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


About 1% of giant stars1 have anomalously high Li abundances (ALi) in their atmospheres, conflicting directly with the prediction of standard stellar evolution models2. This finding makes the production and evolution of Li in the Universe intriguing, not only in the sense of Big Bang nucleosynthesis3,4 or the interstellar medium5, but also for the evolution of stars. Decades of effort have been put into explaining why such extreme objects exist6,7,8, yet the origins of Li-rich giants are still being debated. Here, we report the discovery of the most Li-rich giant known to date, with a very high ALi 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 ALi 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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Fig. 1: Observed spectra and line profile fittings for TYC 429-2097-1.
Fig. 2: Distribution of Li-rich giants.
Fig. 3: Calculated surface abundances and mass fractions of 3He, 7Be and 7Li as functions of the processing time for the mass circulation.


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This research was supported by the National Key Basic Research Program of China (2014CB845700), National Key Research and Development Project of China (2016YFA0400502) and National Natural Science Foundation of China (under grant numbers 11390371, 11603037, 11473033, 11490560, 11505117, 11573032 and 11605097). The Guoshoujing Telescope (LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. This work is supported by the Astronomical Big Data Joint Research Center, co-founded by the National Astronomical Observatories, Chinese Academy of Sciences and Alibaba Cloud. This research uses data obtained through the Telescope Access Program. The authors acknowledge J. Wicker for proofreading the manuscript. We acknowledge the use of Gaia and WISE data, and of the VizieR catalogue access tool.

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H.-L.Y., J.-R.S. and G.Z. proposed and designed the study. H.-L.Y. and J.-R.S. led the data analysis, with contributions from Y.-T.Z., Q.G., J.-B.Z. and Z.-M.Z. Y.-S.C., E.-T.L., S.Z., Z.-H.L., B.G. and W.-P.L. performed the nuclear calculations. S.-L.B. and Y.-Q.W. calculated the evolutionary models and tracks. H.-N.L. carried out the observations. All authors discussed the results and contributed to the writing of the manuscript.

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Correspondence to Jian-Rong Shi.

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Yan, HL., Shi, JR., Zhou, YT. et al. The nature of the lithium enrichment in the most Li-rich giant star. Nat Astron 2, 790–795 (2018).

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