Tidal Evolution and Surface Chemistry in Planetary Engulfment Events — Melinda Soares-Furtado (University of Wisconsin-Madison)

Stars sometimes engulf their own planetary companions. These events leave coupled signatures in two physical channels: tidal interactions, which drive orbital decay and ultimately engulfment, and stellar surface chemistry, which can preserve evidence of the accreted material. Theory predicts a temporary enhancement of surface lithium, but only for stars within a narrow range of mass and evolutionary stage. Using stellar evolution models, we identify this window: stars about 40% more massive than the Sun on the subgiant branch.
We investigate this prediction using TOI-5882, an evolving star that hosts an eccentric, short-period brown dwarf massive enough to gravitationally perturb the system’s inner planets. High-resolution spectroscopy places TOI-5882 among the most lithium-rich stars in a control sample drawn from a large spectroscopic survey. Modeling the dilution of engulfed material within the stellar envelope implies an engulfed mass of roughly 10–100 Earth masses, consistent with the brown dwarf having destabilized and delivered inner bodies into the host star.
We then examine the future evolution of the brown dwarf itself. Coupling stellar evolution models with a state-of-the-art stellar oscillation code that solves the tidal response without simplifying approximations, we show that tidal dissipation through internal gravity waves can shorten the companion’s inspiral by up to 100 million years relative to standard prescriptions. Together, these results connect the chemical fingerprints of past engulfment with the tidal physics governing the future evolution of substellar companions in aging planetary systems.

Horarios: 11 Aug 2026

Publicado por: Gijs Mulders