No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

I model the multi-phase interstellar medium (ISM) randomly heated and shocked by supernovae (SN), with gravity, differential rotation and other parameters we understand to be typical of the solar neighbourhood. The simulations are in a 3D domain extending horizontally 1x1 kpc² and vertically 2 kpc, symmetric about the galactic mid-plane. They routinely span gas number densities 10⁻⁵-10²cm⁻³, temperatures 10-10⁸K, speeds up to 10³km s⁻¹ and Mach number up to 25. Radiative cooling is applied from two widely adopted parameterizations, and compared directly to assess the sensitivity of the results to cooling. There is strong evidence to describe the ISM as comprising well defined cold, warm and hot regions, typified by T 102 ; 104 and 106 K, which are statistically close to thermal and total pressure equilibrium. This result is not sensitive to the choice of parameters considered here. The distribution of the gas density within each can be robustly modelled as lognormal. Appropriate distinction is required between the properties of the gases in the supernova active mid-plane and the more homogeneous phases outside this region. The connection between the fractional volume of a phase and its various proxies is clarified. An exact relation is then derived between the fractional volume and the filling factors defined in terms of the volume and probabilistic averages. These results are discussed in both observational and computational contexts. The correlation scale of the random flows is calculated from the velocity autocorrelation function; it is of order 100 pc and tends to grow with distance from the mid-plane. The origin and structure of the magnetic fields in the ISM is also investigated in nonideal MHD simulations. A seed magnetic field, with volume average of roughly 4 nG, grows exponentially to reach a statistically steady state within 1.6 Gyr. Following Germano (1992), volume averaging is applied with a Gaussian kernel to separate magnetic field into a mean field and fluctuations. Such averaging does not satisfy all Reynolds rules, yet allows a formulation of mean-field theory. The mean field thus obtained varies in both space and time. Growth rates differ for the mean-field and fluctuating field and there is clear scale separation between the two elements, whose integral scales are about 0:7 kpc and 0:3 kpc, respectively. Analysis of the dependence of the dynamo on rotation, shear and SN rate is used to clarify its mean and fluctuating contributions. The resulting magnetic field is quadrupolar, symmetric about the mid-plane, with strong positive azimuthal and weak negative radial orientation. Contrary to conventional wisdom, the mean field strength increases away from the mid-plane, peaking outside the SN active region at |z| ≃ 300 pc. The strength of the field is strongly dependent on density, and in particular the mean field is mainly organised in the warm gas, locally very strong in the cold gas, but almost absent in the hot gas. The field in the hot gas is weak and dominated by fluctuations.

I here present my version of the Kohonen Self-Organising Map (KSOM) as applied to the classification, or rather clustering, of astronomical data. The main body of this work is concerned with the grouping of period-folded stellar lightcurves and clustering based on the lightcurve shape alone. It has been found that the algorithm is an extremely stable grouping mechanism for data of low (3cr signal to noise) to good quality. With further analysis of the results it is possible to locate underpopulated samples of data that exist within the data. This can be successfully achieved for samples of 1%, or less, total population. Additionally the same algorithm has been applied to the extraction of planetary transit lightcurves from those of eclipsing binaries (chapter 5), and to the grouping of X-ray/optical data from the XMM-Subaru deep-field observations (chapter 6). In both cases the algorithm has shown itself to be quite capable of performing such tasks and as such I propose that it could become a very useful astronomical tool. In summary I also present a few ideas for further refinement of the results presented by the KSOM and how these may be used in future study.

M Dwarfs are becoming increasingly important in the investigation of magnetic fields. These low mass stars span a range of masses that coincide with a change in the internal structure from partly convective to fully convective. Despite this, these stars remain extremely magnetically active and exhibit strong, stable magnetic fields. Reconstructed maps of the radial magnetic field component at the stellar surface can be produced through Zeeman-Doppler Imaging (ZDI). In this thesis I extrapolate the 3D coronal magnetic field from the reconstructed magnetic maps and investigate the change in the coronal structure across the fully-convective boundary, for a sample of early-to late-M dwarfs. ZDI has the ability to map surface magnetic fields but only the net large-scale field is detected. I create synthesised maps to model the hidden magnetic field not detected by ZDI and examine the effect this small-scale field has on coronal properties. I find that the dipole component of the magnetic field is prominent on each star and influences the large-scale structure but that the high multipoles cannot be ignored when modelling the open flux bearing the stellar wind. This open flux is responsible for angular momentum loss and the spin down time of the star and I find that the magnitude of the predicted open flux increases with decreasing mass. I examine the X-ray emission measure and reproduce the observed trend of a rise, a saturation and a further decline of the X-ray luminosity with Rossby number. I find that when the synthesised small-scale field is scaled with respect to the large-scale field the X-ray activity-rotation relation is unaffected by the increased surface flux. I also find that the magnetic field structure is not significantly affected by the addition of a carpet of small-scale field. As such the spin-down times and angular momentum loss due to the open flux are also unaffected. For a small sub-section of the stellar sample, I investigate the impact of forcing the magnetic field geometries towards symmetric and anti-symmetric configurations about the equator. I find that these assumptions have only a small effect on coronal properties. At spectral type M7, a eviation from the well-established LX-LR relation occurs in the radio band. I adopt the theory behind Earth's auroral kilometric radiation to demonstrate that the electron cyclotron maser instability, a plausible explanation for radio emission, is able to form within the corona, close to the stellar surface. I also find that the light curve of this radio emission is highly dependent on the magnetic field structure and stellar inclination.

The thesis describes the design, testing and flight results from two Skylark rocket experiments which were primarily intended to make high-resolution searches for line emission in the X-ray spectrum of Scorpius X-1. The observations of Sco X-1, up to the end of 1968, over all frequencies of the electromagnetic spectrum, are summarised, together with the astrophysical models of the object and their implications for the X-ray spectrum. The decision to search for line emission in the spectrum arose from the need to establish whether the X-rays are of bremsstrahlung or synchrotron origin. The first Bragg crystal spectrometer to study a non-solar X-ray source was flown on a sun-pointing British Skylark from Woomera in March 1970, and an improved experiment of the same kind was flown on an E.S.R.O. Skylark from Sardinia in March 1971. The payloads were the first to employ roll stabilisation on an X-ray star using proportional detectors. The proportional detector experiments confirmed the bremsstrahlung nature of the X-ray emission, while the high-resolution spectrometers established that Doppler-broadened Fe XXV line emission is at least an order of magnitude less intense than is expected from a low-density plasma. Fluctuations in the X-ray intensity were observed on 1 minute time scales, as found in the optical data. A summary is given of contemporary work on Sco X-1, and the absence of narrow line emission is found to be consistent with those models of the X-ray source which envisage a high-density, toroidal plasma in orbit around a central white-dwarf or neutron star.