0 v 1 8 D ec 1 99 9 Multiwavelength optical observations of chromospherically active binary system OU Gem

We have analysed several multiwavelength optical observations (Hα, Hβ, Hǫ, Ca ii H & K, Ca ii IRT lines) of chromospherically active binary system OU Gem, taken in three observation runs: March 1996, April 1998 (using the SOFIN spectrograph and the Nordic Optical Telescope) and January 1999 (using the ESA-MUSICOS spectrograph and the Isaac Newton Telescope). The spectra show double Hα and Hβ absorption lines, but after applying the spectral subtraction technique, clear excess emission is seen in both components. The two stars have the Ca ii IRT lines in emission, strong emission in the Ca ii H & K lines and small emission in the Hǫ line. Although they have very similar spectral types, the cool one is more active than the hot one in all runs, except for MUSICOS run, and in all spectral lines, except for Ca ii IRT lines.