SPECTRAL ANALYSES OF THE GALACTIC WOLF-RAYET STARS - HYDROGEN-HELIUM ABUNDANCES AND IMPROVED STELLAR PARAMETERS FOR THE WN CLASS

Almost all known Galactic single WN stars have been analyzed applying non-LTE models for spherically expanding atmospheres. While in a previ ous study we performed ''coarse'' spectral analyses based essentially on helium-line equivalent widths compared to a grid of models, we now present improved results from 25 detailed ''fine'' analyses, i.e. from fitting the line profiles with individual model calculations. The non -LTE models applied now account for a helium-hydrogen composition, and corresponding abundances are determined for each star. 53% of the stu died Galactic WN stars (33 out of 62) are hydrogen-free, populating a luminosity range from 10(4.6) to 10(5.7) L. The occurrence of hydrogen is restricted to those WN stars with lowest stellar temperatures (30 ... 35 kK, with few exceptions), comprising most stars of late subtype (WNL) and part of the weak-lined early-type WN stars (WNE-w). But all WN stars are definitely hydrogen-deficient, compared to the solar val ue. Most WN stars showing hydrogen exhibit mass fractions beta(H) betw een 10% and 30%. They cover the whole luminosity range of the the hydr ogen-free WN stars, but extend also to higher values: a group of ten W NL stars with hydrogen is brighter than 10(5.7) L., i.e. brighter than any hydrogen-free WN star. Only three WN stars are found with hydroge n mass fractions as small as approximate to 5%. A small group of four WN7 stars with high luminosities (> 10(5.6) L.) has outstandingly high hydrogen mass fractions (40 ... 53%).