TY  - JOUR
A1  - Gräfener, Götz
A1  - Hamann, Wolf-Rainer
A1  - Hillier, D. J.
A1  - Koesterke, Lars
T1  - Spectral analyses of WC stars in the LMC
Y1  - 1998
ER  - 
TY  - THES
A1  - Gräfener, Götz
T1  - Spektralanalysen von WC-Sternen in der LMC
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Hamann, Wolf-Rainer
A1  - Koesterke, Lars
A1  - Gräfener, Götz
T1  - Modelling and quantitative analyses of WR spectra : recent progress and results
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Gräfener, Götz
A1  - Hamann, Wolf-Rainer
A1  - Koesterke, Lars
T1  - Spectral analyses of WC stars in the LMC
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Koesterke, Lars
A1  - Hamann, Wolf-Rainer
A1  - Gräfener, Götz
T1  - Inhomogeneities in Wolf-Rayet atmospheres
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Gräfener, Götz
A1  - Hamann, Wolf-Rainer
A1  - Koesterke, Lars
T1  - The impact of iron group elements on the ionizatin structure of WC star atmospheres : WR111
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Hamann, Wolf-Rainer
A1  - Koesterke, Lars
A1  - Gräfener, Götz
T1  - Non-LTE models of WR winds
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Hamann, Wolf-Rainer
A1  - Koesterke, Lars
A1  - Gräfener, Götz
T1  - Spectral analyses of Wolf-Rayet winds
N2  - The analysis of Wolf-Rayet spectra requires adequate model atmospheres which treat the non-LTE radiation transfer in a spherically expanding medium. Present state-of-the-art calculations account for complex model atoms with, typically, a few hundred energy levels and a few thousand spectral lines of He and CNO elements. In the most recent version of our model code, blanketing by millions of lines from iron-group elements is also included. These models have been widely applied for the spectral analysis of WN stars in the Galaxy and LMC. WN spectra can be well reproduced in most cases. WC stars have not yet been analyzed comprehensively, because the agreement with observations becomes satisfactory only when line-blanketed models are applied. The introduction of inhomogeneities (clumping), although treated in a rough approximation, has significantly improved the fit between synthetic and observed spectra with respect to the electron-scattering wings of strong lines. The mass-loss rates obtained from spectral analyses become smaller by a factor 2-3 if clumping is accounted for. A pre-specified velocity law is adopted for our models, but the radiation pressure can be evaluated from our detailed calculation and can be compared a posteriori with the required wind acceleration. Surprisingly we find that the line-blanketed models are not far from being hydrodynamically consistent, thus indicating that radiation pressure is probably the main driving force for the mass-loss from WR stars.
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Gräfener, Götz
A1  - Koesterke, Lars
A1  - Hamann, Wolf-Rainer
T1  - Line-blanketed model atmospheres for WR star
N2  - We describe the treatment of iron group line-blanketing in non-LTE model atmospheres for WR stars. As an example, a blanketed model for the early-type WC star WR 111 is compared to its un-blanketed counterpart. Blanketing affects the ionization structure and the emergent flux distribution of our models. The radiation pressure, as computed within our models, falls short by only a factor of two to provide the mechanical power of the WR wind.
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Koesterke, Lars
A1  - Hamann, Wolf-Rainer
A1  - Gräfener, Götz
T1  - Expanding atmospheres in non-LTE : Radiation transfer using short characteristics
N2  - We present our technique for solving the equations of radiation transfer in spherically expanding atmospheres. To ensure an efficient treatment of the Thomson scattering, the mean intensity J is derived by solving the moment equations in turn with the angle-dependent transfer equation. The latter provide the Eddington factors. Two different methods for the solution of the angle dependent equation are compared. Thereby the integration along short characteristics turned out to be superior in our context over the classical differencing scheme. The method is the basis of a non-LTE code suitable for the atmospheres of hot stars with high mass-loss.
Y1  - 2002
ER  -