Eccentric Dust Ring and Scattering-Induced Polarization in the IRS 48 Transition Disk

Haifeng Yang, Manuel Fernandes-Lopez, Zhi-Yun Li, Ian W Stephens, Leslie W Looney, Zhe-Yu Daniel Lin, Rachel Harrison

Crescent-shaped structures in transition disks hold the key to studying the putative companions to the central stars. The dust dynamics, especially that of different grain sizes, is important to understanding the role of pressure bumps in planet formation. In this work, we present deep polarized dust continuum observation with high resolution towards the Oph IRS 48 system. From the non-polarized flux, we are able to significantly trace and detect emission along 95% of the ring crossing the crescent-shaped structure, for the first time. The ring is hightly eccentric with an eccentricity of 0.27. The flux density contrast between the peak of the flux and its counter part along the ring is about 270. In addition, we detect a compact emission toward the central star. If the emission is an inner circumstellar disk inside the cavity, it has a radius of at most a couple of astronomical units with a dust mass of 1.5e-8 solar mass, or 0.005 earth mass. The polarized flux is detected over 50 beams near the peak of the crescent-shaped structure. The polarization pattern is mostly along the shorter axis of the crescent and is consistent with self-scattering of dust thermal emission. The peak of the polarized flux is shifted from the peak of the total flux, both in radial direction and in azimuthal direction. The radial displacement helps us constrain the scale height of the (large) dust grains, whereas the azimuthal displacement may hold the key to understand the azimuthal segregation of grains of different sizes.