Magnetic suppression of mode amplitudes: A toy model

Internal magnetic fields can suppress the amplitudes of the non-radial modes of red-giant stars when their strength approaches the critical field strength, at which the magnetic forces become comparable to the buoyancy. We performed Hamiltonian ray tracing simulations of magneto-gravity waves to investigate the trapping of oscillation modes in the presence of an internal magnetic field. Our results indicate that the onset of the mode suppression can be described by a simple expression. It smoothly connects the regime without suppression with the regime with complete suppression and depends only on the ratio between the strength of the magnetic field and the critical field strength. Using this expression, we can estimate the occurrence of stars with suppressed dipole modes and the morphology of their power spectra as a function of stellar mass, age, and magnetic field strength.