UBVRI monitoring of five late-type pre-main-sequence stars

Two T Tauri stars (DF Tau and DK Tau) and three pre-main-sequence K stars with weak line emission (WK X-Ray 1, WK X-Ray 2, and FK X-Ray 3) were monitored with UBVRI photometry over a 14-night period during October 1982. Neither T Tauri star shows an obvious rotational modulation in the light curve, but DF Tau did experience a multi-day flare-like brightening similar to the events seen in this star by Zajtseva and Lyutyi (1976). The light variations of the three weak-emission stars are well described by sine curves with periods of 5.6, 2.8, and 7.0 days, respectively; these values presumably represent the axial rotation periods of these stars. The results provide further evidence for K-type pre-main-sequence stars which rotate at least as fast as T Tauri stars but lack strong line and continuum emission.