THE BALDWIN EFFECT IN WOLF-RAYET STARS

The equivalent widths of a number of emission lines in the spectra of WN-type Wolf-Rayet stars are found to inversely correlate with the lum inosity of the underlying continuum. This is the well-known Baldwin Ef fect that has previously been observed in quasars and some Seyfert I g alaxies. The Effect can be inferred from line and continuum prediction s in published non-LTE model helium atmospheres and is explainable in terms of differences in wind density among WN stars. Using a simple wi nd model, we show that the Effect arises from the fact that both the e ffective radius for the local continuum and the emission measure of th e layers above the continuum-forming region depend on the density in t he wind. The Effect provides a new method for distance determinations of W-R stars.