[论文解读] Analysis of 26 Barium Stars II. Contributions of s-, r- and p-processes in the production of heavy elements

D. M. Allen, B. Barbuy|ArXiv.org|Apr 4, 2006

Nuclear physics research studies参考文献 54被引用 23

一句话总结

本研究利用光谱数据分析了26颗钡星，量化了s-、r-和p-过程对重元素生成的贡献。通过将中子捕获截面乘以丰度（σN）曲线拟合到理论模型，发现钡星中s-过程主成分与太阳同位素组成非常接近，中子暴露量（τ₀）范围为0.2至0.8，支持双星演化中来自AGB伴星的质量转移模型。

ABSTRACT

Barium stars show enhanced abundances of the slow neutron capture (s-process) heavy elements, and for this reason they are suitable objects for the study of s-process elements. The aim of this work is to quantify the contributions of the s-, r- and p-processes for the total abundance of heavy elements from abundances derived for a sample of 26 barium stars. The abundance ratios between these processes and neutron exposures were studied. The abundances of the sample stars were compared to those of normal stars thus identifying the fraction relative to the s-process main component. The fittings of the sigmaN curves (neutron capture cross section times abundance, plotted against atomic mass number) for the sample stars suggest that the material from the companion asymptotic giant branch star had approximately the solar isotopic composition as concerns fractions of abundances relative to the s-process main component. The abundance ratios of heavy elements, hs, ls and s and the computed neutron exposure are similar to those of post-AGB stars. For some sample stars, an exponential neutron exposure fits well the observed data, whereas for others, a single neutron exposure provides a better fit. The comparison between barium and AGB stars supports the hypothesis of binarity for the barium star formation. Abundances of r-elements that are part of the s-process path in barium stars are usually higher than those in normal stars,and for this reason, barium stars seemed to be also enriched in r-elements, although in a lower degree than s-elements. No dependence on luminosity classes was found in the abundance ratios behaviour among the dwarfs and giants of the sample barium stars.

研究动机与目标

• 量化s-、r-和p-过程对钡星中重元素丰度的相对贡献。
• 通过σN曲线拟合，确定从AGB伴星转移的物质同位素组成是否与太阳系混合物一致。
• 评估s-过程中中子暴露量（τ₀），并与后AGB星进行比较，以验证双星演化模型。
• 研究光度分类（矮星与巨星）是否影响钡星中的丰度比。
• 评估s-过程丰度模式与理论预测以及正常星和AGB星观测数据的一致性。

提出的方法

• 利用ESO和LNA的数据，对26颗钡星进行光谱丰度分析，大气参数通过迭代方法获得。
• 将观测到的重元素丰度与正常星中的丰度进行比较，以分离出s-过程主成分的贡献。
• 将观测到的σN曲线（中子捕获截面×丰度与原子质量数的关系）拟合到具有不同中子暴露量（τ₀）的理论模型。
• 以太阳同位素组合作为参考，估算每种元素中s-过程主成分的贡献比例。
• 基于对观测数据的拟合优度，评估两种中子暴露模型：单次暴露模型与指数暴露模型。
• 计算丰度比值 [s/Fe]、[ls/Fe]、[hs/Fe]、[hs/ls] 和 τ₀，以评估核合成过程及金属丰度趋势。

实验结果

研究问题

• RQ1 s-、r-和p-过程对钡星中重元素丰度的相对贡献是什么？
• RQ2 从AGB伴星转移的s-过程物质的同位素组成是否与太阳系混合物一致？
• RQ3 钡星中s-过程的中子暴露量（τ₀）范围和行为如何？其随金属丰度的变化趋势如何？
• RQ4 钡星中的丰度比是否与s-过程核合成的理论预测一致？
• RQ5 样本中丰度比是否依赖于光度分类（矮星与巨星）？

主要发现

• 通过σN曲线拟合证实，钡星中s-过程主成分与太阳同位素组成非常接近。
• 中子暴露量τ₀范围为0.2至0.8，部分恒星的拟合效果在单次暴露模型下更优，另一些则在指数暴露模型下更优。
• [hs/ls] 与 τ₀ 的关系呈线性增加，与理论预测一致，且分散度低于理论曲线。
• 在金属丰度范围内，丰度比值 [s/Fe]、[ls/Fe] 和 [hs/Fe] 分别在0.45至1.6、0.4至1.6和0.7至1.75之间变化。
• 未发现丰度比值与光度分类（矮星与巨星）之间存在显著依赖关系，表明在不同演化阶段中保持一致。
• r-元素如Eu、Sm、Gd和Dy在钡星中有所富集，但程度低于s-元素，原因在于它们在s-过程链中可被包含至A ≈ 209。