Masters Degrees (Physics)
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Browsing Masters Degrees (Physics) by Advisor "Meintjes, P. J."
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Item Open Access The development of a UFS-Boyden Photometric pipeline to facilitate the observational study of accretion driven systems(University of the Free State, 2005-05-30) Calitz, Johannes Jacobus; Meintjes, P. J.After the retirement of professor A. Jarrett in 1986, the 1.5-m telescope at Boyden Observatory stood idle for a decade. With the appointment of Dr P. Meintjes, steps were taken to refurbish the telescope with an updated drive control and camera system, which would eventually enable the telescope to be operated as an astrophysical research instrument. After funding became available, upgrading of the drive mechanisms were undertaken by DFM during August and September 2001 and the new SpectraVision 1k 1k CCD camera, that was on loan from Lawrence Livermore National Laboratory (LLNL), was installed during February 2002. After 16 years, the telescope was ready to be used for gathering data for research projects. The camera was installed with only demonstration software. Software was needed to control the camera and also for data reduction and a photometry pipeline. During this project, the problems encountered with the baes, electronics and collimation in the telescope were analized and xed where needed and possible. Manuals were written for the general use of the telescope, as well as the reduction and photometry pipeline. Extinction coecients for Boyden Observatory were determined. Software were developed to control the PixelVision CCD camera. A CCD reduction routine that is easy and automatic as far as possible was written and implemented. A photometry pipeline that can be used with vast amounts of data, while producing a high level of accuracy were developed. The research elds that are making use of the software include gravitational microlens observations, accreting compact objects and Gamma Ray Burst afterglows. A brief overview of these elds are given.Item Open Access The development of an IRAF-based scientific photometric package for the UFS-Boyden 1.5-m telescope(University of the Free State, 2009-03-10) Van Heerden, Hendrik Jacobus; Meintjes, P. J.English: In this dissertation there will be looked at the development of an (Image Reduction and Analysis Facility) IRAF-based scientific photometric package for the UFS / Boyden 1.5-m telescope. The dissertation consist of a discussion on the history of Boyden Observatory and its instruments, with specific emphasis on the Rockefeller 1.5-m telescope. The discussion will include information on the upgrades and improvements the telescope underwent to compete and do research on an international level. In the proceeding chapters charged coupled devices (CCDs) will be discussed, as well as how to characterize CCD photometric observation systems, like the 1.5-m telescope. The chapters will include experimental procedures and results obtained during characterization experiments. Chapters on photometry techniques will follow thereafter as well as the development of the Boyden-IRAF photometric data-analysis system. It will include an overview of IRAF, as well as a more in depth discussion of the Boyden-IRAF package. The discussion will specify as to why and how it was developed and how it works. A final chapter will be presented on the testing of the Boyden-IRAF package through the determining of the Boyden atmospheric extinction coefficients using the newly developed package. With this project, i.e. the development of an IRAF-based photometric program, an attempt is made to fill a void that exists related to the in-house photometric capabilities. A reliable and user-friendly photometric program will definitely also result in Boyden Observatory playing an important role in student training and research programs. Finally a conclusion will be drawn as to the success of the new developments, the IRAF-based photometric package, and what this means for the development of Boyden Observatory and the UFS Astrophysics group i.t.o. research and development.Item Open Access The identification of detectable gravitational wave signatures within the Einstein formalism for various classes of galactic sources(University of the Free State, 2014-01) Maritz, Jacques; Meintjes, P. J.English: A central result of this thesis is the prediction of short period (transient) GW signatures, using General Relativity. This thesis focused on various LIGO and SKA Gravitational Wave (GW) sources such as collapsing supernovae, rapidly spinning magnetars, the coalescence of compact binary objects and the stochastic Gravitational Wave backgrounds produced by Super Massive Black holes. Upper limits for the GW amplitudes and frequencies were predicted by means of numerical and analytic methods. Finally, the prospects of detecting Gravitational Waves from the galactic center will be discussed.Item Open Access An investigation into the nature of the relativistic compact object in the micro-quasar system LS 5039 : a multi-wavelength study(University of the Free State, 2007-11-30) Van Soelen, Brian; Meintjes, P. J.English: LS 5039 is a high mass binary system that shows multi-wavelength broad non-thermal emission. It is also a very high energy gamma-ray emitter, with TeV energy gamma-rays detected by H.E.S.S. (High Energy Stereoscopic System). The nature of the compact object is unknown, but a mass > 1:44M is implied by the lack of an X-ray eclipse. The presence of radio jet-like structures and a proposed mass of 3:7M , under the assumption that the system is pseudosynchronized, has led to the system's classiffication as a microquasar. Another model, in terms of a pulsar wind has also been proposed for the system. This study undertakes a model independent investigation of LS 5039 (neither microquasar nor pulsar), to attempt to determine what conclusions can be drawn from the system from first principles. A brief review of certain aspects of high mass binary theory is first presented, including