The nature of the Li enrichment in the most Li-rich giant star

Subjects: Astronomy >> Star and Galactic System submitted time 2023-12-31

Hong-Liang Yan Jian-Rong Shi Yu-Tao Zhou Yong-Shou Chen Er-Tao Li Suyalatu Zhang Shao-Lan Bi Ya-Qian Wu Zhi-Hong Li Bing Guo Wei-Ping Liu Qi Gao Jun-Bo Zhang Ze-Ming Zhou Hai-Ning Li Gang Zhao

Abstract： About 1% of giants have anomalously high Li abundances in their atmospheres, conflicting directly with the prediction of the standard stellar evolution models. This finding makes the production and evolution of Li in the Universe intriguing, not only in the sense of Big Bang nucleosynthesis or the interstellar medium, but also for the evolution of stars. Decades of efforts have been put into explaining why such extreme objects exist, yet the origins of Lirich giants are still being debated. Here we report the discovery of the most Li-rich giant known to date, with a very high Li abundance of 4.51. This rare phenomenon was observed coincidentally with another short-term event: the star is experiencing its luminosity bump on the red giant branch. Such a high Li abundance indicates that the star might be at the very beginning of its Li-rich phase, which provides a great opportunity to investigate the origin and evolution of Li in the Galaxy. A detailed nuclear simulation is presented with up-to-date reaction rates to recreate the Li enrichment process in this star. Our results provide tight constraints on both observational and theoretical points of view, suggesting that low-mass giants can internally produce Li to a very high level through 7Be transportation during the red giant phase.

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