-Sausage-Enceladus (GSE, 35), stars born in the Milky Way (in situ, 31), and other substructures (21). We find that both GSE and in-situ stars present a similar Li plateau around $A(\mathrm{Li)}\sim 2.17$. GSE shows a clear $α$-knee feature in Mg at $\mathrm{[Fe/H]}\sim-1.60\pm 0.06$, while the $α$-elements of in-situ stars remain nearly constant within the metallicity range. The iron-peak elements show little difference between GSE and in-situ stars except for Zn and Ni, which decrease in GSE at $\mathrm{[Fe/H]}>-1.6$, while they remain constant in in-situ stars. Among heavy elements, GSE shows overall enhancement in Eu, with [Ba/Eu] increasing with the metallicity, while this ratio remains almost constant for in-situ stars, suggesting the contribution of longer time-scale sources to the $s$-process in GSE. Moreover, for the first time, we present the $r$-process abundance pattern for an extremely $r$-process enhanced ($r$-II) GSE star, which appears consistent with the solar $r$-process pattern except for Pr. Further investigation of larger GSE samples using high-resolution spectra is required to explore the reason for the significantly higher Pr in the GSE r-II star. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_07758 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample Xie, Renjing Li, Haining Zhang, Ruizhi Wu, Yin Xue, Xiang-Xiang Zhao, Gang Zhang, Shi-Lin Xie, Xiao-Jin Astrophysics of Galaxies Solar and Stellar Astrophysics The main-sequence turnoff (MSTO) stars well preserve the chemical properties where they were born, making them ideal tracers for studying the stellar population. We perform a detailed chemo-dynamical analysis on moderately metal-poor ($-2.0<\mathrm{[Fe/H]}<-1.0$) MSTO stars to explore the early accretion history of the Milky Way. Our sample includes four stars observed with high-resolution spectroscopy using CFHT/ESPaDOnS and 163 nearby MSTO stars selected from the SAGA database with high-resolution results. Within the action-angle spaces, we identified Gaia-Sausage-Enceladus (GSE, 35), stars born in the Milky Way (in situ, 31), and other substructures (21). We find that both GSE and in-situ stars present a similar Li plateau around $A(\mathrm{Li)}\sim 2.17$. GSE shows a clear $α$-knee feature in Mg at $\mathrm{[Fe/H]}\sim-1.60\pm 0.06$, while the $α$-elements of in-situ stars remain nearly constant within the metallicity range. The iron-peak elements show little difference between GSE and in-situ stars except for Zn and Ni, which decrease in GSE at $\mathrm{[Fe/H]}>-1.6$, while they remain constant in in-situ stars. Among heavy elements, GSE shows overall enhancement in Eu, with [Ba/Eu] increasing with the metallicity, while this ratio remains almost constant for in-situ stars, suggesting the contribution of longer time-scale sources to the $s$-process in GSE. Moreover, for the first time, we present the $r$-process abundance pattern for an extremely $r$-process enhanced ($r$-II) GSE star, which appears consistent with the solar $r$-process pattern except for Pr. Further investigation of larger GSE samples using high-resolution spectra is required to explore the reason for the significantly higher Pr in the GSE r-II star. |
| title | Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2506.07758 |