High time-resolution observations of UV Ceti stars.

Simultaneous, high time-resolution spectroscopic and photometric observations of eight flare events on four UV Ceti-type stars are presented. These observations firmly establish the existence of two phases during a flare: the spike phase, which is dominated by continuum emission, and the slow phase, which shows strong emission-line radiation with decreasing continuum radiation. The time sequence of spectral features during a flare is that the continuum reaches maximum strength first, followed 1 to 19 minutes later by maximum strength in the Balmer emission lines, and finally the peak of the Ca ii K-line strength some 4 to 52 minutes after the continuum peak. The flare phenomenon is spectroscopically complex, with no apparent simple relation between the various flare parameters. The emission lines produce a time-varying contribution to the broad-band color indices of flare light. Subject headings: stars: emission4ine - stars: flare