Distribution and Evolution of the Li Abundance in Red Clump Stars Can Be Explained by Internal Gravity Waves
Distribution and Evolution of the Li Abundance in Red Clump Stars Can Be Explained by Internal Gravity Waves
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DOI：
10.3847/1538-4357/acae9d
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发表时间：
2023-02
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影响因子：
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通讯作者：
Xuefei Li;Jianrong Shi;Yan Li;Hong-liang Yan;Jing-Hua Zhang
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作者：
Xuefei Li;Jianrong Shi;Yan Li;Hong-liang Yan;Jing-Hua Zhang
对红团簇（RC）星中Li现象的研究可以让我们更深入地了解恒星的结构和演化。查纳梅等人。当考虑到在 MS 恒星中观察到的前体质量分布和 MS 期间 Li 的消耗时，仅使用标准的后主序（MS）Li 演化模型自然地解释了 RC Li 丰度分布，因此既不需要额外的 Li 消耗也不需要额外的 Li 生成机制。尽管如此，考虑一些额外机制引起的混合效果还是很有趣的。通过构建不同的模型，我们发现内部重力波引起的混合可以解释观测到的具有低质量前身的RC星的Li丰度。为了解释这一点，我们依靠内部重力波引起的额外混合，这些内部重力波在红巨星分支（RGB）阶段在对流包络底部激发。在RGB阶段，引入内部重力波可以提高扩散系数，加强混合效果。 Li的有效富集发生在RGB阶段后期，要求H燃烧壳层的扩散系数达到∼108 cm2 s−1。我们的模型预测，在核心 He 燃烧阶段结束时，Li 丰度从 ∼1.5 dex 减少到 ∼0.0 dex，从而揭示了观测到的 ∼99% 的 Li 丰度分布。温盐混合调节 RGB 恒星的锂丰度，与内部重力波相结合可以解释大多数巨星的锂丰度。
The study of Li phenomena in red clump (RC) stars can give us a deeper understanding of the structure and evolution of stars. Chanamé et al. explained the RC Li abundance distributions naturally using only standard post-main-sequence (MS) Li evolution models when the distribution of progenitor masses and the depletion of Li during the MS observed in MS stars were considered, thus neither an extra Li depletion nor Li creation mechanism is required. Nevertheless, it is interesting to consider the effects of mixing caused by some extra mechanisms. By constructing different models, we find that the mixing caused by internal gravity waves can explain the observed Li abundances of RC stars with low-mass progenitors. To explain this, we rely on the extra mixing induced by internal gravity waves that are excited at the bottom of the convective envelope during the red giant branch (RGB) stage. During the RGB stage, introducing internal gravity waves can improve the diffusion coefficient and strengthen the mixing effect. The effective enrichment of Li occurs during the late RGB stage and requires the diffusion coefficient of the H-burning shell to reach ∼108 cm2 s−1. Our models predict that the Li abundance decreases from ∼1.5 to ∼0.0 dex at the end of the core He-burning stage, thereby revealing ∼99% of the observed Li abundance distribution. Thermohaline mixing regulates the Li abundance of RGB stars, which combined with internal gravity waves can explain the Li abundances of most giants.