H-alpha in RS CVn binaries

The 1976-78 results of a spectroscopic program to monitor H-alpha in several RS CVn-type binaries are reported. For six objects well observed over orbital phase, four (HR 4665, HR 5110, Sigma Gem, Z Her) show H-alpha as an absorption feature having a constant (plus or minus 15%) equivalent width (EW). AR Lac exhibits an absorption profile also, but the EW varies by a factor of three due to partial filling by emission. This variation is sporadic and not phase dependent. The H-alpha feature in HK Lac shows the most extreme variation: normally seen as an absorption feature with variable EW, it has been observed as a pure emission feature on three spectrograms, showing a blueshift with respect to the photosphere of 50-100 km/sec. On a single occasion HK Lac showed double H-alpha emission with a separation of the peaks of 300 km /sec. These high velocity features are interpreted in terms of prominence-like structure in the atmosphere of the active star