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

TL;DR

This study uses high-resolution imaging and spiral density wave theory to discover small-scale spiral structures in the disk of SAO 206462, providing insights into the disk's physical state and potential planet formation.

Contribution

It presents the first direct imaging of small-scale spirals in the disk and models their origin using spiral density wave theory, linking observations to disk properties and planet formation.

Findings

Detected small-scale spiral structures within 70AU of the star.

Derived a disk aspect ratio of approximately 0.1 from spiral modeling.

Predicted observable evolution of spirals over 10-20 years.

Abstract

We present high-resolution, H-band, imaging observations, collected with Subaru/HiCIAO, of the scattered light from the transitional disk around SAO 206462 (HD 135344B). Although previous sub-mm imagery suggested the existence of the dust-depleted cavity at r~46AU, our observations reveal the presence of scattered light components as close as 0.2" (~28AU) from the star. Moreover, we have discovered two small-scale spiral structures lying within 0.5" (~70AU). We present 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 previous sub-mm observations. This model can potentially give estimates of the temperature and rotation profiles of the disk based on dynamical processes, independently from sub-mm observations. It also predicts the evolution of the spiral structures, which can be observable on timescales of 10-20 years, providing conclusive tests of the model. While we cannot uniquely identify the origin of these spirals, planets embedded in the disk may be capable of exciting the observed morphology. Assuming that this is the case, we can make predictions on the locations and, possibly, the masses of the unseen planets. Such planets may be detected by future multi-wavelengths observations.