Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 22 for “"F510 - Astrophysics"”.
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Radio Observations of Discs around Young Stellar Objects
In this thesis we study the disc surrounding the Young Stellar Object DG Tau B. We present observations at both cm and mm wavelengths using e-MERLIN and the EVLA respectively. We study the cold dust in the disc of DG Tau B by looking at its spectral energy distribution (SED). We also analyse the …
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Identifying intervening absorption systems for use as cosmological probes
Quasars being one of the most luminous objects in the sky can act as cosmological probes for analyzing not only the large-scale structures (LSSs) in the universe, but also to trace the metal absorption systems by probing the gas content (Zibetti et at., 2005; Ménard et at., 2005) that lie on the …
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The variation of coronal holes with solar cycle
Coronal holes are commonly known to be the source of the open magnetic flux and the high-speed solar wind. In EUV and X-ray emission lines, coronal holes are seen as the regions with reduced emission due to lower temperatures and electron density than the surrounding quiet sun. Observing the …
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Large-scale structure of the early universe
The large-scale structure of the universe is one of the most active areas of research in modern astronomy. However, until recently our knowledge of the distribution of matter on large scales has been primarily limited to two epochs - the present epoch and the epoch of recombination - and …
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The Chemical and Dynamical Evolution of Simulated Late-Type Galaxies
In this thesis I discuss two projects that have been a major part of my postgraduate studies. The aim of these projects is to study the dynamics and chemodynamics of simulated Milky Way analogues. Specifically, I investigate chemical abundances in the solar-neighbourhood and of the outflow rates of …
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Metallicities and stellar populations in spiral bulges
A major aim of current astrophysical research is the development of models of galaxy formation that are consistent with observational data. Until recently, the main tools of such research were broadband colours. However, the Lick system of indices has recently provided researchers with a more …
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Application of statistical analysis techniques to solar and stellar phenomena
Currently, solar observers are investigating spectroscopic images of the Sun's outermost atmosphere (the corona), which are challenging long-held views on the density and temperature structure of this environment. The corona is "filled" with magnetic strands but determining their precise nature is …
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The migration of giant planets in massive protoplanetary discs
If giant planets form by disc fragmentation early on during disc evolution, then they interact with the gas in the disc and as a result they will likely migrate, i.e. drift inwards or outwards. This study aims to explore the migration patterns of giant planets in unstable discs using radiative …
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Large groups of quasars in an ultraviolet-excess survey
This thesis describes the objectives, design, construction and analysis of the Chile-UK Quasar Survey, a new wide-field spectroscopic redshift survey of ultravioletexcess quasar candidates. The main objectives of the survey are the construction of a large, homogeneous catalogue of quasars with …
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Parsec-scale polarization of the jet in quasar 4C 71.07
Magnetic fields are of considerable importance in the study of radio jets: longitudinal magnetic fields are thought to help stabilize the jet as it travels outwards from the nucleus and, since magnetic field and jet plasma are frozen together, changes in jet structure are reflected in changes in …
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Quasar formation in the context of large scale structure
We present the results of an investigation of environments of quasars in the context of the large-scale structure in galaxy clusters. Our results are somewhat different from what was previously thought - a direct consequence of this new perspective and more powerful methods of analysis. In contrast …
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Heavily-reddened lines of sight in the galaxy
This thesis presents an investigation into the reddening effects of the diffuse ISM using a subset of stars from the Stephenson (1992) objective prism survey. The survey contained approximately 400 stars, which were originally reported to be heavily-reddened, early-type objects. (B)VRJ photometry …
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The evolution of isotoipc abundances from high-redshift to the local universe
Recent observations of carbon, sulphur, and titanium isotopes at redshifts z-.1 and in the Galactic stellar disc and halo have opened a new window into the study of isotopic abundance patterns and the origin of the chemical elements. Using our Galactic chemical evolution code CEtool, we have …
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Spatial and spectral comparisons of soft X-rays from galaxies of different morphological types
Encounters between galaxies have long been recognised as having a possible influence over a galaxy's evolution. Nevertheless for years such encounters were regarded as rare events, with models incapable of producing the tidal tails, ripples and shells observed in classical mergers. Numerical …
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Observational studies of key stages in stellar evolution
This thesis presents observational investigations into three poorly-understood, but key stages in stellar evolution. Stars undergoing the post T Tauri phase - which lies between the well-studied T Tauri stage of disc accretion and the arrival onto the Main Sequence - are difficult to identify and …
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Beyond the solar surface: an observational study of solar coronal loops
This thesis presents an observational analysis of structures in the solar corona. The plasmafl in the corona is low (<I), therefore, the emitting material is intimately linked to the magnetic fleldlines. The initial aim of this work, outlined in Chapter 3, is to take advantage of this relationship …
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Interpreting the 10um astronomical silicate feature
10pm spectra of silicate dust in the diffuse medium towards Cyg 0B2 no. 12 and towards field and embedded objects in the Taurus Molecular Cloud (TMC) were obtained with CGS3 at the United Kingdom Infrared Telescope (UKIRT). Cold molecular-cloud silicates are sampled in quiescent lines of sight …
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A spectroscopic study of the rapidly oscillating peculiar A star HD 134214
Photometric studies were made of 10 peculiar-A-type (Ap) stars looking for long period oscillations typical of rapidly-oscillating Ap stars (roAp stars) using the 0.75-rn telescope at the South African Astronomical Observatory. Although a promising candidate pulsator was found in HD 156869, no such …
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Polarization VLBI monitoring of BL lacertae - kinematics, faraday effects and intermediate scale structure
This thesis presents the results of a series of polarization VLBI experiments on the wellknown variable radio source BL Lacertae (BL Lac). VLBI provides the only means to study radio sources on scales 1 mas, and the sensitivity to polarization allows the magnetic field structures in the source to …
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Transverse polarization structure of parsec-scale radio jets
The magnetic fields that thread extragalactic radio jets play an important role in the emission properties and evolution of these objects; knowledge of the structure and evolution of these magnetic fields is therefore important in forming a better understanding of jets by imposing constraints on …
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