ALMA Observations of a Gap and a Ring in the Protoplanetary Disk around TW Hya

TL;DR

This paper reports the first ALMA detection of a gap and a ring in the dust continuum emission of the TW Hya protoplanetary disk, linked to the CO snow line, with implications for planet formation and disk chemistry.

Contribution

First observation of a dust gap and ring in TW Hya's disk at 336 GHz, revealing potential planet-disk interactions or chemical processes.

Findings

Gap at 25 au with <15 au width and >23% mass deficit

CO snow line at ~30 au associated with the gap and ring

CO line emission depletion indicating gas freeze-out and surface reactions

Abstract

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.