With recent advances in astronomical instrumentation, individual massive stars in Local Group galaxies are now easily accessible to ground-based telescopes. We present deep, high quality images for two late-type spiral galaxies; NGC300 and M83, located beyond the Local Group at distances in excess of a Mpc. Through the use of narrow-band interference filters, utilizing the strong Wolf-Rayet (WR) emission lines, we have identified a large number of previously unknown WR stars revealing a significant increase in the known WR population of these galaxies, resulting in new catalogues. We have also used a number of modern ground-based optical telescopes with efficient multi-object spectrographs to obtain observations for a representative sample of known extra-galactic WR stars in M33, M31 and IC10, significantly improving on existing data. These galaxies are members of the Local Group and span a metallicity range of approximately a factor of 10, providing us with a variety of environments in which to study individual WR stars. Our large sample has allowed us to re-examine a number of spectral morphologies and to asses their potential multiplicity. We have also re-evaluated the metallicity gradients for three spiral galaxies in which we have observed WR stars, M33, M31 and NGC300 - the results of which are considered in later analysis. For our sample of identified single WR stars we perform detailed, tailored analyses using the non-LTE code, CMFGEN, which assumes a spherically expanding, extended atmosphere subject to line blanketing. Fundamental stellar parameters are derived for each star and subsequently collated, permitting us to investigate the role that metallicity plays on the derived stellar properties for both WN and WC subtypes. The WN stars examined display little difference in the observed properties between the Galactic and LMC samples. Comparison of the single WN stars in the SMC suggest they have significantly reduced mass-loss rates and increased luminosities, implying that WN stars display an observational mass-loss -metallicity relationship comparable to O-type stars (i.e. M alpha Z0.5-0.8). Results for our sample of extra-galactic WC stars appear somewhat less clear, with a range of derived mass-loss rates and luminosities for stars located in a variety of environments. Our results imply that early-type WC stars are relatively uniform and that their wind structure is inherently the same, as indicated through their constant observed line fluxes, after correcting them for distance, and their narrow range of derived properties. Our results call into question whether their mass-loss rates are enhanced with increasing metallicity or whether other factors are important; such as carbon and oxygen significantly aiding line driving and further accelerating the star's atmosphere. Further analysis of more high quality spectroscopic observations are required, for both subtypes of WR stars, located in as many extreme environments as possible to confirm our conclusions.

This dissertation describes my analysis of XMM-Newton observations of six Active Galactic Nuclei (AGN), concentrating on the high resolution spectroscopy of soft X-ray absorption features, and discusses the results in the context of the origins and astrophysical implications of ionised outflows in AGN. I studied two Seyfert galaxies (NGC 3783 and NGC 7469) and four BL Lac objects (1H1219-1-301, H1426-I-428, Markarian 501 and PKS 0548-322), all of which have shown evidence in previous work of soft X-ray ionised absorption. NGC 3783 has very deep soft X-ray absorption. I find that there are at least two main ionisation phases. The low ionisation phase appears to be fairly well concentrated around a single ionisation parameter, whilst the high ionisation phase probably contains a range of ionisation levels. NGC 7469 has a warm absorber with a much lower overall column in our line of sight. Despite this, the detected ions from its absorber span a range of four orders of magnitude in ionisation parameter. In the BL Lac objects, neither the RGS nor the EPIC spectra show any evidence of intrinsic ionised absorption. By looking back over the history of observations of ionised X-ray absorption in these sources, I am able to show that the existence of such features can be ruled out at 93% confidence. I compare the results of these analyses with findings from high resolution X- ray spectroscopic observations of other AGN, in order to come to some conclusions about the origins and importance of the warm absorber phenomenon. I find that Seyfert, NLSyl and certain QSO absorbers are most consistent with an origin in the dusty torus, whilst the outflows in two QSOs are more likely to be accretion disc winds. I show that the kinetic luminosities of the torus outflows must account for less than 1% of the bolometric luminosities of the AGN.

