The properties of X-ray variability from accreting black holes reveal much about conditions close to the event horizon. Observing common timing signals in many objects, suggests similarities within their accretion flows. To further this aim this thesis presents a systematic survey of the short term variability properties in 19 observations of 16 Ultraluminous X-ray Sources (ULXs) taken with XMM-Newton using the power spectra. Significant short term variability is detected in 8 observations, but 4 of those remaining have upper limits on levels of variability below those observed in Galactic Black Hole Binaries (BHBs). Suggested causes for this suppression include large scale optically thick outflows destroying correlated variability from the source, or that the variability concentrated over shorter timescales than those studied here. Tests for a positive linear correlation between the amplitude of variability (rms) and flux within an observation are presented for archival observations of 9 BHBs. Revealing that this relation is ubiquitous in the broad-band noise for all long, bright observations with sufficient variability to measure the rms. Interestingly, comparisons between the properties of the rms-flux relations over the course of many outbursts, reveal that the x-axis offsets become strongly positive as the source moves into the hard intermediate state. The presence of a linear rms-flux correlation is also found in the light curve from a ULX (NGC 5408 X-1) and in some observations of the type C QP0 from the 1998 outburst of XTE 11550-564. In the latter case the rms-flux relation is found to be dependent on the frequency of the QPO, becoming constant or even negative once the QPO moves above ~5 Hz. A possible time lag between soft and hard emission is also identified from the ULX.

This thesis concerns the electron and X-ray microanalysis of planetary materials: from Comet 81P/Wild2 to the surface of Mars. Advanced techniques in electron microscopy and X-ray spectroscopy have been developed for the microanalysis of the nakhlite martian meteorites and Comet 81P/Wild2 samples from the Stardust Mission. Electron microprobe analysis and a Focussed Ion Beam - Scanning Electron Microscope (FIB-SEM) technique for Transmission Electron Microscopy (TEM) was used to analyse the secondary mineral assemblages in the nakhlites. Fracture-filling assemblages in the nakhlites are found to be dominated by an amorphous, hydrated Fe-silicate - a ‘gel’. The gel decreases in Mgat/Mgat+Feat ratio going up the expected depth profile of the nakhlites. Other phases, especially 2:1 smectites - 1:1 phyllosilicate and carbonate are associated with the gel. Newly discovered 1:1 phyllosilicate, suggested to be serpentine, is also found in the mesostasis of Lafayette. A model is proposed describing the formation of the nakhlites’ secondary assemblages by an impact-induced hydrothermal system based on the mineralogical and geochemical differences between different samples. A suite of Stardust cometary samples have also been analysed using FIB-TEM and microfocus X-ray spectroscopy that includes: X-ray Fluorescence Spectroscopy (XRF), X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) at the Diamond synchrotron. Attempts have been made to distinguish the cometary material from that formed by capture heating in aerogel via the identification of ferric-oxides at track entrances. Finally, the mineralogy and morphology of a terminal particle from Stardust track #154 was studied by analytical TEM. The results show that Comet Wild2 contains a unique Al-diopside-bearing grain, having affinities with the minerals found in refractory objects from the inner Solar System. Upon comparison with different early Solar System materials, the grain’s mineral assemblage most closely resembles Al-rich chondrules. This adds to the refractory inventory identified in Comet 81P/Wild2.

