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The first stars and the convective-reactive regime

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dc.contributor.author Clarkson, Ondrea
dc.date.accessioned 2021-01-12T07:37:40Z
dc.date.available 2021-01-12T07:37:40Z
dc.date.copyright 2020 en_US
dc.date.issued 2021-01-11
dc.identifier.uri http://hdl.handle.net/1828/12548
dc.description.abstract Due to their initially metal-free composition, the fi rst stars in the Universe, which are termed Population III (Pop III) stars, were fundamentally different than later generations of stars. As of now, we have yet to observe a truly metal-free star although much effort has been placed on this task and that of nding the second generation of stars. Given they were the first stars, Pop III stars are expected to have made the fi rst contributions to elements heavier than those produced during the Big Bang. For decades signi cant mixing between H and He burning layers has been reported in simulations of massive Pop III stars. In this thesis I investigate this poorly understood phenomenon and I posit that interactions between hydrogen and helium-burning layers in Pop III stars may have had a profound impact on their nucleosynthetic contribution to the early universe, and second generation of stars. First, I examined a single massive Pop III star. This was done using a combination of stellar evolution and single-zone nucleosynthesis calculations. For this project I investigated whether the abundances in the most iron-poor stars observed at the time of publication, were reproducible by an interaction between H and He-burning layers. Here it was found that the i process may operate under such conditions. The neutrons are able to ll in odd elements such as Na, creating what is sometimes called the `light-element abundance signature' in observed CEMP stars. I also present the finding that it is possible to produce elements heavier than iron as a result of the i process operating in massive Pop III stars. A parameter study I conducted on H-He interactions in a grid of 22/26 MESA stellar evolution simulations is then described. I grouped these interactions into four categories based on the core-contraction phase they occur in and the convective stability of the helium-burning layer involved. I also examine in detail the hydrogen burning conditions within massive Pop III stars and the behaviour of the CN cycle during H-He interactions. The latter is compared to observed CN ratios in CEMP stars. Finally, I describe the first ever 4pi 3D hydrodynamic simulations of H-He shells in Pop III stars. I also examine the challenges in modelling such con gurations and demonstrate the contributions I have made in modelling Pop III H and He shell systems in the PPMStar hydrodynamics code. My contributions apply to other stellar modelling applications as well. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights Available to the World Wide Web en_US
dc.subject Stars en_US
dc.subject Population III en_US
dc.subject Stellar Evolution en_US
dc.subject Nucleosynthesis en_US
dc.title The first stars and the convective-reactive regime en_US
dc.type Thesis en_US
dc.contributor.supervisor Herwig, Falk
dc.degree.department Department of Physics and Astronomy en_US
dc.degree.level Doctor of Philosophy Ph.D. en_US
dc.identifier.bibliographicCitation Clarkson, O., Herwig, F., & Pignatari, M. (2018). Pop III i-process nucleosynthesis and the elemental abundances of SMSS J0313-6708 and the most iron-poor stars. Monthly Notices of the Royal Astronomical Society, 474(1), L37-L41. doi:10.1093/mnrasl/slx190 en_US
dc.identifier.bibliographicCitation Clarkson, O., Herwig, F., Andrassy, R., Woodward, P., Pignatari, M., & Mao, H. (2019). H-he shell interactions and Nucleosynthesis in massive population III stars. (pp. 321-325). Cham: Springer International Publishing. doi:10.1007/978-3-030-13876-9_56 en_US
dc.identifier.bibliographicCitation Clarkson, O., Herwig, F., & Pignatari, M. (2019). Pop III i-process nucleosynthesis and the elemental abundances of SMSS J0313-6708 the most iron-poor stars (vol 474, pg L37, 2018). Monthly Notices of the Royal Astronomical Society, 488(1), 222-223. doi:10.1093/mnras/stz1676 en_US
dc.description.scholarlevel Graduate en_US


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