The thesis focuses on the asteroseismology of main sequence B-type stars, particularly β Cephei and Be stars. Photometric observations of these stars were analysed in order to detect stellar oscillations. The photometric data analysed in this thesis were collected using the Solar Mass Ejection Imager (SMEI). The analysis initially focussed on known β Cephei stars, to refine information on previously detected frequencies and detect further oscillations. A survey was then conducted using data from the SMEI instrument to search for further β Cephei stars. The results from this survey were analysed, and individual stars were examined in more detail which may possibly be β Cephei like. Due to the long duration of light curves obtained with the SMEI instrument, stellar oscillations can be analysed for evidence of amplitude and phase change. This type of analysis was completed on two Be stars, Achernar and \(\zeta\) Oph, and significant amplitude changes in the oscillations of both of these stars were detected. There is evidence that the amplitude variations may be linked with the outburst events that occur on Be stars, and therefore this analysis may be used to help solve the puzzle of the Be phenomenon.

The sensitivity of the next generation of interferometric gravitational wave detectors will be limited in part by thermal noises of the optics. It has been proposed that using higher-order Laguerre-Gauss (LG) beams in the interferometers can reduce this noise. This thesis documents progress made in assessing the compatibility of higher-order LG beam technology with the existing precision interferometry framework used in the gravitational wave detector community. A numerical investigation was made into techniques for generating higher-order LG modes with a phase modulating surface. The optimal conditions for mode conversion were determined using fast Fourier transform (FFT) simulations, and predictions were made for the mode purity achievable with this method. Table-top experiments performed at Birmingham demonstrated the generation of higher-order LG modes using a spatial light modulator, and showed for the first time the feedback control of an optical cavity on resonance for higher-order LG modes. An increase in the purity of LG\(_{33}\) modes from 51% to over 99% upon transmission through the cavity was shown. Investigations were carried out at the Glasgow 10m prototype detector into the performance of the LG\(_{33}\) mode in a suspended 10m cavity, providing useful insights into the compatibility of LG modes with larger scale interferometers.

Massive stars have very strong stellar winds which interact with their environment. This work has involved the study of these interactive winds at radio and other wavelengths. Radio observations have been made of the massive runaway star BD+43◦ 3654 and its bow shock which is interacting with the inter-stellar medium. These observations, together with archive data at other wavelengths, have revealed stratified dust and turbulent gas in this interaction zone. Further radio studies have been undertaken of the interaction zones of the colliding winds of massive binary systems. Observations of the colliding wind binary WR 147 at 5GHz have revealed a curved collision zone, suggestive of simple interactive models. Measurements of the flux from the Wolf-Rayet component of this massive binary system has allowed a mass-loss rate to be derived and though the companion O-star is not detected, an upper flux limit has allowed upper limits on the mass-loss rate and limits on the terminal velocity to be inferred. Also revealed is a curious ’bridge’ feature previously observed in WR 147 which occurs between the two binary components. One mechanism is suggested to explain this anomalous feature, the ionising flux of one binary component, the O-star, may be ionising the wind of the other, the WR component. Modelling of the ionisation structure of the stellar winds has been undertaken to verify that this may be occurring. Radio observations of massive stars made at low-frequency have produced detections of WR 147 and the brighter colliding wind binary, WR 146. These detections have allowed modelling of the non-thermal emission in order to deduce where the non-thermal absorption turn-over occurs in these systems. The resultant modelling has illustrated that these colliding wind regions are complex, with multiple absorption regions best describing their nature.

