The tidal excitation of r modes in a solar type star orbited by a giant planet companion and the effect on orbital evolution I: The aligned case

TL;DR

This paper investigates how resonant excitation of r modes in a solar-type star by a close-in giant planet influences orbital evolution, highlighting the importance of stellar rotation and resonance effects on tidal interactions.

Contribution

It provides a detailed analysis of r mode excitation in a rotating star due to a planetary companion, emphasizing the role of resonances in accelerating orbital evolution.

Findings

Resonant excitation of r modes can significantly enhance tidal dissipation.

Orbital evolution is slow away from resonance but accelerates near resonant frequencies.

Stellar spin-down can sustain near-resonance conditions, affecting long-term orbital dynamics.

Abstract

It has been suggested that tidal interaction is important for shaping the orbital configurations of close orbiting giant planets. The excitation of propagating waves and normal modes (dynamical tide) will be important for estimating time scales for orbital evolution. We consider the tidal interaction of a Jupiter mass planet orbiting a solar type primary. Tidal and rotational frequencies are assumed comparable making the effect of rotation important. Although centrifugal distortion is neglected, Coriolis forces are fully taken into account. We focus in detail on the potentially resonant excitation of $r$ modes associated with spherical harmonics of degrees three and five. These are mostly sited in the radiative core but with a significant response in the convective envelope where dissipation occurs. Away from resonance significant orbital evolution over the system lifetime is unlikely. However, tidal interaction is enhanced near resonances and the orbital evolution accelerated as they are passed through. This speed up may be sustained if near resonance can be maintained. For close orbits with primaries rotating sufficiently rapidly, this could arise from angular momentum loss and stellar spin down through a stellar wind bringing about significant orbital evolution over the system lifetime.