Abundance stratification and pulsation in the atmosphere of the roAp star  Equulei^*

¹ Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia e-mail: ryabchik@inasan.rssi.ru
² Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Wien, Austria e-mail: last_name@astro.univie.ac.at
³ Uppsala Astronomical Observatory, Box 515, 751 20, Sweden e-mail: piskunov@astro.uu.se, oleg@astro.uu.se
⁴ Tavrian National University, Yaltinskaya 4, 330000 Simferopol, Crimea, Ukraine e-mail: vad@ccssu.crimea.ua

Corresponding author: W. W. Weiss, weiss@astro.univie.ac.at

Received: 11 October 2001
Accepted: 10 January 2002

Abstract

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 . This stratification profile agrees well with diffusion theory for Ca and Cr, developed for cool magnetic stars with a weak mass loss of  yr^-1. Pr and Nd from the rare earth elements have an opposite profile. Their abundance is more than 6 dex higher above 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.