An instrument with the ability to image neutral atomic hydrogen (HI) to cosmic redshift will allow the fundamental properties of the Universe to be more precisely determined; in particular the distribution, composition, and evolutionary history of its matter and energy. The Square Kilometre Array (SKA) is a radio survey telescope conceived with this aim. It will have the observational potential for much further fundamental science, including strong field tests of gravity and general relativity, revealing the origin and history of cosmological re-ionisation and magnetism, direct measures of gravitational radiation, and surveys of the unmapped Universe. And it is the advance of instrumentation that will enable it. This thesis makes three central contributions to radio instrumentation. Digital aperture arrays are a collector technology proposed for the key low- and mid- frequency ranges targeted by the SKA that have the potential to provide both the collecting area and field of view required for deep, efficient all-sky surveys of HI. The 2-Polarisations, All Digital (2-PAD) aperture array is an instrumental pathfinder for the SKA, novel in being a densely-spaced, wide-band aperture array that performs discrete signal filtering entirely digitally. The digital design of the 2-PAD radio receiver and the deployment of the aperture array and signal processing system at Jodrell Bank Radio Observatory is detailed in this thesis. The problem of element anisotropy in small arrays, the atomic unit of the SKA station array, ultimately affects beam quality. Addressing this issue, a metaheuristic digital beam-shape optimisation technique is applied to a small beamformed array, and is shown to outperform traditional analytic solutions. Digital processing for aperture arrays is challenging. A qualitative framework shows that energy, computational and communication requirements demand optimised processing architectures. A quantitative model reveals the physical limitations on architecture choice. An energy-optimised architecture, the IBM BIT integer array processor, is investigated in detail; a cycle-accurate architectural simulator and programming language are developed and used to build signal processing algorithms on the array architecture.

In this dissertation, I examine the optical linear polarization of quasi-stellar objects (QSOs) and BL Lacertae objects. I present extensive polarimetric observations of a large sample of QSOs, systematically analyze the correlations between polarization and other properties of QSOs, compare t

This thesis describes an investigation into weak gravitational lensing, a unique and powerful astronomical tool for the study of dark matter on large scales. Lensing distorts background images, inducing correlations in the observed ellipticities of galaxies, and these correlations can be used to estimate many characteristics of the Universe. Key to all weak lensing studies is a reliable and unbiased method to detect weak lensing distortions from observed galaxy images that are contaminated by Earth and telescope-based shearing and smearing distortions. A new galaxy model-fitting technique is presented that has been developed in order to satisfy this requirement, which will also permit future signal-to-noise optimised measurements of weak lensing shear. Model-fitting provides a good alternative to the standard scite{KSB} method (KSB), and comparisons between the two techniques are drawn from an analysis of deep {it R} band imaging from the COMBO-17 survey, revealing strong evidence for the presence of bias in KSB galaxy shape measurement. With the galaxy model-fitting technique, an investigation into the effectiveness of the Oxford Dartmouth Thirty degree survey (ODT) for gravitational lensing studies is presented, resulting in the detection of weak gravitational lensing by large scale structure, or `cosmic shear', in 0.7 square degrees of the best seeing ODT images. One concern for all cosmic shear studies is that the weak lensing signal, manifest in the weakly correlated ellipticities of distant galaxies, is contaminated by the intrinsic alignment of close galaxy pairs, potentially induced during galaxy formation by physical interactions such as tidal forces. This contamination is investigated theoretically, through numerical simulations, and observationally, with an analysis of the COMBO-17 survey and the study of published results from the Red-sequence Cluster survey and the VIRMOS-DESCART survey, concluding that the intrinsic alignment effect is at the lower end of the range of theoretical predictions. The impact of intrinsic galaxy alignments on cosmological parameter estimation is investigated, with an analysis of the weak lensing results from the COMBO-17 survey. When marginalising over the observationally constrained intrinsic alignment signal, the amplitude of the matter power spectrum sigma_8 is reduced by ~0.03 to sigma_8(Omega_m / 0.27)^{0.6} = 0.71 pm 0.11, where Omega_m is the matter density parameter. With distance information from either spectroscopy or photometric redshifts, the down-weighting of nearby galaxy pairs in weak lensing analysis can be optimised to virtually eliminate the systematic errors in the shear signal arising from intrinsic galaxy alignments, leaving a much smaller, largely statistical error. This method is applied to the photometric redshift sample of the COMBO-17 survey. Weak lensing measurements from the forthcoming SuperNova/Acceleration Probe weak lensing survey (SNAP), and the Canada-France-Hawaii Telescope Legacy survey, are expected to be contaminated on scales >1 arcminute by intrinsic alignments at the level of ~ 1% and ~2% respectively. Division of the SNAP survey for lensing tomography significantly increases the contamination in the lowest redshift bin to ~7% and possibly higher. Removal of the intrinsic alignment effect by the downweighting of nearby galaxy pairs will therefore be vital for the lensing tomography studies of SNAP.

