The Treatment of Non‐LTE Line Blanketing in Spherically Expanding Outflows

Abstract

Extensive modiÐcations to the non-LTE radiative transfer code of Hillier have been made in order to improve the spectroscopic analysis of stars with stellar winds. The main improvement to the code is the inclusion of blanketing due to thousands of overlapping lines. To implement this e ect, we have used the idea of super levels Ðrst pioneered by Anderson. In our approach, levels with similar excitation energies and levels are grouped together. Within this group, we assume that the departure coefficients are identi-cal. Only the population (or equivalently, the departure coefficient) of the super level need be solved in order to fully specify the populations of the levels within a super level. Our approach is a natural exten-sion of the single-level LTE assumption, and thus LTE is recovered exactly at depth. In addition to the line blanketing modiÐcations, the code has been improved signiÐcantly in other regards. In particular, the new code incorporates the e ect of level dissolution, the inÑuence of reso-nances in the photoionization cross sections, and the e ect of Auger ionization. Electron scattering with a thermal redistribution can be considered, although it is normally treated coherently in the comoving frame (which still leads to redistribution in the observerÏs frame). Several example calculations are described to demonstrate the importance of line blanketing on spec-troscopic analysis. We Ðnd that the inclusion of blanketing modiÐes the strengths of some optical CNO lines in Wolf-Rayet (W-R) stars by factors of 2È5. In particular, the strengths of the WC classiÐcation lines C III j5696 and C IV j5805 are both increased because of iron blanketing. This should help alleviate problems found with nonblanketed models, which were incapable of matching the strengths of these lines. We also Ðnd that, in the UV (1100È1800 the inÑuence of Fe is readily seen in both emission A Ž), and absorption. The emission is sensitive to the iron abundance and should allow, for the Ðrst time, Fe abundances to be deduced in W-R stars. The improvements made to our code should greatly facilitate the spectroscopic analysis of stars with stellar winds. We will be able to determine the importance and inÑuence of line blanketing, as well as of several other e ects that have been included in the new code. It will also allow us to better determine W-R star parameters, such as luminosity, elemental abundances, wind velocity, and mass-loss rate. With future application to related objects, such as novae and supernovae, our new code should also improve our understanding of these objects with extended outÑowing atmospheres.