Engulfment of Eccentric Planets by Giant Stars: Hydrodynamics and Light Curves

TL;DR

This study uses 3D hydrodynamical simulations to explore how eccentric giant planets are engulfed by giant stars, producing observable light curves with luminosity boosts and dust obscuration effects.

Contribution

It provides the first detailed hydrodynamical modeling of eccentric planet engulfment and predicts associated light curves and observational signatures.

Findings

Engulfment causes shock-driven ejecta and luminosity increase.

A hydrogen recombination plateau appears in the light curve.

Dust formation leads to rapid late-time dimming.

Abstract

Recent observations suggest that planetary engulfment by a giant star may produce radiation that resembles subluminous red novae. We present three-dimensional hydrodynamical simulations of the interaction between an eccentric $5 \,M_J$ giant planet and its $1\,M_\odot$ red-giant host star. The planet's pericenter is initially $60\%$ of the stellar radius and is fully engulfed after tens of orbits. Once inside the stellar envelope, the planet generates pressure disturbances that steepen into shocks, ejecting material from the envelope. We use post-processing to calculate the light curves produced by planetary engulfment. We find that the hot stellar ejecta enhances the stellar luminosity by several orders of magnitude. A prolonged hydrogen recombination plateau appears when the ejecta cools to about $10^4\,\rm{K}$. The late-time rapid dimming of the light curve follows dust formation, which obscures the radiation. For planets with lower eccentricity, the orbital decay proceeds more slowly, although the observable properties remain similar.