The exploration of radio emission from the relativistic jets of X-ray binaries has become key to understanding accretion onto compact objects. Upgrades to existing radio telescope arrays have improved the ability of these instruments to detect faint sources and their unique behaviours. In this thesis I address the use of one such instrument in observing several X-ray binary systems: the Australia Telescope Compact Array - Compact Array Broadband Backend (ATCA-CABB). Firstly, a study of the adverse effects that may arise when imaging spectrally variable sources using broad bandwidths, with emphasis on ATCA-CABB. Images are produced from model data and examined to find any false structures. I then discuss complications that such features may cause when attempting to interpret real structure in images. Secondly, the results of attempts to observe the black hole X-ray binaries, GRO J1655-40 and XTE J1550-564, in quiescence with ATCA-CABB are presented. Upper limits from the non-detection of these sources are used in exploring the lower luminosity region of the radio/X-ray correlation for hard state black hole X-ray binaries and the implications of “universal” scatter is discussed. Thirdly, a 16 day campaign observing the radio emission of the neutron star Xray binary Circinus X-1 over a complete orbit during an historically faint state is presented. Variability in the source is examined and corrected images are compared with archival maps in order to find any differences. I discuss my findings in terms of secular changes in jet geometry and behaviour. Finally, the first successful millimetre detections of neutron star X-ray binaries Circinus X-1 and Scorpius X-1 are presented. Sub-arcsecond jet structure in Circinus X-1 is compared to the existing centimetre maps, providing additional support for theories proposed earlier in the thesis. The radio to mm spectrum of both sources is estimated and discussed. This thesis concludes with a description of the broader impacts of the above projects, as well as possibilities for future research in each field.

Cataclysmic Variables (CV) are binary systems where a main-sequence star transfers mass onto a white dwarf (WD). According to standard evolutionary theory, angular momentum loss drives CVs to initially evolve from longer to shorter orbital periods until a minimum period is reached (≈ 80 minutes). At roughly this stage, the donors becomes degenerate, expand in size, and the systems move towards longer orbital periods. Theory predicts that 70% of all CVs should have passed their minimum period and have sub-stellar donors, but until recently, no such systems were known. I present one CV showing evidence of harbouring a sub-dwarf donor, SDSS J1507+52. Due to the system’s unusually short orbital period of ≈ 65 minutes, and very high space velocity, two origins for SDSS J1507+52 have been proposed; either the system was formed from a young WD/brown-dwarf binary, or the system is a halo CV. In order to distinguish between these two theories, I present UV spectroscopy and find a metallicity consistent with halo origin. Systems close to the minimum period are expected to be faint and have low accretion rates. Some of these CVs show absorption in their spectra, implying that the underlying WD is exposed. This yields a rare opportunity to study the WD in a CV. I introduce two new systems showing WD signatures in their light curves and spectra, SDSS J1457+51 and BW Sculptoris. Despite the fact that CVs close to the minimum period should be faint, we find systems that aremuch too bright for their orbital periods. Such a system is T Pyxidis – a recurrent nova with an unusually high accretion rate and a photometrically determined period < 2 hours. The systemis ∼ 2 times brighter than any other CV at its period. However, to confirm the status of this unusual star, a more reliable period determination is needed. Here, I present a spectroscopic study of T Pyxidis confirming its evolutionary status as a short-period CV. In this thesis, I discuss what implications these systems may have on the current understanding of CV evolution, and the importance of studying individual systems in general

No description available.

Glitches are sudden increases in the otherwise extremely regular spin rate of pulsars. One theory proposed to account for these glitches is the starquake model, in which the spinup is caused by a sudden rearrangement of the neutron star crust. Starquakes can be expected to excite some of the oscillation modes of the neutron star. These oscillations are of interest as a source of gravitational waves, and may also modify the pulsar radio emission. In this thesis we develop a toy model of the starquake and calculate which modes of the star are excited. We start by making some order-of-magnitude upper estimates on the energy made available by the starquake and the amplitude of the modes excited, before moving on to a more detailed calculation based on a speci�c model of the starquake in which all strain is lost instantaneously from the star at the glitch. To find out which modes are excited by the starquake, we construct initial data describing the change in the star at the glitch, and then project this against the basis of normal modes of the star. We first carry out this procedure for a simplified model in which the star has spun down to zero angular velocity before the starquake. We find that the majority of the energy released goes into a mode similar to the fundamental mode of a uid star. Finally, we describe the extension of this model to the more realistic case where the star is rotating before the glitch. We calculate the change in the normal modes of the star to first order in the rotation; these are no longer orthogonal, but we construct a scheme that still enables us to project our initial data against this set of modes, and discuss some preliminary results of the model.

