  We made mid-infrared observations of the 10Msun Herbig Be star HD200775 with
the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2m Subaru
Telescope. We discovered diffuse emission of an elliptical shape extended in
the north-south direction inabout 1000AU radius around unresolved excess
emission. The diffuse emission is perpendicular to the cavity wall formed by
the past outflow activity and is parallel to the projected major axis of the
central close binary orbit. The centers of the ellipse contours of the diffuse
emission are shifted from the stellar position and the amount of the shift
increases as the contour brightness level decreases. The diffuse emission is
well explained in all of geometry, size, and configuration by an inclined
flared disk where only its surface emits the mid-infrared photons. Our results
give the first well-resolved infrared disk images around a massive star and
strongly support that HD200775 is formed through the disk accretion. The disk
survives the main accretion phase and shows a structure similar to that around
lower-mass stars with 'disk atmosphere'. At the same time, the disk also shows
properties characteristic to massive stars such as photoevaporation traced by
the 3.4mm free-free emission and unusual silicate emission with a peak at
9.2micron, which is shorter than that of many astronomical objects. It provides
a good place to compare the disk properties between massive and lower-mass
stars.
