The active RS Canum Venaticorum binary II Pegasi III. Chromospheric emission and flares in 1994-1996

We analyse observations of the very active RS CVn-type star II Peg carried out simultaneously in chromospheric and photospheric lines in 1994-1996. We describe the correlation of the strength of the He I D-3, Ca II K and Ca I I 8498 Angstrom emissions with the spot position on the stellar disk. A two -component structure is suggested in the chromosphere of II Peg, similar to that in the corona: nonvariable component (cool plages) with constant cont ribution to the Line emission and variable, active one (hot plages) showing a growth of its activity during 1994-1996. The active component is related to the spots seen in the photosphere. Two subsequent hares on July 19-23, 1995 were observed in the He I D3 and C arl K and 8498 Angstrom lines showing strong narrow red-shifted emissions. The development of the flares took a few hours and decay lasted several day s. At the maximum of the flaring, in addition to the narrow components, bro ad blue-shifted emissions appeared in He I and Ca II K and in the cores of many strong absorption lines. The broad components are attributed to the pr ocess of the explosive evaporation from the low chromosphere. The amount of energy released in different lines is determined. From the radial velocity curve of the He I emission the location of the radiating matter is deduced . It appears to be related to the largest active region which is seen in th e stellar image. The flare occurred concurrently with the break of the exte nded group on two well separated spots. On October 26, 1996 another hare wa s observed in three spectra, as narrow emissions in the He I and Ca II 8498 Angstrom lines but without development in other lines. It probably was a l ate stage of the flare decay.