Pulsations and radial velocity variations in pulsating Ap stars.: I.: Analysis of γ Equulei

We present precise radial velocity measurements of the pulsational motions on the rapidly oscillating Ap star gamma Equulei taken with an iodine absorption cell. These measurements indicate that the pulsational amplitude is higher in those spectral regions dominated by weak lines. A more detailed analysis of the individual lines of Cr, Fe, and Ti indeed shows that the pulsational amplitudes for strong lines are less than 100 m s(-1), whereas for weak lines they are above 200 m s(-1) and in one case as high as 1000 m s(-1). Also, the mean pulsation amplitude derived from chromium and titanium lines is higher than that derived from iron lines. Time series measurements of radial velocity shifts of single lines are a powerful tool for measuring ion distributions on Ap stars, not only as a function of surface location but of depth as well. This kind of measurement will also be useful in checking predictions of diffusion theory since we can now compare how different ions can move up and down along and across magnetic field lines.