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Tidal Interactions between Binary Stars Can Drive Lithium Production in Low-mass Red Giants

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Angelou,  George C.
Max Planck Research Group in Stellar Ages and Galactic Evolution (SAGE), Max Planck Institute for Solar System Research, Max Planck Society;

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Hekker,  Saskia
Max Planck Research Group in Stellar Ages and Galactic Evolution (SAGE), Max Planck Institute for Solar System Research, Max Planck Society;

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Citation

Casey, A. R., Ho, A. Y. Q., Ness, M., Hogg, D. W., Rix, H.-W., Angelou, G. C., et al. (2019). Tidal Interactions between Binary Stars Can Drive Lithium Production in Low-mass Red Giants. The Astrophysical Journal, 880(2): 125. doi:10.3847/1538-4357/ab27bf.


Cite as: http://hdl.handle.net/21.11116/0000-0005-EF5B-9
Abstract
Theoretical models of stellar evolution predict that most of the lithium inside a star is destroyed as the star becomes a red giant. However, observations reveal that about 1% of red giants are peculiarly rich in lithium, often exceeding the amount in the interstellar medium or predicted from the big bang. With only about 150 lithium-rich giants discovered in the past four decades, and no distinguishing properties other than lithium enhancement, the origin of lithium-rich giant stars is one of the oldest problems in stellar astrophysics. Here we report the discovery of 2330 low-mass (1-3M(Theta)) lithium-rich giant stars, which we argue are consistent with internal lithium production that is driven by tidal spin-up by a binary companion. Our sample reveals that most lithium-rich giants have helium-burning cores (80(-6)(+7)%), and that the frequency of lithium-rich giants rises with increasing stellar metallicity. We find that while planet accretion may explain some lithium-rich giants, it cannot account for the majority that have helium-burning cores. We rule out most other proposed explanations for the origin of lithium-rich giants. Our analysis shows that giants remain lithium-rich for only about two million years. A prediction from this lithium depletion timescale is that most lithium-rich giants with a helium-burning core have a binary companion.