Further evidence for rotational modulation of the light from T Tauri stars

The T Tauri stars BP Tau, DN Tau, GK Tau, GI Tau, and RY Tau were monitored using UBVRI photometry during autumn 1983. BP and DN Tau showed light variations well fitted by sine curves of periods 7.6 and 6.6 days, respectively. The light variations of GK and GI Tau showed significant power peaks at periods of 4.6 and 7.2 days, respectively. All four periods are presumed to be the surface rotation periods of these stars. The light and color variations of BP, DN, GK, and GI Tau are explained by rotational modulation due to bright and dark regions on the stellar surfaces. This provides evidence that such activity is a primary cause of T Tauri star variability. A comparison of these four T Tauri stars with five pre-main-sequence non-T Tauri stars of similar mass and temperatures shows that, on average, the T Tauri stars are more luminous, have larger radii, and rotate more slowly than the non-T Tauri stars.