Physics of Magnetic Stars, 2007, pp. 315{324 Propagation of pulsation waves in roAp atmospheres

We present a detailed analysis of the vertical cross-section of the roAp pulsation modes in eight rapidly oscillating (roAp) stars basing on spectroscopic time-series observations. We propose to use the phase-amplitude diagram as the rst step in the interpretation of roAp pulsational observations. Such an approach has an advantage of being suitable to compare the behaviour of dierent elements, which is impossible for studies of phase / amplitude dependence on line intensity. Although the overall pulsational behaviour of roAp stars is not identical, we found certain common features. The phase shifts of the RV curves are arranged in the following sequence: the lowest RV amplitudes are detected in the layers of Eu ii (and Fe in 33 Lib) line formation, then pulsations go through the layers where the Hcore, Nd and Pr lines are formed, the RV amplitude reaches a maximum and after that, in most stars, shows a decrease of the amplitude. The phases of RV curves of the rst ions are always followed by the second ones. The largest phase shifts are detected in the Tb iii and Th iii lines. A pulsational variability of the Th iii lines has been detected and studied for the rst time. In the atmospheres of roAp stars with the pulsation frequency below the cut-o frequency, pulsations have a standing wave character in the deeper layers and then behave like a running wave in the outer layers