Application of the spectral subtraction technique to the CaII H & K and H$ε$ lines in a sample of chromospherically active binaries

Abstract

We present new spectroscopic observations in the Ca~{\sc ii} H \& K line region for a sample of 28 chromospherically active binary systems (RS$~$CVn and BY$~$Dra classes), with different activity levels. By using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of similar spectral type and luminosity class) we obtain the active-chromosphere contribution to the Ca~{\sc ii} H \& K lines and to the H$ε$ line when it is present. We have compared the emission equivalent widths obtained with this technique with those obtained by reconstruction of the absorption line profile below the emission peak(s). The emissions arising from each individual star were obtained when it was possible to deblend the contribution of both components. The Ca~{\sc ii} line profiles corresponding to different seasons and orbital phases are analysed in order to determine the contribution of each component and to study the chromospheric activity variations.