The intrinsic ionizing fluxes of the evolved Wolf-Rayet stars are a necessary but uncertain input to stellar synthesis models. These fluxes have been modeled recently, but have not been checked empirically. In this work we are trying to calibrate the ionizing (Lyman continuum) fluxes for Wolf-Rayet stars as a function of spectral type. Here we present Hα photometry of thirteen Wolf-Rayet nebulae where the exciting stars are all of WN type. We derive the Hα flux of the nebulae, using spectroscopy to correct for the reddening and the presence of NII emission within the Hα bandpass, which in turn yields the Lyman continuum photon flux from the exciting stars. Since the nebulae are not necessarily ionization-bounded, this flux is actually a lower limit on NLyc, the number of Lyman continuum photons radiated per second by the ionizing star. We have also considered the problem of shock-ionized nebulae vs photo-ionized nebulae. We present our new measurements of NLyc as a function of spectral type. We also compare our results for NLyc to those predicted from recent models for W-R stars (Vacca 1991), and to recent re-determinations of NLyc for main-sequence O and B stars (Vacca et al. 1996.) The fluxes are surprisingly internally consistent (considering the ionization vs density bounded problem), and also lower than expected from the models. KM acknowledges the support of the NSF REU program at NAU.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1997