The potential to detect hydrogen cyanide (HCN) spectral signatures and retrieve HCN volume mixing ratios (VMR) in the Upper Troposphere and Lower Stratosphere (UTLS) from a space-borne infrared limb-sounding spectrometer is assessed. The primary aim of this project is to search for new molecular signatures using the infrared spectrometers and identify a unique tracer of pollution to separate two sources of pollution namely: industrial transport/non-coal emissions and biomass burning. HCN is an important trace gas constituent in the atmosphere and it is suggested as a sensitive tracer of biomass burning. Present knowledge of the sources and sinks of HCN, and its role in atmospheric chemistry and biogeochemistry is highly uncertain. The atmospheric distribution of HCN is variable and previous space-based measurements do not give detailed tropical and sub-tropical distributions of HCN. Atmospheric limb-emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard the ENVIronment SATellite (ENVISAT) has been successfully used to detect spectral signatures of HCN in MIPAS-E spectra. These signatures were detected in the ranges 744.300–744.525 (HCN_0102) and 746.775–747.825 (HCN_0105) cm−1 for a single scan #2 (orbit 08585), for four selected MIPAS-E spectra from different latitude bands and later for the whole month of October 2003 using an automated detection technique. Retrievals of HCN profiles are also promising, particularly at 12 km MIPAS-E nominal altitude. HCN data have been retrieved for October 2003 in 747.350–747.500 cm−1. The HCN data retrieved at 12 km nominal altitude in the tropics appears to be the most successful. In addition, there is a potential to obtain vertical profiles of HCN on a global basis throughout the UTLS. For more accurate detection and retrieval of HCN, methyl chloride (CH3Cl) and dinitrogen pentoxide (N2O5) need to be fitted well enough in both HCN_0102 and HCN_0105 MW (MW) regions.

This PhD thesis is an investigation of the characteristics and detection limits for transit signals due to sub-stellar and terrestrial companions to white dwarfs in the SuperWASP survey. The work is described as follow: there is an introductory chapter on the field of white dwarfs and exoplanets. In chapter 2 I describe the SuperWASP project, the two SuperWASP telescopes the problematics of data analysis and the results obtained so far. In chapter 3 I discuss the simulations I performed to investigate the characteristics of the transit signals due to sub-stellar and planetary companions to white dwarfs and the detection limits derived for SuperWASP light-curves by means of my optimised version of Box-Least Square (BLS) algorithm. In chapter 4 I present a study of 194 spectroscopically identified white dwarfs which are a cross-correlation of the McCook & Sion catalogue and the SuperWASP archive. In addition, I derive upper limits to the frequency of sub-stellar and planetary companions to white dwarfs using my sample and the results obtained from my simulations. In chapter 5 I present a variability study for the sample of 194 white dwarfs. I have investigated the light-curves of the 194 white dwarfs in the sample to search for photometric variability due to non-radial pulsations, the presence of star spots in magnetic white dwarfs, and to irradiation and reflection effects on low-mass close companions. Finally, in chapter 6 I conclude and present my project for future work.

In this thesis I present a new near-infrared photometric search for unresolved ultracool companions and debris disks to white dwarfs in UKIDSS DR5. 24 DA white dwarfs were found with multiple excesses indicative of a low mass companion, with 7 of these having a predicted mass in the range associated with brown dwarfs. The results of this survey show that the unresolved brown dwarf companion fraction to DA white dwarfs is 0.5 ≤ fWD+BD ≤ 1.8 ± 0.7%. I also calculate the unresolved L-dwarf companion fraction to be 0.5 ≤ fWD+dL ≤ 1.5 ± 0.6%, which is much higher than the previous estimate of Farihi, Becklin & Zuckerman (2005). However, the results are consistent with previous estimates of the brown dwarf companion fraction to main sequence stars. I analyse the near-infrared spectra of eleven known DA white dwarf + M-dwarf binaries, and compare the spectral types assigned using optical photometry against those assigned using near-infrared spectra. I search for evidence that the known short period systems once existed in a common envelope phase. No such evidence was found. I also present the spectroscopic analysis of two particularly interesting binaries; PG 1234+ 482 and PHL 5038. PG 1234+482 is the hottest and youngest DA white dwarf with a cool companion on the stellar-substellar borderline. I discuss the possibility that the companion is a brown dwarf, and the possibility that the secondary is the source of contamination by heavy metals in the white dwarf's atmosphere. PHL 5038 was identified to have a near-infrared excess in UKIDSS, and the spectroscopic analysis in this thesis confirms that the secondary in this system can be resolved at a projected orbital separation of 55AU, and is a brown dwarf with spectral type L8-L9. This is only the second such pair found (over 20 years later) after GD165AB. The secondary in this system has the potential to be used as a benchmark brown dwarf for testing substellar atmospheric models.

