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Title: Wolf-Rayet stars and chemical enrichment
Author: Dray, L. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2003
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Computational models of Wolf-Rayet and other massive stars are presented at solar metallicity and at a range of non-solar metallicities from Z = 0.03 to Z = 0.0001. The effects of differing mass-loss rates, evolutionary paths and initial mass distributions are quantified and the resulting Wolf-Rayet star populations compared to observations in this and other galaxies. It is found that observations may be reproduced with lower (and more realistic) mass-loss rates than the ones currently used in the literature, with a number of exceptions. The enrichment from these stars is calculated and compared to that from other sources of CNO. It is found that, whilst nitrogen originates mainly from intermediate-mass stars and oxygen from type II supernovae as expected, the origin of carbon is not clear-out and depends on a variety of sources. The effect of input parameters such as the adopted AGB yields and the binary fraction are discussed. Binary star models are presented and compared to observation. It is found that the majority of Wolf-Rayet stars at low metallicities are those which originate from mass transfer in binary systems, but that Wolf-Rayet CNO enrichment at all metallicities is still primarily from the single stars. Finally, a further use for the set of massive star models evolved here is considered - their use as gamma-ray burst progenitor models. It is found that the expected circumstellar mass distribution around a Wolf-Rayet star at the end of its lifetime may help to explain some features of gamma-ray burst afterglow light curves.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available