Direct detection of a flared disk around a young massive star HD200775 and its 10 to 1000AU scale properties

Abstract

We made mid-infrared (MIR) observations of the 10 M ⊙ Herbig Be star HD200775 with the Cooled Mid-Infrared Camera and Spectrometer on the 8.2m Subaru Telescope. We discovered diffuse emission of an elliptical shape extended in the north-south direction in an ∼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 (the shape and the shift), size, and configuration by an inclined flared disk where only its surface emits the MIR 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 of massive stars such as photoevaporation traced by the 3.4mm free-free emission and unusual silicate emission with a peak at 9.2μm, 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. © 2009. The American Astronomical Society. All rights reserved.