Gravitational waves have now twice been detected emanating from the merging of binary black hole systems. In this thesis we detail the methods used to search for binary merger gravitational wave signals associated with short gamma-ray bursts, focusing on systems that include at least one neutron star. We first cover the background theory behind gravitational wave emission, the means of detection via interferometry, and the types of astrophysical sources that could be detected now or in the near future. We follow this with a review of gamma-ray burst theory and observations, focusing in particular those bursts with short durations. These are likely to be caused by the mergers of binaries that include a neutron star and a black hole, or two neutron stars - events of great interest to gravitational wave astronomy. We then discuss the methods used to search gravitational wave data in a targeted way, using the prior observation of a short gamma-ray bursts to focus the analysis and improve the chances of making a detection. We also summarise early searches of this kind and present the results of a search carried out on LIGO and Virgo data spanning 2005-2010, targeting short gamma-ray bursts detected by the InterPlanetary Network. We then turn our attention to the current, second generation of gravitational wave detectors. We present a detailed calculation of the prospects of success for the targeted short gamma-ray burst search technique, and find that we might reasonably expect to make up to a few detections per year around the turn of the decade. We then outline a new search structure for use during the second generation of detectors, and an astrophysical event alert system for the control rooms of gravitational wave observatories. We end with a presentation of the results of the new and improved search carried out during the first observing run of Advanced LIGO.

The aim of this thesis is to investigate the suitability of hydroxide catalysis bonding for use in sapphire and silicon suspensions in future detectors.

Solar flares are known to accelerate electrons to high energies, resulting in the movement of these particles throughout the Sun's atmosphere. Although this has been known since the middle of the last century, it is still unknown quite how these particles are accelerated, how they are transported and where the energization takes place. This thesis is concerned with these key questions of solar physics, using a mixture of analytical and numerical modelling in conjunction with the valuable diagnostic tool of the X-rays observed by the Reuven-Ramaty High Energy Solar Spectroscopic Imager (RHESSI). First, imaging spectroscopy with RHESSI is shown, focussing on how to infer to the underlying electron distribution producing the X-ray photons and how this can be used to produce more realistic models. Secondly, a model where the region in which the electrons are accelerated, stopped and emit X-rays is the same is presented, driven specifically by observations of such sources by RHESSI. This admits a steady-state kappa distribution solution and it is shown that the relaxation of an originally thermal Maxwellian population of electrons to this final state proceeds as a wavefront in velocity space. Finally, a model which takes account of recent studies showing the extended nature of the acceleration region within the loops of solar flares is considered. For the first time the intrinsic spatial dependencies of acceleration and transport are explicitly studied, showing the importance of accounting for this in future modelling of solar flares.

Classical and Recurrent novae (CNe/RNe) are interacting close binary systems in which mass is transferred from a donor star to the surface of an accreting compact companion resulting in an outburst. Their study is important for our understanding of several branches of modern day astrophysics. The work presented in this thesis has focused on three particular topics: (i) Nova V458 Vulpeculae and its surrounding planetary nebula; (ii) Detailed nova light curves from the Solar Mass Ejection Imager (SMEI); and (iii) Vl721 Aquilae, an usually fast, luminous, and highly extinguished nova. A brief account is also given of more generalised work on novae in M31, and areas for future investigation are discussed. Nova V458 Vulpeculae is one of only two novae observed to lie within a planetary neb- ula (PN). Due to the outburst a light echo effect within the PN is experienced. Using Ha data taken over four years the illumination of the PN with time has been examined and a 3D visualisation obtained. Comparison of light echo data from PN models gen- erated with the morphokinematical modelling tool XS5 to observed PN light echo data indicate the presence of a PN with a bipolar external shell and an elliptical internal shell. Results have also confirmed that the PN is at a distance of 13 kpc. SMEI is a space-borne instrument based on-board the Coriolis satellite. It provides precision visible-light photometry of point sources down to 8th magnitude and near complete sky-map coverage at 102-minute cadence. Using SMEI data detailed light curves of novae have been obtained which offer unprecedented temporal resolution around, and especially before, maximum light, a phase of the nova eruption normally not covered by ground-based observations. They have allowed the exploration of fun- damental parameters for individual objects including the epoch of the initial explosion, the reality and duration of any pre-maximum halt, the presence of secondary maxima, speed of decline of the initial light curve, plus precise timing of the onset of dust for- mation. The SME1 data archive undoubtedly holds a plethora of transient events and variable stars. A code designed to search for such events has been created and imple- mented on four years of SME1 data from one of its three cameras generating over 1500 variable objects, some of which were un-catalogued and are potentially very interest- mg. Finally data on the unusually fast and luminous Nova Vl721 Aquilae has been exam- ined. Pre-outburst N1R images from the 2MASS catalogue revealed the presence of a progenitor system, the absolute magnitudes and colours of which suggested the object to have a sub-giant secondary, and so belong to the U Sco class of RNe. Post-outburst spectra of the object revealed the presence of triple-peaked Ha and 01 profiles. Spec- tral fitting of these profiles indicated a high ejection velocity of 3350 km S-l. The triple-peaked nature of the Ha profile suggested that the accretion disc of the system is viewed face-on. This is supported by models created in XS5, which also indicated an axis ratio of rv 1.4 for the ejecta.

