A new nonlocal thermodynamical equilibrium radiative transfer method for cool stars

International audienceContext: 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 oftenunable 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 circumventthese problems, using nonstationary numerical techniques and taking advantageof parallel computers. Methods: The technique we develop may be seen as a generalization of thecoupled escape probability method. It solves the statistical equilibriumequations in all layers of a discretized model simultaneously. The numericalscheme adopted is based on the generalized minimum residual method. Result:. The code has already been applied to the special case of the waterspectrum in a red supergiant stellar atmosphere. This demonstrates the fastconvergence of this method, and opens the way to a wide variety ofastrophysical problems