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Non-Thermal Emission From Jets of Massive Protostars

Obonyo, Willice Odhiambo (2020) Non-Thermal Emission From Jets of Massive Protostars. PhD thesis, University of Leeds.

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Abstract

This thesis details the outcome of a study of non-thermal radio emission from a sample of massive protostellar jets. The jets are ionized and can interact with magnetic fields within their vicinity to generate non-thermal emission. A search for the emission was conducted on a sample of fifteen massive protostars, observed using the JVLA at 1.5GHz in 2015. Emission from the objects was characterised based on their spectral indices and spectral index maps, generated from their 1.5GHz (L-band) data, and previous observations at 6.0GHz (C-band) and 44.0 GHz (Q-band). 40% of the jets have characteristic non-thermal lobes, associated with synchrotron emission, especially sources of higher bolometric luminosity. All the cores, on the other hand, were found to be thermal, driving out material at rates that lie in the range 3×10^{-7} to 7×10^{-6} solar masses per year. Spectral energy distributions (SEDs) and spectral index maps of some of the protostellar jets displayed evidence of variability. As a result, four protostellar jets, previously observed in 2012 at C-band were identified and re-observed in 2018, at the same frequency, to study their variability property. Two of the protostars, S255 NIRS3 and W3 IRS5, displayed significant flux and positional variabilities respectively. S255 NIRS3 was in outburst while W3 IRS5 manifested clear proper motions and precession. Lastly, some of the observable properties of the protostellar cores were used in simulating their features. Numerical calculations of their hydrodynamic properties were performed, followed by computation of their spectra using a ray-tracing code. Examples of the properties that were used to initiate the hydrodynamic simulations include; mass-loss rates, velocities and opening angles. The radio emission of the cores were generally found to be stable unless the input parameters were varied. Indeed, a change in the velocities and mass-loss rates of the thermal jets led to a corresponding change in their fluxes.

Item Type: Thesis (PhD)
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds)
Identification Number/EthosID: uk.bl.ethos.804577
Depositing User: WILLICE OBONYO
Date Deposited: 04 May 2020 05:57
Last Modified: 11 May 2020 09:53
URI: http://etheses.whiterose.ac.uk/id/eprint/26460

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