This thesis sets out to further develop our understanding of accretion processes in symbiotic stars, in particular the accretion disc formation radius and mass capture fraction from a stellar wind. I then explore how these potentially large discs can deliver mass onto the white dwarf at the nuclear burning rate, allowing the white dwarf to grow in mass rather than going through nova explosions. Finally, if this is not possible, I investigate how nova explosions interact with the disc the white dwarf star may harbour. Using smoothed particle hydrodynamics, I present circularisation radii and mass capture rates for 8 different symbiotic binary star systems undergoing mass transfer from a stellar wind. I explore the wind velocity and secondary star rotation parameter space. I compare these radii against one another and the expected circularisation radii for Roche lobe overflow. Using RS Oph as an example, I determine that it is unlikely for the disc to be maintained in the hot and steady state. Furthermore, unless the mass loss from the red giant is unusually large, the wind velocity must be very slow to enable the required mass transfer from the red giant to the disc to explain RS Oph’s ~ 20 year outburst cycle. I present an analytical method to describe the outburst and recurrence time of 18 cataclysmic variable stars (including 4 Z Cam, 9 U Gem and 5 SW Uma). Using the Markov chain Monte Carlo method, the parameter space is constrained. Extrapolating the analytical method to long period cataclysmic variables, the periods during which average mass transfer through the disc lies within the nuclear burning regime, and the irradiation from this promoting more of the disc into the hot, more viscous state to drive prolonged outbursts, was found. This could enable a 1Mסּ white dwarf to grow to the Chandrasekhar mass in a minimum time of approximately 1 million years. Finally, a new test (the Richtmyer-Meshkov instability) on Godunov smoothed particle hydrodynamics was performed and compared against standard smoothed particle hydrodynamics. Using the same code, nova blast waves into discs of constant and varying density are simulated and compared against the Sedov solution and the Kompaneet approximation respectively. Using simple energy arguments, I calculate how much of the nova and disc material remains bound to the WD. In the less energetic novae, approximately 40% of the disc and more than 80% of the nova material remains bound to the white dwarf, whilst in high energy novae approximately none of the disc and less than 50% of the nova material remains bound to the white dwarf.

Broad absorption line quasars show broad blue shifted absorption indicative of high velocity outflowing material. The mechanism responsible for accelerating these outflows is a matter of much debate. In this thesis I investigate the possibility that radiative line driving is responsible for driving the outflows in some objects. Various metrics have been proposed to compile homogeneous samples of BALQSOs. Using a new hybrid algorithm we have compiled a sample of 3552 BALQSOs representing approximately 12.5% of the quasars for which SDSS spectra (from DR5) covering the C IV broad absorption line region are available. From this BALQSO catalogue we have selected the largest sample of objects exhibiting evidence for radiative line driving (the ghost of Ly-α), a feature observed in the BAL troughs of around 1% of BALQSOs. Using this sample we test the criteria purported necessary for ghost-formation in order to confirm whether the identified feature is in fact a ghost. This investigation suggests that the feature observed in the majority of objects arises from the superposition of multiple absorption components, which mimic the appearance of a ghost and unrelated to interactions between N V and Ly-α. Follow up spectroscopic observations of some of the ghost candidate objects taken using the William Herschel Telescope and the Gemini North telescope are presented. The reduction of these data is described in detail. The criteria for ghost formation are tested on the new spectra with similar results. One object whose absorption has undergone significant changes is identified and photo-ionisation models used to provide constraints on the physical conditions within the absorber. These models suggest that the changes are due to an increase in the ionisation parameter and not due to changes in the gas covering fraction. The location and mass outflow rate in this object is consistent with previous estimates in similar systems. The work presented within this thesis does not preclude radiative line driving as a mechanism responsible for high velocity quasar outflows. It does however suggest that the ghost of Ly-α, previously considered the strongest evidence for radiative line driving is rarely observed.

