Detailed structure of the outer disk around HD 169142 with polarized light in H-band

TL;DR

This study uses polarized light imaging to reveal the detailed structure of the outer disk around HD 169142, identifying potential signs of a protoplanet and complex disk features.

Contribution

It provides the first detailed polarized light imaging of HD 169142's outer disk, revealing a double power-law distribution, a potential protoplanet signature, and disk asymmetries.

Findings

Detection of scattered light from 29 to 174 AU.

Identification of a gap and a potential protoplanet at 40-70 AU.

Evidence of disk surface irregularities and asymmetries.

Abstract

Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2" <= r <= 1.2", or 29 <= r <= 174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r=29-52 AU and r=81.2-145 AU respectively show r^{-3}-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r=40-70 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at \lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner power-law region (r< 50 AU) is derived to be <= 0.16 from a simple model calculation. The obtained PI image also shows small scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and shadowing effect by a puffed up structure in the inner power-law region.