Ya-Wen Tang, Stephane Guilloteau, Vincent Pietu, Anne Dutrey, Nagayoshi Ohashi, Paul T. P. Ho
The circumstellar disc of AB Aurigae has garnered great attentions due to the apparent existence of spirals at a relatively young stage and also the asymmetric disc traced in thermal dust emission. However, the physical conditions of the spirals are still not well understood. The origin of the asymmetric thermal emission is unclear. We observe the disc at 230 GHz (1.3 mm) in both continuum and the spectral line ^12 CO 2-1 with IRAM 30 m, the PdBI and the SMA to sample all spatial scales from 0.37" to about 50". To combine the data obtained from these telescopes, several methods and calibration issues have been checked and discussed. The 1.3 mm continuum (dust) emission is resolved into inner disc and outer ring. The emission from the dust ring is highly asymmetric in azimuth, with intensity variations by a factor 3. Molecular gas at high velocities traced by the CO line is detected aside the stellar location. The inclination angle of the disc is found to decrease toward the center. At larger scale, based on the intensity weighted dispersion and the integrated intensity map of ^12 CO 2-1, four spirals are identified, where two of them are also detected in the near-infrared. The total gas mass of the 4 spirals (M_spiral) is ~10^-6 M_sun, which is 3 orders of magnitude smaller than the mass of the gas ring. Surprisingly, the CO gas inside the spiral is apparently counter-rotating with respect to the CO disc and exhibits only small radial motion. Although an hypothetic fly-by cannot be ruled out, the most likely explanation of the AB Aurigae system may be inhomogeneous accretion well above/or below the main disc plane from the remnant envelope, which can explain both the rotation and large scale motions detected with the 30-m image.
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http://arxiv.org/abs/1209.1299
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