1994A&A...290..510H

This paper is concerned with the problem of modelization of a collisional radiative shock in an atomic and molecular hydrogen gas. The temperature (1000-5000K) and the density (10^–8-10^–14g/cm³) are typical of those found in cool pulsating stars (W Virginis, RV Tauri and Mira stars). Our purpose is to analyse the influence of the Lyman-α radiation, coming from the wake, on the precursor structure. This study is made using a model for the precursor including three mean-photons (Lyman-α, Lyman and Balmer continua). This approach within the framework of the "mean photon approximation", leads to some specific difficulties concerning the radiative transfer in the Lyman-α line, for which some approximations are thus proposed. Their validity is discussed together with their consistency with other approximations used in our model. The Lyman-α photons coming from the wake are absorbed in the precursor close to the shock front. The region in which the absorption takes place defines a sub-structure hereafter called "the Lyman-α precursor"; its influence on the precursor, and hence on the whole structure, is in close relation with the strength of the shock. In particular, the photodissociation of molecules (in strong enough shocks) seems to have significant influence. The size of the whole precursor is reduced when the Lyman-α is taken into account. The influence of the Balmer flux is also investigated.