This thesis deals with aspects of gravitational wave detection relating directly to the proposed LISA mission. The thesis begins with a review of gravitational wave astrophysics, starting with a brief description of the prediction and nature of gravitational radiation as a consequence of General Relativity. A short description of possible astrophysical sources is given along with current estimates of signal sources and strengths. The history of gravitational wave detectors is then briefly outlined, from the early 1960s and the first resonant bar, through to the modern long baseline laser interferometers currently under construction. Discussion then turns to the joint ESA/NASA space-borne interferometer, LISA. LISA involves picometre precision laser interferometry between spacecraft separated by millions of kilometres. Among the considerable technical challenges involved are the need for laser and clock frequency stabilisation schemes, active phase-locked laser transponders and precision telescope design. After an overview of the mission concept, the thesis deals with the issue of gravitational wave signal extraction from the various interferometric data streams produced in the six LISA spacecraft. A scheme for obtaining the necessary transfer of clock stability around the set of spacecraft is presented. LISA is planned to use diode-pumped solid state lasers. Experiments carried out to characterise the frequency noise of such a laser over the timescales of interest to the LISA mission are then described. Active frequency stabilisation to a triangular Fabry-Perot reference cavity is undertaken, with independent measurements of residual frequency noise obtained from a second analyser cavity. In LISA, the divergence of the laser beams as they propagate along the long arms of the interferometer means that only a very small amount of light is received by any spacecraft. The phase locking system has to function with this low received intensity and should, ideally, produce a transponded beam with relative phase fluctuations determined by the photon shot noise of the weak received light. A test and demonstration of the phase-locked laser transponder scheme for LISA is then presented. The frequency stabilised laser is used as the master oscillator, and a second identical laser is used as the slave. Results are obtained both from within the stabilisation system and also from out-of-Ioop measurements using an independent optical path. At relative power levels approaching those in LISA, performance close to the shot noise limit was demonstrated over part of the frequency spectrum of interest. Some excess noise was, however, found at milliHertz frequencies, most probably due to thermal effects. The thesis then continues with an investigation of far-field wavefront aberrations caused by errors in the transmitting telescopes originally planned for LISA. Any phase variation across the near field wavefront (defined as the wavefront on the primary mirror), caused, for example, by a mis-alignment of the telescope mirrors, will produce phase variation in the far-field wavefront. Coupled with pointing fluctuations of the incoming light, these wavefront distortions can cause excess displacement noise in the interferometer readout. The starting point of the investigation was to redesign the LISA telescope in order to remove both spherical and coma aberrations. Using Gaussian ray tracing techniques, the effect of near field aberrations on the far field phase was explored. A revised Ritchey-Chretien telescope design is described and numerical simulations presented. Finally the thesis concludes with a summary of the work carried out, setting the results in the context of the development of the LISA mission.

