Dynamical constraints on planet engulfment as the origin of lithium enhancement in TOI-5882

Abstract

As stars evolve off the main sequence, changes in stellar structure can alter the dynamical architecture of planetary systems and, in some cases, lead to planet engulfment events capable of producing observable chemical signatures such as lithium enhancement. TOI-5882 is a lithium-rich subgiant hosting a 22 m_Jup brown dwarf on a 7.1-day orbit, where the enrichment could plausibly result from the recent engulfment of a super-Earth to Neptune-mass planet. We assess the dynamical viability of a planet engulfment scenario in the TOI-5882 system that could explain its observed Li enrichment. We combine stellar evolution models with N-body simulations that incorporate time-dependent stellar properties as the host star leaves the main sequence, exploring a broad range of pre-engulfment planetary masses and orbital configurations. Planet engulfment is the most probable outcome under the explored configurations. However, only 5% of the simulations produce engulfment within the short detectability window of the lithium-enrichment signature. Engulfment therefore remains a viable explanation for the observed Li enhancement in TOI-5882, but only for a relatively uncommon subset of the initial conditions considered here. Under our simplified architecture, recent engulfment cannot be ruled out as the origin of the observed lithium enhancement. However, because successful cases represent only a small fraction of the initial conditions explored here, and because additional processes such as wind-induced drag forces were not included, additional constraints on the system's primordial architecture are needed to assess how likely this scenario is for TOI-5882.