Crowther, Paul Adrian; (1993) Model atmosphere studies of Wolf-Rayet stars. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The fundamental properties of Population I Wolf-Rayet stars have been determined from analyses of their optical, IR and UV spectra using sophisticated model atmosphere codes (Hillier, 1987, 1990), Terminal velocities, stellar luminosities, temperatures, mass loss rates and abundances of hydrogen, helium, carbon, nitrogen and oxygen are determined, Grids of models are presented as a function of these different stellar parameters detailing their effect on line profiles and continua. The distance to HDE 313846 (WN9+abs) is determined to be 5±1 kpc, confirming its previously suspected high absolute magnitude of M = -7.1±0.8. A detailed quantitative analysis of 24 Galactic WN stars is presented, based on new optical spectroscopy, included as an atlas in the Appendix, Stellar parameters are derived using diagnostic lines and interstellar reddenings found from fitting theoretical continua to observed energy distributions. WN stars are found to fall into one of four broad groups depending on line strengths and elemental abundances. It is concluded that WNL+abs stars are the next evolutionary stage of massive Of stars. N/He and C/N ratios are found to be broadly in agreement with evolutionary models of Schaller et al (1992). Enhanced O/N and O/C is found for HD 104994 (WN3p) suggesting a peculiar evolutionary history. The stellar parameters of HD 62910 (WN6/WC4) are determined with abundance ratios indicating it is a single transition WN-WC star, broadly consistent with the evolutionary theory of Langer (1990). Four LMC Ofpe/WN9 stars have been analysed using new optical spectroscopy. It is proposed that WN9 or WN10 classifications are more appropriate for these stars. Their H/He, N/He derived abundances are found to be in excellent agreement with the latest evolutionary predictions from Maeder (1990) for WNL stars at low metallicity. The distance, interstellar reddening and stellar parameters of the LBV candidate He 3- 519 have been determined. This star is found to have a slow, dense unstable wind, as evidenced by dramatic Balmer line profile variability. Both He 3-519 and the LBV AG Carina, at minimum, are found to be spectrally and chemically cool members of the WN sequence (WN11) and closely related to P Cygni type stars.

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