Radio signals from astronomical sources are extremely weak and easily distorted/- corrupted or overwhelmed by man-made radio signals such as cellphones, satellites, aircraft and telescope electronics. These Radio Frequency Interference (RFI) are increasingly threatening radio observatories due to our increasingly technological world. To detect and mitigate RFI, observatories need to understand their RFI environment, what contributes to it and how it is changing. While there are few dedicated RFI monitoring systems on the MeerKAT site, the most sensitive RFI detector is the MeerKAT array itself. In this thesis we use approximately 1500 hours of MeerKAT observations to create a multi-dimensional view of the RFI at the MeerKAT site. Here we investigate a probabilistic approach to characterise the RFI environment around the MeerKAT radio telescope. In order to achieve our goal, we propose the MeerKAT Historical Probability of RFI (KATHPRFI) framework. We produced the high level requirements of the KATHPRFI framework driven by the needs of the MeerKAT users. The design approach and the design decision of the framework is presented that cover both the software and hardware constraints. The KATHPRFI produces a 5-dimensional array of the RFI probability as measured by the MeerKAT telescope during the commissioning phase (May 2018 - December 2018) for each observation file. From the 5-D array, we extracted various statistics and characterised the RFI environment around MeerKAT site. We found that there is a correlation between RFI occupancy and the time of the day which is most probably related to human activities. Furthermore, we found a correlation between the time of the day and flights passing over a region of site. Our results showed that the highest probability of RFI points towards a region including nearby towns. The results obtained are consistent with the argument that the major RFI sources for MeerKAT site are the Global Positioning System (GPS) satellite, flight Distance Measurement Equipment (DME) and the Global System for Mobile Communications (GSM). Our data also showed that the RFI occupancy decreases with an increase of baseline length, this is a result of moving RFI sources with respect to the static sky. Therefore, the phase of the RFI changes rapidly on long baselines compared to short baselines. As a result when a correlation is carried out the RFI amplitude will vanish less on short baselines compared to the long baselines. Our results provide the first highly detailed view of the MeerKAT RFI environment allowing us to track the historical evolution of the RFI, both on average, and as a function of frequency, baseline and direction. With historical baselines known, one can also provide alerts about sudden changes. This could be due to new sources of RFI or stem from any outliers in the data, which could signal telescope or correlator issues. Hence the KATHPRFI framework also provides a window into the operational health of the telescope.

Includes bibliographical references. / This is the first time to the author's knowledge that a catalogue of galaxy photographs has been prepared on a uniform physical scale. Of the many interesting aspects which result from such an investigation, we mention here the fundamentally new appreciation both of the diversity of spiral arm texture, and in the range of the intrinsic diameters of galaxies, particularly the spirals. Small, high surface brightness spiral galaxies form an important subgroup; these present a saturated or predominantly saturated image on the SRC IIIa-J Survey. An intercomparison of their appearance on the J-film copies and those of the "Quick Blue" Survey shows an inner morphology often indicative of substantial differential rotation effects. One of our galaxies in the sample shows significant signs of warping; the spiral has no bright, close companions. Also of note are faint, featureless outer envelopes in some of the spirals, and galaxies with faint outer spiral arms whose pitch angles are significantly different from those of the central inner region. Further results are discussed in chapter 3 onwards. A by-product of this investigation is the identification of the largest known (type b) barred spiral.

