Time-resolved spectroscopy of the roAp star γ Equ *
1
Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
2
Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia e-mail: ryabchik@inasan.rssi.ru
3
Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria e-mail: ryabchik@tycho.astro.univie.ac.at
Corresponding author: O. Kochukhov, oleg@astro.uu.se
Received:
7
December
2000
Accepted:
17
May
2001
We report results of the spectroscopic monitoring
of the roAp star γ Equ with the ESO 3.6-m telescope. During 1.5 hours of
observations a series of very high-resolution and high 
spectra was obtained for this star
in the 6138-6165 Åspectral region. Short exposure times allowed us
to resolve changes of γ Equ line profiles due to the rapid pulsations
and to follow profile variations over 5 oscillation cycles. From this unique
observational material information on amplitudes and phase shifts of
radial velocity (RV) variations was extracted for 29 lines of 17 individual ions.
We confirmed that spectral lines of rare-earth elements (REE) have
the largest pulsation amplitudes, reaching up to 0.8 km s-1. Moreover, we
detected a phase shift between RV variations of singly and doubly ionized
REE, discovered significant RV shifts of weak Nai
lines and analysed line profile variations of Priii and Ndiii spectral features.
This rich observational material opens a
possibility to obtain a detailed picture of the vertical stratification of
chemical elements and extract the main characteristics of the pulsational mode(s).
In our observations we did not find support for the existence of the unique
dependence of RV amplitude
on line strength suggested in earlier spectroscopic studies of roAp stars. Instead,
we argue that the individuality of the variations of all ions is a result of
the complex interplay between inhomogeneous vertical and horizontal distributions
of chemical elements and individual pulsation modes of γ Equ.
We show that the extra line broadening observed in γ Equ spectrum is most likely caused by pulsations.
A detailed analysis of Priii and Ndiii line profile variations resulted in the
estimate of 
or 3, 
or 
and 
km s-1 for the p-mode of the
main pulsation frequency.
Key words: stars: chemically peculiar / stars: oscillations / stars: individual: γ Equ
© ESO, 2001