PHOTOMETRIC AND SPECTROSCOPIC MONITORING OF AA TAU, DN TAU, UX TAU-A,T-TAU, RY TAU, LK CA-4, AND LK CA-7

We report the results of a UBVRI Photometric monitoring campaign for t hree classical T Tauri stars (AA Tau, DN Tau, and UX Tau A) and two we ak emission line T Tauri stars (Lk Ca 4 and Lk Ca 7). Observations wer e obtained at three sites during a core observing period spanning UT 1 985 October 14 through UT 1985 December 25, with additional observatio ns continuing until UT 1986 April 6. Concurrent spectrophotometric obs ervations were obtained for all main program stars except Lk Ca 7 and additionally for T Tau, RW Aur, and RY Tau. Periodic photometric varia bility, assumed to be the stars' rotation periods, were found for AA T au, DN Tau, Lk Ca 4, and Lk Ca 7, respectively, as 8.2, 6.3, 3.4, and 5.7 days. Several U-filter flares were observed for Lk Ca 4 and Lk Ca 7, which are strongly concentrated toward phases of minimum light. We find that there are no correlations between the strengths of Halpha, H beta, or Hgamma and V magnitude or phase for T Tau. However, we do fin d correlations between Halpha line strengths and V magnitudes for AA T au and RY Tau. An analysis of absolute color variations of classical T Tauri stars confirms that hot spots are the predominant cause of thes e stars' variability. This is supported by the spectrophotometric resu lts which show a strong correlation of the amplitude of variation of H alpha equivalent width with photometric amplitude of variability for c lassical T Tauri stars. Our overall results are consistent with earlie r findings that long-lived cool spots are responsible for most of the variability found for weak-emission T Tauri stars, while temporal hot spots are primarily responsible for the observed variability found in classical T Tauri stars.