SAO 206462 polarised Ks image

This technique allows one to image the polarized scattered light from the disk without any occulting mask and to reach an inner working angle of ~0.1". A face-on disk is detected in H and K_s_ bands between 0.1" and 0.9". No significant differences are seen between the H and K_s_ images.

In addition to the spiral arms, these new data allow us to resolve for the first time an inner disk cavity for small dust grains. The cavity size (=~28AU) is much smaller than what is inferred for large dust grains from (sub-)mm observations (39 to 50AU). This discrepancy cannot be ascribed to any resolution effect.

The interaction between the disk and potential orbiting companion(s) can explain both the spiral arm structure and the discrepant cavity sizes for small and large dust grains. One planet may be carving out the gas (and, thus, the small grains) at 28AU, and generating a pressure bump at larger radii (39AU), which holds back the large grains. We analytically estimate that, in this scenario, a single giant planet (with a mass between 5 and 15M_J_) at 17 to 20AU from the star is consistent with the observed cavity sizes.