Magnetic activity and spectral behavior of RS CVn binary system (IM Pegasi) in the ultraviolet.

We present observations from the International Ultraviolet Explorer (IUE) covering the period from 1981 to 1992 of the long-period single-lined RS Canum Venaticorum (RS CVn) binary star, IM Pegasi, to elucidate the spectral behavior and physical conditions within its atmosphere. The ultraviolet observations reveal signs of flare activity occurring in the chromosphere and transition region of the primary star. In addition to the flaring activity, the emission lines exhibit a spectrum of variations categorized as high, intermediate, and low. The relation between line fluxes and orbital phases has been established. The flaring activity was notably observed in 1985. The reddening of IM Pegasi was assessed using the 2200 Å absorption feature, yielding an estimate of E (B-V) = 0. The average mass loss rate is calculated to be approximately 1.2 × 10- 10 M[Formula: see text] yr- 1, while the average temperature of the emitting region, determined through Planck's equation, is approximately 9.2 × 104 K. The energy associated with the flare is estimated to be around 5.6 × 1039 erg, and the average ultraviolet luminosity is approximately 1.23 × 1030 erg s- 1. We attribute the observed spectral variations to a cyclic behavior of the underlying magnetic field, and the flaring activity can be interpreted through the current sheet model.