CO rovibrational emission as a probe of inner disk structure

TL;DR

This study investigates CO rovibrational emission in various protoplanetary disks to understand inner disk structure, revealing correlations with luminosity, differences between disk types, and insights into gas and dust temperature relations.

Contribution

It provides a detailed analysis of CO emission line profiles and inner radii, highlighting systematic differences across disk types and their relation to stellar luminosity.

Findings

CO inner radii correlate with system luminosity and match dust sublimation radii.

Transitional disks have larger CO inner radii and smaller emitting areas than classical T Tauri disks.

Rotational temperatures are similar to or slightly below blackbody grain temperatures at the CO inner radius.

Abstract

We present an analysis of CO emission lines from a sample of T Tauri, Herbig Ae/Be, and transitional disks with known inclinations, in order to study the structure of inner disk molecular gas. We calculate CO inner radii by fitting line profiles with a simple parameterized model. We find that, for optically thick disks, CO inner radii are strongly correlated with the total system luminosity (stellar plus accretion), and consistent with the dust sublimation radius. Transitional disk inner radii show the same trend with luminosity, but are systematically larger. Using rotation diagram fits, we derive, for classical T Tauri disks, emitting areas consistent with a ring of width ~0.15 AU located at the CO inner radius; emitting areas for transitional disks are systematically smaller. We also measure lower rotational temperatures for transitional disks, and disks around Herbig Ae/Be stars, than for those around T Tauri stars. Finally, we find that rotational temperatures are similar to, or slightly lower than, the expected temperature of blackbody grains located at the CO inner radius, in contrast to expectations of thermal decoupling between gas and dust.