This dissertation presents a technique for the identification and classification of late-type stars and for the estimation of M star metallicities. The technique uses broad-band, V and I, CCD images to identify red stars and two intermediate-band CCD images to classify these as carbon or M types. One of the intermediate passbands is centered on a TiO absorption band at 7750Å and the other is centered on a CN absorption band at 8100Å. Color-color plots of V-I versus the intermediate-band index, 77-81, clearly distinguishes carbon from M stars. Observations of both early- and late-type stars were used to define the 77-81 system based upon the intermediate-band filters. The TiO bandstrength deduced from the 77-81 color as a function of V-I color was investigated for field giants and giants in 12 globular clusters. A linear correlation between [Fe/H] and the V-I color at a given TiO bandstrength was found. This correlation can be used to estimate the metallicity of M giants. The stellar population of a field in Baade's Window was examined using this technique. Many late-M stars and no carbon stars were found. The color-color diagram for Baade's Window suggests a range of metallicities for the M giants of [Fe/H] ≈ -0.4 to > +0.2. The stellar population of the Sagittarius Dwarf Irregular galaxy (Sagdig) was examined using the 77-81 system. A method for estimating reddening based upon the color mode of foreground stars was developed for the analysis of the Sagdig data. Sagdig is estimated to be ~ 1.3 megaparsecs distant. Bright blue and red stars in Sagdig are evidence for recent star formation. Carbon stars were identified in Sagdig. They display a bimodal luminosity and color distribution which suggests distinct epochs of star forming activity between 1 and 10 Gyr ago. The spatial distribution of carbon stars and bright red stars in Sagdig shows this galaxy to be much larger than previously thought.

