| Non－LTE Analysis of the Sodium Abundance of Metal－Poor Stars in the Galactic Disk and Halo |
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| 作者单位： | Yoichi Takeda(Komazawa University, Komazawa, Setagaya, Tokyo 154-8525, Japan;);Gang Zhao,Yu-Qin Chen(National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012);Masahide Takada-Hidai(Liberal Arts Education Center, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan);Yu-ji Saito(Department of Physics, Faculty of Science, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan);Hua-Wei Zhang(Department of Astronomy, School of Physics, Peking University, Beijing 100871;CAS-Peking University Joint Beijing Astrophysical Center, Beijing 100871) |
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| 基金项目： | 国家自然科学基金，the framework of the China-Japan collaboration project，the Japan Society for the Promotion of Science(JSPS) |
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| 摘 要： | We performed an extensive non-LTE analysis of the neutral sodiumlines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo starsof types F-K covering a wide metallicity range (-4 Fe/H] +0.4), using ourown data as well as data collected from the literature. For comparatively metal-rich disk stars (-1 Fe/H] +0.4) where the weaker 6154/6161 lines are thebest abundance indicators, we confirmed Na/Fe] ～ 0 with an "upturn" (i.e., ashallow/broad dip around -0.5 Fe/H] 0) as already reported in previousstudies. For the metal-deficient halo stars, where the much stronger 5890/5896 or8183/8195 lines subject to considerable (negative) non-LTE corrections amountingto 0.5 dex have to be used, our analysis suggests mildly "subsolar" Na/Fe] valuesdown to ～ -0.4 (with a somewhat large scatter of ～±0.2 dex) on the average at thetypical halo metallicity of Fe/H] ～ -2, followed by a rise again to a near-solar ratioof Na/Fe] ～ 0 at the very metal-poor regime Fe/H] ～ -3 to -4. These resultsare discussed in comparison with the previous observational studies along with thetheoretical predictions from the available chemical evolution models.
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| 关 键 词： | 辐射变换 演化 金属星 非LTE分析 银河系 晕圈 |
Non-LTE Analysis of the Sodium Abundance of Metal-Poor Stars in the Galactic Disk and Halo |
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| Authors: | Yoichi Takeda Gang Zhao Masahide Takada-Hidai Yu-Qin Chen Yu-ji Saito Hua-Wei Zhang |
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| Abstract: | |
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| Keywords: | Galaxy: evolution - radiative transfer - stars: abundances -stars: atmospheres- stars: late-type |
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