No description available.

Impulse over-voltage is a common phenomenon in electric power systems. A switching impulse is created by a switching surge or local fault while a lightning impulse is due to direct lightning strike to high voltage plant such as an overhead line. Both impulse events create travelling waves in the system, damaging insulation components and equipment. This work is concerned with the hypothesis that lightning impulses can lead to accelerated ageing of extruded polymeric cables. The results show that there may well be a reduction in electric field strength of the insulation of a power cable that experiences a lot of impressed lightning impulse over-voltages. Pre-designed shaped polyethylene material sample discs have been manufactured using a mould tool. The samples then have been electrically aged using an impulse generator. A real-time software based monitoring tool has been designed to control the impulse wave-shape and process the measurement data. Sets of identical lightning impulses were applied to samples and this was then followed by ramped AC breakdown tests. The obtained results were analyzed using the Weibull distribution to identify any differences in lifetime between aged and un-aged samples. This thesis also provides insight into the dominant ageing processes through the analysis of dielectric spectroscopy and space charge measurement data. In order to quantify the effects of dielectric ageing due to impressed lighting impulse over voltages, experiments have also been undertaken using samples that have been aged under UV light and thermally. Analysis of obtained results reveals that mechanisms of these two ageing processes are significantly different from the mechanisms due to lightning impulse ageing

Neutron stars are some of the most magnetic objects that have ever been observed, and so they provide physicists with unique environments where fundamental laws of physics can be tested. Neutron stars are typically thought to have magnetic fields between 108 and 1014 G. The effects of the quantum electrodynamics are important above the quantum critical field (BQED) of 4.4×1013 G. In this thesis, I provide evidence that there may be many more neutron stars with B > BQED than previously thought, and that all neutron stars in binary systems that are close to spin equilibrium follow the same relationship between spin period (P) and magnetic field. In Chapter 2, I determine the long-term average X-ray luminosity, spin period, and rate of change of spin period for 42 Be X-ray binaries (BeXB) in the Small Magellanic Cloud (SMC). I use this information, combined with orbital data, to show that the neutron stars in all of these systems are disc-accreting, and that 85% are close to spin equilibrium. All systems with P & 100 s are predicted to have B > BQED. This applies to 2/3 systems. These predicted magnetic fields are higher than those of neutron stars in Galactic BeXB that have had their magnetic fields directly measured via cyclotron resonance scattering features (CRSF). I conclude that this is because the CRSF sources are not close to spin equilibrium. In Chapter 3, I look at pulse-profiles for the neutron stars discussed in Chapter 2 and find that they contain an array of features that vary both across and within individual systems. I suggest that BeXB containing neutron stars with relatively longer spin periods transition from a pencil to a fan beam at lower luminosities. In Chapter 4, I apply the methods used in Chapters 2 and 3 to LXP187, a BeXB in the Large Magellanic Cloud (LMC) that is not close to spin equilibrium. Results for LXP187 help confirm the conclusions of Chapter 2 - that � 2/3 BeXB contain neutron stars with B > BQED.

Outflows are ubiquitous in active galactic nuclei (AGN). They can take the form of either dramatic radio jets, which extend vast distances into the inter-galactic medium, or of much smaller scale winds - whose existence can be inferred only indirectly via their influence on the observed spectra. There is good evidence to show that winds are likely to arise from the accretion disks thought to form the central engine of all AGN; they should therefore be observable in all such systems. The clearest observational signature comes in the form of the broad, blue-shifted absorption features seen in the spectra of broad absorption line quasars (BALQSOs) and the aim of this work is to investigate how the geometry and physical parameters of disk winds affect their absorption spectra. We first discuss the changes made to an existing Monte Carlo radiative transfer code, python, in order to extend its capabilities to include modelling of AGN. These changes include the implementation of an approximate ionization scheme which takes account of arbitrary illuminating spectral energy distributions (SEDs), and the inclusion of heating and cooling effects likely to be important in the presence of high energy photons. Next, we describe the second stage of the project which was to gain insight into the general properties of a wind exhibiting broad absorption line (BAL) features. We did this by performing radiative transfer and ionization calculations on a simple kinematic wind representation using python. We show that BAL features can be produced for plausible AGN parameters. Finally, we present calculations carried out on a more complex wind geometry, generated from a hydrodynamic simulation of a line driven disk wind. This calculation does not produce BAL features at all, and in fact the wind is too highly ionised to permit efficient line driving. This result is significant because it illustrates the importance of detailed radiative transfer in hydrodynamic modelling, and suggests future work.

