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Title: Wolf-Rayet populations in local group metal poor galaxies
Author: Tehrani, Katie
ISNI:       0000 0004 8509 3380
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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Wolf-Rayet (WR) stars are curious beasts. Characterised by broad emission line spectra and strong stellar-winds driving huge mass-loss rates, these stars are rare and unusual. Understanding these stars has many implications for massive star evolution and stellar feedback, however numerous obstacles prevent progress, such as incomplete samples and gaps in our knowledge regarding their formation, binary status, stellar properties and final stages. Within this thesis we have focused on addressing some of these issues through studying the WR population residing in Local Group dwarf galaxies, specifically within IC10 and the 30 Doradus region of the LMC. Using Gemini/GMOS narrow-band optical imaging of IC10 we have completed a thorough search of the region for WR stars, identifying both previously confirmed and new candidates. Follow-up spectroscopy confirmed 3/11 new candidates with the remaining requiring further follow-up. We classified each star and used the spectra to search for evidence of binarity. We update the WC/WN ratio to 1.0 +/- 0.4, and using nebular emission lines we also revise the metallicity estimate, finding that IC10 is not as metal poor as previously considered. We also used X-ray data from the T-ReX Chandra X-ray visionary programme to study the 30 Doradus WR population. Our main focus here was to assess the binary status of these stars by looking for signatures of colliding winds. Our results identify 4 clear binary candidates; Mk34, R140a, R136c and Mk39. Using VFTS data we confirm Mk39 as an SB2. Finally, an optical follow-up campaign using VLT/UVES to monitor Mk34 revealed an SB2 system with clear radial velocity variations. We derive the orbital parameters and obtain direct mass estimates for each component (M(a)sin{3}(i) = 65 +/- 7 Msol and M(b)sin{3}(i) = 60 +/- 7 Msol). We also perform spectroscopic and evolutionary modelling, the results of which suggests Mk34 is the most massive binary system known to date.
Supervisor: Crowther, Paul Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available