The amplitudes of acoustic modes in solar-like stars are intrinsically linked to the properties of turbulent convection in their outer envelopes, which acts as their excitation source. The detection of these oscillations provides the most accurate determination of the fundamental global properties of these stars (such as their masses, radii, and ages), which are essential for characterising their planetary systems and galactic environment.
Recent observational studies based on data from the Kepler space mission have shown that acoustic oscillations are not detected in a significant fraction of solar-type stars, despite the presence of convective envelopes where such modes are expected to be excited. This non-detection has been shown to depend on both stellar rotation and magnetic activity. One possible explanation is that the excitation source term becomes too weak to sustain detectable oscillations. In addition, observations of solar-type stars reveal that acoustic mode amplitudes are modulated over their magnetic activity cycles.
Rotation and magnetism affect mode excitation through two distinct mechanisms. First, they strongly modify the properties of turbulent convection itself. Second, they introduce additional excitation sources that are generally neglected in current theoretical models used to predict acoustic mode amplitudes.
In this work, I first introduce a model of rotating and magnetised convection based on Mixing-Length Theory. I then extend the state-of-the-art formalism for the stochastic excitation of stellar acoustic modes to consistently account for the effects of rotation and magnetic fields. I will show that turbulent source terms are significantly modified in the presence of rotation and magnetism, leading to a modulation of acoustic mode amplitudes as a function of stellar rotation period and magnetic activity level. Finally, I will compare these theoretical results with direct numerical simulations of rotating solar-like stars performed with the MUSIC code.
These results open numerous perspectives, such as the excitation of gravity waves and inertial waves, angular momentum transport, and seismology of giant planets.
