  The circumstellar dust disk of the Herbig Ae star AB Aur has been found to
exhibit complex spiral-like structures in the near-IR image obtained with the
Subaru Telescope. We present maps of the disk in both 12CO (3-2) and dust
continuum at 345 GHz with the SMA at an angular resolution of 1.0"x0.7" (144AU
x 100AU). The continuum emission traces a dust disk with a central depression
and a maximum overall dimension of 450AU (FWHM). This dust disk exhibits
several distinct peaks that appear to coincide with bright features in the
near-IR image, in particular the brightest inner spiral arm. The CO emission
traces a rotating gas disk of size 530AU x 330AU with a deprojected maximum
velocity of 2.8km/s at 450AU. In contrast to the dust disk, the gas disk
exhibits an intensity peak at the stellar position. Furthermore, the CO
emission in several velocity channels traces the innermost spiral arm seen in
the near-IR. We compare the observed spatial-kinematic structure of the CO
emission to a simple model of a disk in Keplerian rotation, and find that only
the emission tracing the main spiral arm clearly lies outside the confines of
our model. This emission has a net outward radial motion compared with the
radial velocity predicted by the model at the location of the main spiral arms.
The disk of AB Aur is therefore quite different from the Keplerian disks seen
around many Herbig Ae stars. The spiral-like structures of the disk with
non-Keplerian motions we revealed in 12CO (3-2), together with the central
depression of the dust disk, may be explained to be driven by the possible
existence of a giant planet forming in the disk.