New UV and EUV observations of off-limb and upper solar corona made by the UltraViolet Coronagraph Spectrometer (UVCS) and the Coronal Diagnostic Spectrometer (CDS) on SOHO (Solar and Heliospheric Observatory) are presented in this thesis. These data were used to establish the physical properties, such as temperature, density and element abundances, of different structures of the off-limb and upper corona. For this project, the UVCS team provided UV spectra of the extended solar corona, which included lines of primary interest for the characterization of this region and the solar wind. CDS data consisted of NIS (Normal Incidence Spectrometer) EUV spectra of the low corona. The data included several density-sensitive and temperature-sensitive lines which enabled diagnostic studies to be made. Absolute element abundances were derived from UVCS data; relative element abundances were derived from CDS data. The Differential Emission Measure (DEM) technique was used (for the first time on UVCS data) as the primary method for abundance study. Electron temperatures along the line of sight were derived applying the line ratio and the DEM techniques to both CDS and UVCS data. From the CDS data, electron densities along the line of sight were derived using the line ratio technique. For the UVCS data, the density was inferred using the 0 VI radiative and collisional components of the line. One equatorial and two mid-latitude streamers were observed with the two instruments, in the low corona and at about 1.6 R®. Electron density and temperature profiles with the solar distance were derived. They appeared to satisfy the hydrostatic equilibrium condition. The equatorial streamer appeared to be cooler than the mid-latitude one. Moreover, while the former tended to isothermal values already in the low corona, the latter was multithermal at the base and isothermal at 1.6 R®. The derived composition at 1.6 R®. showed a depletion with respect to the photospheric values for almost all the elements. The Fe/O ratio found here was consistent with values found in the solar wind. Moreover, a depletion in element composition with increasing solar distance was also found. While observing off-limb in the south polar coronal hole, CDS observations of a macrospicule were obtained. For the first time the background emission was isolated from that of the macrospicule itself, and a diagnostic study of both regions was made. The ambient coronal hole appeared to have a density of = 2 x 108 cm -3 that was about half the density found in the streamer base studied in this thesis. Multithermal components were found at the coronal hole base. The macrospicule spectrum indicated chromospheric and transition region temperatures, and fluctuations in density along the feature were registered. In particular, the data showed the presence of an outward-moving cloud of cool material. Its time evolution and velocity were studied. The maximum (initial) outflow velocity was about 80km s-1 , consistent with the outflow velocity measured in interplume regions. An off-limb hot loop system was observed with CDS at mid-latitude. Its top and base were selected for diagnostic studies. Some newly observed hot lines were identified. The loop system appeared to be composed of multi-thermal plasma. The highest temperature registered was log T=6.4 at the top of the loop. A depletion of element abundances which mainly involves the plasma at the top of the loop was found. A coronal hole bounded by a loop system was observed with CDS. Electron density appeared up to a factor two higher in the boundary than in the coronal hole, and the loop system appeared multi-thermal. The ambient coronal hole temperature appeared to be enhanced by the proximity of this loop arcade. Abundances were derived in both regions, and the coronal hole boundary showed slight depletions relative to photospheric values. New coordinated observations with CDS and UVCS were made during one of the SOlO-Ulysses quadratures. Preliminary results regarding temperatures and densities of the core and boundary regions of streamers were obtained from UVCS data.

This thesis is about an investigation into the formation of spheroidal type galaxies. The investigation began with modelling studies of early-type galaxies and spiral bulges (SBs). From galaxy formation modelling studies led by experiments with a sample galaxy, some results were obtained; nonsolar abundance ratios in Elliptical galaxies (Es) achieved better fits between model and data than solar abundance ratios. For both early-type and late-type galaxies, best fits with non-solar abundance ratios were more constrained than in the solar abundance ratio case. A strong link between star formation histories and the supernova Ia rate for the early and late-type galaxies was shown. The model code itself was tested by way of pseudo galaxy experiments, and shown to reliably reproduce model parameters. In the topic area of galaxy formation, regions of spectra particularly sensitive to a galaxy's age and metallicity were measured as equivalent widths and then calibrated to the common scale of the Lick Indices. The Lick Indices were used in deriving all key results throughout the thesis. The modelled sample of galaxies from Proctor & Sansom (2002) lacked data on low velocity dispersion (a) galaxies for line strengths versus kinematics correlations. In regards to low a galaxies, Low Luminosity Es (LLE5) were considered to be likely candidates. Long-slit spectra of a sample of 12 LLEs, taken at the European Southern Observatory New Technology Telescope, were sub-selected for their low velocity dispersions. The spectra of 10 of these LLEs were successfully reduced. Line strengths and kinematics were measured. The Lick Indices of these LLEs were correlated with velocity dispersion (a), alongside the previously modelled companion data set. Ages and metallicities of the LLEs were estimated. From these results, the LLEs were found to have significant correlations of line strength versus a with SBs. However, the LLEs do not appear to be younger than SBs, but younger than Es. The LLEs seem to consist of a low metallicity group (possibly misclassified dwarf spheroidal galaxies) and a high metallicity group. Future possible work that may uncover which models of galaxy formation for high and low metallicity LLEs these results support is suggested.

