利用X-Shooter对贫金属恒星的详细丰度测定 II. —— 化学分解银晕、银盘和GSE
Detailed Abundance Determination of Metal-Poor Stars with X-Shooter II. - Chemically Disentangling the Halo, Disk and GSE
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中文总结 AI 辅助
研究结合X-Shooter观测与文献数据，将贫金属恒星按运动学分类后，发现顺行银盘与银晕的[Sc/Mg]趋势差异显著，还识别出一颗r-I星的特殊丰度特征。
中文摘要 AI 辅助
我们对7颗利用X-Shooter观测到的极贫金属（EMP）恒星候选体开展了详细的化学分析，并将其与第一篇论文（Paper I）中的16颗EMP恒星候选体结合。我们测定了16种元素的丰度，结果与已发表的成果吻合度极高。我们还利用文献中的高分辨率数据，将样本进一步扩展至315颗贫金属恒星。随后，我们通过运动学方法将全样本分为顺行银盘、逆行银盘、Gaia-Sausage Enceladus（GSE）和银晕四类。结合运动学与化学信息，我们发现顺行银盘的[Sc/Mg]随金属丰度增加呈现出显著的负线性趋势，斜率为每 dex -0.6 dex，这与银晕的趋势（每 dex -0.04 dex）形成鲜明对比，两者差异达到3.95σ的显著水平。在金属丰度范围-4.2 ≤ [Fe/H] ≤ -1.9内，顺行银盘的趋势由低金属丰度下的低[Mg/Fe]以及高金属丰度下的低[Sc/Fe]共同驱动，这可能源于顺行银盘前身星早期Mg富集程度较低，后续才发生Mg富集，或与后期气体吸积事件相关。不过，当前核合成模型尚未解释高金属丰度下Sc亏损的物理起源；在由不同银晕势推导的运动学分类中，该结果仍保持>3σ的显著性。此外，我们还识别出一颗r-I星，其Ti增强、Sc中度增强且C亏损（与演化状态无关），这些丰度特征表明其前身星可能是大质量喷流驱动的超超新星，但需测量Zn来验证这一结论。
英文摘要
We present a detailed chemical analysis of seven extremely metal-poor (EMP) star candidates observed with X-Shooter, combining them with 16 EMP candidates from Paper I. We measured abundances for 16 elements, showing excellent agreement with previously published results. The sample was further extended using high-resolution literature data for 315 metal-poor stars. The full sample was then kinematically separated into prograde disk, retrograde disk, Gaia-Sausage Enceladus (GSE) and halo classifications. Combining dynamics with chemistry, we demonstrate that the prograde disk exhibits a distinct negative linear trend in [Sc/Mg] with increasing metallicity, with a slope of -0.6 dex per dex. This contrasts with the halo trend at -0.04 dex per dex, a difference significant at the 3.95$σ$ level. Within the metallicity range -4.2 $\leq$ [Fe/H] $\leq$ -1.9, the prograde disk trend is driven by low [Mg/Fe] at lower metallicities, along with low [Sc/Fe] at higher metallicities. This could be due to reduced early Mg enrichment in the progenitor prograde disk, followed by subsequent Mg enrichment, possibly associated with a later gas accretion event. However, the physical origin of the higher-metallicity Sc depletion remains unexplained by current nucleosynthesis models. The result remains significant at the >3$σ$ level across kinematic classifications derived from a different Galactic potential. Additionally, we also identified an r-I star with enhanced Ti, moderately-enhanced Sc, and depleted in C (unrelated to its evolutionary state). These abundances suggest a massive jet-induced hypernova progenitor, though a measurement of Zn is needed to verify this.
