Multiwavelength optical observations of chromospherically active binary systems. II. EZ Pegasi

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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 Hₐlpha, Hbeta, 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 Hₐlpha, Ca II H & K, Hₑpsilon, and Ca II IRT lines, and a strong filling-in of the Hbeta 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 Hₐlpha and Ca II IRT lambda 8498 and lambda 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.