Rotational Line Emission from Water in Protoplanetary Disks

TL;DR

This study uses radiative transfer and chemical modeling to assess how far-infrared water emission lines can reveal the structure of protoplanetary disks, especially regarding gas-phase water distribution.

Contribution

It demonstrates the diagnostic potential of Herschel-observed water lines for probing disk regions between 5-100 AU, highlighting limitations in detecting the snow line.

Findings

Water line profiles inform about gas-phase water in disks.

Line ratios help distinguish water distribution regions.

Observability of water lines depends on disk conditions.

Abstract

Circumstellar disks provide the material reservoir for the growth of young stars and for planet formation. We combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for probing disk structure. We discuss the observability of pure rotational H2O lines with the Herschel Space Observatory, specifically the residual gas where water is mainly frozen out. We find that measuring both the line profile of the ground 110-101 ortho-H2O transition and the ratio of this line to the 312-303 and 221-212 line can provide information on the gas phase water between 5-100 AU, but not on the snow line which is expected to occur at smaller radii.