Theory of Wolf-Rayet Atmospheres

Theoretical modeling of line and continuum formation in Wolf-Rayet (W-R) atmospheres is reviewed. We examine the basic premises on which the models are built, and critically compare theoretical models with observation. Discrepancies between theory and observation are analyzed to determine their implication for our understanding of W-R atmospheres. Line formation, continuum formation, and the ionization structure of W-R envelopes are examined in detail. Abundance determinations are briefly reviewed.

Empirical Photospheric Fluxtube Models from Inversion of Stokes V Data

We present results of an inversion procedure that derives the turbulent velocity, the magnetic field strength, and the temperature stratification of the photospheric layers of solar magnetic fluxtubes from 10 FeI and FeII Stokes V line profiles around 5250 Å and from the continuum contrast. The free parameters of two-dimensional magnetohydrostatic fluxtube models are determined by minimizing the difference between observed and calculated Stokes V parameters in an iterative manner. Results of this inversion procedure applied to observations of a plage and a network region at disk center indicate a temperature deficit (at equal geometrical height) of the fluxtubes at the level of continuum formation and a temperature excess at the highest levels of line formation in general agreement with the latest theoretical fluxtube models.

Radiative Transfer Problems in Planetary Nebulae

In view of the enormous importance of the UV observations of planetary nebulae made possible by the IUE, this review will concentrate primarily on the formation of resonance lines in nebulae; an important special case is that of He II Lyα and its role in the Bowen mechanism. Special attention is given to the effects of dust on the line and continuum formation.