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Astron. Astrophys. 330, 155-168 (1998)

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Multiwavelength optical observations
of chromospherically active binary systems

II. EZ Pegasi *

D. Montes, J. Sanz-Forcada, M.J. Fernández-Figueroa, E. De Castro and A. Poncet

Departamento de Astrofsica, Facultad de Fsicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain (dmg@astrax.fis.ucm.es)

Received 28 May 1997 / Accepted 17 September 1997

Abstract

The star EZ Peg, long ago classified as cataclysmic variable, has been shown to be a chromospherically active binary system of the RS CVn-type. In this paper we have analysed, using the spectral subtraction technique, simultaneous spectroscopic observations of the H [FORMULA], H [FORMULA], Na I D1 and D2, He I D3, Mg I b triplet, Ca II H & K, and Ca II infrared triplet lines. We have found that the hot component is the active star of the system, showing strong emission in the H [FORMULA], Ca II H & K, H [FORMULA], and Ca II IRT lines, and a strong filling-in of the H [FORMULA] line, however the Na I D1 and D2 and Mg I b triplet lines do not present filled-in. The He I D3 could present a total filling-in due to microflaring. The observed variations (in different epochs and with the orbital phase) of the different activity indicators, formed at different height in the chromosphere, are correlated. Very broad wings have been found in the subtracted profiles of H [FORMULA] and Ca II IRT [FORMULA] 8498 and [FORMULA] 8662 lines. These profiles are well matched using a two-component Gaussian fit (narrow and broad) and the broad component could be interpreted as arising from microflaring. The higher luminosity class of the hot component, that our spectra seem to indicate, could explain why the hot component is the active star of the system.

Key words: stars: activity – stars: binaries: close – stars: chromospheres – stars: late-type – stars: individual: EZ Peg

* Based on observations made with the Isaac Newton, William Herschel and Jacobus Kapteyn telescopes operated on the island of La Palma by the Royal Greenwich Observatory at the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofsica de Canarias

Send offprint requests to: D. Montes

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© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998
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