The study of exoplanets has rapidly developed in the last twenty years, and the detailed characterization of planetary atmospheres has become a key area of research. For transiting planets around bright stars, atmospheric features can be detected with transmission spectroscopy. I will present a low resolution transmission spectrum of WASP-52b, and show that the most likely interpretation is that the planet is shrouded with an opaque cloud layer. By using transmission spectroscopy at much higher resolution, in this thesis I will present the first spatially resolved measurements of a weather system in an exoplanet. By modeling the absorption profile of sodium on HD189733b, I show that the planet atmosphere has an excess velocity not explained by planetary rotation. HD209458b is evaporating under intense irradiation from its star, and may lose as much as 1010 g s-1. Mechanisms of mass loss are poorly understood, in particular the efficiency. To calculate this rate for HD209458b a key component is missing - the high energy flux of the star. I will demonstrate that it is possible to recover this flux by building a coronal model for the star, using constraints for different temperatures of plasma from UV and X-ray sources. I will present commissioning data gathered with NGTS that are the most precise ever gathered with a ground based wide field transit survey. Simulations of the performance of NGTS in this thesis show that the survey can be expected to detect ~200 low mass planets. The simulations of NGTS also show that a sample of bright super-Earths and hot-Neptunes can be expected to be detected, which would be sensitive to the same techniques performed on hot Jupiters in this thesis. One day, these same techniques could be important tools for characterizing the atmospheres of Earth analogs.

Gamma-ray bursts are the most violent of known astrophysical events, with up to 10^53 ergs of energy released on the order of seconds. These extreme explosions, first observed in 1960s, form a fast moving field of research within astrophysics which relies on multi-wavelength observations of these transient events to probe the early- time (< 15 minutes) parameter space of these events. In the optical regime, follow-up observations to the prompt emission are ideally suited to the 2.0 metre Liverpool Tele- scope (LT), situated at an altitude of 2363m on the Observatorio Roque de las Mucha- chos (ORM), La Palma, Canary Islands. The LT is fully robotic and able to respond automatically to triggers of new gamma-ray burst (GRB) events, starting within 2-3 minutes of the detection of the prompt emission. The observed radiation from GRBs is released from relativistic jets. Launched from a black hole central engine, the energy within the jets is converted to the observed radi- ation predominantly through a synchrotron process, which can produce highly linearly polarised radiation. Polarimetric observations of this radiation are a key resource to infer the magnetic field structure of the emission region and distinguish between baryonic and magnetic models of jet physics. For this reason, the Liverpool Telescope has hosted the RINGO series of polarimeters which use a novel design to enable early-time polarimetric measurements of these highly variable optical sources. RINGO was mounted on the LT in 2005, and observed GRB 090102A providing a measure of 10.2 ± 1.3% average linear polarisation in the period of 160-220s post burst. RINGO2, mounted in June 2009 improved on the original design utilising a triggered electron multiplying CCD system. Both RINGO and RINGO2 were single band instruments. The development of RINGO3 extended the design of RINGO2 into a simultaneous 3 band polarimeter. This work focuses on the characterisation of RINGO2 and analysing the sample of GRB observations made during its lifetime. The observations of GRB 120308A provide measurements with a high confidence, inferring the existence of stable, or- dered magnetic fields within the jet. Analysis of other GRB afterglows observed with RINGO2 provides confidence in this result and confirm that jets can be highly magne- tised, with the majority of energy being contained in magnetic field recombination and not through kinetic energy of baryonic matter. RINGO3, a multi-band extension to RINGO2, was developed and tested within the Astrophysics Research Institute labs before being commissioned on the Liverpool Telescope in November 2012. Lab tests of instrument throughput with calculations of the signal to noise ratio across the operating wavelength defined the optimal cut-offs of the 3 wavelength bands. This instrument was then characterised using similar methods to RINGO2, and whilst not an ideal instrument was found to be within the required performance for the prime science goal of early-time GRB afterglow observations.