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 wind may be partially accreted by 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~$\mathrm{M}_\mathrm{J}$, each at initial orbital distances of 5, 10, and 20~AU, orbiting a 2~M$_\odot$ 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 their initial planetary mass. Even for the most massive planet, 13 $\mathrm{M}_\mathrm{J}$ at 5 AU, the total mass accreted was $\sim0.56$\% of the planet's initial mass; nevertheless, we find that the accretion luminosities of the simulated planets, with the exception of one planet, exceed their expected equilibrium luminosities, suggesting that such emission could be potentially detected. This result is key for the detection of planets around AGB stars, which have no confirmed detections as of yet. We also estimated the accretion and luminosities of two detected two-planet systems over a few orbits, obtaining results consistent with 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 the orbital evolution, wind accretion remains relevant for the planetary luminosity.

Figures (14)

• Figure 1: Evolutionary track of the 2 M$_\odot$ stellar model used in our simulations. The portion of the segment of the track corresponding to the RGB and TPAGB phases, which are the stages considered in all simulations, is highlighted.
• Figure 2: Evolution of the stellar mass-loss rate ($\dot{M}_\mathrm{w}$) and wind velocity ($v_\mathrm{w}$) obtained from our 2 M$_\odot$ stellar model. The left panels show the complete evolution of $\dot{M}_\mathrm{w}$ and $v_\mathrm{w}$ through the RGB to the TPAGB phases, while the right panels focus specifically on the TPAGB evolutionary phase.
• Figure 3: Evolution from the RGB phase to the TPAGB phase of all planetary systems with a 2.5 $\mathrm{M}_\mathrm{J}$ planet. The panels show the evolution of the semi-major axis $a$ (top left), orbital velocity $v_o$ (top middle), mass accretion efficiency $\eta$ (top right), mass accretion rate $\dot{{M}}_{\text{acc}}$ (bottom left), planetary mass ${m}_{2}$ (bottom middle), and mass ratio $q$ (bottom right). The solid line over the shaded area indicates the evolution of the stellar radius.
• Figure 4: Same as Fig. \ref{['Fig:3']}, but showing the parameter evolution exclusively during the TPAGB phase.
• Figure 5: The same panels as Fig. \ref{['Fig:3']} but showing the evolution of the whole integration time of a 13 $\mathrm{M}_\mathrm{J}$ planet.