Chromospheric imaging of the active binary system V 711 Tauri equals HR 1099 in December 1992

Spectroscopic observations of the bright RS CVn-type system V711 Tau = HR 1 099 (K1 IV + G5 V) were obtained by IUE during the same period of a Multi-S ite Continuous Spectroscopy (MUSICOS) campaign between 12-18 December 1992 (Huang et al. 1995). We report on the results of a "Doppler Imaging" analysis of the Mg II h lin e. Broad, variable and extended wings have been detected and successfully f itted using a broad Gaussian, which accounts for a large fraction of flux f rom the global stellar Mg II h emission. This broad component is present in all spectra and presents velocity shifts with respect to the K1 star rest- frame that are variable in the range between -19 and +44 km s(-1). Similar results have been obtained from Doppler Imaging of the other relevant chrom ospheric line (H-alpha) in other RS CVn stars (c.f. Hatzes, 1995 and Hatzes , 1998). Furthermore, our analysis suggests that these shifts could be due to rotational modulation produced by an active region, that essentially str addles the pole of the K1 star in which down-flows dominate on up-flows. Fi nally, emitting matter between the two stars has been detected, indicating that mass-exchange is present in the binary system. Five flare episodes with strong flux enhancements in several transition reg ion lines were observed. These flares were preliminarily reported by Neff e t al. (1995). We analyse in this paper the Mg II h and k line emission duri ng the major of these five flare (1992 December 14), since only a weak enha ncement was observed in the Mg II h and Ic lines during the other four flar es. Spectral imaging of the Mg II lines during this flare indicates a flaring s ite on the visible K1 star hemisphere with mass ejection from the K1 star t owards the G5 companion. The Mg II emission shows a large broadening with F WHM reaching 1000 km s(-1) at flare peak and decreasing to 700 km s(-1) two hours after the peak. Our analysis have been carried out using both IUESIPS and NEWSIPS processed spectra. We find that the shapes of the spectral profiles are quite differ ent when spectra are processed by IUESIPS or NEWSIPS procedures, the IUESIP S processed spectra showing a spurious excess of flux on the red wing of th e lines. A comparison with results from GHRS-HST Mg II spectra of V711 Tau (Dempsey et al. 1996, Wood et al. 1996) shows that, thanks to the complete phase cov erage together with the improved quality obtained by the NEWSIPS reduction procedures, the bulk of information derived from GHRS data can be extracted also from the IUE spectra, which continues to be the most complete UV data set that is nowadays available on this source.