EDP Sciences
Free access
Volume 384, Number 2, March III 2002
Page(s) 545 - 553
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020057

A&A 384, 545-553 (2002)
DOI: 10.1051/0004-6361:20020057

Abundance stratification and pulsation in the atmosphere of the roAp star $\boldmath\gamma$ Equulei

T. Ryabchikova1, 2, N. Piskunov3, O. Kochukhov3, V. Tsymbal4, P. Mittermayer2 and W. W. Weiss2

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

(Received 11 October 2001 / Accepted 10 January 2002 )

We present the evidence for abundance stratification in the atmosphere of the rapidly oscillating Ap star $\gamma$ 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.

Key words: stars: chemically peculiar -- stars: abundances -- stars: oscillations -- stars: individual: $\gamma$ Equ

Offprint request: W. W. Weiss, weiss@astro.univie.ac.at

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