Solar flares release an enormous amount of energy (up to 10^32 erg) which is transported through the Sun`s atmosphere until it is deposited in the chromosphere, resulting in a broadband enhancements to the solar radiative output. The bulk of the flare radiative output originates from the chromosphere. Despite the importance of the chromosphere we do not yet have a comprehensive understanding of the radiation produced there following flare energy deposition, and the diagnostic potential of radiation from this layer of the atmosphere has not been fully exploited. Additionally, there is evidence that the standard model of flare energy transport via non-thermal electron beams might not be the complete scenario. Chromospheric radiation will be crucial in discriminating between the standard model and alternative energy transport mechanisms. Through near-UV spectroscopy, optical imaging, and radiation hydrodynamic modelling using both the electron beam model and energy transport via Alfven waves, the chromospheric response to flare energy input was investigated. One of the first detailed analyses of the response of the Mg II h & k spectral lines to flare energy input is presented. These are strong, optically thick, lines formed in multiple locations of the chromosphere. In addition to showing a strong intensity enhancement, the lines were redshifted, showed a blue wing asymmetry in the most intense sources, and were substantially broadened. The lines were also single peaked during the flare, in contrast to their double peaked, centrally-reversed structure in the non-flaring Sun. Despite this, the analysis suggested they remained optically thick during the flare. Using snapshots from radiation hydrodynamic flare simulations in combination with a radiation transfer code capable of modelling partial redistribution effects, the Mg II h & k line formation properties during flares were analysed. These simulations showed the same qualitative behaviour as observations, but instead of being single peaked they contained a shallow central reversal. Additionally the lines were too narrow, suggesting the lower chromosphere was too cool in the simulations. Line core Doppler shifts were well-correlated with atmospheric velocity. The lines were formed lower than in the quiet Sun, with source functions (and therefore emergent intensities) that were more strongly coupled to the Planck function during the flare - that is, they reflected the local conditions to a greater degree. While the lines did indeed remain optically thick during the flare, some optically thin contributions resulted in asymmetries. However, the strongest blue wing asymmetries were the result of a stationary component to the line profile when the line core was redshifted. Optical continuum enhancements are amongst the strongest emission during solar flares, though are relatively rare to observe. Understanding the emission mechanism responsible is important for models of flare energy transport, but there remains debate as to the dominant mechanism. This emission may originate from the heated photosphere, or from an overionised region of the chromosphere. Imaging in three optical passbands during a strong flare was used to analyse the temperature enhancement and luminosity of optical sources were under the assumption of two simple models. This was in an effort to determine the most likely emission mechanism. The models were a photospheric (blackbody) model and a chromospheric model with enhanced recombination radiation. Observations were most consistent with the photospheric origin, although some evidence that both mechanisms play a role is discussed. Additionally, initial analysis of observations of a flare in which both the optical continuum and near-UV continuum were observed is presented. Finally, a radiation hydrodynamic numerical model was adapted to include flare energy transport via the dissipation of Alfven waves. Some representative simulations surveying the parameter space are discussed. Additionally, a detailed comparison is presented between a simulation using the standard model of energy transport via non-thermal electron beams, and a simulation using Alfv\'en wave dissipation. Both the hydrodynamic response is compared, as well as the radiative response of the Ca II 8542 and Mg II k-line. It was found that Alfven waves are able to sufficiently heat the chromosphere during flares, making them a viable candidate for energy transport, and that there is the potential for discriminating between energy transport models using observations of chromospheric radiation.

This thesis investigates the effect of rapid accretion and differential rotation on neutron star oscillations. The research is motivated by the fact that vibrating neutron stars are a promising source of gravitational waves. The first part of the thesis is a study of a nascent neutron star accreting supernova remnant material. We model an unstable r-mode oscillation that leads to the emission of gravitational waves, and the torques and heating associated with rapid accretion onto a star with a magnetic field. We consider the consequences for both gravitational wave emission and the rotation rate of the star. The main part of the thesis addresses differential rotation. This is likely to arise at times, such as the immediate aftermath of the supernova, when we expect strong vibrations. We focus on two factors unique to differentially rotating systems; dynamical shear instabilities, and the existence of a corotation band (a frequency band in which mode pattern speed matches the local angular velocity). Using a simple model, we find dynamical shear instabilities that arise where modes cross into the corotation band, if the degree of differential rotation exceeds a certain threshold. Recently, several authors have reported the discovery of dynamical instabilities in differentially rotating stars at low values of the ratio of kinetic to potential energy. We demonstrate that our instability mechanism explains all of the reported features of these instabilities. We also investigate the nature of oscillations within the corotation band. The band gives rise to a continuous spectrum whose collective physical perturbation exhibits complicated temporal behaviour. We also report the existence of modes within the continuous spectrum that appear physically indistinguishable from the discrete modes outside the band, despite the singular nature of their eigenfunctions.

