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Post Info TOPIC: HD200775
Blobrana


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RE: HD200775
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A team of astronomers from Ibaraki University, Japan Aerospace Exploration Agency, Kanagawa University, University of Tokyo, Academica Sinica, and National Astronomical Observatory of Japan have used the Subaru Telescopes Cooled Mid-Infrared Camera and Spectrometer (COMICS) to capture the first direct, well-resolved infrared images of a circumstellar disk around a young massive starHD200775. Their findings contribute to understanding the role of circumstellar disks in massive star formation in particular and to the birth of stars in general.
HD200775 is located 1400 light-years from Earth and is actually a close binary system that contains at least one massive star that is about 10 times the mass of the Sun. A large cavity of molecular gas surrounds the star and extends east to west from the central stars. Molecular gas is dense within the cavity wall, and HD200775 illuminates the gas closest to the star, forming the reflection nebula NGC7023. The binary orbit extends in the north-south direction, indicating that the binary is almost seen in its orbital plane.
The infrared images captured by COMICS revealed an elliptical emission with the same direction as the binary orbit. The research team found that the emission arises from a circumbinary disk (a disk that surrounds both stars of the binary system) around HD200775, the orbital plane of which is similar to that of the binary. The direction is consistent with the fact that an outflow generally occurs in a direction perpendicular to a disk. The images taken this time are significant because they are the first clear and direct infrared images of a disk around a massive star.

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Blobrana


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Title: Direct detection of a flared disk around a young massive star HD200775 and its 10 to 1000AU scale properties
Authors: Yoshiko Kataza Okamoto, Hirokazu Kataza, M. Honda, H. Fujiwara, M. Momose, N. Ohashi, T. Fujiyoshi, I. Sakon, S. Sako, T. Yama****a, T. Miyata, T. Onaka

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 in about 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.

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