Pre-transitional disk nature of the AB Aur disk

Abstract

The disk around AB Aur was imaged and resolved at 24.6\,$\mu$m using the Cooled Mid-Infrared Camera and Spectrometer on the 8.2m Subaru Telescope. The gaussian full-width at half-maximum of the source size is estimated to be 90 $\pm$ 6 AU, indicating that the disk extends further out at 24.6\,$\mu$m than at shorter wavelengths. In order to interpret the extended 24.6\,$\mu$m image, we consider a disk with a reduced surface density within a boundary radius $R_c$, 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 $f_c$ for the inner disk, we determine that the best match with the observed radial intensity profile at 24.6\,$\mu$m is achieved with $R_c$=88 AU and $f_c$=0.01. We suggest that the extended emission at 24.6\,$\mu$m 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 $R_c$. 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.

10 pages, 4 figures, accepted for publication in ApJ

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• The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps
• Consistent dust and gas models for protoplanetary disks III. Models for selected objects from the FP7 DIANA project
• Cloudlet capture by Transitional Disk and FU Orionis stars
• The Structure of Pre-transitional Protoplanetary Disks I: Radiative Transfer Modeling of the Disk+Cavity in the PDS 70 system
• DIGIT survey of far-infrared lines from protoplanetary discs: II. CO
• Water ice at the surface of HD 100546 disk
• Large dust gaps in the transitional disks of HD 100453 and HD 34282
• High-resolution 25 μm imaging of the disks around Herbig Ae/Be stars
• Chemical composition of the circumstellar disk around AB Aurigae
• Constraining the Movement of the Spiral Features and the Locations of Planetary Bodies within the AB Aur System