Spectral Analyses with the Standard Model. Part II: Wolf-Rayet Stars
W.-R.Hamann and L. KoesterkeUniversität Potsdam, Germany
The quantitative analysis of Wolf-Rayet type spectra requires non-LTE models for expanding atmospheres which became available in the last decade. Idealizing assumptions of the so-called standard model are spherical symmetry, homogeneity and stationarity. Synthetic spectra calculated under these assumptions are in general agreement with observation. However, specific observational facts (spectrum variability, X-ray emission) indicate that the standard assumptions are violated to some degree. The standard model has been extensively applied to analyze the "classical", massive Wolf-Rayet stars of Population I. The galactic WN class has been studied comprehensively on the basis of helium-hydrogen models. The recent inclusion of their nitrogen lines by means of corresponding models confirms the results for WNL (i.e. late subtype WN) stars, while for part of the WNE (early subtype) stars a revision of the temperature scale is to be expected. Some work remains to be done with the WC stars, which require models with carbon for their analysis. Only WC stars of intermediate subtype have been studied so far in the Pop. I domain. WC-type spectra are also shown by a considerable fraction of central stars of planetary nebulae. Recent spectral analyses of these low-mass stars, covering an extreme range of different subtypes, confirm the good experiences made with the standard model.
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