FUNDAMENTAL PARAMETERS OF WOLF-RAYET STARS .2. TAILORED ANALYSES OF GALACTIC WNL STARS

Quantitative analyses of 9 Galactic WNL (WN7-8) stars, with particular reference to the hydrogen, helium, carbon and nitrogen abundances, ar e presented. These analyses are based on extensive UV, optical and IR spectroscopy, and have been undertaken using the Wolf-Rayet (WR) stand ard model. Our results compare well with those from previous non-LTE a nalyses confirming that the influence of CNO elements is of minor impo rtance for WN stars. Observed profiles of hydrogen and helium are gene rally reproduced to high precision, with some exceptions, while metal lines are simultaneously matched to within a factor of about two. We a lso investigate the influence of line blanketing on the resulting stel lar parameters. We find that WNL stars belong to two distinct groups. Firstly, the WN7-8 stars with a fairly strong HeI signature, are found to have low terminal velocities (850 km s(-1)), moderate luminosities (L/L(.)similar to 10(5.5+/-0.3)) and very low hydrogen contents (X(H) =15+/-15%). Secondly, those single stars classified WN7+abs (i.e. abso rption components present in the upper Palmer series) were found to ha ve high velocity winds (2150 km s(-1)), high luminosities (L/L(.)simil ar to 10(5.9)), and a considerable hydrogen content (X(H)=48+/-4%). Ca rbon and nitrogen abundances are broadly in line with those expected f or CNO-processed material from recent evolutionary models. A hydrogen content of <2% by mass was found for WR123 demonstrating that not all WNL stars contain substantial hydrogen. The evolutionary and mass-loss implications of our results are discussed elsewhere (Paper III, Crowt her et al. 1994b).