Radiation-driven winds of hot luminous stars: XIII. A description of NLTE line blocking and blanketing towards realistic models for expanding atmospheres

Abstract

Spectral analysis of hot luminous stars requires adequate model atmospheres which take into account the effects of NLTE and radiation driven winds properly. Here we present significant improvements of our approach in constructing detailed atmospheric models and synthetic spectra for hot luminous stars. Moreover, as we regard our solution method in its present stage already as a standard procedure, we make our program package WM-basic available to the community (download is possible from the URL given below). The most important model improvements towards a realistic description of stationary wind models concern: (i) A sophisticated and consistent description of line blocking and blanketing. Our solution concept to this problem renders the line blocking influence on the ionizing fluxes emerging from the atmospheres of hot stars -mainly the spectral ranges of the EUV and the UV are affected -in identical quality as the synthetic high resolution spectra representing the observable region. In addition, the line blanketing effect is properly accounted for in the energy balance. (ii) The atomic data archive which has been improved and enhanced considerably, providing the basis for a detailed multilevel NLTE treatment of the metal ions (from C to Zn) and an adequate representation of line blocking and the radiative line acceleration. (iii) A revised inclusion of EUV and X-ray radiation produced by cooling zones which originate from the simulation of shock heated matter. This new tool not only provides an easy-to-use method for O-star diagnostics, whereby physical constraints on the properties of stellar winds, stellar parameters, and abundances can be obtained via a comparison of observed and synthetic spectra, but also allows the astrophysically important information about the ionizing fluxes of hot stars to be determined automatically. Results illustrating this are discussed by means of a basic model grid calculated for O-stars with solar metallicity. To further demonstrate the astrophysical potential of our new method, we first provide a detailed spectral diagnostic determination of the stellar parameters, the wind parameters, and the abundances by an exemplary application to one of our grid-stars, the O9.5Ia O-supergiant α Cam. Our abundance determinations of the light elements indicate that these deviate considerably from the solar values.