A sample of 170 sources from the IRAS Point Source Catalog (PSC) having / b / ≥ 40°, 100μm flux F₄ ≥ 2.5 Jy, and upper limit fluxes at 12, 25 and 60μm was studied on POSS and ESO photographic plates. 151 of these sources are identified as 'infrared cirrus,' thirteen as galaxies, and one as a planetary nebula; four sources lie in the Small Magellanic Cloud (SMC), and the remaining source is Saturn. Accurate infrared fluxes were obtained for 29 cirrus sources, the galaxies, and the planetary nebula. The colors of the cirrus sources support the hypothesis that the radiation is coming from a mixture of large, cool grains and Polycyclic Aromatic Hydrocarbons (PAHs), with large variation in relative abundances. Optical colors and surface brightness were obtained for one cirrus cloud using data from the CCD Transit Instrument on Kitt Peak.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: In this thesis we addressed some issues concerning the automation of the detection, processing and the analysis of gravitational microlensing events, which are currently being used in the search for extra-solar planets. We were provided with a series of data images containing a microlensing event. Using these images we address several practical problems: registration, background subtraction and some PSF modelling. Registration is accomplished by using the intersection points of circular arcs drawn around stellar objects. After which the influence of the sky background is removed by using the watershedding algorithm and plane fitting. Our analysis is based on relative brightness - to counter seeing, the brightness of stars are calculated by isolating the objects from the background and summing over the area. A brightness variation curve is plotted and the trend of the lensing event and the posi tion of a blip are extracted using wavelets, calculating general trends and LOESS. The trend of the brightness variation curve can be used for both identification and classification of various events. It can also be used for the identification and classification of variable stars. Blip analysis is used to detect the presence of a planet (or dark body) in the vicinity of the source. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf tegnieke om die identifikasie, prosessering en analise van gravitasie mikro-lens gebeure te outomatiseer. Die analise van hierdie gebeure is belangrik aangesien dit gebruik word vir die opsporing van planete buite ons sonnestelsel. Om gebruik te maak van 'n reeks beelde wat een van hierdie gebeure vertoon moet ons die volgende probleme aanspreek: beeld registrasie, verwydering van die agtergrond en die modulering van die verspreiding van die lig van 'n puntbron deur die atmosfeer. Ons verkry registrasie deur die berekening van die snypunte van sirkels met middelpunte by sekere voorwerpe op die beeld. Na registrasie kan ons die invloed van die agtergrond bepaal deur gebruik te maak van die waterskeidingsalgoritme. Dit stelons in staat om die relatiewe helderheid van die voorwerpe ondersoek deur die voorwerpe te isoleer en te sommeer oor die area van 'n voorwerp. 'n Grafiese voorstelling van die helderhede dui vir ons die relatiewe variasies in die helderhede van die mikrolens objek tussen die beelde aan. Ons ondersoek die vorm van die kromme asook die moontlike voorkoms van 'n 'blip' deur middel van wavelet analiese en die LOESS metode. Die vorm van die kromme word gebruik vir die identifikasie en klassifikasie van die verskillende mikro-lens gebeure en kan uitgebrei word om ook veranderlike sterre te ondersoek. Die teenwoordighied van 'n 'blip' op die data wys op die moontlik teenwoordigheid van 'n planeet nabyaan die bron wat ons ondersoek.

When an astronomical observer discovers a transient event in the sky, how can the information be immediately shared and delivered to others? Not too long time ago, people shared the information about what they discovered in the sky by books, telegraphs, and telephones. The new generation of transferring the event data is the way by the Internet. The information of astronomical events is able to be packed and put online as an Internet feed. For receiving these packed data, an Internet feed listener software would be required in a terminal computer. In other applications, the listener would connect to an intelligent robotic telescope network and automatically drive a telescope to capture the instant Astrophysical phenomena. However, because the technologies of transferring the astronomical event data are in the initial steps, the only resource available is the Perl-based Internet feed listener developed by the team of eSTAR. In this research, a Java-based Internet feed listener was developed. The application supports more features than the Perl-based application. After applying the rich Java benefits, the application is able to receive, parse and manage the Internet feed data in an efficient way with the friendly user interface. Keywords: Java, socket programming, VOEvent, real-time astronomy

A considerable number of Very Long Baseline Interferometry (VLBI) surveys have been conducted in the northern hemisphere and very few in the southern hemisphere mostly because of a lack of telescopes and therefore adequate baseline coverage. Thus there is a deficit of calibrator sources in the southern hemisphere. Further, some of the most interesting astronomical objects eg. the galactic centre and the nearest galaxies (the small and large Magellanic Clouds) lie in the southern hemisphere and these require high resolution studies. With a major expansion of radio astronomy observing capability on its way in the southern hemisphere (with the two SKA (Square Kilometre Array) precursors, meerKAT (Karoo Array Telescope) and ASKAP (Australian SKA Pathfinder), leading to the SKA itself) it is clear that interferometry and VLBI in the southern hemisphere need a dense network of calibration sources at different resolutions and a range of frequencies. This work seeks to help redress this problem by presenting an analysis of 31 southern sources to help fill the gaps in the southern hemisphere calibrator distribution. We have developed a multi-parameter method of classifying these sources as calibrators. From our sample of 31 sources, we have 2 class A sources (Excellent calibrators), 16 class B sources (Good calibrators), 9 class C sources (Poor calibrators) and 4 class D sources (Unsuitable calibrators).