In this thesis I present the work of two studies into the population of low-mass stars and brown dwarfs within the open galactic clusters of Praesepe and Blanco 1 using optical and infrared photometry. Observing these objects within clusters is of great importance as their known ages and distances allow for comparisons to be made between the observed results and those predicted from theoretical formation and evolutionary models, whilst expanding our understanding of the initial mass function. Following an introduction to the formation, evolution and observational history of brown dwarfs in Chapter 2 an overview of the principle data reduction processes and instruments used in this thesis is given in Chapter 3. Chapter 4 presents the result of the survey carried out in Praesepe using archival 2MASS, SDSS and UKIDSS data in a range of filters. Proper motion information is combined with colour magnitude cuts to select out and classify objects that are considered to be cluster members. Over 280 members have been identified with a cluster mass function that is consistent with the values presented for other clusters found. This mass function is in disagreement with previous values found for Praesepe. Chapter 5 presents the results of a follow up J band survey using WFCAM to the CFHT12k I and z survey of Moraux et al. (2007). The data reduction and membership selection procedure are discussed with 27 low-mass objects found to be members. Chapter 6 in contrast to the previous chapters presents a study not of brown dwarfs but of a suspected main-sequence, magnetic white-dwarf binary system found during an archival search of the UKIDSS DR3 database for objects with unusual Y band colours. The evidence for this system being a Polar is presented along with a discussion as to the assumed system properties. Follow up observations using the IAC-80 telescope, UKIRT and the SWIFT satellite are also presented. Finally in Chapter 7 I summarise the results from each chapter and identify areas of future work.

The thesis investigates Ultra Low Frequency waves in the band 0.1 Hz to 5 Hz in the terrestrial magnetosphere-ionosphere system. Utilising mid-high latitude ground-based induction coil magnetometers, continuous (Pc1-2) and irregular (Pi1-c) pulsations are explored through the application of digital spectral analysis. An assessment of two spectral analysis techniques is conducted. From which it is concluded that, for routine ground-based analysis of Pc1-2 pulsations, treating the horizontal components of magnetic field variation as a single complex signal is computationally beneficial with minimal loss of useful information. Polarisation parameters and values of cross spectral phase are derived using a weighted histogram technique and are subsequently used to distinguish discrete pulsations and infer their location through simple triangulation. The results of a statistical study of ~1200 discrete Pc1-2 events over the full year of 2007, during the declining phase of solar cycle 23, are presented. This study, for the first time, reports the ground-based polarisation properties of Pc1-2 waves as a function of latitude. The derived diurnal frequency behaviour supports the suggestion that the Ionospheric Alfvén Resonator may play a part in the filtration of ground-based Pc1 observations. Pc1-2 behaviour over the course of 26 geomagnetic storms is also presented, with support being found for the association of pulsation enhancement with plasmaspheric plume formation in the recovery phase. A case study, combining coherent and incoherent radar, in situ particle measurements and ground based magnetometry, has focused on high latitude Pi-c activity during a period of enhanced dayside reconnection. This study has provided support for the association of Electromagnetic Ion cyclotron waves with the SuperDARN spectral width enhancements observed in the flanks of the ionospheric cusp.

We present new measurements of the spatial distribution of cool and hot gas in the local interstellar medium as a result of a search for O VI absorption in the FUV spectra of 100 white dwarfs at distances between 50 and 300 pc. We have carried out a detailed velocity analysis on the detected O VI lines to ascertain the degree of contamination from the background star. The position of the stars relative to the local cavity is calculated through cold gas phase column density measurements. Through curve of growth analysis we note that the local cavity is depleted in metals relative to hydrogen by a factor of 5 -10 compared to the space beyond. Whereas the O VI producing hot gas was originally thought to be observed in the interface regions between hot and cold gas, i.e. the cavity wall, our investigation nds no unambiguously hot gas in lines of sight that span such regions. We do, however, nd hot gas at high galactic latitudes where there are no such walls. We discuss the wider context of this result by comparing the position of these detections to the soft X-ray background. This work ultimately changes our picture of the local interstellar environment and its processes by removing the ubiquitous million degree gas that was once thought to surround the solar system. One possible explanation worthy of further investigation is that the local cavity has recently begun to be inundated by hot gas spilling out of the loop 1 supernova remnant. In support of this work there is an enclosed CD that contains the data and models used in this thesis. Examples of the information found on this CD can be found in the appendix. Explanations of the data, charts and graphs can be found in the body of the text when required.