This thesis is an account of work carried out at the Institute for Gravitational Research (IGR), in the University of Glasgow between October 2010 and March 2014. The research presented contributes to the design of ultra-low mechanical loss suspensions for use in gravitational wave detectors and other kinds of interferometry. This thesis focuses on measuring the parameters of mechanical loss in fused silica suspensions that will limit the sensitivity of advanced gravitational wave detectors and other kinds of interferometers where fused silica suspensions are used. These investigations were carried out under the supervision of Dr Giles Hammond and Professor Sheila Rowan. Chapter 1 gives an introduction to gravitational wave astronomy and provides an insight into which astrophysical objects are able to emit gravitational radiation. The chapter goes on to describe current and future detection techniques that are used and planned in order to make the first direct detection of gravitational waves, noting some results and limits which have been achieved to date. The chapter also introduces the different noise sources that will limit the sensitivity of gravitational wave detectors. The information detailed in this chapter has all been derived from previously published literature. Chapter 2 introduces the theory of thermal noise and derives the relationship between the mechanical loss and thermal noise in fused silica suspensions via the fluctuation dissipation theorem. Discussion covers how this limits the sensitivity of a gravitational wave detector. The chapter includes the theory of loss mechanisms present in fused silica. Again the information contained in this chapter has all been derived from previously published literature. Chapter 3 contains details and results of an experiment, where the expansion coefficient of fused silica fibres was measured under varying amounts of stress. Results demonstrate that the effective thermal expansion co-efficient of a fused silica fibre can be nulled by placing the fibre under a particular level of stress. This nulling of the effective thermal expansion coefficient should lower the thermoelastic noise contribution in silica suspensions, essential for allowing second generation gravitational wave detectors to reach their target thermal noise sensitivity of below 10^{-19}m/sqrt{Hz} at 10Hz. The experimental work in this chapter was conceived by Professor James Faller with a prototype demonstrated by Dr Stuart Reid. The set-up was then revised and modified by the author and Dr Giles Hammond to achieve the results presented in this thesis. Throughout this experiment Colin Craig helped with the machining of the invar set-up and Dr Kirill Tokmakov with suspending the silica fibres placed under large amounts of stress. Experimental measurements and analysis were carried out by the author. Chapter 4 describes an experiment in which a fused silica fibre was held under tension and the harmonic violin mode losses over a range of frequencies were measured. The fibre was then cut and cantilever modes of the fibre measured. The contributions from excess losses were calculated and shown not to limit the experiment. A theoretical dilution factor was determined along with the modal strain distribution of the violin and cantilever modes from finite element analysis (FEA). The FEA was aided by Dr Rahul Kumar and Dr Alan Cumming. The data measured was then compiled with a loss model to give information about the loss contributions of fused silica such as thermoelastic loss, surface loss and weld loss. Designing of the silica pendulum system used in this experiment was helped by Russell Jones and the machining of the silica mass holders for CO2 welding was done by Steven Craig. Construction of the silica pendulum system was undertaken by Dr Giles Hammond and the author, who carried out the experimental measurements. Analysis of the data presented in this chapter was aided by Dr Matthew Pitkin who contributed a Markov Chain Monte Carlo regression fitting code. Chapter 5 repeats the above experiment; where the author used a modified fused silica fibre to measure violin mode losses. The modified silica fibre allowed loss measurements to be made at a much lower frequency than in the previous violin mode set-up. In an attempt to study the nonlinear thermoelastic loss in more detail. The stress on the silica was also varied to observe the nulling of the effective thermal expansion coefficient directly through measurements of the mechanical loss. This experiment used many of the components described in chapter 4 and so the same people are acknowledged for their contribution. Construction of the silica pendulums used was carried out by Dr Giles Hammond, Dr Kirill Tokmakov and the author. Chapter 6 focuses on measuring the mechanical loss of 20-30micron diameter fused silica fibres, for use in the Hannover AEI 10m prototype interferometer. This chapter illustrates the problems faced when trying to measure the mechanical losses of thin fibres. The mechanical loss data was then compiled with a loss and finite element model to give information about the loss contributions of fused silica such as thermoelastic, surface and weld loss in thin silica fibres. This experiment was constructed initially by Dr Stuart Reid with some of the welding being performed by Dr Kirill Tokmakov. All of the experimental measurements and analysis were the work of the author. Chapter 7 details the conclusions that can be drawn from the various experiments in previous chapters. The results will be be applicable across many areas of research where low mechanical thermal noise is required. More generally the results can be used as a basis for research that requires mechanical systems at room temperatures for example systems needed to produce stable optical cavities. A further important discovery emerging from this thesis is the ability to cancel and reverse the effective thermal expansion coefficient of fused silica by placing the silica under stress. This process allows stressed silica to be used in systems were low thermal expansion coefficient materials are needed. Thus fused silica can be used as an alternative to composite materials such as invar.

