COLOR EXCESSES, INTRINSIC COLORS, AND ABSOLUTE MAGNITUDES OF GALACTIC AND LARGE MAGELLANIC CLOUD WOLF-RAYET STARS

Using IUE archival data in the wavelength range 1200-3200 Å, we have developed a new quantitative method of nulling the 2175 A interstellar absorption feature observed in stellar spectra and have used this method to determine the color excesses and UV spectral indices for 44 Galactic and 32 Large Magellanic Cloud (LMC) Wolf-Rayet stars. In order to determine the most accurate values possible, we have chosen only those stars located in regions for which the reddening law is either well known or expected to be similar to the Galactic or LMC mean. Our method assumes that the intrinsic UV continuum of Wolf-Rayet stars can be well represented by a power law of the form Fλ∼λ-α. Through the use of a χ2-minimization technique, the method provides an objective determination of the color excess and its statistical error. We have combined our values of color excesses with published line-free spectrophotometry to derive line-free intrinsic colors for Wolf-Rayet stars of nearly all spectral subtypes. In general, there is no correlation of intrinsic color or UV spectral index with spectral subtype for single WN and WC stars. This result agrees with previous suggestions that there is a large range in the values of intrinsic parameters for stars within a given Wolf-Rayet subtype. Our results demonstrate the need for a two-parameter spectral classification scheme for WN stars. We have compared our intrinsic colors with those predicted by current models of Wolf-Rayet stars and find generally good agreement. In addition, we find that early WN stars in the LMC have smaller spectral indices and redder intrinsic colors than early WN stars in the Galaxy. We have also derived absolute magnitudes for the LMC Wolf-Rayet stars and those Galactic stars with reliable distance estimates. There is a clear separation in absolute magnitude between early and late WN stars. The values derived for Galactic WN stars are similar to those for LMC WN stars.