Continuous mass ablation of planets engulfed in stellar envelopes

Abstract

Most stars host short-period planets that are expected to be engulfed during post-main-sequence expansion. The dissolution of engulfed planets has been proposed as a possible mechanism for producing stars enriched in lithium and refractory elements. We performed three-dimensional hydrodynamical simulations of a Jupiter-like planet engulfed within a stellar envelope using the code. Unlike previous studies that represent the planet as a point mass or rigid sphere, we adopted a wind-tunnel setup that resolves the planet's gaseous structure. We find that a continuous mass-ablation process operates during planetary engulfment, contrary to the common assumption that destruction occurs at a specific depth due to ram pressure, tidal forces, or thermal evaporation. The ablation rate scales nearly linearly with the wind momentum flux and is largely insensitive to the Mach number, consistent with an analytical model based on Kelvin--Helmholtz instability developing at the planetary surface. Our study provides a framework for large parameter-space studies of planetary engulfment using parametrised drag and mass-loss models. We define efficiency coefficients for drag and ablation, finding pressure-drag coefficients of 0.44--0.56 and ablation efficiencies of 0.054--0.11. Applying these coefficients to a numerically integrated inspiral through a stellar profile, we find that continuous ablation could deposit a significant fraction of the planet's mass within the convective envelope, producing observable lithium enrichment at the stellar surface. This result suggests that chemical enrichment occurs over a broader range of stellar parameters than previously thought. Seven-League Hydro