Abundance stratification and pulsation in the atmosphere of the roAp star

We present the evidence for abundance stratification in the atmosphere of the rapidly oscillating Ap star γ Equ. Ca, Cr, Fe, Ba, Si, Na seem to be overabundant in deeper atmospheric layers, but normal to underabundant in the upper layers with a transition in the typical line forming region of $-1.5<\log\tau_{5000}<-0.5$. This stratification profile agrees well with diffusion theory for Ca and Cr, developed for cool magnetic stars with a weak mass loss of ${\approx}2.5\times10^{-15}~M_{\odot}$ yr-1. Pr and Nd from the rare earth elements have an opposite profile. Their abundance is more than 6 dex higher above $\log\tau_{5000}\,\approx\,-8.0$ than in the deeper atmospheric layers. We further discuss the implications of abundance stratification in the context of radial velocity amplitudes and phases observed by Kochukhov & Ryabchikova (2001) for a variety of spectral lines and elements using high spectral and time resolved, high S/N observations