The torsion balance is one of the key pieces of apparatus used in experimental searches for weak forces. In the search for an understanding of a Unified Theory, physicists have suggested a number of signatures that are detectable in laboratory measurements. This thesis describes the development of a new torsion balance facility, relocated from the BIPM (Bureau International des Poids et Mesures) [1], which has excellent environmental stability and benefits from a new compact interferometric readout for measuring angular motion which has been characterised and installed onto the torsion balance. The interferometer has sensitivities of 5 \( \times\) 10\( {-11}\) radians\(\char{cmti10}{0x2f}\)\(\sqrt{Hz}\) between 10\( {-1}\) Hz and 10 Hz, an angular range of over \(\pm\)1\( \circ\) and significantly reduces sensitivity to ground tilt. With the new facility the first experiment searching for temporal variations in the Newtonian gravitational constant has been undertaken with a null result for \( \delta\)\(\char{cmti10}{0x47}\)\(\char{cmti10}{0x2f}\)\(\char{cmti10}{0x47}\)\(_0\) for both sidereal and half sidereal signals at magnitudes greater than 5\( \times\)10\( {-6}\). These results have been used to set an upper limit on some of the parameters within the Standard Model Extension framework [2]. The thesis also reports on the design and manufacture of prototype test masses with a high electron-spin density of approximately 10\( {24}\) and negligible external magnetic field \( \leq\) 10\( {-4}\)\(\char{cmr10}{0x54}\). These test masses can be used within the facility to potentially make it sensitive enough to conduct future spin-coupling experiments.

The first direct detection of gravitational waves last year was the beginning of a new field of astronomy. While we have already learned a great deal from the signals sensed by the LIGO interferometers in their first observation run, research is already underway to improve upon the sensitivity of the state of the art detectors. Novel mirror designs, new interferometer topologies and larger, more advanced detectors are all being considered as future improvements, and these topics form the focus of this thesis. A reduction in the thermal noise arising from the mirrors within gravitational wave detectors will enhance sensitivity near their most sensitive frequencies, and this can potentially be achieved through the use of waveguide mirrors employing gratings. It has been shown that the thermal noise is reduced in waveguide mirrors compared to standard dielectric mirrors whilst retaining the required reflectivity, but an open question regarding their suitability remains due to the potential for increased technical noise coupling created by the substructure. We place an upper limit on this coupling with a suspended cavity experiment, showing that this approach to the design of grating mirrors has promise. While the use of higher classical laser input initially increases interferometer sensitivity, eventually the Michelson interferometer topology employed in existing detectors reaches the standard quantum limit preventing further enhancement. Efforts are being made to test the suitability of so-called quantum non-demolition (QND) technologies able to surpass this limit, one of which involves the use of a new interferometer topology altogether. An experiment to demonstrate a reduction in quantum radiation pressure noise in a QND-compatible Sagnac speed meter topology is underway in Glasgow, and we introduce novel techniques to control this suspended, audio-band interferometer to inform the technical design of future detectors wishing to measure beyond the standard quantum limit. In particular, the problem of controlling the interferometer at low frequencies is discussed. Due to the nature of the speed meter topology, the response of the interferometer vanishes towards zero frequency, while the interferometer's noise does not. This creates a control problem at low frequencies where test mass perturbations arising from, for example, seismic and electronic noise, can lead to loss of interferometer sensitivity over the course of minutes to hours. We present a solution involving the blending of signals from different readout ports of the interferometer, facilitating measurements with almost arbitrary integration times. The longer, larger Einstein Telescope facility planned as part of the next generation of detectors will push the Michelson interferometer topology to the limit. The low frequency interferometer will utilise optomechanical interactions to enhance its sensitivity at low frequencies, and the control problems associated with this technique have not been investigated in detail. Following the approach taken in the current generation of detectors we show that the interferometer can be controlled without adversely affecting its sensitivity to gravitational waves, paving the way for a future technical design.