  To explore young star variability on a large range of timescales, we have
used the MOST satellite to obtain 24 days of continuous, sub-minute cadence,
high-precision optical photometry on a field of classical and weak-lined T
Tauri stars (TTS) in the Taurus-Auriga star formation complex. Observations of
AB Aurigae, SU Aurigae, V396 Aurigae, V397 Aurigae, and HD 31305 reveal
brightness fluctuations at the 1-10% level on timescales of hours to weeks. We
have further assessed the variability properties with Fourier, wavelet, and
autocorrelation techniques, identifying one significant period per star. We
present spot models in an attempt to fit the periodicities, but find that we
cannot fully account for the observed variability. Rather, all stars exhibit a
mixture of periodic and aperiodic behavior, with the latter dominating
stochastically on timescales less than several days. After removal of the main
periodicity, periodograms for each light curve display power law trends
consistent with those seen for other young accreting stars. Several of our
targets exhibited unusual variability patterns not anticipated by prior
studies, and we propose that this behavior originates with the circumstellar
disks. The MOST observations underscore the need for investigation of TTS light
variations on a wide range of timescales in order to elucidate the physical
processes responsible; we provide guidelines for future time series
observations.
