FUNDAMENTAL PARAMETERS OF WOLF-RAYET STARS .3. THE EVOLUTIONARY STATUS OF WNL STARS

New high S/N optical observations of 9 Galactic WNL (WN7-8) stars are presented. The spectra have been analysed using tailored non-LTE model atmospheres by Crowther et al. (1994c). Here we use the derived stell ar parameters and abundances for a thorough investigation of the evolu tionary status and mass-loss properties of WNL stars. We have identifi ed two distinct groups of WNL stars from their observed properties. Th e WNL+abs and WN7 stars have high luminosities (log L/L(.)similar to 5 .9) and form a continuity in morphology and physical parameters from t he Of stars. They appear to be intimately related to these stars, conf irming the suspicion of Walborn (1973) and are descended from extremel y massive progenitors (M(initial)>60 M(.)) through the sequence O-->Of -->WNL+abs-->WN7 (-->WNE)-->WC-->SN. In contrast, the evolutionary seq uence for WN8 stars is identified as O-->LBV or RSG-->WN8-->WNE-->WC-- >SN. These stars, with lower luminosities (log L/L(.)similar to 5.5), are descended from less massive stars, and have either red supergiant (RSG, 25 M(.)<M(initial)<40 M(.)) or Luminous Blue Variable (LBV, 40 M (.)<M(initial)<60 M(.)) progenitors. Indeed, we identify many properti es that WN8 stars have in common with LBVs, e.g. spatial distribution, association with ejecta nebulae, low binary frequency, large photomet ric variability. We also find that those stars with the highest termin al velocities (WN7+abs stars) have the lowest variability while the WN 8 stars and LBVs (low wind velocities) are the most variable. The smoo th progression of mass loss properties from O supergiants to WNL stars found by Lamers & Leitherer (1993) is confirmed with the WNL+abs star s lying intermediately between the WN8 stars and O stars. The spectros copic differences between Ofpe and WNL+abs stars appear to be attribut able principally to a difference in wind density. This naturally expla ins the often ambiguous Of-WN spectral classification of some Of and W NL stars (Conti & Bohannan 1989). Finally, interstellar reddenings are determined using two independent methods based on the model atmospher e continuum distributions and the observed ubv colours. We find that t he UV reddening towards WR25 (WN7+abs) is highly anomalous (R=4.6), co nfirming the findings of Tapia et al. (1988) for stars in Tr 16 in the Carina nebula.