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Magnetic fields during the early phase of massive star formation

Seifried, Daniel Jürgen

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The goal of this work is to improve our current understanding of the formation process of massive stars in the presence of magnetic fields by means of numerical simulations. In particular, I focus on protostellar accretion rates, the evolution and the properties of protostellar discs and their associated outflows, and the interplay of turbulence and magnetic fields and its impact on protostellar disc formation. In a systematic parameter study I show that the accretion rates are remarkably constant over a wide range of initial conditions. Furthermore, I show that in the absence of turbulence for strong initial magnetic fields only sub-Keplerian discs can form which is attributed to the strong magnetic braking effect. This result seems to be in contrast to observational results. The morphology of the outflows, which shows a strong dependence on the initial conditions, can ultimately be linked to the structure of the underlying disc. Well-collimated outflows with high outflows velocities only develop if a Keplerian protostellar disc is present, otherwise slowly expanding, sphere-like outflows develop. Furthermore, I analyse the driving mechanism of outflows with an analytical criterion derived in the course of this work. When including supersonic, turbulent motions in the simulations, Keplerian protostellar discs form in contrast to the non-turbulent simulations. This result is in agreement with observations of early-type protostellar objects.

Item Type: Dissertation
Supervisor: Banerjee, Prof. Dr. Robi
Date of thesis defense: 19 December 2012
Date Deposited: 30 Jan 2013 06:56
Date: 25 January 2013
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
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