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

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 ⊙ 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 enhance the stellar luminosity by several orders of magnitude. A prolonged hydrogen recombination plateau appears when the ejecta cool to about 10 4 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.