Discovery of Small-Scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory

摘要

We present high-resolution, H-band, imaging observations, collected withSubaru/HiCIAO, of the scattered light from the transitional disk around SAO206462 (HD 135344B). Although previous sub-mm imagery suggested the existenceof the dust-depleted cavity at r~46AU, our observations reveal the presence ofscattered light components as close as 0.2" (~28AU) from the star. Moreover, wehave discovered two small-scale spiral structures lying within 0.5" (~70AU). Wepresent models for the spiral structures using the spiral density wave theory,and derive a disk aspect ratio of h~0.1, which is consistent with previoussub-mm observations. This model can potentially give estimates of thetemperature and rotation profiles of the disk based on dynamical processes,independently from sub-mm observations. It also predicts the evolution of thespiral structures, which can be observable on timescales of 10-20 years,providing conclusive tests of the model. While we cannot uniquely identify theorigin of these spirals, planets embedded in the disk may be capable ofexciting the observed morphology. Assuming that this is the case, we can makepredictions on the locations and, possibly, the masses of the unseen planets.Such planets may be detected by future multi-wavelengths observations.