A new nonlocal thermodynamical equilibrium radiative transfer method for cool stars

TL;DR

This paper introduces a novel nonlocal thermodynamical equilibrium radiative transfer method that employs nonstationary numerical techniques and parallel computing, enabling efficient solutions for complex stellar atmosphere models.

Contribution

It presents a new generalized method based on the coupled escape probability approach and the generalized minimum residual method for solving non-LTE radiative transfer problems.

Findings

Demonstrated fast convergence on water spectrum in a red supergiant atmosphere

Handles large-scale systems effectively

Potentially applicable to diverse astrophysical problems

Abstract

Context: The solution of the nonlocal thermodynamical equilibrium (non-LTE) radiative transfer equation usually relies on stationary iterative methods, which may falsely converge in some cases. Furthermore, these methods are often unable to handle large-scale systems, such as molecular spectra emerging from, for example, cool stellar atmospheres. Aims: Our objective is to develop a new method, which aims to circumvent these problems, using nonstationary numerical techniques and taking advantage of parallel computers. Methods: The technique we develop may be seen as a generalization of the coupled escape probability method. It solves the statistical equilibrium equations in all layers of a discretized model simultaneously. The numerical scheme adopted is based on the generalized minimum residual method. Result:. The code has already been applied to the special case of the water spectrum in a red supergiant stellar atmosphere. This demonstrates the fast convergence of this method, and opens the way to a wide variety of astrophysical problems.