From traffic jams to roadblocks: The outer regions of TW Hya with ALMA Band 8

TL;DR

This study uses ALMA observations across multiple wavelengths to reveal and analyze faint ring structures in the outer disk of TW Hya, providing insights into dust grain sizes and disk substructures.

Contribution

It introduces new high-resolution ALMA observations and advanced modeling techniques to detect and characterize faint outer disk features in TW Hya.

Findings

Confirmed outer disk emission at 60-110 au in multiple wavelengths.

Resolved a new continuum gap and ring, D79 and B86.

Detected a faint ring with high spectral index indicating small dust grains.

Abstract

We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 0.65 mm with 0.5 arcsecond angular resolution, together with high angular resolution archival observations at 0.87 mm, 1.3 mm, 2.1 mm and 3.1 mm. We constrain the outer disk emission with both image-plane retrieval, and visibility-plane modeling with non-parametric and parametric fitting tools. Our results confirm emission in the outer disk regions of TW Hya (60 au <= R <= 110 au) at 0.65 mm, 0.87 mm and 1.3 mm. With image-plane retrieval, we resolve the new continuum gap and ring, namely D79 and B86, at 0.87 mm and 1.3 mm. With visibility-plane modeling, we also detect this substructure at 0.65 mm in the form of a quasi-constant emission at the 1-sigma level. Furthermore, it has a high spectral index of 3.7, which may indicate dust grain sizes << 1 mm. It may be a dust trap or a traffic jam, that has a flux density of 60 mJy and a mass (1.59 earth masses) that accounts for up to 2% of the dust disk at 0.65 mm. In conclusion, we confirm the existence of a faint ring in the outer regions of TW Hya at multiple millimeter wavelengths. With visibility-plane modeling, we are able to set constrains that are 3 times better than the resolution of our Band 8 observations.