钡星的理论解释
Barium Stars: Theoretical Interpretation
摘要：
钡星是外生的渐近巨星分支（AGB）星。它们呈现出AGB星和后AGB星的s-增强特征，但处于较早的演化阶段（主序星矮星、次巨星、红巨星）。它们被认为是在双星系统中形成的，在双星系统中，一个质量更大的伴星演化得更快，在它的AGB阶段产生了s元素，通过恒星风污染了现在的钡星，成为一颗白矮星。这里分析了Allen & Barbuy（2006）和Smiljanic等人（2007）的钡星样本。在高分辨率和高S/N下获得两种样品的光谱。我们将这些观察结果与使用不同初始质量和13 C口袋效率分布的AGB核合成模型进行了比较。一旦找到整个元素丰度分布的一致解决方案，就应用适当的稀释因子。这种稀释的解释是，从AGB转移到现在观察到的恒星的富S物质与吸积体的信封混合。我们还分析了质量转移过程，得到了已知轨道周期的巨星和亚巨星的风速。我们发现的证据表明，温盐混合作用的内部主序星矮星，我们提出了一种方法来估计其深度。
英文摘要：
Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth.
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