U-band flares and sympathetic flaring on Gl 65

We present contemporaneous observations in the U and K bands of some 26 flares, on the active flare star Gl 65. Over a period of 27 yr, the frequency of flaring seems to have changed little. We suggest that this is due to sympathetic flaring, caused by a Moreton-wave type phenomenon, the propagation of fast MHD waves from the flare site out into the corona that are reflected back to the chromosphere. We have also redetermined the time-averaged U-band flare luminosity, which is a factor of two less than previously reported. The flares fall into two main categories, with longer duration flares releasing a smaller (20 percent) fraction of their energy over the initial rise and decay to half maximum than the shorter-lived flares 50 percent. We also find that the evolution of some of the flares can be fitted by conduction and radiation from a hot thermal plasma. We have also been able to fit Gurzadyan (1988) model of a flare on the hidden hemisphere of the star, to two broad, low-amplitude continuum enhancements. (Author)