Fine structure in the circumstellar environment of a young, solar-like star: The unique eclipses of KH 15D

Results of an international campaign to photometrically monitor the unique pre-main-sequence eclipsing object KH 15D are reported. An updated ephemeris for the eclipse is derived that incorporates a slightly revised period of 48.36 days. There is some evidence that the orbital period is actually twice that value, with two eclipses occurring per cycle. The extraordinary depth (similar to3.5 mag) and duration (similar to18 days) of the eclipse indicate that it is caused by circumstellar matter, presumably the inner portion of a disk. The eclipse has continued to lengthen with time, and the central brightness reversals are not as extreme as they once were. V-R and V-I colors indicate that the system is slightly bluer near minimum light. Ingress and egress are remarkably well modeled by the passage of a knife edge across a limb-darkened star. Possible models for the system are briefly discussed.