1995A&A...293..403C

Quantitative analyses of 9 Galactic WNL (WN7-8) stars, with particular reference to the hydrogen, helium, carbon and nitrogen abundances, are presented. These analyses are based on extensive UV, optical and IR spectroscopy, and have been undertaken using the Wolf-Rayet (WR) standard model. Our results compare well with those from previous non-LTE analyses confirming that the influence of CNO elements is of minor importance for WN stars. Observed profiles of hydrogen and helium are generally reproduced to high precision, with some exceptions, while metal lines are simultaneously matched to within a factor of about two. We also investigate the influence of line blanketing on the resulting stellar 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 (850km/s), moderate luminosities (L/L_☉∼10^5.5±0.3) and very low hydrogen contents (X_H=15±15%). Secondly, those single stars classified WN7+abs (i.e. absorption components present in the upper Balmer series) were found to have high velocity winds (2150km/s), high luminosities (L/L_☉∼10^5.9), and a considerable hydrogen content (X_H=48±4%). Carbon and nitrogen abundances are broadly in line with those expected for 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, Crowther et al. 1995A&A...293..427C).