Solar prominences are structures located within the solar corona. The flow of energy within them is through radiative processes and this needs to be studied using radiative transfer, which is dependent upon the radiation entering the prominence. For a full understanding of the radiative processes within the prominence we need to fully account for all the radiation that originates outwith the prominence but still influences it. Previous studies have only looked at the radiation from the disc, this thesis will add to this the radiation from the corona and investigate the effects of this. Chapter 1 introduces the Sun and prominences, to explain the conditions prominences occur in. In chapter 2 radiative transfer is discussed, it is shown where the 1-D form of the radiative transfer equation and the statistical equilibrium equation comes from. Previous studies of prominences using radiative transfer are discussed, and we explain the radiative transfer code which will be modified to include the coronal radiation. To add the radiation from the corona it is necessary to know what the coronal radiation would be visible to the prominence as spectra observed from outside the corona would not be suitable for the light an object within the corona receives and so in chapter 3 the radiation that a prominence within the corona would receive is calculated. The methods for determining the radiation from the corona which would be visible to the prominence are explained. The results for this at various heights are shown, and this shows that there would be sufficient difference between the radiation recevied by prominencies at different heights to justify recalculating the coronal radiation for different heights. The coronal radiation is added to the incident radiation below 912 ̊A in chapter 4. The radiative transfer code is modified so that it can receive the light from either individual lines or from many lines averaged over a wavelength range. It is demonstrated that different lines will have different degrees of influence over the ionisation of the prominence by moving an individual test line and so when we addii radiation from lines average over wavelength ranges we take this into account. It is shown that the effects of coronal radiation on the hydrogen in the prominence for iso- thermal iso-baric slabs, and for slabs with a PCTR (Prominence to Corona Transition Region). The coronal radiation is then added to the helium continua in chapter 5. The effects of the coronal radiation on the helium in the prominence for iso-thermal iso-baric slabs and for slabs with a PCTR are shown. The coronal radiation has a significant effect on the condition and emissions of a prominence, and must be taken into account to fully understand the radiative processes of a prominence.

This thesis deals with the theoretical and numerical modelling of partially ionized plasmas. The study of partially ionized plasmas is important in both astrophysical and laboratory contexts and we present a novel finite difference approach to modelling a magnetohydrodynamic plasma and hydrodynamic gas as well as some interaction terms between them. In particular we model fluid limits of a collisional drag, momentum coupling term and a critical velocity (Alfv ́en ) ionization term. Chapter 1 reviews the necessary background material relevant to this thesis. We introduce relevant plasma parameters that are useful to help understand the regimes at which MHD operates and which are later used when placing criteria on the conditions required for, and the rate equations of, ionization. We introduce the fluid limit model of non-resistive plasmas (ideal MHD), as well as theoretical models for gas-plasma collisions and Alfv ́en ionization. Chapter 2 lays out the model of a linear finite difference gas-MHD momentum coupling code (GMMC) that we modify by the addition of a fluid Alfv ́en ionization term. We explore the codes stability and fidelity and we explore Fresnel interference patterns as a test scenario. Chapter 3 lays out the model equations and derivation of a non-linear finite difference gas-MHD interactions code (GMIC). Chapter 4 uses the code GMIC to explore the momentum coupling between the gas and plasma fluids in a non-linear regime. We show that the presence of a frictional drag term effects both fluids in a variety of simulated scenarios. Propagation of waves and diffusion are effected significantly across a range of parameter space. We show theformation of ‘plasmoids’ by interacting, momentum coupled waves. We see that the momentum coupling has a somewhat similar effect on plasmas as a resistive term does. Chapter 5 uses both the linear and non-linear codes to simulate Alfv ́en ionization in a variety of scenarios. With both codes we see that waves and flows can be sources of ionization of the relative velocity between the two simulated fluids exceeds a pre-set threshold. This ionization effects the dynamics of the system significantly, firstly the extraction of kinetic energy in order to ionize introduces a directional and amplitude dependant damping of waves; secondly by providing a source of new plasma that the fluid is forced to react to. Also in this chapter we discuss how Alfv ́en ionization might play a role in astrophysical contexts, in particular, the solar photosphere and brown dwarf atmospheres. Chapter 6 deviates from the previous work to explore the possibility that dielec-trophoretic forces may be able to stratify the dynamic atmosphere of the Sun. We derive a simple expression for the DEP-force due to a neutral particle moving through a magnetic field and becoming polarized and we examine the displacement caused by this field and the ambipolar field. We also simulate the ability of a hypothetical DEP-force to separate elements based on their polarizability to mass ratio. Chapter 7 summarises the conclusion of the previous chapters and includes a brief discussion about possible extensions to this work.

