2016/05/31 by Claudia Aguilera-Gómez, Julio Chanamé, Marc Pinsonneault +3
Physics and Astronomy · Social Sciences · #Accretion (finance) #Astronomy and Astrophysical Research #Brown dwarf #Educational Leadership and Practices #Giant planet #Planet #Planetary mass #Planetary system #Stars #Stellar evolution #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.3847/0004-637x/829/2/127
Accepted for publication, ApJ. 25 pages, 13 figures
openalex created_date 2016/06/24 · arxiv created 2016/07/20 · openalex publication_date 2016/09/29 · arxiv updated 2016/10/05 · openalex updated_date 2026/08/05
ABSTRACT A small fraction of red giants are known to be lithium (Li) rich, in contradiction with expectations from stellar evolutionary theory. A possible explanation for these atypical giants is the engulfment of an Li-rich planet or brown dwarf by the star. In this work, we model the evolution of Li abundance in canonical red giants including the accretion of a substellar mass companion. We consider a wide range of stellar and companion masses, Li abundances, stellar metallicities, and planetary orbital periods. Based on our calculations, companions with masses lower than dissolve in the convective envelope and can induce Li enrichment in regimes where extra mixing does not operate. Our models indicate that the accretion of a substellar companion can explain abundances up to A(Li) ≈ 2.2, setting an upper limit for Li-rich giants formed by this mechanism. Giants with higher abundances need another mechanism to be explained. For reasonable planetary distributions, we predict the Li abundance distribution of low-mass giants undergoing planet engulfment, finding that between 1% and 3% of them should have . We show that depending on the stellar mass range, this traditional definition of Li-rich giants is misleading, as isolated massive stars would be considered anomalous while giants engulfing a companion would be set aside, flagged as normal. We explore the detectability of companion engulfment, finding that planets with masses higher than produce a distinct signature, and that descendants of stars originating in the Li dip and low-luminosity red giants are ideal tests of this channel.