The IUE observations of the active binary 2 Pegasi = HD 224085

We present and analyze IUE spectra (1150-3200 A) of the surface active binary 2 Pegasi. The spectra show many emission lines originating in the chromosphere and within the chromosphere - corona transition region. The intensity of the emission lines is very strong; the surface fluxes of the prominent lines are about 20-120 times those of the quiet Sun. The ultraviolet emission lines are probably associated with the primary, visible component of the system and connected with dark, spotted areas on the stellar surface. The resemblance of the ultraviolet spectrum to the typical RS CVsub(n) stars HR 1099 and UX Ari implies a very close connection between 2 Peg and this group of stars. The presence of a white dwarf as the secondary in the system seems to be excluded. The slope of the continuum suggests the radius of the primary over 2 solar radii. From the density diagnostic line ratios, a value of 0.3 dynes/cm2 for the transition region pressure is derived. This is in disagreement with the result from the scaling relation, which suggests a non-conductively heated transition region. The X-ray flux of 2 Peg is predicted from the He 2 1637 line flux and shown to be in general agreement with the recent direct measurements. (author)