Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. II. Line-Blanketed Models

Abstract

We present new or improved methods for calculating NLTE, line-blanketed model atmospheres for hot stars with winds (spectral types A to O), with particular emphasis on a fast performance. These methods have been implemented into a previous, more simple version of the model atmosphere code FASTWIND (Santolaya-Rey et al.1997) and allow to spectroscopically analyze rather large samples of massive stars in a reasonable time-scale, using state-of-the-art physics. We describe our (partly approximate) approach to solve the equations of statistical equilibrium for those elements which are primarily responsible for line-blocking and blanketing, as well as an approximate treatment of the line-blocking itself, which is based on a simple statistical approach using suitable means for line opacities and emissivities. Furthermore, we comment on our implementation of a consistent temperature structure. In the second part, we concentrate on a detailed comparison with results from those two codes which have been used in alternative spectroscopical investigations, namely CMFGEN (Hillier & Miller 1998) and WM-Basic (Pauldrach et al. 2001). All three codes predict almost identical temperature structures and fluxes for lambda > 400 A, whereas at lower wavelengths a number of discrepancies are found. Optical H/He lines as synthesized by FASTWIND are compared with results from CMFGEN, obtaining a remarkable coincidence, except for the HeI singlets in the temperature range between 36,000 to 41,000 K for dwarfs and between 31,000 to 35,000 K for supergiants, where CMFGEN predicts much weaker lines. Consequences due to these discrepancies are discussed.Comment: 30 pages incl. 20 figures, accepted by A&