Determination of the Interstellar Extinction Toward WN Stars from Observed UBV Color Indices

Extract

Recent observations of Wolf-Rayet stars by Massey (1984) and Torres-Dodgen and Massey (1988) have yielded high quality, absolutely calibrated spectra of nearly all known Wolf- Rayet objects. These observations also indicate that discontinuities, or “jumps”, are present in the continuum spectra of some Wolf-Rayet stars. Such continuum jumps are predicted by the current theoretical models of Wolf-Rayet atmospheres. In general, these models provide good fits to the observed spectra of Wolf-Rayet stars. The models also indicate that, between jumps, the intrinsic continuum can be closely approximated by a power law in wavelength. In this case, we have the following relation between the intrinsic colors: where and Z₃₆₄₅ is the strength of the He II (η = 4) jump at 3645 Å in mags. This relation holds because the central wavelength of the u filter (λ_u = 3650 Å) is nearly coincident with that of the He II jump. In addition, models of WN stars with helium-dominated atmospheres predict a correlation between D₃₆₄₅ and (6 - v)o: