The Arcminute Microkelvin Imager (AMI) is a dual-array radio interferometer sited at Lord's Bridge, near Cambridge. Although it was designed specifically for studying galaxy clusters via observations of the Sunyaev-Zel'dovich (SZ) effect, it is also an ideal instrument for Galactic science. This thesis describes science programmes investigating both Galactic objects and galaxy clusters that I have carried out with AMI. A new data analysis pipeline is described which has been developed to allow the automated processing of data taken by AMI in drift-scan mode, pointing the telescope at a fixed azimuth and elevation and observing the sky that drifts past. This is a very efficient mode for large-scale surveys, but the different character of the data has required innovative algorithms for effective processing. The AMI Galactic Plane Survey uses drift-scanning to cover the northern Galactic plane between |b| < approximately 5 degrees. It is the first Galactic plane survey at cm-wave frequencies to achieve crucial mJy-sensitivity levels at arcminute-scale resolution over a wide area, and as such provides a unique opportunity to investigate hitherto unusual objects such as ultra- and hyper-compact HII regions. I describe my work on the survey strategy and its implementation and on some of the science I have extracted so far including the follow-up of candidate hyper-compact HII regions. The recently-released Planck satellite results include the largest catalogue of SZ-selected clusters of galaxies to date. I describe the AMI follow-up programme to observe the clusters within the AMI observation limits, and present the first results from the programme including an interesting discrepancy between the cluster parameters according to AMI and Planck. Since the two instruments are observing the same physical process, this indicates a fundamental problem with the 'universal' pressure profile currently favoured for modelling clusters. In an attempt to address the discrepancy, I use simulations to investigate the effect of allowing the shape of the pressure profile to vary. The derived parameter constraints are found to vary when clusters are not simulated and recovered with the same model; the effects are dependent on angular size, worsening for larger clusters. I also assess the potential for using AMI data to constrain the cluster shape parameters, and conclude that weak constraints on the shape parameters are possible with a careful choice of prior.

No description available.

In this thesis we perform a range of highly accurate density functional theory (DFT) calculations for a GaAs (110) slab containing almost all of the near-surface single atomic dopants from groups III, IV and V of the periodic table. We look in detail at the relaxed geometry and local density of states of the doped surface, and using the theory of Tersoff and Hamann we generate STM images of the different dopant systems. Where possible we compare to experimental results obtaining excellent qualitative and quantitative agreement, with bond lengths and shifts in STM contrast agreeing to within 0.03 Å and 0.09 Å respectively. We are able to show very clear trends in both the relaxed positions and STM image contrasts for the range of dopants. These trends are determined by the covalent radius of the dopants. Dopants with larger radii relax out of the surface and ones with smaller radii relax into the surface, and these relaxations cause the different contrasts in the STM images. These trends fit very well with existing results for nitrogen and silicon doped systems, and also allow us to fill in the gaps for those systems that have not been as thoroughly investigated. Our analysis applies equally across the three groups of dopants from the periodic table covering isovalent, donor and acceptor cases. By developing a geometrical model based on the covalent radii of the dopants and host atoms, we show how the covalent radius determines the geometry of the surface, which in turn determines the contrast seen in the STM images. Using this model we are able to explain and predict the relaxation and STM images for all the dopants in this work to a high degree of accuracy without relying on DFT simulations.

No description available.

No description available.

The Ariel-6 spacecraft was launched during 1979 and remained operational for &sim; 3 years. The satellite payload is discussed, with an emphasis on the medium energy detectors, their calibration and performance. We present observations of spectral variability, in both galactic and extra-galactic sources, made with this instrument in the 1-50 keV energy range. Three galactic sources were observed, these consisted of two X-ray pulsators, 4U0115+63 and GX 1+4; the former being fortuitously seen during outburst. Both sources were found to show a significant phase dependence in their X-ray spectra. In GX 1+4 an Iron emission feature was detected, the equivalent width of which was also phase dependent. Pulse timing was performed on the data from both sources and in the case of 4U0115+63 yields a revised set of orbital parameters. The third galactic source presented is 3A1822-371, we find that our data are not only consistent with the presence of an accretion disc corona in the system, but strongly suggests the presence of such a corona in many disc fed systems. Three Seyfert galaxies, NGC 4151, MCG 8-11-11 and IIIZw2 were observed, this being the first reported X-ray spectrum of IIIZw2. NGC 4151 was found to have a spectrum consistent with that seen &sim; 3 years earlier, whilst MCG 8-11-11 was softer than seen hitherto and now shows evidence for an Iron emission line. The BL Lac, Mkn 421 was found to have a two component spectrum; comparison with earlier reported spectra indicates that both components vary independently of each other and therefore arise in physically differing regions of the source. Finally a forward-look is made which considers the improvements in medium energy spectroscopy that can be anticipated over the next decade or so.

X-ray emission from galactic supernova remnants X-ray images and spectra are used to determine the structure and physical conditions of shock heated interstellar gas and stellar ejecta within three galactic supernova remnants (SNRs). Parameters describing the initial supernova explosions (total energy, ejected mass) and ambient interstellar medium (density, homogeneity) are then derived. The interior density of the "middle-aged" SNR W44 is found to be fairly uniform, and inconsistent with the standard Sedov model, but similar to that predicted by models in which thermal conduction and/or heating and evaporation of engulfed, cold, interstellar clouds are important. This expanding bubble of hot, high pressure gas is likely to be an example of the formation of the hot component of interstellar medium, as detected in the vicinity of the Sun. In addition, it is likely that the SNR has collided with a nearby dense molecular cloud. The SNR W49B is found to be probably the remnant of a Type II supernova which occurred in a relatively dense medium 2000-5000 years ago. The abundance of hot iron in the ejecta is consistent with the cosmic value. The youngest SNR studied, SN1006, is found to be the remnant of a Type I supernova which occurred in a region of low, but fairly uniform (to within a factor of 2), interstellar density. Emission from reverse shocked ejecta may be most prominent in a limited area of the SNR, explaining a discrepancy between previous X-ray spectra of the remnant. A common result in all three SNRs is the detection of hot gas at their centres; the likely effects of a reverse shock and thermal conduction within SNRs are emphasized.

