Eclipses by a circumstellar dust feature in the pre-main-sequence star KH 15D

Photometry and spectroscopy of the unique pre-main-sequence eclipsing object KH 15D in the young cluster NGC 2264 are presented. The orbital period is 48.34 days, and both the length (similar to 16 days) and depth (similar to3 mag) of the eclipse have increased with time. A brightening near the time of central eclipse is confirmed in the recent data but at a much smaller amplitude than was originally seen. Spectra taken when the star is bright show that the primary is a weak T Tauri star of spectral type K7. During eclipse there is no detectable change in spectral type or reddening, indicating that the obscuration is caused by rather large dust grains and/or macroscopic objects. Evidently, the star is eclipsed by an extended feature in its circumstellar disk orbiting with a semimajor axis of similar to0.2 AU. Continued photometric monitoring should allow us to probe the disk structure with a spatial resolution of similar to3 x 10(6) km or better.