NLTE water lines in Betelgeuse-like atmospheres

TL;DR

This paper emphasizes the importance of considering non-LTE effects in modeling water lines in Betelgeuse-like atmospheres, challenging the need for additional MOLsphere components and providing a new computational approach.

Contribution

It introduces a novel code using preconditioned Krylov subspace methods to accurately model non-LTE effects in large-scale stellar atmospheres.

Findings

NLTE effects cause deeper water absorption bands

NLTE effects lead to additional cooling in the atmosphere

Classical LTE models are inadequate for large molecular systems

Abstract

The interpretation of water lines in red supergiant stellar atmospheres has been much debated over the past decade. The introduction of the so-called MOLspheres to account for near-infrared "extra" absorption has been controversial. We propose that non-LTE effects should be taken into account before considering any extra-photospheric contribution. After a brief introduction on the radiative transfer treatment and the inadequacy of classical treatments in the case of large-scale systems such as molecules, we present a new code, based on preconditioned Krylov subspace methods. Preliminary results suggest that NLTE effects lead to deeper water bands, as well as extra cooling.