  V651 Mon is the binary central star of the bipolar planetary nebula NGC 2346.
The star showed the second-ever deep fading in 1996-1997, which was presumably
caused by obscuration by a dust cloud in the planetary nebula, as was proposed
to explain the 1981-1985 event. The entire duration of the 1996-1997 event was
\~400 d, remarkably shorter than the 1981-1985 event, suggesting that the
obscuring body was smaller or had a larger tangential velocity. The most
remarkable feature in this event was the presence of a sharply defined
transient clearing (brightening). From the time-scale of the variation, we
propose an upper limit of the projected scale of several times ~10^11 cm of the
structure responsible for the brightening. This observation provides the first
evidence for a sharply defined, small lucent structure within the obscuring
body around the central star of NGC 2346
