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Ahmadi, Aida

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This thesis is dedicated to the search and characterization of disks in high-mass star formation. The work presented is part of the CORE survey, a large observational program making use of interferometric observations from the NOrthern Extended Millimetre Array (NOEMA)for a sample of 20 high-mass protostellar objects in the 1.3 millimetre wavelength regime. An in-depth analysis of the W3(H2O) star forming region examines its fragmentation into two hot cores, separated by 2300 au and engulfed in a rotating circumbinary envelope of dense gas. Higher resolution observations reveal that embedded within each core is a rotating disk-like structure with outflows being ejected along the disk rotation axes. Studying the stability of the disk-like structures confirms that they are gravitationally unstable and prone to disk fragmentation. In an effort to understand the uncertainties involved, we created synthetic observations of a high-resolution 3D radiation-hydrodynamic simulation that leads to the fragmentation of a massive disk at different inclinations and distances. We find that the kinematics of differentially rotating disks resemble rigid-body-like rotation in poorly resolved observations, leading to overestimation of protostellar masses. Despite the lack of resolution, we find that the stability analysis correctly predicts disk fragmentation regardless of the uncertainties. Studying the kinematics of the full CORE sample, we find rotational signatures in dense gas perpendicular to bipolar molecular outflows in most regions. Modelling the level populations of various rotational transitions of the dense gas tracer CH3CN, we find the disk candidates to be on average warm (200 K). Applying the robust stability analysis, we find that most high-mass young stellar objects are prone to disk fragmentation early in their formation due to high disk to stellar mass ratio. Since most high-mass stars are found to have companions, disk fragmentation seems to be an important mechanism by which such systems may be formed.

Item Type: Dissertation
Supervisor: Beuther, Prof. Dr. Henrik
Place of Publication: Heidelberg
Date of thesis defense: 10 January 2020
Date Deposited: 28 Jan 2020 13:29
Date: 2020
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Service facilities > Max-Planck-Institute allgemein > MPI for Astronomy
Subjects: 520 Astronomy and allied sciences
530 Physics
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