2009A&A...495..287B

The IUE database provides several UV high and low-resolution spectra of RS CVn-type stars from 1978 to 1996. In particular, many of these stars were monitored continuously during several seasons by IUE. Our main purpose is to study the short and long-term chromospheric activity of the RS CVn systems most observed by IUE: HD 22468 (V711 Tau, HR 1099, K1IV+G5V), HD 21242 (UX Ari, K0IV+G5V), and HD 224085 (II Peg, K2IV).We first obtained the Mount Wilson index S from the IUE high and low-resolution spectra. Secondly, we used the Lomb-Scargle periodogram to analyse the mean annual index <S> and the amplitude of the rotational modulation of the index S.For HD 22468 (V711 Tau, HR 1099), we find a possible chromospheric cycle with a period of ∼18-years and a shorter cycle with a period of ∼3-years, which could be associated to a chromospheric ``flip-flop'' cycle. The data of HD 224085 (II Peg) also suggest a chromospheric cycle of ∼21-years and a flip-flop cycle of ∼9-years. Finally, we obtained a possible chromospheric cycle of ∼7-years for HD 21242 (UX Ari).