FUNDAMENTAL PARAMETERS OF WOLF-RAYET STARS .1. OFPE WN9 STARS/

A detailed study has been carried out for 4 LMC Ofpe/WN9 ('slash') sta rs, and the sole Galactic WN9 star WR108 (HDE 313846), using new high S/N spectroscopy and archive UV and near-IR spectroscopy. Our observat ions reveal that photospheric Of features such as He II lambda 4542 ar e absent from the optical spectra of our sampled stars. All observed o ptical lines are formed in the stellar wind, and so we prefer WN9 or W N10 classifications based on the relative strengths of N II lambda 399 5 and N III lambda 4634-41, with BE 381 and Sk-66 degrees 40 prototype WN9 and WN10 stars, respectively. HDE 269927c and R84 are given WN9 c lassifications, with WR108 newly assigned WN9+abs due to the spectral appearance of the upper Balmer series. The distance to WR108 is determ ined from an analysis of its interstellar spectrum. Previously WR108 h as been considered to be a possible member of Sgr OB1 (1.6 kpc, Lundst rom & Stenholm 1984) which results in a uniquely low stellar luminosit y for this type of object. Using the standard Galactic rotation curve of Fich et al. (1989) we derive 5+/-1 kpc, resulting in a luminosity v ery similar to R84. Tailored analyses using the WR standard model, inc luding metals, result in the following stellar parameters for all star s: T=29.5+/-1.0kK, L/L.=10(5.65+/-0.2), M=3.5+/-1x10(-5) M. yr(-1) an d v(infinity)=400+/-100 km s(-1) (v(infinity)=1170 km s(-1) for WR108) . The stellar parameters determined for R84 compare well with those de termined previously by Schmutz et al. (1991) indicating that the effec t of CNO elements is negligible for WN stars. The metallicity of the L MC stars is around Z similar to 0.008 while Z similar to 0.035 results for the Galactic WN9 star. Abundances for the LMC stars (H/He=2.5+/-1 , N/He similar to 0.003, C/N similar to 0.1) are in reasonable agreeme nt with the results of evolutionary models at low metallicity (Schaere r et al. 1993a) although observed luminosities are significantly lower than predictions for stars entering the WR phase. The luminosity and chemistry of R84 are identical to that of the Luminous Blue Variable ( LBV) R71 indicating that it is probably associated with an LBV phase r ather than a post-red supergiant as suggested by Schmutz et al. (1991) . The status of the remaining LMC stars is less clear, although their common spectral characteristics suggest that they are also related to LBVs, with Sk-66 degrees 40 the least evolved of the present sample. F or WR108, its spectral appearance, derived parameters and abundances ( H/He=1.5, C/N similar to 0.10) suggest an intimate relationship with e xtreme Galactic Ofpe stars, with the wind density being the principal difference, and evolution probably proceeding directly from Of to Wolf -Rayet.