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

Andrew R. Casey, Anna Y.Q. Ho, Melissa Ness, David W. Hogg, Hans Walter Rix, George C. Angelou, Saskia Hekker, Christopher A. Tout, John C. Lattanzio, Amanda I. Karakas, Tyrone E. Woods, Adrian M. Price-Whelan, Kevin C. Schlaufman

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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 (1-3 M o) 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 (), 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.

Original languageEnglish
Article number125
Number of pages11
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 1 Aug 2019


  • binaries: general
  • stars: abundances
  • stars: low-mass

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