THE TREATMENT OF NON-LTE LINE BLANKETING IN SPHERICALLY EXPANDING OUTFLOWS

Extensive modifications to the non-LTE radiative transfer code of Hill ier have been made in order to improve the spectroscopic analysis of s tars with stellar winds. The main improvement to the code is the inclu sion of blanketing due to thousands of overlapping lines. To implement this effect, we have used the idea of super levels first pioneered by Anderson. In our approach, levels with similar excitation energies an d levels are grouped together. Within this group, we assume that the d eparture coefficients are identical. Only the population (or equivalen tly, the departure coefficient) of the super level need be solved in o rder to fully specify the populations of the levels within a super lev el. Our approach is a natural extension of the single-level LTE assump tion, and thus LTE is recovered exactly at depth. In addition to the l ine blanketing modifications, the code has been improved significantly in other regards. In particular, the new code incorporates the effect of level dissolution, the influence of resonances in the photoionizat ion cross sections, and the effect of Auger ionization. Electron scatt ering with a thermal redistribution can be considered, although it is normally treated coherently in the comoving frame (which still leads t o redistribution in the observer's frame). Several example calculation s are described to demonstrate the importance of line blanketing on sp ectroscopic analysis. We find that the inclusion of blanketing modifie s the strengths of some optical CNO lines in Wolf-Rayet (W-R) stars by factors of 2-5. In particular, the strengths of the WC classification lines C III lambda 5696 and C IV lambda 5805 are both increased becau se of iron blanketing. This should help alleviate problems found with nonblanketed models, which were incapable of matching the strengths of these lines. We also find that, in the UV (1100-1800 Angstrom), the i nfluence of Fe is readily seen in both emission and absorption. The em ission is sensitive to the iron abundance and should allow, for the fi rst time, Fe abundances to be deduced in W-R stars. The improvements m ade to our code should greatly facilitate the spectroscopic analysis o f stars with stellar winds. We will be able to determine the importanc e and influence of line blanketing, as well as of several other effect s that have been included in the new code. It will also allow us to be tter determine W-R star parameters, such as luminosity, elemental abun dances, wind velocity, and mass-loss rate. With future application to related objects, such as novae and supernovae, our new code should als o improve our understanding of these objects with extended outflowing atmospheres.