SIMBAD references

Hα spectrophotometry of 33, chromospherically active, close binaries (mostly RS CVn), obtained at the Catania Astrophysical Observatory, is reported. We define the Hα emission component for each observed system as the difference between the observed spectrum and a synthetic "composite" spectrum made up by the weighted sum of spectra of non active stars similar in spectral types to the components of the system. This procedure allows us to detect an emission component in the Hα core, also for some systems which apparently present a normal Hα absorption profile. We investigate the possible correlation between this net Hα surface flux and luminosity as a function of (B-V) and the rotational period. In particular we find that the net Hα surface flux correlates moderately well with the rotational period, in agreement with previous results. The trend of increasing activity with decreasing rotational period can be described either by a power law or an exponential law.