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Astron. Astrophys. 338, 661-673 (1998)

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Photospheric metal abundances in active stellar atmospheres

R. Ottmann 1, M.J. Pfeiffer 2 and T. Gehren 2

1 Max-Planck-Institut für Extraterrestrische Physik, D-85748 Garching, Germany
2 Institut für Astronomie und Astrophysik der Universität München, Scheinerstrasse 1, D-81679 München, Germany

Received 9 April 1998 / Accepted 8 July 1998

Abstract

With a sophisticated analysis we determine the photospheric metal abundances of active stars to investigate the abundance stratification in active stellar atmospheres. For selected single stars and RS CVn binaries we have taken high-resolution, high-SN and partially phase-resolved spectra of the entire visible range. With a purely spectroscopic, self-consistent method based on line profile synthesis and an equivalent width analysis, we derive the effective temperature [FORMULA], surface gravity [FORMULA], microturbulence [FORMULA] and the abundances of Fe, Mg and Si with high internal accuracy ([FORMULA] K, [FORMULA] dex, [FORMULA] km/s, [FORMULA] dex). Stellar parameters and metal abundances are obtained for the single stars [FORMULA] Cet, [FORMULA] Cet and [FORMULA] UMa as well as for the RS CVn binaries AY Cet, VY Ari, EI Eri, IM Peg, [FORMULA] And and II Peg. The effect of stellar activity features (spots and plages) on the derived parameters is investigated by phase-resolved spectroscopy; we find that one out of four systems shows a significant variation of the Mg and Si abundances with rotational phase. The results help solving the puzzle about the photospheric Fe abundances of RS CVn binaries; specifically, we obtain [FORMULA] for all systems, indicating that they definitely are not metal-poor. In II Peg and [FORMULA] And, the metals are strongly depleted in the corona relative to the photosphere; in [FORMULA] Cet and [FORMULA] UMa, Fe and Si are weakly depleted, but Mg is enhanced (with [FORMULA] significance). The abundance stratifications are discussed in terms of the FIP-effect and the hydrostatic equilibrium stratification.

Key words: stars: abundances – stars: activity – stars: atmospheres – stars: fundamental parameters – stars: individual: RS CVn binaries

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© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998
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