Hydrodynamic model atmospheres for WR stars

Self-consistent modeling of a WC star wind

¹ Institut für Physik, Astrophysik, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany e-mail: goetz@astro.physik.uni-potsdam.de
² Institute of Astronomy, ETH Zentrum SEC , Scheuchzer Str. 7, 8092 Zürich, Switzerland
³ PMOD/WRC, 7260 Davos Dorf, Switzerland

Received: 26 July 2004
Accepted: 20 October 2004

Abstract

We present the first non-LTE atmosphere models for WR stars that incorporate a self-consistent solution of the hydrodynamic equations. The models take iron-group line-blanketing and clumping into account, and compute the hydrodynamic structure of a radiatively driven wind consistently with the non-LTE radiation transport in the co-moving frame. We construct a self-consistent wind model that reproduces all observed properties of an early-type WC star (WC5). We find that the WR-type mass-loss is initiated at high optical depth by the so-called “Hot Iron Bump” opacities (–xvi). The acceleration of the outer wind regions is due to iron-group ions of lower excitation in combination with C and O. Consequently, the wind structure shows two acceleration regions, one close to the hydrostatic wind base in the optically thick part of the atmosphere, and another farther out in the wind. In addition to the radiative acceleration, the “Iron Bump” opacities are responsible for an intense heating of deep atmospheric layers. We find that the observed narrow emission lines in the optical spectra of WC stars originate from this region. From their dependence on the clumping factor we gain important information about the location where the density inhomogeneities in WR-winds start to develop.