Dessart, Luc; (1999) Quantitative studies of Wolf-Rayet stars in Local Group galaxies. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Fundamental properties of Wolf-Rayet (WR) stars in Local Group galaxies have been obtained using high quality UV, optical and IR spectroscopy coupled with a sophisticated model atmosphere code including line-blanketing and clumping. Quantitative analyses of WR stars in the cores of two giant H II regions, HD97950 in NGC3603 and R136a in 30 Doradus - is presented, based on archive HST spectroscopy. We find very large luminosities (~10⁶L☉) for these H-rich objects (H/He ~ 3-6). In the two core regions, WNL stars provide about 20% of the total ionizing flux and about 60% of the total kinetic energy injected into the ISM, despite representing ≤10% of the massive star population. HD97950 and R136a overall show similar global properties, although R136a is embedded in a denser (and older) region than its Galactic counterpart. I studied the recently discovered He I emission line stars in the Galactic Centre region using K and L band observations obtained at UKIRT, making use of He II 3.09μm to derive reliable surface temperatures. That line was observed in three objects, for which stellar parameters were determined, revealing properties typical of LMC or Galactic WN8-9 stars. I present an analysis of Galactic WC5-8 stars, including ISO-SWS datasets. For all stars studied (WR146, WR90, WR135, and WR11), the derived neon abundance shows a strong enrichment, though up to 50% lower than evolutionary expectations. Earlier discrepancies arose from unrealistic distances and/or mass loss rates. Analyses of seven LMC WC4 and one WO stars were carried out. LMC WC4 stars reveal an overlap in surface composition and temperature with Galactic WC4-8 stars, differing from these principaly by their lower surface mass flux and/or higher wind expansion velocity. While no trend in C/He is found between Galactic WCE and LMC WC4 stars, the WO star studied, Br93, possesses the greatest C/He and O/He values in the present WH sample. Finally, multifibre observations of 47 WR stars in M33 are presented, with new classifications and line information obtained. I confirm the absence of WO stars, and provide a precise determination of most WC subtypes.

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