Most stars in the Galaxy are found in multiple systems of two or more stars orbiting together. Two stars orbiting around their centre of mass are called binary stars. In close binary stars, the evolution of one star affects its companion and evolutionary expansion of one star allows for mass exchange between the components. In most cases, the material from the less massive star forms an accretion disc around the heavier companion that has evolved into a compact stellar remnant, the final state of stellar evolution. We call these systems compact binary stars (CBs). The study of CBs is key to the development of two fundamental phenomena: accretion and evolution of binary stars. Statistical information on CBs can be deduced by extracting common properties and characteristic system parameter distributions from observed data. But, despite being fundamental for a wide range of astronomical phenomena, our comprehension of their formation and evolution is still poor, mainly because of the limited knowledge of crucial orbital parameters. This lack of reliable orbital parameters estimation is mainly due to observational handicaps, namely, the accretion disc outshines the system components. Astronomers have developed different techniques to overcome this, but are often very dependant of the signal to noise ratio of the data or are only able to obtain via target of opportunity programs (wait until the target is brighter). The focus of this work is to test and develop techniques, based on indirect imaging methods, that can overcome the main observational handicaps to estimate orbital parameters of CBs. We combine these techniques with the exploitation of more “exotic” emission lines that trace the irradiated face of the donor star, namely Ca II NIR triplet and the Bowen blend. We made use of empirical properties of Doppler tomography to estimate the values of the phase zero Á0 and the velocity of the irradiated face of the secondary star (Kem). We then used synthetic models accounting for an irradiated secondary to fit our measured Kem and perform a K-correction to derive the radial velocity of the secondary K2. To derive K1, we used the centre of symmetry technique, testing its validity among several emission lines and the stability of the results depending on the selected area. Having strong constraints for K1 and K2, we find estimates for the mass ratio q. Furthermore, we developed a variation from the Doppler tomography secondary emission method to constrain the value of the systemic velocity ƴ. We derive meaningful uncertainties of these parameters with the bootstrap technique. Using these techniques, we have successfully set dynamical constraints on the radial velocities of the binary components of CBs and derived fundamental orbital parameters, including the mass ratio, using basic properties of Doppler tomography.

Electron capture supernovae (EC-SNe) are the deaths of approximately 8-10M stars. In this thesis, the evolution of 8-12M stars is calculated using the MESA stellar evolution code. The aims of this thesis are to produce the most advanced and up-to-date progenitor models for electron capture supernovae (EC-SNe) and to study the behaviour of stars across the transition mass range between AGB stars and massive stars. These new stellar models will be the first of their kind since the 1980s and highlight new computational successes and persisting challenges in the field of stellar physics.

This thesis presents three higher-mass star forming regions (Mon R1, Mon R2 and NGC 2264) as observed by Herschel, and also the JCMT (SCUBA-2), and the IRAM 30-m telescope, with additional data from the Spitzer and WISE archives. The Herschel observations, using the SPIRE and PACS instruments over a range of 70 m{500 m, were taken as part of the HOBYS Key Programme, and the data were reduced using the HIPE mapmaking environment with sources identified and characterised by the 'get-sources' routine. The Herschel observations cover the peaks of cold dust SEDs, allowing robust estimates of mass and temperature to be made. Comparisons of the Herschel observations of the three regions suggest a picture of star formation in which the densest parts of certain molecular clouds can accrete matter via filaments from the surrounding regions, fuelling far more star formation than occurs in the outer regions. My study of these regions has led to the potential classification of two separate regimes of star formation. The first occurs in filamentary regions (generally observed with a column density of 3 10²¹ cm⁻²-1.5 10²²cm⁻²), and is associated with gravitational accretion. The second occcurs in dense ridges and filamentary hubs (>1.5 10²² cm⁻²), in which intense star formation is fed by material flowing inward, with feedback from newly-formed stars interacting with the infalling material. The identification of these distinct populations is backed up by characterisation of the probability density functions (PDFs) and by determination of local core formation efficiency (CFE), both of which show a regime change at 1.5 10²²cm⁻². Comparisons of source mass, FWHM, and luminosity also indicate a separate population of cores forming in such regions.