Corotation resonance
= Corotation resonance
{title2=$\Omega_\varphi=\Omega_{\mathrm p}$}
A rotating gravitational pattern resonates with a <stellar orbit> when their azimuthal <frequencies> agree. In <action-angle variables>, this is the $k_R=0$ resonance of an azimuthal harmonic. Its torque changes azimuthal <angular momentum> without changing <radial action> to leading order, allowing <stellar radial migration> with little heating. The circular-orbit location is the <corotation radius>.