STUDY OF THE CHROMOSPHERIC ACTIVITY IN BINARY SYSTEMS

Abstract

ABSTRACT A sample of 83 chromospherically active binary systems including the RS Canum Venaticorum binaries (RS ~ CVn) and BY Draconis (BY ~ Dra) classes has been studied. 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 H-alpha line in 51 systems, and to the Ca II H and K lines in 73 systems and 19 single active stars. We have determined the excess H-alpha and Ca II H and K emission equivalent widths and converted them to surface fluxes. The H-alpha emissions arising from each component star were obtained when it was possible to deblend both contributions. The Ca 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, finding that several stars show variability with the phase and other exhibit time variations possibly due to activity cycles. We test the width-luminosity correlations (the Wilson-Bappu (WB) effect, and (W1, MV)) in these very active stars. After analysing the influence of the activity level (the intensity effect, IK3) and the rotational broadening (V sin i) in the (log W0K, MV) we find that stars with strong emission intensities, IK3, and large values of V sin i present larger values of W0K than resulted from WB relation, being more remarkable the effect of the rotational velocity. On the contrary W1K is strongly influenced by IK3 but the effect of the rotational broadening is lesser. We also found that the increase of W1 and IK1 with IK3 presents a flattening for the most active stars which is different for each value of W0. The behaviour of the excess H-alpha and Ca II H & K emissions as a function of the rotation has been analyzed. A slight decline toward longer rotational periods, Prot, and larger Rossby numbers, R0, is present. The derived excess H-alpha emission fluxes has been compared with those obtained in the Ca II ~ K and H-epsilon lines finding that a good correlation exists between these three chromospheric activity indicators. The H-alpha losses seem to be more important than Ca II K losses for cooler stars, in fact all the system with H-alpha emission above the continuum are cooler than 5000 K. Correlations with other activity indicators, (C IV in the transition region, and X-rays in the corona) indicate that the exponents of the power-law relations increase with the formation temperature of the spectral features.