SIMBAD references

We have used archival CCD data, Fourier analysis, and self-correlation analysis to study the photometric time variability of 162 T Tauri stars and related objects, including Herbig Ae/Be stars. Many show periodic variability, presumably due to rotation of a spotted star in most cases. For the nonperiodic stars, we have estimated an upper limit to the periodic variability. We have also analyzed 26 stars suspected to have periods longer than about 10 days. Of these 26 stars, at least 14 have periods significantly longer than 10 days; their variability may be due to processes in the disk, or the effect of a companion, since most (but not all) T Tauri stars have rotational periods less than this value. For a few of the rotational variables, namely AA Tau, DK Tau, DL Tau, DN Tau, GK Tau, GM Aur, Rox 29, V1121 Oph, V410 Tau, and V649 Ori, we have found long-term variability of the amplitude, presumably due to activity cycles; the time scales are 1500-4000 days.