accretion, binary motion, non-thermal radiation and mass out ow processes. The analysis looks at thermal evaporation from a disc structure in a black hole system, showing that this is unlikely, given the required temperature and the lack of thermal emission observed. The required conversion efficiency > 20% of accretion power in the black hole scenario also suggests that an additional reservoir of power is needed. The presence of a rotating magnetized neutron star, provides not only the magnetic field required to produce the non-thermal emission, it also supplies an additional power source, i.e the rotational kinetic energy of the neutron star. The magnetic field strengths and electron energies (for single particles) required to produce the very high energy gamma-rays is considered. An analysis of a fast rotating magnetosphere suggests that the centrifugal force exerted on the wind material could prevent accretion in the system. The power for the system is then extracted by a turbulent MHD process near the Alfv en radius.Item Open Access Mode identification in delta δ Scuti stars(University of the Free State, 1998-10) Evers, Elizabeth Anne; Balona, L. A.; Meintjes, P. J.This thesis discusses mode-identification from multicolour photometry. First, the need for a better mode identification technique for stars that have significant phase differences between the light curves in different colours is addressed. The necessary equation needed for modeidentification from photometry is then derived and briefly discussed. Then, a new, statistically based algorithm for mode-identification is developed by extending and adapting a method that has been applied to pulsating white dwarfs, to include the information provided by the different phases of the light curves in different wavelengths. This new algorithm allows the best estimate of the spherical harmonic degree l to be determined, as well as a confidence level from which the uniqueness of the mode-identification can be ascertained. The algorithm is then applied to a selection of well-observed 8 Seuti stars with the necessary multicolour photometry. It is found that it works well for high amplitude 8 Set stars, but that discrimination between the l = 0 and l = 1 modes is sometimes poor for the low amplitude stars. An algorithm to deduce the effective temperature, luminosity and equatorial velocity from the observed frequencies is also proposed. It is found that some mode-identification is necessary to obtain a unique solution of the stellar parameters. The method is applied to a subset of the 8 Set stars which have a suitable number of frequencies and suitable mode identifications.Item Open Access A multi-wavelength study of super soft X-ray sources in the Magellanic Clouds(University of the Free State, 2012-02) Odendaal, Alida; Meintjes, P. J.English: Supersoft X-ray Sources (SSS) form Cl, highly luminous class of objects that emit more Than ~ 90% of their energy in the supersoft X-ray band, i.e. below 0.5 keV. They are generally believed to consist of a white dwarf with a more massive binary companion, resulting in thermal time-scale mass transfer to the white dwarf and associated accretion. The high accretion rate of material onto the white dwarf is sufficient to drive nuclear burning and accompanying soft X-ray emission on the white dwarf surface, and may imply the presence of an accretion disc and significant mass outflow from some of these sources. However, SSS do not form a homogeneous class and also include objects like planetary nebulae, symbiotic novae and cataclysmic variables exhibiting nova outbursts. To investigate the phenomenon of accretion and the nature of possible mass outflow in SSS. a sample of 3 candidate sources in the Magellanic Clouds were identified for optical spectroscopic and X-ray studies: CAL 83, N67 and SMC 13. The galactic symbiotic nova RR Tel was also included in the study due to the evidence for an accretion disc implied by the double-peaked Raman-scattered 0 VI emission. Signatures of disc accretion and mass ejection in close binary supersoft sources (CBSS) like CAL 83, may provide evidence that such systems can evolve towards another class of binary system, namely the cataclysmic variables. Optical spectroscopic studies of CAL 83, NG7 and RR Tel were performed with the Southern African Large Telescope (SALT) and the SAAO l.9-m Telescope, and archived Chandm and XMM-Newton observations of the sources SMC 13 and CAL 83 were also analysed. The optical spectra of CAL 83 exhibit evidence of line broadening due to radial motion in an accretion disc, and a signature of possible disc outflows is also present. A search for periodicity in the X-ray data of CAL 83 revealed indication of consistent periodic modulations at P ~ 67 s, which could possibly be associated with the rotation period of a spun-up white dwarf. The presence of a fast rotating WD could provide a mechanism to explain the outflow inferred from the optical spectrum. The widths of nebular emission lines of the planetary nebula N67, as well as that of typical nebular lines in RR Tel are consistent with the known expansion velocities of nebulae surrounding the central objects in these systems.Item Open Access The search for high-energy gamma-ray emission from the close binary system AR Scorpii using Fermi-LAT data(University of the Free State, 2021-10) Kaplan, Quinton; Meintjes, P. J.; Van Heerden, H. J.AR Scorpii (AR Sco) is an enigmatic close binary system which is observable across most of the electromagnetic spectrum. Multi-wavelength emission consists of both thermal and non-thermal components, where pulsed non-thermal emission has been observed from radio to X-ray. The apparent lack of accretion in the system also suggests that the highly magnetic white dwarf is primarily spin-powered, similar to pulsars, where particles can be accelerated to produce non-thermal emission. The multi-wavelength nature from radio to X-ray of AR Sco has been extensively studied and presented since 2016, showing a clear non-thermal synchrotron component from optical to X-ray. However, the