Hydrodynamic model atmospheres for WR stars: Self-consistent modeling of a WC star wind

TL;DR

This paper introduces the first self-consistent hydrodynamic non-LTE atmosphere models for Wolf-Rayet stars, successfully reproducing observed properties and revealing details about wind acceleration and atmospheric heating.

Contribution

It presents the first self-consistent hydrodynamic models for WR star atmospheres that include iron-group line-blanketing and clumping effects.

Findings

WR-type mass-loss is driven by iron-group opacities at high optical depths.

The wind acceleration occurs in two regions, near the base and farther out.

Deep atmospheric heating explains observed OVI emission features.

Abstract

We present the first non-LTE atmosphere models for WR stars that incorporate a self-consistent solution of the hydrodynamic equations. The models account for iron-group line-blanketing and clumping, 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 (Fe IX-XVI). The acceleration of the outer wind regions is performed by 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 OVI-emissions in the optical spectra of WC stars originate from this region. By their dependence on the clumping factor we gain important information about the location where the density inhomogeneities in WR-winds start to develop.