We report the first detection of a gap and a ring in 336 GHz dust continuum emission from the protoplanetary disk around TW Hya, using the Atacama Large Millimeter/Submillimeter Array (ALMA). The gap and ring are located at around 25 and 41 au from the central star, respectively, and are associated with the CO snow line at ~30 au. The gap has a radial width of less than 15 au and a mass deficit of more than 23%, taking into account that the observations are limited to an angular resolution of ~15 au. In addition, the 13CO and C18O J = 3 - 2 lines show a decrement in CO line emission throughout the disk, down to ~10 au, indicating a freeze-out of gas-phase CO onto grain surfaces and possible subsequent surface reactions to form larger molecules. The observed gap could be caused by gravitational interaction between the disk gas and a planet with a mass less than super-Neptune (2M_{Neptune}), or could be the result of the destruction of large dust aggregates due to the sintering of CO ice.
@article{arxiv.1512.05440,
title = {ALMA Observations of a Gap and a Ring in the Protoplanetary Disk around TW Hya},
author = {Hideko Nomura and Takashi Tsukagoshi and Ryohei Kawabe and Daiki Ishimoto and Satoshi Okuzumi and Takayuki Muto and Kazuhiro D. Kanagawa and Shigeru Ida and Catherine Walsh and T. J. Millar and Xue-Ning Bai},
journal= {arXiv preprint arXiv:1512.05440},
year = {2016}
}