Theoretical understanding of radial-velocity pulsations observed in roAp stars

High-resolution spectroscopic time-series of rapidly oscillating Ap stars show evidence that standing and running waves can co-exist in their atmospheric layers. In order to understand these observations we have carried out a theoretical analysis of the pulsations in the outermost layers of these stars. By using the analytical solutions for the velocity components appropriate to the model considered we derive an estimate of the velocity component parallel to the line of sight averaged over the visible stellar disk, and derive the relative amplitude and the phase for our model as a function of height in the atmosphere.