parameters and processes towards the high-energy regime still need to be clearly verified and explored. Hence, a search for non-thermal γ-ray emission from AR Sco using archival Fermi data from the past decade has been performed. By using updated Fermi-LAT software and Pass 8 analysis methods, low-level upper-limit emission has been observed above 100 MeV, with a possible low-level pulsed signal at the spin period (Ps = 117 s) of the white dwarf. Given the results, the possibility of non-thermal emission at higher energies can not be excluded. An updated spectral energy distribution using Fermi-LAT data was also produced to serve as a template for future studies using more sensitive Cherenkov telescope detectors like e.g. the Cherenkov Telescope Array (CTA).Item Open Access The search for pulsed radio and gamma-ray emission from the cataclysmic variable system AE Aquarii using MeerKAT and Fermi-LAT data(University of the Free State, 2021-12) Madzime, Spencer Tendai; Meintjes, P. J.; Van Heerden, H. J.The nova-like AE Aquarii was extensively studied using 11 years of data and contemporaneous optical data with the aim to establish pulsed gamma-ray emission at the rotational period (33.08 s) of the white dwarf and the first harmonic (16.54 s). In addition the study was also aimed at identifying pulsed radio emissions at or near the fundamental frequency. Therefore the search of pulsed radio and gammaray emission using MeerKAT (radio) data and upgraded Fermi-LAT pass 8 (gammaray) datasets is presented. The L-band 45 mins observation of AE Aquarii resulted in the first detection of this source by the MeerKAT telescope. Also, the pulsed radio emission search resulted in the first detection of pulsed emission modulated at the white dwarf’s rotational period (33.08 s). Further investigation resulted in no indication of any pulsations at the first harmonic (16.54 s). The pulsed signal’s overall strength is confined to lower L-band frequencies at the onset of the flare event. No pulsations were significant at the peak of the flare-like event. The spectral variation investigations revealed an optically thin spectrum. This optically thin spectrum observed in the MeerKAT data appears to be uncorrelated to the overall radio spectrum up to 1000 GHz. Hence, a correlation between the MeerKAT data and observations at higher frequencies could be an exciting topic for in-depth follow-up studies. Investigation for gamma-ray emission from AE Aquarii was conducted using an 11-year baseline of the archived upgraded Fermi-LAT pass 8 dataset. The standard binned and unbinned analyses techniques resulted in no detection of any significant gamma-ray excess in the region of AE Aquarii. However, the search for transient burst-like gamma-ray emission through a light curve revealed sections of the data with an excess significance of 2 s. A search for pulsed gamma-ray emission from these sections resulted in substantial evidence of pulsed signal from some of these sections with excess significance. An additional search for pulsed gamma-ray emission using shorter time bins resulted in detecting more significant pulsations at both the fundamental (33.08 s) and the first harmonic (16.54 s) frequencies. The stacked periodogram displayed clear evidence of particle acceleration from two polar zones of the white dwarf in AE Aquarii, which resulted in a double pulse. Periods contemporaneous to observed optical flares displayed weak pulsations in the noise level. After stacking the periodograms, a significance of over 4 s is seen at the fundamental frequency (33.08 s). A further search for evidence of sporadic burst-like gamma-ray emission from AE Aquarii using refined or more selective filtered data resulted in the detection of AE Aquarii with a significance of 14 s from both the binned and unbinned analyses techniques. The gamma-rays detected from a more constrained refined filtered dataset show clear gamma-ray spectral hardening above the galactic gamma-ray emission. These results have significant implications for follow-up studies of AE Aquarii using ground-based Cherenkov telescopes.Item Open Access Secondary star surface magnetic activity and mass transfer in cataclysmic variables(University of the Free State, 2005) Jurua, Edward; Meintjes, P. J.In this study it is shown that secondary star magnetic fields influence the mass transfer process in close interacting binaries, especially cataclysmic variables (CVs) and thus play a fundamental role in the whole mass transfer process, and evolution of these systems. The Mestel and Spruit (1987) stellar wind theory is used to model the surface magnetic field of the secondary star in CVs, particularly the intermediate polars, constraining the angular momentum that is required to drive the observed mass transfer rate through Roche lobe overflow. This in turn allows solving for the mass transfer rates, via magnetic braking, and the surface polar magnetic field of these stars. These field strengths are used to study and constrain magnetic advection from the secondary star to the primary star, and its effect on the mass flow in the funnel in magnetic CVs. This has important consequences for the so-called magnetic viscosity in the accretion discs of disc accreting magnetic cataclysmic variables, which are fed by these magnetic secondary stars. It is shown that the mass transfer rates in these systems vary with orbital period, with lower mass transfer rates in more compact systems than in the wider systems. It is also shown that advection of magnetic flux into the funnel results in severe magnetic viscosity at the L1 region. The advected magnetic field into the funnel flow results in a magnetized flow and enhanced magnetic pressure in the L1 region. Since the magnetic pressure in the L1 region exceeds the flow ram pressure, continuous flow of material through the L1 region is prevented. It is shown that matter can easily cross the funnel if pressure builds up behind the barrier. This therefore implies that the mass transfer in these systems is not continuous but fragmented in the form of blobs.