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Astron. Astrophys. 322, 234-241 (1997)


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Abundance analysis of roAp stars

III. [FORMULA] Equulei *

T.A. Ryabchikova 1, S.J. Adelman 2, 3, W.W. Weiss 4 and R. Kuschnig 4

1 Institute for Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia (ryabchik@inasan.rssi.ru)
2 Department of Physics, The Citadel, 171 Moultrie Street, Charleston, SC 29409, USA (adelmans@citadel.edu)
3 Guest Investigator, Dominion Astrophysical Observatory
4 Institute for Astronomy, Univ. Vienna, Türkenschanzstr. 17, A-1180 Vienna, Austria (last_name@galileo.ast.univie.ac.at)

Received 7 October 1996 / Accepted 18 November 1996

Abstract

A spectroscopic analysis of the rapidly oscillating chemically peculiar star [FORMULA] Equ yields [FORMULA] = 7700 K, [FORMULA] = 4.20, a microturbulence and [FORMULA] which cannot be determined reliably, but which must be close to zero, because line broadening can be modelled by magnetic field effects alone. A mean magnetic field modulus of B = 4.0 kG is estimated by comparing synthetic Zeeman pattern with observations. This value provides another phase point for magnetic field variations of [FORMULA] Equ, a CP2 star with the longest hitherto known magnetic field period of about 77 years. For a simple dipolar field geometry, the angle between the line of sight and the magnetic axis [FORMULA].

We discuss in some detail the problems for abundance determinations in the presence of a strong magnetic field and we increase substantially the number of ions to 42, for which abundances are now available. In particular, we obtain a more reliable abundance of [FORMULA] = -10.24, and find Fe and the light elements, C to Ca, to have nearly solar abundances. Co is clearly overabundant, and Nb and Mo are the most overabundant elements in [FORMULA] Equ relative to the Sun.

Key words: stars: abundances; chemically peculiar; magnetic field; oscillations; individual (fl Equ)

* Based on observations obtained at the European Southern Observatory (La Silla, Chile), Dominion Astrophysical Observatory, Observatoire de Haute-Provence, and at the Crimean Astrophysical Observatory

Send offprint requests to: Werner W. Weiss

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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