Wind Accretion onto Planets Orbiting an Evolving Solar-Like Star and their Detectability

Abstract

As stars evolve, they undergo significant changes in their physical properties, which can have a profound impact on the planets orbiting them. In particular, the mass lost through stellar winds may be partially accreted by the orbiting planets. We present the results of 18 simulations of one-planet systems with planetary masses of 0.5, 1, 2.5, 5, 10, and 13 M_J, each at initial orbital distances of 5, 10, and 20 AU, orbiting a 2 M_⊙ star through its red giant branch and thermally pulsating asymptotic giant branch phases. Our results show that planets with smaller orbits and higher masses accrete more stellar wind material than their wider-orbit and lower-mass counterparts, although the total mass accreted across all simulations remains small compared to the initial planetary masses. Even for the most massive planet, 13 M_J at 5 AU, the total mass accreted was ~ 0.56% of the planet’s initial mass. Nevertheless, we found that the accretion luminosities of the simulated planets, except for one planet, exceeded their expected equilibrium luminosities, suggesting that such emissions could potentially be detected. This result is key for the detection of planets around AGB stars, which have not yet been confirmed. We also estimated the accretion and luminosities of the two detected two-planet systems over a few orbits, obtaining results that are consistent with those of the one-planet simulated systems. Additional tests without wind accretion and with stellar wind drag force showed that while both have a negligible effect on orbital evolution, wind accretion remains relevant for planetary luminosity.