H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks

TL;DR

This study detects and analyzes water and hydroxyl gas emissions in the inner regions of protoplanetary disks around T Tauri stars, providing insights into the chemical environment during terrestrial planet formation.

Contribution

First detection of multiple water and hydroxyl emission lines in protoplanetary disks using infrared spectroscopy, revealing their spatial origin and physical conditions.

Findings

Water and OH gases originate between 0.5 and 5 AU from the stars.

Significant columns of water and OH suggest active transport of volatiles.

Emission extends radially, indicating complex excitation processes.

Abstract

We present detections of numerous 10-20 micron H2O emission lines from two protoplanetary disks around the T Tauri stars AS 205A and DR Tau, obtained using the InfraRed Spectrograph on the Spitzer Space Telescope. Follow-up 3-5 micron Keck-NIRSPEC data confirm the presence of abundant water and spectrally resolve the lines. We also detect the P4.5 (2.934 micron) and P9.5 (3.179 micron) doublets of OH and 12CO/13CO v=1-0 emission in both sources. Line shapes and LTE models suggest that the emission from all three molecules originates between ~0.5 and 5 AU, and so will provide a new window for understanding the chemical environment during terrestrial planet formation. LTE models also imply significant columns of H2O and OH in the inner disk atmospheres, suggesting physical transport of volatile ices either vertically or radially; while the significant radial extent of the emission stresses the importance of a more complete understanding of non-thermal excitation processes.