Authors

M. Honda, A. K. Inoue, Y. K. Okamoto, H. Kataza, M. Fukagawa, T. Yamashita, T. Fujiyoshi, M. Tamura, J. Hashimoto, T. Miyata, S. Sako, I. Sakon, H. Fujiwara, T. Kamizuka and T. Onaka

Affiliations

Kanagawa University, Osaka Sangyo University, Ibaraki University, ISAS/JAXA, Osaka University, NAOJ, NAOJ, NAOJ, NAOJ, Univeristy of Tokyo, Univeristy of Tokyo, Univeristy of Tokyo, ISAS/JAXA, Univeristy of Tokyo, Univeristy of Tokyo

Abstract

The disk around AB Aur was imaged and resolved at 24.6 -m using the Cooled Mid-Infrared Camera and Spectrometer on the 8.2m Subaru Telescope. The gaussian FWHM of the source size is estimated to be 90 +/- 6 AU, indicating that the disk extends further out at 24.6 micron than at shorter wavelengths. In order to interpret the extended 24.6 micron image, we consider a disk with a reduced surface density within a boundary radius Rc, which is motivated by radio observations that suggest a reduced inner region within about 100 AU from the star. Introducing the surface density reduction factor fc for the inner disk, we determine that the best match with the observed radial intensity profile at 24.6 micron is achieved with Rc=88 AU and fc=0.01. We suggest that the extended emission at 24.6 micron is due to the enhanced emission from a wall-like structure at the boundary radius (the inner edge of the outer disk), which is caused by a jump in the surface density at Rc. Such reduced inner disk and geometrically thick outer disk structure can also explain the more point-like nature at shorter wavelengths. We also note that this disk geometry is qualitatively similar to a pre-transitional disk, suggesting that the AB Aur disk is in a pre-transitional disk phase.