Bibliography: pages 171-176. / Seyfert galaxies have compact nuclei with luminosities only surpassed by quasars, to which they are believed to be related. The most common interpretation of these objects is that their central power source is a black hole with matter accreting towards it. An understanding of these powerful energy sources would vastly increase our knowledge of high energy physics and cosmology. One unexplained characteristic of Seyfert nuclei is that their luminosities are often variable. Some questions relating to this fact are: What is the nature of the variability? How much obscuration is there from matter in the line of sight? What is the shape of the flux continuum? What is the relationship between the variability and other properties of the galaxy and nucleus? This thesis seeks to answer some of these questions, as they critically affect any model put forward to explain the Seyfert phenomenon. 29 southern Seyfert galaxies were chosen for observation. Flux measurements through five colour filters in the 0.3 to 1 μm range were made regularly in the period September 1986 to October 1989 with a single channel photometer and a CCD camera. These were analysed in conjunction with similar data collected by other investigators. Flux changes of 10% or more were observed in most objects. Fluxes through individual colour filters varied proportionally to each other, indicating that the shape of the continuum at these wavelengths remains constant. The flux distribution derived in this manner is shown to be similar for all objects examined. A procedure potentially superior to existing methods is developed to estimate the extinction of Seyfert nuclei from the flux distribution. Spectroscopic observations in the 0.34-0.72 μm range were made for most objects. From these spectra the gas densities and temperatures, degrees of activity and spectral line intensities and widths were derived. Possible spectral variations were investigated. No definite periodic changes in the light curves could be found. However the possibility of regular variations is not completely excluded. The relative amplitude and rate of flux variations are shown to be independent of the luminosity and other nuclear properties.

No description available.

The observations of the 12 known magnetic white dwarfs are reviewed and a list of mechanisms is discussed which could give rise to the observed absorption and polarization spectra. Particular emphasis is placed on the observations of, and mechanisms important in the 3 magnetic white dwarfs to be modelled - BPM 25114, G 99-47 and GD 90. The calculation of continuum flux and polarization in these stars is discussed: the ATLAS computer programme (Kurucz,1970) is outlined and the linear theory of circular dichroism (Lamb and Sutherland,1974) is described together with its effects on radiative transfer. The line absorption and polarization is treated in the context of Unno's (1956) equations and the line broadening theory and method of solution of the equations are presented. The computer programme to combine all aspects of the models is described in some detail, the calculated absorption and polarization spectra are presented and compared with the observations. Good overall agreement was achieved. The successes and failures of the approach are discussed together with suggestions for future work. The current observational and theoretical picture for the ZZ Ceti stars is discussed and the analysis of ZZ Ceti (Robinson et al.,1976) is examined in detail. An extensive programme of high-speed photometry on L 19-2 is reported, and the data reduction techniques described. Initial analysis of the reduced data with the approach of Robinson et al. was found to be fraught with difficulties. Instead, frequency analysis was performed using the technique of power spectra of unequally-spaced data (Deeming,1975). Five oscillation periods were discovered: 350, 192, 143, 113 and 118 seconds. Each of these was found to be amplitude variable. The 192 s oscillation was found to be comprised of a nearly equally spaced triplet of frequency components. Second-order effects in the frequency splitting were discovered. Thus, strong evidence was provided for the presence of rotational splitting of oscillation modes in the low amplitude ZZ Ceti stars. The remaining four oscillation modes were found to have two components each, with a third suspected in two cases. No equal frequency splitting was seen in any of these. No other frequencies with amplitudes exceeding 0.0001 mag were detected in the 100 to 1000 s period range. A proposed mode identification is given and the uncertainties in the theory discussed. L 19-2 was found to have no detectable period variations over the 4.5 year interval spanned by all available observations and was thus found to be another very stable white dwarf pulsator.

Includes abstract. / Includes bibliographical references (p. 261-273.) / In this thesis I investigate emerging telescope technologies and demonstrate, within the context of accretion in cataclysmic variables (CVs), their role in contributing to the stellar variability studies which help drive their development.

