FUNDAMENTAL PARAMETERS OF WOLF-RAYET STARS .5. THE NATURE OF THE WN CSTAR WR-8/

A detailed study has been carried out on the Galactic WN/C star WR 8 ( HD 62910), based on ultraviolet, optical and infrared spectroscopy. Ou r standard model analysis allows a determination of its stellar parame ters and chemical abundances of hydrogen, helium, carbon, nitrogen and oxygen. We find that the WN and WC spectral features are consistent w ith formation in the same stellar wind and derive stellar parameters o f T=48kK (T-eff=32kK), log(L/L(.))=5.1, log(M/M(.) yr(-1))=-4.2, v(in finity)=1590 km s(-1). The chemistry of WR 8 (H/He similar or equal to 0, C/He-0.02, C/N similar or equal to 3, C/O similar or equal to 4 by number) is indeed found to be intermediate between normal WN and WC s tars, and explains the peculiar WC line spectrum of WR 8. In common wi th previous WN analyses (e.g. Crowther et al. 1995d) all high and low excitation features cannot be simultaneously reproduced at present, wh ich we attribute to the neglect of line blanketing. We also determine physical parameters and C/He ratios for two other WN/C stars, WR145 (M R111) in the Galaxy and Brey 29 (HDE 269485) in the LMC. The physical properties of these stars are found to be very similar to WR 8, with C /N ratios also estimated to be of order unity. Overall, our results co nfirm that mixing does take place at the boundary of the convective He core in Wolf-Rayet stars, with an estimated timescale of similar or e qual to 10(4) years and are in excellent agreement with the theoretica l predictions of Langer (1991, 1994, private communication) in which s low mixing is produced through semi-convection.