Submillimetre dust polarisation and opacity in the HD163296 protoplanetary ring system

TL;DR

This study uses ALMA observations to analyze the submillimetre dust polarisation and spectral index in the HD163296 protoplanetary disk, revealing polarization patterns consistent with self-scattering and regions of high optical depth.

Contribution

It provides detailed polarization and spectral index maps of HD163296, supporting a self-scattering model for dust polarization without additional alignment mechanisms.

Findings

Polarisation fraction peaks between dust rings.

Polarisation vectors align with the disk minor axis in the core.

Spectral index minima indicate high optical depths in certain regions.

Abstract

We present ALMA images of the sub-mm continuum polarisation and spectral index of the protoplanetary ringed disk HD163296. The polarisation fraction at 870{\mu}m is measured to be ~0.9% in the central core and generally increases with radius along the disk major axis. It peaks in the gaps between the dust rings, and the largest value (~4%) is found between rings 1 and 2. The polarisation vectors are aligned with the disk minor axis in the central core, but become more azimuthal in the gaps, twisting by up to +/-9degrees in the gap between rings 1 and 2. These general characteristics are consistent with a model of self-scattered radiation in the ringed structure, without requiring an additional dust alignment mechanism. The 870/1300{\mu}m dust spectral index exhibits minima in the centre and the inner rings, suggesting these regions have high optical depths. However, further refinement of the dust or the disk model at higher resolution is needed to reproduce simultaneously the observed degree of polarisation and the low spectral index.