To support the potential development of an AO system for SALT, a site monitoring campaign of the Sutherland site was initiated in 2010. This campaign also led to the participation in the development of a new instrument to characterize the atmospheric turbulence. The results from five years of site testing were used in AO simulations in order to demonstrate the potential capabilities of an AO system on SALT. The site testing study produced up-to-date seeing values and provided a measurement of the atmospheric turbulence profiles. I found a median seeing value of 1.51". The main contributor to the turbulence is clearly the ground layer, below 1 km, responsible for 83% of the turbulence. The next most significant contributor is the wind shear layer around 3 km. Seasonal trends show that slightly worse seeing conditions occur during the winter months due to predominant East, South-easterly winds that are associated with degraded seeing conditions. In addition to the main site testing campaign, I helped develop the "Profileur de Bord Lunaire" (PBL, Profiler of Moon limb in English), a new instrument that uses the Moon limb to measure the atmospheric turbulence profile. The work on the data processing and inversion method led to the extraction of high altitude-resolution profiles of the turbulence strength. I present here those results along with a comparison with profiles obtained with the Multi-Aperture Scintillation Sensor (MASS). Using the results from the site testing campaign along with the SALT optical design, I simulated the general dimensioning of a system for SALT that would use a single natural guide star (NGS). The trade-off between performances and sky coverage resulted in a 34x34 system using NGS in the range 10 to 14 magnitude in R-band. The 34x34 dimensions refer to the number of subapertures of the Shack-Hartmann wavefront sensor. I conclude with the significant improvement in spectroscopic performance for SALT that could be achieved by implementing an AO system. The gains in encircled/enslited energy are most significant in the near infrared where gains of 183% could be achieved at 1600 nm for the planned Near-infrared upgrade to the Robert Stobie Spectrograph (RSS). The gains in enslited and encircled energy at 700 nm for the visible arm of RSS and the High-Resolution Spectrograph (HRS) are limited to a maximum of 22% and 34%, respectively, due to the large apertures adapted to seeing-limited observations. Further gains could be achieved by designing the next generation of SALT instrumentation to take full advantage of an AO system.

In this thesis, we investigate the flow field in and around the major large-scale structures in the southern Zone of Avoidance as derived from peculiar motions of galaxies. The peculiar velocities were derived from a galaxy sample based on the systematic deep Parkes HI Zone of Avoidance survey (HIZOA) using a newly optimized Near InfraRed (NIR) Tully-Fisher (TF) relation. The NIR imaging data of the HIZOA galaxies were obtained with the Infrared Survey Facility (IRSF) on the 1.4-m telescope at the South African Astronomical Observatory, which allows simultaneous three-colour (J; H; and Ks) imaging. We first calibrate the NIR Tully-Fisher relation for isophotal magnitudes, using the same 888 calibrator galaxies that were used for the derivation of the 2MASS TF relation for total magnitudes. The isophotal NIR TF relation allows for a significant improvement in the scatter of low surface brightness galaxies, and galaxies obscured by dust. We also simulate the effect of dust extinction on the shape of galaxies and derive a correction model. We show the ability of this model to reproduce the intrinsic axial ratio from the observed parameters up to extinction levels of AV ~ 11 mag. We present new narrow-band HI 21-cm observations for 394 selected galaxies from the HIZOA survey with improved velocity resolution. These new observations with high resolution allow a robust measurement of five different types of linewidth. We used a Bayesian mixture model to derive conversion equations between these five widths, which will be used to combine data sets of differently-derived linewidths. We present deep near-infrared (J; H; and Ks bands) observations of 1108 detections from the HIZOA survey. The average seeing, sky background and the isophotal magnitude errors are 1:38 arcsec, 20:1 mag, and 0:02 mag respectively, which are of sufficient accuracy for a Tully-Fisher analysis. Through comparisons with 2MASS and UKIDSS images we demonstrate the reliability of the IRSF photometry. We use these data and the isophotal Tully-Fisher relation to measure distances and peculiar velocities for 287 galaxies, which covers the whole southern ZOA. We derive the HI mass function to make predictions for the Malmquist bias, thus enabling us to correct the measured distances accordingly. The slope of the HI mass function agrees with both HIPASS Bright Galaxy Catalog (BGC) and ALFALFA, whereas the characteristic HI mass aligns more closely with ALFALFA than the HIPASS BGC. We map the velocity field around the major large-scale structures in the southern ZOA, such as the Great Attractor (GA), the Local Void (LV), and the Puppis region. In the GA region, we find a clear infall into the GA from both sides. Our analysis of the LV shows that the void galaxies are moving away from the center which confirms the recent results which show the draining of the LV. We also find outflow from the Puppis region. We present comparisons between the velocity field derived in this thesis, the 2MASS TullyFisher observations (2MTF), the 2MASS Redshift Survey (2MRS), as well as the IRAS Point Source Catalog Redshift Survey (PSCz) reconstructions. We find good agreement at low redshift with the 2MTF observations, better than the 2MRS and the PSCz reconstructions. At high redshift, our results disagree with the 2MTF observations, the 2MRS, and the PSCz reconstructions.

