TAILORED ANALYSES OF 24 GALACTIC WN STARS

The fundamental properties of 24 Galactic WN stars are determined from analyses of their optical, UV and IR spectra using sophisticated mode l atmosphere codes (Hillier, 1987, 1990). Terminal velocities, stellar luminosities, temperatures, mass loss rates and abundances of hydroge n, helium, carbon, nitrogen and oxygen are determined. Stellar paramet ers are derived using diagnostic lines and interstellar reddenings fou nd from fitting theoretical continua to observed energy distributions. Our results confirm that the parameters of WN stars span a large rang e in temperature (T = 30-90,000 K), luminosity (log L*/L. = 4.8-5.9), mass loss (M = 0.9-12 x 10(-5) M. yr-1) and terminal velocity (upsilo n(infinity) = 630-3300 km s-1). Hydrogen abundances are determined, an d found to be low in WNEw and WNEs stars (<15% by mass) and considerab le in most WNL stars (1-50%). Metal abundances are also determined wit h the nitrogen content found to lie in the range N/He = 1-5 X 10-3 (by number) for all subtypes, and CIN - 0.02 in broad agreement with the predictions of Maeder (1991). Enhanced O/N and O/C is found for HD 104 994 (WN3p) suggesting a peculiar evolutionary history. Our results sug gest that single WNL+abs stars may represent an evolutionary stage imm ediately after the Of phase. Since some WNE stars exist with non-negli gible hydrogen contents (e.g. WR136) evolution may proceed directly fr om WNL+abs to WNE in some cases, circumventing the luminous blue varia ble (LBV) or red supergiant (RSG) stage.