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Astron. Astrophys. 344, 221-230 (1999)


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Photospheric metal abundances of AR Lacertae *

Thomas Gehren 1, Renate Ottmann 2 and Johannes Reetz 1

1 Institut für Astronomie und Astrophysik der Universität München, Scheinerstrasse 1, D-81679 München, Germany
2 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching, Germany

Received 6 November 1998 / Accepted 7 January 1999

Abstract

High-resolution spectra of the RS CVn system AR Lac taken during total eclipse of the primary component lead to a precise determination of the stellar effective temperature of the secondary, [FORMULA] K, and a surface gravity [FORMULA]. The small-scale motions are well represented by a microturbulence velocity of [FORMULA] km s-1. Examination of a number of spectral windows by means of spectrum synthesis based on solar spectrum reference fits produces a pattern of photospheric metal abundances that is essentially represented by solar or slightly enhanced values. This is at variance with the subsolar metal abundances reported from X-ray observations with the ROSAT and ASCA satellites.

The effective temperature determined here restricts the surface fraction of cool matter such as confined in star spots during the present observations to values around 0.3. For a close binary system with an active chromosphere the photospheric spectra are normal. No spectrum variations on a half hour time scale are detected.

Key words: stars: starspots – stars: individual: AR Lac – stars: coronae – stars: binaries: eclipsing – stars: abundances

* Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, Spain

Send offprint requests to: T. Gehren (gehren@usm.uni-muenchen.de)

© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999

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