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

  • Takashi Tsukagoshi
  • ,
  • Takayuki Muto
  • ,
  • Hideko Nomura
  • ,
  • Ryohei Kawabe
  • ,
  • Kazuhiro D. Kanagawa
  • ,
  • Satoshi Okuzumi
  • ,
  • Shigeru Ida
  • ,
  • Catherine Walsh
  • ,
  • Tom J. Millar
  • ,
  • Sanemichi Z. Takahashi
  • ,
  • Jun Hashimoto
  • ,
  • Taichi Uyama
  • ,
  • Motohide Tamura


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