# Discovery of an au-scale excess in millimeter emission from the protoplanetary disk around TW Hya

## TL;DR

This paper reports the discovery of a small, bright dust clump in the protoplanetary disk around TW Hya, likely caused by a vortex or forming planet, using high-resolution ALMA observations at 1.3 mm.

## Contribution

First detection of a small-scale dust excess in TW Hya's disk, revealing potential planet formation activity with high-resolution ALMA data.

## Key findings

- Detected a 1.5 times brighter dust excess at 52 au from the star.
- Estimated dust mass of the excess is approximately 0.03 Earth masses.
- The feature is unlikely to be a background source, indicating a local disk structure.

## Abstract

We report the detection of an excess in dust continuum emission at 233~GHz (1.3~mm in wavelength) in the protoplanetary disk around TW~Hya revealed through high-sensitivity observations at $\sim$3~au resolution with the Atacama Large Millimeter/submillimeter Array (ALMA). The sensitivity of the 233~GHz image has been improved by a factor of 3 with regard to that of our previous cycle 3 observations. The overall structure is mostly axisymmetric, and there are apparent gaps at 25 and 41 au as previously reported. The most remarkable new finding is a few au-scale excess emission in the south-west part of the protoplanetary disk. The excess emission is located at 52 au from the disk center and is 1.5 times brighter than the surrounding protoplanetary disk at a significance of 12$\sigma$. We performed a visibility fitting to the extracted emission after subtracting the axisymmetric protoplanetary disk emission and found that the inferred size and the total flux density of the excess emission are 4.4$\times$1.0~au and 250~$\mu$Jy, respectively. The dust mass of the excess emission corresponds to 0.03~$M_\oplus$ if a dust temperature of 18~K is assumed. Since the excess emission can also be marginally identified in the Band 7 image at almost the same position, the feature is unlikely to be a background source. The excess emission can be explained by a dust clump accumulated in a small elongated vortex or a massive circumplanetary disk around a Neptune mass forming-planet.