2005MNRAS.364..864E

In a high-resolution spectral survey of nearly half the 34 known rapidly oscillating Ap (roAp) stars, using the Ultraviolet-Visual Echelle Spectrograph on the Very Large Telescope, we have discovered remarkably large amplitude pulsations in the roAp star HD99563 with some spectral lines showing radial velocity amplitudes up to 5km/s (10km/s peak-to-peak) with a pulsation period of 10.7min. As for many other roAp stars, we find the largest pulsation amplitudes for lines of some rare earth elements and in the core of the Hα line. The highest amplitudes of 5km/s are seen in rather weak lines of Euii and Tmii. Stronger lines of Priii and Ndiii have pulsation amplitudes in the range 0.7 to 3.5km/s for different lines. In the narrow Hα core, the average amplitude is 2.6km/s, but, as is the case for other lines, the amplitude and phase vary strongly with line depth (atmospheric height), with the amplitude of the radial velocity variations of the line bisector reaching a maximum of 4.3km/s at the bottom of the core. Some other elements show pulsation amplitudes 0.1 to 0.7km/s. Variations in velocity amplitude and phase for several spectral lines were studied using line-bisector measurements to obtain information about the vertical structure of the pulsation modes and the stellar atmosphere.