Gas inside the 97 au cavity around the transition disk Sz\,91

TL;DR

This study uses ALMA observations to analyze the gas and dust distribution in the transition disk Sz 91, revealing a large cavity and gas presence inside it, suggesting planet formation activity.

Contribution

First detailed ALMA study of Sz 91 revealing a 97 au dust cavity and gas inside it, supporting planet formation scenarios.

Findings

Dust cavity radius is approximately 97 au, the largest around a T Tauri star.

Gas, including CO, is present well inside the dust cavity.

Disk model indicates a ring of millimeter emission between 97 and 140 au.

Abstract

We present ALMA (Cycle 0) band-6 and band-3 observations of the transition disk Sz\,91. The disk inclination and position angle are determined to be $i=49.5\degr\pm3.5\degr$ and $\mathrm{PA}=18.2\degr\pm3.5\degr$ and the dusty and gaseous disk are detected up to $\sim220$ au and $\sim400$ au from the star, respectively. Most importantly, our continuum observations indicate that the cavity size in the mm-sized dust distribution must be $\sim97$ au in radius, the largest cavity observed around a T Tauri star. Our data clearly confirms the presence of \co(2-1) well inside the dust cavity. Based on these observational constrains we developed a disk model that simultaneously accounts for the \co and continuum observations (i.e., gaseous and dusty disk). According to our model, most of the millimeter emission comes from a ring located between 97 and 140 au. We also find that the dust cavity is divided into an innermost region largely depleted of dust particles ranging from the dust sublimation radius up to 85 au, and a second, moderately dust-depleted region, extending from 85 to 97 au. The extremely large size of the dust cavity, the presence of gas and small dust particles within the cavity and the accretion rate of Sz\,91 are consistent with the formation of multiple (giant) planets.