利用Th II 5989埃谱线研究中度贫金属恒星中的r-过程多样性
Investigating r-Process Diversity in Mildly Metal-Poor Stars Using the Th II 5989 Angstrom Line
查看机构详情
- Graduate School of Science, University of Hyogo（兵库县立大学理学研究科）
- Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo（兵库县立大学天文学中心西はりま天文台）
机构由 AI 辅助整理，请以论文原文为准。
浏览论文内容
中文总结 AI 辅助
本研究利用Th II 5989埃谱线对中度贫金属恒星进行系统丰度分析，在42颗样本中探测到32颗的Th，发现[Th/Eu]比值总体恒定但离散度随金属丰度增加，揭示了r-过程产出的均匀化与多样性来源。
中文摘要 AI 辅助
最重元素的起源仍然是一个基本谜团，其中“锕系元素增强”（钍元素过丰度）是r-过程核合成条件的关键诊断指标。虽然这种多样性在极贫金属（EMP）恒星中已有充分记录，但在中度贫金属（MMP）区域（-2.0 < [Fe/H] < -0.5）中，由于常用4019埃谱线的混合问题，其出现频率受到的约束很少。我们利用相对无混合的Th II 5989埃谱线，对中度贫金属恒星进行了系统的丰度分析。使用群马天文台1.5米望远镜配备的GAOES获取了高色散光谱，并通过SMOKA检索了斯巴鲁望远镜/HDS的档案数据作为补充。我们在42颗样本恒星中的32颗中成功探测到了Th。我们的分析表明，5989埃谱线是测量冷红巨星中Th丰度的有效诊断工具。平均[Th/Eu]比值在MMP金属丰度范围内几乎保持恒定，这表明银河化学演化过程中星际介质的逐步均匀化会减少从单个r-过程事件继承的丰度变化，或者主导的r-过程事件可能具有相似的初始Th/Eu产生比值。虽然[Th/Eu]比值在MMP区域内总体几乎恒定，但其离散度似乎向该区域的金属丰度较高端增加，并在接近太阳金属丰度时达到约1 dex。这种行为可能反映了前身天体初始Th/Eu产生比值的变化、r-过程产物在星际介质中的混合以及Th在恒星寿命期间的放射性衰变的综合效应。
英文摘要
The origin of the heaviest elements remains a fundamental mystery, with the "actinide-boost" (Thorium overabundance) serving as a critical diagnostic of r-process nucleosynthesis conditions. While this diversity is well documented in extremely metal-poor (EMP) stars, its frequency in the mildly metal-poor (MMP) regime ($-2.0 < $ [Fe/H] $< -0.5$) is poorly constrained due to blending issues in the commonly used 4019 angstrom line. We present a systematic abundance analysis of mildly metal-poor stars, exploiting the relatively unblended Th II 5989 angstrom line. High-dispersion spectra were obtained using the 1.5 m telescope at Gunma Astronomical Observatory with GAOES, complemented by archival data from the Subaru Telescope/HDS retrieved via SMOKA. We successfully detected Th in 32 out of 42 sample stars. Our analysis demonstrates that the 5989 angstrom line is a useful diagnostic for Th abundance measurements in cool red giants. The mean [Th/Eu] ratio remains nearly constant over the MMP metallicity range, suggesting that progressive homogenization of the interstellar medium during Galactic chemical evolution would reduce abundance variations inherited from individual r-process events, or the dominant r-process events may share similar initial Th/Eu production ratios. While the [Th/Eu] ratio is nearly constant overall in the MMP regime, its dispersion appears to increase toward the metal-rich end of this regime and reaches approximately 1 dex near solar metallicity. This behavior may reflect the combined effects of variations in the initial Th/Eu production ratios of the progenitor objects, the mixing of r-process products in the interstellar medium, and the radioactive decay of Th over stellar lifetimes.
