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Universität Tübingen

1. Kölligan, Anders. From accretion to outflows of massive protostars .

Degree: 2018, Universität Tübingen

Massive stars live short but intense lives. While less numerous than low-mass stars, they enormously impact their surroundings by several feedback mechanisms. They form in opaque and far-away regions of the galaxy, such that one of these feedback mechanisms also becomes one of few records of their evolution: their bright large-scale outflows. Their emergence and related phenomena, such as the accretion disk that launches them, comprise the main focus of this thesis. In chapter 2, we present our magneto-hydrodynamic (MHD) simulations that were conducted with non-ideal MHD, self-gravity, and very high resolutions, as they have never been achieved before. In our comprehensive convergence study, we investigate computational conditions necessary to resolve (pseudo-) disk formation, and outflow launching processes and we analyze possible caveats. We explore the magneto-hydrodynamic processes of the collapse of a massive prestellar core, including an analysis of the forces involved and their temporal evolution. We follow the initial 100 M cloud core for up to two free-fall times, during which it collapses under its own self-gravity to self-consistently form a dense disk structure that eventually launches outflows. The setup allows us not only to show a comprehensive evolutionary picture of the collapse, but also enables the resolution of highly collimated magneto-centrifugal jets and magnetic pressure driven tower flows as separate structures. This is only possible in very high resolutions and is, to our knowledge, the first time this has been achieved. Of the two outflow components, the tower flow dominates angular momentum transport, while the mass outflow rate is dominated by the entrained material from the interaction of the jet with the stellar environment and just a part of the ejected medium is directly launched from the accretion disk. Taking into account both the mass launched from the disk’s surface as well as the entrained material from the envelope, we find an ejection-to-accretion efficiency of 10%. Additionally, a tower flow can only develop to its full extent when much of the original envelope has already dispersed as otherwise the ram-pressure of the infalling material inhibits the launching on wider scales. We argue that non-ideal MHD is required to form centrifugally supported accretion disks and that the disk size is strongly dependent on spatial resolution. We find that a converged result for disk and both outflow components requires a spatial resolution of ∆x ≤ 0:17 au at 1 au and sink cell sizes ≤ 3:1 au. Our results indicate that massive stars not only possess slow wide-angle tower flows, but also produce magneto-centrifugal jets, just as their low-mass counterparts. Therefore, the actual difference between low-mass and high-mass star formation lies in the embededness of the high-mass star. This implies that the jet and tower flow interact with the infalling large-scale stellar environment, potentially resulting in entrainment. In chapter 3, we investigate the occurrence of observed asymmetries in… Advisors/Committee Members: Kuiper, Rolf (Dr.) (advisor).

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APA (6th Edition):

Kölligan, A. (2018). From accretion to outflows of massive protostars . (Thesis). Universität Tübingen. Retrieved from http://hdl.handle.net/10900/84630

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Kölligan, Anders. “From accretion to outflows of massive protostars .” 2018. Thesis, Universität Tübingen. Accessed November 20, 2018. http://hdl.handle.net/10900/84630.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Kölligan, Anders. “From accretion to outflows of massive protostars .” 2018. Web. 20 Nov 2018.

Vancouver:

Kölligan A. From accretion to outflows of massive protostars . [Internet] [Thesis]. Universität Tübingen; 2018. [cited 2018 Nov 20]. Available from: http://hdl.handle.net/10900/84630.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Kölligan A. From accretion to outflows of massive protostars . [Thesis]. Universität Tübingen; 2018. Available from: http://hdl.handle.net/10900/84630

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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