Abstract
The circumstellar dust disk of the Herbig Ae star AB Aurigae has been found to exhibit complex spiral-like structures in the near-IR. We present maps of the disk in both $^{12}$CO (3-2) and dust continuum at 345~GHz with the SMA at an angular resolution of $1''\!\!.0$ $\times$ $0.7''\!\!$~(144AU $\times$ 100AU). The continuum emission traces a dust disk of a maximum overall dimension of 450AU (FWHM) with a central depression, and exhibits several distinct peaks that appear to coincide with bright features in the near-IR image, in particular the brightest spiral arm. The CO emission traces a rotating gas disk of size 530AU $\times$ 330AU with a deprojected maximum velocity of 2.8~km~s$^{-1}$ at 450~AU. In contrast to dust, the gas disk is not entirely devoid of material at its center. Furthermore, the CO emission in several velocity channels traces the spiral-like structure seen in the IR. However, the spatial-kinematic structure of the CO emission cannot be fit by a disk in Keplerian rotation, and the spiral arms appear to exhibit an excess outward radial motion. The disk of AB Aur is therefore quite different from the Keplerian disks seen around many lower mass T Tauri and Herbig Ae stars. We constrain the Toomre's Q parameter to investigate the possibility that the disk is gravitationally unstable, as well as discuss the effect of a giant planet perturbation to excite the spiral pattern seen in the disk of AB Aur.