Studies of the electrodynamics of the high latitude ionosphere contribute to the understanding of the coupling between the solar wind, magnetosphere and upper atmosphere. This thesis describes an experimental investigation of high latitude E-region convection flows carried out with the Sweden And Britain auroral Radar Experiment (SABRE). The ionospheric observations have been related to satellite measurements of the interplanetary medium and hence interpreted in terms of models of solar wind-magnetosphere-ionosphere coupling processes. A close relationship has been established between various solar wind parameters and the daily mean SABRE backscatter intensity, a quantity which is rarely employed in geophysical studies. Empirical IMF-dependent models of the convection flows observed by SABRE are developed and statistical studies of the occurrence time of the Harang discontinuity are presented. High spatial resolution, two dimensional maps of the ionospheric projection of the dayside merging region, for both polarities of the azimuthal component of the IMF, are obtained for the first time. Two examples of strong nightside convection flows observed throughout the SABRE latitude range indicate that the convection flows may penetrate at least as far south as 61.5° N, geomagnetic latitude, during strongly northward IMF. The study indicates that, in the long term, the structure of the solar wind can be deduced from the mean backscatter intensity measured by a SABRE radar. In addition, the azimuthal component of the IMF exherts a crucial influence on the convection flows observed by SABRE in the cusp region. This effect is not confined to the noon sector but is also apparent in the vicinity of the Harang discontinuity. In general, the convection pattern exhibits a dependence on the north-south component of the IMF consistent with established reconnection mechanisms. However, there is evidence that existing models are insufficient to explain the anomalous convection flows observed under conditions of strongly northward IMF.

X-ray observations of three classes of interacting binary are presented. The systems studied are believed to be undergoing mass transfer by Roche lobe overflow onto a compact object. The observations were made between 1983 and 1989 with the EXOSAT and Ginga satellite observatories. The dwarf nova SS Cygni was subject to extensive monitoring using EXOSAT. In quiescence, the source has a hard spectrum which shows thermal iron K? and possibly K? emission. In outburst, emission is dominated by a soft component which emits at energies below &sim; 1 keV. This soft emission shows large amplitude, quasi-coherent sinusoidal modulation at periods in the range 7.4 to 10.8 sec. The evolution of the properties of this oscillation through outburst are studied in detail. A two day Ginga observation of the x-ray pulsar 1E 2259+586 is described. The pulse arrival times were searched for orbited modulation, and an upper limit (3?) to the projected semi-major axis was found to be ar sin i < 140 It-msec for periods from 1000 to 5000 sec. The source spectrum shows a broad line feature at &sim; 7 keV. It is suggested that this may arise from cyclotron processes. Details axe given of the Ginga observations of low mass x-ray binary systems which show 'dip' variability, the sources being XB 1916-053, XBT 0748-676, and X 1624-490. A re-analysis of the EXOSAT observations of X 1624-490 is also presented. Modulation in dippers arises from occultation of the compact x-ray emitting regions by structure in the accretion disc. Timing measurements constrain on the size of the emitting region and the distribution of the obscuring material. Spectral changes in dip events require a two-component model of absorption. By simulation, it is shown that this behaviour may arise from single component absorption if the column density changes rapidly. Revised estimates for the metal abundances of the three sources are given.

Near-infrared (1.2-2.2 micron) surface brightness measurements across the faces of a sample of nearby galaxies are presented, employing a variety of instrumental techniques. NGC 2683, 4565, and 5907 are seen almost edge-on, and for two of these, optical (V) data were obtained simultaneously with the infrared, using a widethrow-chop two channel photometer developed at Leicester by Dr. D.J. Adams. The results of these observations are presented in a single Chapter (3), in which the infrared measurements are used to define obscuration-free scale sizes for the disks, and the optical- infrared colours place constraints on possible mechanisms for the production of colour-index gradients. The remaining observational chapters (2 & 4) are a chronological record of use of the infrared system of the Anglo-Australian Telescope, documenting steps toward DC-mapping of extended objects, begun in 1980 with semi-DC observations of NGC 5128 at 2.2 microns (Chapter 2). Significant data were obtained in the course of these experiments, and in the final chapter we present J, H and K maps of M83, a large face-on spiral, which were obtained with the intention both of resolving the controversy over the Freeman Type I- Type II surface brightness profiles, and of detecting the density wave in the "old disk", suspected to drive the optical spiral star formation pattern. Our discussion of these observations also contains a number of warnings about the pitfalls which lurk in the DC-measurement process, most of which are concerned with the knowledge (or lack of it) of the sky background level when observing very extended objects. The first chapter gives a short introduction to some of the outstanding problems of extragalactic astronomy, and the uses to which infrared measurements can be put in tackling these problems. The overall objective of the Thesis is to illustrate, through observational results, the wide range of applications which near- infrared imaging finds in studies of galaxies. The contrast between the three observational chapters highlights this point.