1995A&A...304..269C

A detailed study has been carried out on the Galactic WN/C star WR 8 (HD62910), based on ultraviolet, optical and infrared spectroscopy. Our standard model analysis allows a determination of its stellar parameters and chemical abundances of hydrogen, helium, carbon, nitrogen and oxygen. We find that the WN and WC spectral features are consistent with formation in the same stellar wind and derive stellar parameters of T_*=48kK (T_eff=32kK), log(L/L_☉)=5.1, log({dot}(M)/M_☉/yr)=-4.2, v_∞=1590km/s. The chemistry of WR 8 (H/He≃0, C/He≃0.02, C/N≃3, C/O≃4 by number) is indeed found to be intermediate between normal WN and WC stars, and explains the peculiar WC line spectrum of WR 8. In common with previous WN analyses (e.g. Crowther et al. 1995d) all high and low excitation features cannot be simultaneously reproduced at present, which we attribute to the neglect of line blanketing. We also determine physical parameters and C/He ratios for two other WN/C stars, WR145 (MR111) 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 confirm that mixing does take place at the boundary of the convective He core in Wolf-Rayet stars, with an estimated timescale of ≃10⁴ years and are in excellent agreement with the theoretical predictions of Langer (1991, 1994, private communication) in which slow mixing is produced through semi-convection.