2005MNRAS.357.1059M

In recent years, an increasing number of publications have been devoted to the peculiar and mysterious pre-main-sequence star V582 Mon, also known as KH 15D. This extraordinary T Tauri star, located in the young star cluster NGC 2264, appears to be an eclipsing variable. In the present paper, we report a unique and self-consistent set of light curves in the blue and near-infrared (IR) bands, spanning a 15-yr interval (epoch 1955-1970). Our photometric data show clearly that the beginning of the eclipse stage occurred in early 1958 in the blue, and perhaps around 4yr later in the IR. The light-curve period turns out to be the same reported by recent observations (about 48.3d), so that no evidence for a period change results. On the other hand, in our data the light-curve shape appears to be sinusoidal and is therefore different from the one displayed today. The photometric behaviour, determined with time-series and colour-index analysis, suggests that V582 Mon (KH 15D) could initially be surrounded by an accretion disc/torus seen edge-on, with subsequent thin dust formation at the beginning of the blue radiation absorption. The dust could then aggregate into larger particles providing the transition between selective and total absorption, accompanied with eclipsing variability in the IR. The minima of the periodic light curve become deeper owing to the increasing dimension and number of dust grains, and then flatten owing to a contraction in the disc.