The 12CO Gas Structures of Protoplanetary Disks in the Upper Scorpius Region

TL;DR

This study uses ALMA 12CO spectral line data to analyze gas structures in protoplanetary disks in Upper Scorpius, revealing sizes, temperature profiles, and surface heights, and demonstrating how to derive disk properties from such observations.

Contribution

The paper presents a comprehensive analysis of 12CO emission in protoplanetary disks, including new measurements of disk sizes, temperature layers, and surface heights in the Upper Scorpius region.

Findings

Median CO disk radius ~84 au

Correlation between CO brightness temperature and stellar luminosity

Derived CO emission surface height profiles with median aspect ratio ~0.16

Abstract

We present measurements of key protoplanetary disk properties inferred from parametric models of ALMA 12CO spectral line visibilities. We derive gas-disk radii, integrated fluxes, optically thick emission layers, and brightness temperature profiles for the disk population of the old (4 - 14 Myr) Upper Scorpius star-forming region. We measure CO emission sizes for 37 disks with bright CO J=3-2 emission (S/N > 10 on the integrated flux; out of the 83 disks with CO detections), finding that the median radius containing 90% of the flux is ~84 au, with radii spanning from 23 up to 243 au. We report a correlation between the 12CO brightness temperatures and stellar luminosities, with a Pearson coefficient of 0.6, and we use it to prove that the 12CO optically thick emission layer primarily emanates from a region below the super-heated dust, which is optically thin to the stellar irradiation. Moreover, we derive 33 CO emission surface height profiles, finding a median aspect ratio <z/r> ~ 0.16 in a range from ~0.01 up to ~0.45 over the sample. Finally, we comment on the multiple systems in our sample, of which only some were already known. These results re-affirm how it is possible to derive bulk disk properties by modeling moderate angular resolution ALMA visibilities.