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Title: Mass-loss properties of the most massive stars in 30 Doradus
Author: Bestenlehner, Joachim Michael
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2013
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Our understanding of high-mass star evolution is tightly connected to our understanding of their mass-loss properties. The initial and final mass are significantly different as a result of mass loss. Massive stars have strong stellar winds and high ionising fluxes and are the main sources for mechanical and radiative feedback in giant H II regions. However, the wind and mass-loss properties and how they change during their evolution are not understood. To provide new observational evidences and to test current theoretical predictions, this thesis explores the mass-loss rate range from optically thin O-star winds to optically WR-star winds. In the context of the VLT-Flames Tarantula Survey we study the transition region from O-stars to very massive WNh-stars. For this study, we selected 62 0, Of, Of/WN, and WNh-stars in the Tarantula Nebula. For the analysis, we used the non-LTE radiative transfer code CMFGEN to obtain accurate stellar parameters, and to investigate the mass-loss propelties and evolution of these massive stars. We show that Of/WN-stars are transition objects from optically thin O-star winds to optically thick WR-star winds. Our sample covers an age range from 1 to 3 Myr. Of/WN and WNh-stars show hydrogen depletion at the surface on much shorter timescales (< 1 Myr) than the less luminous 0- stars. The predictions of the wind momenta for the' most luminous O-stars are overestimated and for the WNh-stars are underestimated. This is an indication that new theoretical mass-loss predictions are required for the most luminous stars. In our analysis yve could confirm the theoretical predictions which suggest a notable change of the mass-loss behaviour at a certain Eddington factor. The Eddington factor is well defined in evolutionary models. Using this mass loss-Eddington factor relation it is possible to provide more accurate mass-loss rates for new evolutionary models.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available