Spectroscopy and hydrodynamics of dense stellar winds
Wolf-Rainer Hamann, Goetz Graefener, Lidia M. Oskinova, Achim Feldmeier
Universitaet Potsdam, Germany
Armagh Observatory, Northern Ireland
Analyzing the spectra from Wolf-Rayet stars requires adequate non-LTE
modeling of their expanding atmosphere. The numerical schemes for
solving the radiative transfer in the co-moving frame of reference have
been developed by Mihalas and co-workers 30 years ago. The most
elaborate codes can cope today with many hundred explicit non-LTE levels
or super-levels and account for metal-line blanketing.
The limited agreement with observed spectra indicates that the model
simplifications are still severe. One approximation that has to be
blamed is homogeneity. Stellar-wind clumping on small scales was
easily implemented, while "macro-clumping" is still a big challenge. First
studies showed that macro-clumping can reduce the strength of predicted
P-Cygni line profiles in O-star spectra, and largely affects the X-ray
line spectra from stellar winds.
The classical model for radiation-driven winds by Castor, Abbot and
Klein fails to explain the very dense winds from Wolf-Rayet stars. Only
when we solved the detailed non-LTE radiative transfer consistently with the
hydrodynamic equations, mass-loss rates above the single-scattering
limit have been obtained.
Reference: "Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics", proceedings of conference to honor 70th Birthday of D. Mihalas
Status: Conference proceedings