The Variability of T Tauri, RY Tauri, and RW Aurigae from 1899 to 1952

We present the historical light curve of T Tau derived from photographic plates in the Harvard College Observatory archives. We find that the optical light of T Tau varied by 2–3 (or more) mag on timescales as short as a month prior to ∼1917, consistent with the 1949 results of Lozinskii. Extreme light fluctuations of greater than 2 mag abruptly ceased in the late 1910s and, to the best of our knowledge, have not repeated since this time. We compare the observed light variations of T Tau with the T Tauri stars RY Tau and RW Aur, whose light curves we also constructed from inspection of the archival plates. We find that variable extinction along the line of sight to the star is the most likely explanation for the observed light fluctuation of T Tau during the early part of the 20th century.