在太阳金属丰度下利用恒星年龄约束r-和s-过程的延迟时间分布
Constraining the Delay Time Distribution of the r- and s-Process from Stellar Ages at Solar Metallicity
- Max-Planck Institute for Astronomy（马克斯·普朗克天文学研究所）
- National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文提出利用太阳金属丰度下恒星年龄直接约束r-和s-过程延迟时间分布的新方法，发现约60%的Eu和Ba来自强延迟过程，且延迟产生率随延迟时间上升，暗示存在NS-NS并合之外的延迟中子俘获来源。
AI中文摘要：
我们提出了一种约束控制r-和s-过程元素产生的延迟时间分布（DTD）的新方法。我们不是使用金属丰度作为时间的代理，而是直接在太阳金属丰度下利用恒星年龄，此时化学平衡模型最为适用。我们分析了两组互补的样本：来自LAMOST的超过10,000颗太阳金属丰度的红团簇（RC）薄盘恒星，以及具有高精度丰度的太阳孪生星；两者都具有确定良好的恒星年龄τ。我们分别对每个样本中[Eu/Mg](τ)和[Ba/Mg](τ)的演化拟合具有幂律DTD的化学平衡模型，将铕视为典型的r-过程元素，钡视为s-过程元素，每种元素都以镁为参照，镁是一种近瞬时产生、主要由核塌缩超新星（CCSNe）贡献的元素。为验证该方法，我们首先将其应用于[Fe/Mg](τ)，并恢复出约70%的铁来自一个延迟通道，其DTD递减，∝t^{-1.2}，这与热核超新星中铁产生的公认结果一致。该方法还表明，今天形成的约60%的Eu和Ba起源于强延迟过程，并且推断出的Eu和Ba的延迟产生率随延迟时间增加而上升，这与热核超新星的情况相反。这些结果为r-和s-过程增丰提供了直接的时间约束，补充了基于金属丰度的化学演化研究。由于我们模拟了以Mg为参照的丰度，并且在不同引导中心半径的恒星中恢复了相同的趋势，这似乎不受径向迁移和随银心半径变化的化学演化的影响。如果得到证实，这表明存在中子星-中子星（NS-NS）并合之外的延迟中子俘获产生机制。
英文摘要：
We present a new approach to constraining the delay time distribution (DTD) governing r- and s-process element production. Rather than using metallicity as a proxy for time, we work directly with stellar ages at solar metallicity, where chemical equilibrium models are most applicable. We analyze two complementary samples: more than $10,000$ red clump (RC) thin disk stars at solar metallicity from LAMOST, and solar twins with high-precision abundances; both have well-determined stellar ages $τ$. We fit chemical-equilibrium models with power-law DTDs to the evolution of [Eu/Mg]$(τ)$ and [Ba/Mg]$(τ)$ in each sample, taking europium as a canonical r-process element and barium as an s-process element, each referenced to magnesium as a near-instantaneous, CCSNe-dominated element. To validate the method, we first apply it to [Fe/Mg]$(τ)$ and recover that $\approx\!70\%$ of Fe comes from a delayed channel with a declining DTD $\propto t^{-1.2}$, in agreement with well-established results for iron production in thermonuclear supernovae. It also shows that about $60\%$ of Eu and Ba forming today originate from strongly-delayed processes, and the inferred delayed-production rates of both Eu and Ba rise with delay time, opposite to that of thermonuclear supernovae. These results provide direct temporal constraints on r- and s-process enrichment, complementary to metallicity-based chemical-evolution studies. Because we model abundance referenced to Mg, and the same trend is recovered across stars of different guiding-center radii, this appears unaffected by radial migration and chemical evolution varying with Galactocentric radius. If confirmed, it points to delayed neutron-capture production beyond NS--NS mergers.
