Lithium Enrichment Signatures of Planetary Engulfment Events in Evolved Stars

Planetary engulfment events have long been proposed as a lithium (Li) enrichment mechanism contributing to the population of Li-rich giants (A(Li) >= 1.5 dex). Using MESA stellar models and A(Li) abundance measurements obtained by the GALAH survey, we calculate the strength and observability of the surface Li enrichment signature produced by the engulfment of a hot Jupiter (HJ). We consider solar-metallicity stars in the mass range of 1-2 M (circle dot) and the Li supplied by a HJ of 1.0 M (J). We explore engulfment events that occur near the main-sequence turn-off (MSTO) and out to orbital separations of R similar to 0.1 au = 22 R (circle dot). We map our results onto the Hertzsprung-Russell Diagram, revealing the statistical significance and survival time of Li enrichment. We identify the parameter space of masses and evolutionary phases where the engulfment of a HJ can lead to Li enrichment signatures at a 5 sigma confidence level and with meteoritic abundance strengths. The most compelling strengths and survival times of engulfment-derived Li enrichment are found among host stars of 1.4 M (circle dot) near the MSTO. Our calculations indicate that planetary engulfment is not a viable enrichment pathway for stars that have evolved beyond the subgiant branch. For these sources, observed Li enhancements are likely to be produced by other mechanisms, such as the Cameron-Fowler process or the accretion of material from an asymptotic giant branch companion. Our results do not account for second-order effects, such as extra mixing processes, which can further dilute Li enrichment signatures.

Automated summary

This study investigates the impact of hot Jupiter engulfment on surface Li enrichment using MESA stellar models and GALAH abundance measurements. The results show that engulfment of a hot Jupiter can lead to significant Li enrichment signatures in stars near the main-sequence turn-off.