2D disc modelling of the JWST line spectrum of EX Lupi

TL;DR

This paper advances protoplanetary disc modeling by introducing new methods for line escape, dust settling, and UV shielding, applied to interpret JWST spectra of EX Lupi, revealing insights into molecular emissions and disc structure.

Contribution

It presents novel 2D thermo-chemical disc modeling techniques, including a new line escape probability method and dust settling scheme, applied to JWST spectra analysis.

Findings

Successful fit of the spectral energy distribution and JWST spectrum of EX Lupi

Identification of high HCN and C2H2 abundances due to stellar X-ray irradiation

Detailed spatial structure of molecular line emission regions

Abstract

We introduce a number of new theoretical approaches and improvements to the thermo-chemical disc modelling code ProDiMo to better predict and analyse the JWST line spectra of protoplanetary discs. We develop a new line escape probability method for disc geometries, a new scheme for dust settling, and discuss how to apply UV molecular shielding factors to photorates in 2D disc geometry. We show that these assumptions are crucial for the determination of the gas heating/cooling rates and discuss how they affect the predicted molecular concentrations and line emissions. We apply our revised 2D models to the protoplanetary disc around the T Tauri star EX Lupi in quiescent state. We calculate infrared line emission spectra between 5 and 20 mic by CO, H2O, OH, CO2, HCN, C2H2 and H2, including lines of atoms and ions, using our full 2D predictions of molecular abundances, dust opacities, gas and dust temperatures. We develop a disc model with a slowly increasing surface density structure around the inner rim that can simultaneously fit the spectral energy distribution, the overall shape of the JWST spectrum of EX Lupi, and the main observed molecular characteristics in terms of column densities, emitting areas and molecular emission temperatures, which all result from one consistent disc model. The spatial structure of the line emitting regions of the different molecules is discussed. High abundances of HCN and C2H2 are caused in the model by stellar X-ray irradiation of the gas around the inner rim.