Multisite observations of surface structures on AB Doradus in 1994 November

We present time-resolved optical spectroscopy and broad-band photometry of the rapidly rotating southern K0 dwarf star AB Doradus, obtained during 199 4 November. The data were obtained as part of a collaboration dedicated to MUlti-SIte COntinuous Spectroscopy (MUSICOS), and entailed coordinated obse rvations on three continents to obtain the fullest phase coverage possible subject to Limitations of local weather conditions. The Doppler images from the three consecutive nights of the run show excellent mutual agreement, w ith a dark polar cap and numerous intermediate- and low-latitude features. Simultaneous optical photometry showed numerous short-duration U-band flare s, and two longer duration optical flares with durations of the order of ho urs. The latter produced broad-band continuum enhancements throughout the o ptical spectrum. Where simultaneous spectroscopy was available, both types of flare were seen to have counterparts in H alpha and the Ca II H line. Si multaneous time-resolved ultraviolet spectroscopy from the Goddard High Res olution Spectrograph (GHRS) aboard the Hubble Space Telescope, reported els ewhere, shows that at least one of the short-duration U-band flares was als o observed in Cry with the GHRS, Time-series H alpha spectra showed signifi cant evolution of the circumstellar prominence system over five consecutive stellar rotations, One prominence underwent a dramatic increase in distanc e from the stellar rotation axis. We speculate that this event may have bee n associated with one of the long-duration flares.