More and more circumstellar discs around pre-main-sequence stars are found to have complex structures, such as great cavities seen in thermal dust emission and spiral-like features seen in the optical near-infrared images. Among them, AB Aurigae exhibits a spectacular spiral pattern. One popular formation mechanism often invoked for these two structures is the gravitational perturbation created by embedded companion/brown dwarf in the discs. However, the explanations of the spiral formations are purely based on the morphologies due to the lack of the kinematic information. We have made the combined Submillimeter Array (SMA), IRAM 30-m and the Plateau de Bure Interferometer (PdBI) observations toward AB Aurigae with high sensitivity and high angular resolution to trace the kinematics of the spirals using CO lines. Using the 12CO 2-1 images with 0.5" resolution of AB Aurigae, we found the "spiral" like features appear counter-rotating with respect to the circumstellar disc. Late accretion from the envelope above and below the disc plane is the simplest explanation for this. Dense disk surrounding AB Aurigae is resolved into an inner disk and an outer dust ring as traced with the thermal dust continuum emission at 1.3 mm. The dust ring is highly asymmetric as a function of azimuth, suggesting that the disk is perturbed.< Leer menos