C3PO III: On the Lithium Signatures Following Planet Engulfment by Stars

TL;DR

This study investigates lithium signatures in stars following planet engulfment, revealing that intrinsic stellar variability complicates using lithium abundance as a definitive indicator of such events.

Contribution

The paper provides the largest homogeneous dataset of lithium abundances in co-moving star pairs, highlighting the challenges in identifying planet engulfment signatures due to stellar intrinsic scatter.

Findings

Lithium enhancement signatures are only detectable among very similar stellar twins.

Intrinsic scatter in lithium abundance can be as high as 0.6 dex, masking planet engulfment signatures.

Reliance solely on lithium as an indicator for planet engulfment is problematic due to stellar variability.

Abstract

Planet engulfment has been identified as one of the mechanisms for enhancing lithium abundance in stars. However, comprehensive investigations into lithium signatures following such events remain limited. Stars born together, sharing a common origin and stellar characteristics, provide a unique opportunity to study these signatures and compare lithium abundances. We demonstrate that the distinctive signature of planet engulfment in lithium abundance is only discernible among highly similar stellar twins. We present lithium abundance measurements for 125 co-moving pairs of stars, representing the largest sample to date with a single, homogeneous assessment of high-precision lithium abundance. While lithium abundance enhancements in pairs showing planet engulfment signatures are within 0.35 dex, we find that even at fixed stellar parameters (temperature and age), the intrinsic scatter in lithium abundance is typically 0.35 dex for G/F dwarfs and can be as large as 0.6 dex for older and cooler stars due to internal stellar evolution processes. Since the planet engulfment signature from lithium can be masked by stellar intrinsic scatter, our findings raise questions about relying solely on lithium as an indicator for planet engulfment or attributing lithium-richness in stars primarily to planet engulfment events.