A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra
Very metal-poor (VMP) stars provide a record of the chemical composition and dynamics of the early Galaxy. Based on the high-resolution and high signal-to-noise ratio spectra from the Subaru Telescope for 103 VMP stars, in this series of papers we homogeneously investigate the nonlocal thermodynamic...
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2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/adc127 |
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| author | Jianrong Shi Gang Zhao Shuai Liu Zeming Zhou Haining Li Hongliang Yan Sofya Alexeeva Huawei Zhang Wako Aoki Tadafumi Matsuno Jingkun Zhao Huiling Chen Yufu Shen |
| author_facet | Jianrong Shi Gang Zhao Shuai Liu Zeming Zhou Haining Li Hongliang Yan Sofya Alexeeva Huawei Zhang Wako Aoki Tadafumi Matsuno Jingkun Zhao Huiling Chen Yufu Shen |
| author_sort | Jianrong Shi |
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| description | Very metal-poor (VMP) stars provide a record of the chemical composition and dynamics of the early Galaxy. Based on the high-resolution and high signal-to-noise ratio spectra from the Subaru Telescope for 103 VMP stars, in this series of papers we homogeneously investigate the nonlocal thermodynamic equilibrium (NLTE) abundances of important astrophysical elements. This sample covers a wide metallicity range from [Fe/H] ∼ −1.7 dex down to −4.3 dex, including 13 objects with [Fe/H] ≤ −3.0 dex. Here, we present a set of homogeneous stellar atmospheric parameters, including the effective temperature, surface gravity, metallicity, and microturbulence velocity with the spectroscopic method, and the NLTE line formation for both Fe i and Fe ii in the classical one-dimensional model atmospheres have been considered. The NLTE effects of the Fe i lines range from ∼0.03 dex to ∼0.3 dex, and increase with decreasing metallicity. In addition, they depend on the surface gravity, which generally increases with decreasing ${\mathrm{log}}\,g$ . The largest NLTE effects can be found for the giants of ${\mathrm{log}}\,g$ ∼ 2.5 dex. For dwarfs and subgiants, our final effective temperatures are consistent with those derived from the T _IRFM scales of A. Alonso et al. with a mean difference of 7.1 ± 100.2 K, while for giants, our results are slightly lower than those from the T _IRFM scales of A. Alonso et al. with a mean difference of −69.5 ± 94.1 K. For dwarfs and subgiants, the spectroscopically derived surface gravity is consistent with that estimated based on the Gaia DR3 parallax; however, for giants, the former leads to a 0.2 dex lower surface gravity. |
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| institution | OA Journals |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-3f2bec6ad4e24fa2991fa5bc14dd39972025-08-20T02:26:59ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01983212710.3847/1538-4357/adc127A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution SpectraJianrong Shi0https://orcid.org/0000-0002-0349-7839Gang Zhao1https://orcid.org/0000-0002-8980-945XShuai Liu2https://orcid.org/0000-0001-5193-1727Zeming Zhou3https://orcid.org/0000-0002-1619-1660Haining Li4https://orcid.org/0000-0002-0389-9264Hongliang Yan5https://orcid.org/0000-0002-8609-3599Sofya Alexeeva6https://orcid.org/0000-0002-8709-4665Huawei Zhang7https://orcid.org/0000-0002-7727-1699Wako Aoki8https://orcid.org/0000-0002-8975-6829Tadafumi Matsuno9Jingkun Zhao10Huiling Chen11Yufu Shen12National Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cn; School of Astronomy and Space Science, University of Chinese Academy of Sciences , Beijing 100049, People’s Republic of China; School of Physics and Technology, Nantong University , Nantong 226019, People’s Republic of ChinaNational Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cn; School of Astronomy and Space Science, University of Chinese Academy of Sciences , Beijing 100049, People’s Republic of ChinaNational Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cnDepartment of Astronomy, Beijing Normal University , Beijing 100875, People’s Republic of ChinaNational Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cnNational Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cn; School of Astronomy and Space Science, University of Chinese Academy of Sciences , Beijing 100049, People’s Republic of ChinaNational Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cnDepartment of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of China; Kavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of ChinaNational Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Department of Astronomical Science, School of Physical Sciences, The Graduate University of Advanced Studies (SOKENDAI) 2-21-1 Osawa , Mitaka, Tokyo 181-8588, JapanAstronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg , Mönchhofstraße 12-14, 69120 Heidelberg, GermanyNational Astronomical Observatories , Chinese Academy of Sciences A20 Datun Road, Chaoyang, Beijing 100101, People’s Republic of China ; sjr@nao.cas.cn, gzhao@nao.cas.cn, hlyan@nao.cas.cnDepartment of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of China; Kavli Institute of Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of ChinaChangchun Observatory , National Astronomical Observatories, Chinese Academy of Sciences, Jingyuetan National Scenic Area, Changchun 130117, People’s Republic of ChinaVery metal-poor (VMP) stars provide a record of the chemical composition and dynamics of the early Galaxy. Based on the high-resolution and high signal-to-noise ratio spectra from the Subaru Telescope for 103 VMP stars, in this series of papers we homogeneously investigate the nonlocal thermodynamic equilibrium (NLTE) abundances of important astrophysical elements. This sample covers a wide metallicity range from [Fe/H] ∼ −1.7 dex down to −4.3 dex, including 13 objects with [Fe/H] ≤ −3.0 dex. Here, we present a set of homogeneous stellar atmospheric parameters, including the effective temperature, surface gravity, metallicity, and microturbulence velocity with the spectroscopic method, and the NLTE line formation for both Fe i and Fe ii in the classical one-dimensional model atmospheres have been considered. The NLTE effects of the Fe i lines range from ∼0.03 dex to ∼0.3 dex, and increase with decreasing metallicity. In addition, they depend on the surface gravity, which generally increases with decreasing ${\mathrm{log}}\,g$ . The largest NLTE effects can be found for the giants of ${\mathrm{log}}\,g$ ∼ 2.5 dex. For dwarfs and subgiants, our final effective temperatures are consistent with those derived from the T _IRFM scales of A. Alonso et al. with a mean difference of 7.1 ± 100.2 K, while for giants, our results are slightly lower than those from the T _IRFM scales of A. Alonso et al. with a mean difference of −69.5 ± 94.1 K. For dwarfs and subgiants, the spectroscopically derived surface gravity is consistent with that estimated based on the Gaia DR3 parallax; however, for giants, the former leads to a 0.2 dex lower surface gravity.https://doi.org/10.3847/1538-4357/adc127Stellar abundancesChemical abundances |
| spellingShingle | Jianrong Shi Gang Zhao Shuai Liu Zeming Zhou Haining Li Hongliang Yan Sofya Alexeeva Huawei Zhang Wako Aoki Tadafumi Matsuno Jingkun Zhao Huiling Chen Yufu Shen A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra The Astrophysical Journal Stellar abundances Chemical abundances |
| title | A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra |
| title_full | A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra |
| title_fullStr | A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra |
| title_full_unstemmed | A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra |
| title_short | A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. I. Global Stellar Parameters Based on High-resolution Spectra |
| title_sort | systematic nlte study of very metal poor stars with metallicity down to 4 3 dex i global stellar parameters based on high resolution spectra |
| topic | Stellar abundances Chemical abundances |
| url | https://doi.org/10.3847/1538-4357/adc127 |
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