Tailored Analyses of the WN 8 Stars WR 40 and WR 16

Abstract

We present the results of tailored spectral analyses of two WN 8 Wolf-Rayet stars: WR 40 (HD 96548) and WR 16 (HD 86161). These analyses were 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 35000 Å, including the complex iron pseudocontinuum between 1200-2100 Å. The inclusion of iron and other metals (O, Ne, Mg, Al, Si, S, Ar, and 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 owing 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 and metallicity gradients 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 5 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 WN 8 stars. Our model parameters achieve good fits simultaneously to the H, He, and N III-IV features of the spectra, a feat that has eluded previous efforts. Comprehensive identification of lines and line complexes are provided, and the effects of the inclusion of metals on the strengths of diagnostic lines are discussed.

Tailored Analyses of the WN 8 Stars WR 40 and WR 16

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