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

Abstract

Context. Current ALMA surveys often underestimate protoplanetary disk sizes as many disks have extended low surface-brightness regions that fall below ALMA’s detection limits. To effectively capture faint millimeter continuum emission in these outer regions, increased sensitivity is required. Aims. In order to gain insights on the connection between disk structure and planet formation, we aim to uncover continuum emission in the outer regions of the disk around TW Hya. Additionally, we aim to investigate the evolution of this disk by studying its dust properties. Methods. 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 0.87,1.3, 2.1 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. Results. Our results confirm emission in the outer disk regions of TW Hya (60 au ≤ R ≤ 110 au) at 0.65, 0.87 and 1.3 mm. With image-plane retrieval, we resolve the new continuum gap and ring, namely D79 and B86, at 0.87 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 1σ 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 M⊕) that accounts for up to 2% of the dust disk at 0.65 mm. Conclusions. 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.