Published online by Cambridge University Press: 03 August 2017
Current knowledge of Wolf-Rayet continua is reviewed and observed continuum energy distributions are compared with model predictions. Good agreement is found. For WN stars a large range in intrinsic color is found for each subclass and the so far unexplained large range in the observed reddening-free continuum indices can be understood on the basis of atmospheric models. The strength of the continuum discontinuities determines the value of the index. Because of severe blending by the emission lines in WC spectra it can not be decided whether the intrinsic colors of WC stars of a given spectral type vary over a range of values or whether all stars of a given spectral type are similar. The reliability of model calculations for Wolf-Rayet stars is further tested by comparing observed and predicted correlations of helium line strengths. Satisfactory agreement is found for the Kiel/JILA models but not for the Bhatia-Underhill models. Methods used to determine the reddening due to interstellar extinction are reviewed and their accuracies estimated.