Rotational modulation of the ultraviolet line fluxes from the RS CVn star II Pegasi

Abstract

The exceptional in-orbit performance of the International Ultraviolet Explorer (IUE) for more than eighteen years has made it possible to accumulate an invaluable database of ultraviolet observations of a wide variety of objects and, in particular of active stars. \citeN{BS98} -hereafter Paper I- have presented a multiwavelength campaign of observations of the RS CVn star II Peg, partially based on one of the latest series of IUE spectra of this system. Here we investigate issues raised in Paper I such as the rotational modulation of chromospheric and transition region line fluxes and the long-term trends in the ultraviolet emission during the operational period of the instrument, the definition of a mean quiescent state and the changes operated in the radiative output by the ocurrence of the most energetic flare detected in this star. We also perform a differential emission measure analysis based on the emission line fluxes and construct empirical models of the atmosphere of this star.