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J.E. Herald, D.J. Hillier, R.E. Schulte-Ladbeck (University of Pittsburgh)
I present the results of a tailored spectral analysis of the WN8 Wolf-Rayet star WR40 (HD~96548). This analysis was carried out utilizing line blanketed non-LTE model atmospheres with provisions for a clumped wind. For the first time in WN analyses, stellar parameters are derived by attempting to match the entire observed spectrum from 900 to 35,000\,Å, including the complex iron pseudo-continuum between 1200--2100\,Å. We use Far-UV HUT data to constrain the HI and \rm{H}2 column densities towards WR40. The inclusion of iron and other metals (O, Ne, Mg, Al, Si, S, Ar, & Ca) in the model atmosphere results in a decrease in derived stellar radii by ~20% from previous, nitrogen-line analyses, while mass-loss rates are decreased by a factor of ~3 due to clumping.
The abundance of iron and other metals are constrained with uncertainties of about 50%, demonstrating that Wolf-Rayet stars can be used to determine metallicities in other galaxies. We find the presence of metals significantly increases the radiative line force the wind experiences, allowing the outer wind to be driven to its theoretical velocity structure, and coming within a factor of five of the needed line force in the inner region (an improvement over earlier radiative transfer models). Coupled with the substantial reduction in the derived performance numbers (factor of ~3), this indicates that radiation pressure alone may be sufficient to drive the winds of WN8 stars.
Our model parameters achieve good fits simultaneously to the H, He, and NIII-IV features of the spectra, a feat that has eluded previous efforts.
This work is part of a dissertation titled ``The Winds of Massive Stars'', consisting primarily of both observational and theoretical investigations into the winds of WN stars. It has been partially funded by NASA grants NAG5-8211 and NAG8-1073.