FUNDAMENTAL PARAMETERS OF WOLF-RAYET STARS .6. LARGE MAGELLANIC CLOUDWNL STARS

We present a detailed, quantitative study of late WN (WNL) stars in th e LMC, based on new optical spectroscopy (AAT, MSG) and the Hillier (1 990) atmospheric model. In a previous paper (Crowther et al. 1995a), w e showed that 4 out of the 10 known LMC Ofpe/WN9 stars should be re-cl assified WN9-10. We now present observations of the remaining stars (e xcept the LBV R127), and show that they are also WNL (WN9-11) stars. w ith the exception of R99. Our total sample consists of 17 stars, and r epresents ail but one of the single LMC WN6-11 population and allows a direct comparison with the stellar parameters and chemical abundances of Galactic WNL stars (Crowther et al. 1995b; Hamann et al. 1995a). P reviously unpublished ultraviolet (HST-FOS, IUE-HIRES) spectroscopy ar e presented for a subset of our programme stars. We find observational evidence for lower metallicities in LMC WNL stars compared to the Gal axy, though this is not reflected in their stellar properties. For Gal actic and LMC stars we find: (i) a similar range in temperature and lu minosity, in contrast to evolutionary predictions; (ii) comparable win d performance values ((M) over dot upsilon(infinity) /[L/c]) and hydro gen composition, with a broad correlation between increasing helium co ntent and wind performance number; (iii) a general trend to lower wind velocities at lower stellar temperature, with possibly slower winds f or LMC WN9-11 stars. Some 30 Dor WNL stars show exceptional properties : Brey 89 (HD 38282, WN6h) has the highest luminosity (log (L/L.)simil ar to 6.25) and mass-loss rate (log ((M) over dot/(M. yr(-1))) similar to-3.6) known for any WR star, while Brey 80 (R135, WN7h) has an enor mous wind performance number of 50. The observed physical properties o f our sample of LMC WNL stars supports the Crowther et al. (1995c) evo lutionary scheme for Galactic stars, in that the most massive O stars, exclusive to 30 Dor, evolve directly to O3 If/WN6 and subsequently WN 6-7 stars (e.g. Brey 89), without passing through an intermediate LBV phase. In contrast, lower initial mass stars evolve through a LBV phas e, encompassing a WN9-11 stage (e.g. BE294), with WN8 stars being thei r immediate successors.