A scaling relation between the surface density of star formation and gas in the disks of galaxies has become the basis of our understanding of extragalactic star formation on scales of hundreds of parsecs and larger. This is an empirical law but star formation is a complex process - the presence of gas at sufficiently high densities to collapse and form stars depends on a wide variety of physical processes. These processes can be thought of in terms of the stability of galaxy disks, which is a balance between the gravitational force and competing forces such as the outward force due to pressure. In this study I explore how star formation is related to galaxy dynamics in the central regions of galaxies. This is done by determining the dominant contributor to the inner dynamics of galaxies and developing star formation models based on self-regulating disks that maintain a constant sub-critical stability parameter. Stability parameters for a gas-only disk and a two- uid disk containing both gas and stars are considered. These models are tested in the central regions of a sample of galaxies with a wide range of Hi masses, sizes, morphologies and stellar masses. The analysis is performed using Hα integral field spectroscopy, R-band, narrowband Hα, and near-infrared photometry to determine the star formation rates and kinematics of the galaxies. In agreement with previous studies I find that the central stellar surface density is tightly correlated with the central velocity gradient, which traces the steepness of the inner gravitational well. The baryonic fractions found in the analysis suggest that baryons dominate the central density of most galaxies in the sample, but better constraints on these are needed to make more firm conclusions. There are correlations between the star formation surface density and velocity gradient, however the observed relations do not match predictions from the models. Tests suggest that the failure of the models is due to the implied stability parameters in the galaxy centers not being constant across the galaxy sample, and that the star formation laws used in the analysis may not hold over the full parameter space of the sample.

Includes bibliographical references. / In this thesis I present the work I performed during the initial construction and deployment of the second telescope in the KELT project and I report the results of the search for transiting exoplanets and variable stars using one of the first commissioning datasets obtained with the telescope. The KELT-South telescope is located in Sutherland, South Africa and construction started in 2008. The telescope has been operating at full capacity since 2010, after two commissioning seasons from late 2008 to early 2010. I developed all the code that allows it to be fully automatic and robotic and over the last 5 years I have been responsible for the observing operations and general maintenance of the telescope. I also developed many other software tools that help with the identification of the exoplanet candidates. The Kilodegree Extremely Little Telescope (KELT) project at present consists of two robotic, wide field, small aperture telescopes that are designed primarily to find transiting exoplanets around bright stars in the magnitude range 8 < V < 11. Transiting planets orbiting bright stars can be studied with intense follow-up programs with relative ease on larger telescopes, making them favourable targets to determine the atmospheric composition of the planet as well as a host of other properties that cannot be obtained from planets orbiting fainter stars. Of the known 1811 (August 2014) exoplanets only 60 are transiting stars with V < 11 and only 16 of those have been found from the southern hemisphere. The discovery of more of these exoplanets will help constrain the theories of formation and evolution of short period, gas giant exoplanets. Data reduction on one of the commissioning datasets was completed in 2012. The dataset spans 46 days and lightcurves for 78297 objects were obtained. I performed a search for periodicities in the lightcurves and found that 1411 stars showed clear signs of variability and these objects were compiled into a catalogue of possible variable stars. 1018 of the catalogue members were not previously known to be variable. I searched for planetary transits and eight possible exoplanet candidates were identified. Photometric follow-up observations of two targets eliminated them as exoplanet candidates, each being a blended eclipsing binary system. The remaining six candidates are awaiting follow-up observations at present. Although the commissioning dataset served primarily to refine the data reduction pipeline and the procedures I used to find variable stars, I have demonstrated that the KELT-South telescope is capable of detecting the kinds of signals required for exoplanet discovery.