What do nonlinear terms reveal about δ Scuti stars oscillations?
Miriam Rodriguez Sanchez, Valencia
δ Scuti stars have a complex power spectrum in which numerous radial and nonradial modes are excited. Despite this, nonlinear contributions to the oscillations have generally not been taken into account and most studies have remained within the linear regime due to the complexity of the problem. In this seminar, I will present the challenges and results of studying the nonlinear contributions. This work is based on analyzing the fundamental hydrodynamic equations expanded to second order in perturbations in terms of the displacement vector. The analysis considers no rotation, no magnetic fields, no viscosity, adiabaticity, and no turbulent convection. I evaluate the relative importance of the nonlinear terms by focusing on the simplest case of radial modes and the maximal temporal contribution. I computed these terms using stellar models together with the eigenfunctions of the linear adiabatic oscillation equations. The results show that some nonlinear terms can locally reach magnitudes comparable to the linear contributions of the continuity, momentum, and energy equations. This indicates that nonlinear terms have a non-negligible role in the internal dynamics of δ Scuti oscillations.