期刊
ASTROPHYSICAL JOURNAL
卷 829, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.3847/0004-637X/829/2/127
关键词
planet-star interactions; stars: abundances; stars: chemically peculiar
资金
- CONICYT-PCHA Doctorado Nacional [2013-21130353]
- Chilean Ministry for the Economy, Development, and Tourism's Programa Iniciativa Cientifica Milenio [IC120009]
- Centro de Astronomia y Tecnologias Afines [PFB-06]
- Proyecto FONDECYT Regular [1130373]
- NASA [NNX15AF13G]
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 15 M-J 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) approximate to 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 A(Li) >= 1.5. 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 similar to 7 M-J 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.
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