Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim

TL;DR

This paper presents ProDiMo, a comprehensive thermo-chemical model for protoplanetary disks that integrates radiative transfer, chemistry, and hydrostatic equilibrium to interpret gas emission lines and disk structure.

Contribution

The paper introduces a new, self-consistent disk modeling code that combines radiative transfer, chemistry, and hydrostatics, providing detailed insights into disk structure and emission.

Findings

Inner rim is puffed-up and dense midplane is surrounded by a hot atomic gas layer.

Gas temperature decouples from dust temperature beyond 100AU, reaching about twice the dust temperature.

Gas energy balance critically influences the vertical disk structure.

Abstract

This paper introduces a new disk code, called ProDiMo, to calculate the thermo-chemical structure of protoplanetary disks and to interpret gas emission lines from UV to sub-mm. We combine frequency-dependent 2D dust continuum radiative transfer, kinetic gas-phase and UV photo-chemistry, ice formation, and detailed non-LTE heating & cooling balance with the consistent calculation of the hydrostatic disk structure. We include FeII and CO ro-vibrational line heating/cooling relevant for the high-density gas close to the star, and apply a modified escape probability treatment. The models are characterized by a high degree of consistency between the various physical, chemical and radiative processes, where the mutual feedbacks are solved iteratively. In application to a T Tauri disk extending from 0.5AU to 500AU, the models are featured by a puffed-up inner rim and show that the dense, shielded and cold midplane (z/r<0.1, Tg~Td) is surrounded by a layer of hot (5000K) and thin (10^7 to 10^8 cm^-3) atomic gas which extends radially to about 10AU, and vertically up to z/r~0.5. This layer is predominantly heated by the stellar UV (e.g. PAH-heating) and cools via FeII semi-forbidden and OI 630nm optical line emission. The dust grains in this "halo" scatter the star light back onto the disk which impacts the photo-chemistry. The more distant regions are characterized by a cooler flaring structure. Beyond 100AU, Tgas decouples from Tdust even in the midplane and reaches values of about Tg~2Td. Our models show that the gas energy balance is the key to understand the vertical disk structure. Models calculated with the assumption Tg=Td show a much flatter disk structure.