ROTATIONAL MODULATION AND FLARES ON THE RS CANUM-VENATICORUM BINARY-II PEGASI IN JULY SEPTEMBER 1990 - SPOTS AND FLARES ON II PEG

During ultraviolet spectroscopic observations of the RS CVn star II Pe g in September 1990 a long duration (greater-than-or-equal-to 3 hrs.) flare was observed. During the early stage of the event, a feature at 1354angstrom was present, however, within the spectral resolution of t he data it is not possible to identify this line. A contribution from the hot coronal ion Fe XXI is suspected. From line diagnostic ratios, the electron pressure at flare peak was estimated to be 10(17) cm-3 K, decreasing to 10(16) cm-3 K towards the end of the flare. One other f lare was observed with IUE, and three optical flares (unfortunately no ne of these were observed simultaneously). The chromospheric and trans ition region losses from the larger of the two IUE flares was approxim ately 3 10(31) erg s-1 at flare maximum, with total chromospheric/tran sition region radiative losses over the duration of the event being ap proximately 1.5 10(35) erg. Continuum radiative losses over the wavele ngth region 1150angstrom to 1950angstrom were approximately 3% of the above figure. At flare maximum, the N V 1240angstrom line showed an en hancement factor of approximately 3 over the preflare value compared t o 9 for the C IV 1550angstrom line. We interpret this difference as du e to an underabundance of nitrogen during the flare, possibly related to photoionization of lower chromospheric material by soft X-ray photo ns sometime prior to the flare. No evidence of rotational modulation w as present in any of the transition region lines, although the chromos pheric lines did show a phase variation. However, these lines (Halpha, Ca II K and Mg II h&k) were not consistent with one another although it is clear that the H alpha equivalent width showed variations faster than the star's rotation period, being perhaps related to the decay/a ctivation of individual active regions.