EXCESS H-ALPHA EMISSION IN CHROMOSPHERICALLY ACTIVE BINARIES

We study the behaviour of the excess H alpha emission in a sample of 5 1 chromospherically active binary systems (RS CVn and BY Dra classes), of different activity levels. This sample include the 27 stars analys ed by Fernandez-Figueroa et al. (1994) and the new observations of 24 systems described by Montes et al. (1994b). By using the spectral subt raction technique (subtraction of a synthesized stellar spectrum const ructed from reference stars of similar spectral type and luminosity cl ass) we obtain the active-chromosphere contribution to the H alpha lin e in these 51 systems. We have determined the excess H alpha emission equivalent widths and converted it to surface fluxes. The H alpha emis sions arising from each component star were obtained when it was possi ble to deblend both contributions. The comparison of the excess H alph a emission, obtained with the spectral subtraction technique, with oth er H alpha activity indices allows us to conclude that this is the pre ferable activity indicator for binaries. The behaviour of the excess H alpha emission as a function of the rotation has been analyzed. A sli ght decline toward longer rotational periods, P-rot, and larger Rossby numbers, R(0), is present in agreement with previous results using ot hers activity indicators. We have compared the derived excess H alpha emission fluxes with those obtained in the Ca II K and H epsilon lines finding that a good correlation exits between these three chromospher ic activity indicators. The H alpha losses seem to be more important t han Ca II K losses for cooler stars, in fact all the system with H alp ha emission above the continuum are cooler than 5000 K. Correlations w ith other activity indicators, (C IV in the transition region, and X-r ays in the corona) indicate that the exponents of the power-law relati ons increase with the formation temperature of the spectral features.