The History of the Mysterious Eclipses of KH 15D: Asiago Observatory, 1967-1982

We are gathering archival observations to determine the photometric historyof the unique and unexplained eclipses of the pre-main-sequence star KH 15D.Here we present a light curve from 1967-1982, based on photographic plates fromAsiago Observatory. During this time, the system alternated periodicallybetween bright and faint states, as observed today. However, the bright statewas 0.9 mag brighter than the modern value, and the fractional variationbetween bright and faint states (Delta I = 0.7 mag) was smaller than observedtoday (3.5 mag). A possible explanation for these findings is that the systemcontains a second star that was previously blended with the eclipsing star, butis now completely obscured.Comment: Accepted to AJ. 24 pages, 10 figures, 2 tables. v2: Phase error corrected in figures 8 and 1