New ALMA Observation at 1 au Resolution for TW Hya; Resolved Structure and Time Variation of a Localized Substructure in the Disk

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

We present the results of our new ALMA observations for the TW Hya disk at 1au resolution in the Band 6 continuum and 13CO and C18O molecular lines conducted in Cycle 7. Our observation confirmed the presence of a localized, blob-like continuum emission at a radius of 52au, as previously reported by Tsukagoshi et al. (2019), and we found that it moves in a clockwise direction during the observation epochs in 2017 and 2021. The azimuthal velocity v$_\phi$ is 3.3 km/s, which is comparable to the Keplerian rotation at 52au. We did not detect any radial motion. Moreover, we identified substructures within the blob emission that are separated into two components along the azimuthal direction. The separation of the components was 0.6 au, and their distribution was slightly skewed inward toward the downstream-side. The brightness temperature was measured to be approximately 8K, suggesting that the components are not self-luminous. Using our high-resolution and high-sensitivity continuum map, we deduced the shape of the gap at 1 au. Fitting the radial profile of the gap, we found that the gap shape cannot be reproduced by a simple power-law form, which implies that the innermost disk has been dissipated or that there is a bump at the outer edge of the gap. The molecular line emission was only detected within a radius of approximately 25 au, and we did not detect any gas emission component associated with the blob-like continuum emission.

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