This work uses X-ray and radio data to examine the interaction between radio-loud AGN and their environments. The first half of this work concentrates on how a cluster environment influences the morphology of wide-angle tailed radio sources (WATs). It is found that existing models of WAT formation are unable to explain the phenomenon in light of the data. It is argued that the cluster environment is responsible for determining the location of the plume base, and that conditions inside the plume determine the jet flaring. WATs with very bent jets are discussed in light of jet speeds inferred from a homogenous sample of WATs, and it appears that highly disturbed cluster environments are required for such bending. The second half of this thesis concentrates on whether radio sources can prevent catastrophic cooling. It is found that whilst there are some differences between groups with radio loud brightest galaxies and those without, it is unlikely that radio sources irreversibly raise the entropy in g,TOUp centres. Rather, it appears that current radio sources act to prevent catastrophic cooling in the centres of groups, whilst repeated outbursts may have a longer lasting effect, particularly if the physical size of the outburst is large.

Most bulge-dominated galaxies host a supermassive black hole and yet ongoing nuclear activity is observed in only ~5% of nearby galaxies. Reignition of dormant black holes is therefore required and a key unanswered question is whether the ignition mechanism is related to the galaxy host properties, in particular the fuel transportation mechanisms. The nuclear activity in distant and luminous quasars is related to galaxy interactions and the high-luminosity active galactic nuclei (AGN) are found in giant elliptical galaxies associated with past mergers of lower mass galaxies. In contrast, the low-luminosity AGN, such as the Seyfert galaxies, are not found preferentially in interacting systems or in barred galaxies and fuelling these low-luminosity AGN remains an unsolved problem. Recent results suggest the presence of identifiable dynamical differences between Seyfert and intive galaxies in the central kpc regions. Probing the dynamics of Seyfert galaxies requires spectroscopic data and integral-field spectroscopy (IFS) is particularly well-suited to the investigation of complex structures of nearby galaxies. A comprehensive and statistically-significant study of the neutral gas, ionised gas and stellar kinematics of a well-defined distance-limited sample of Seyfert galaxies paired with control inactive galaxies with carefully matched optical properties was then initiated, using the VLA and the AURON integral field unit (IFU).

We present an observationally constrained model of mass outflow for galactic discs, derived from star formation rate. This is used to supplement a model of the non-linear, mean-field, α2Ω galactic dynamo in the presence of shear. Outflows affect the magnetic pitch angles unexpectedly. This resolves a long standing problem in non-linear dynamo theory, marking a fundamental improvement in the degree of agreement with observations. The mean-field equations are reduced using a modified version of the no-z approximation, to allow for observed flaring of gaseous galactic discs, leaving us with a flared thin-disc model. We have explored two non-linearities to describe the α-effect. We use recent spatially dependent observations of various galaxy properties to evolve the dynamo equations in time. We present results of the steady state magnetic field for both nonlinearities and demonstrate that observables such as local magnetic field strength and magnetic pitch angle can be closely reproduced, using optimum, physically acceptable values of outflow velocity. We apply the model to a number of well observed galactic systems with similar kinematic properties and discuss several sensitivities of the model whilst modifying data sets within the ranges of observational uncertainty.

We have implemented a full 3-dimensional model to generate the X-ray lightcurves and spectra of intermediate polars using the traditional accretion curtain model as a basis. The model constitutes an improvement over previous works because it includes the effects of tall, structured accretion columns, electron scattering by the post-shock flow, and photoelectric absorption by the pre-shock flow by accurately considering the 3-dimensional dipolar geometry of the accretion curtains. A systematic parameter study has been undertaken using this model revealing that both occultation of the Xray emitting regions and electron scattering can produce energy-dependent modulations. Including the effects of tall, structured accretion columns introduces sensitivities to parameters such as the white dwarf mass that Kim & Beuermann (1995) found to have little effect. The energy-dependent modulation is found to vary for each parameter in a systematic but unique manner. These results imply that it may be possible to fit this model to observational data and extract information about many system parameters. We have analysed 5 RXTE observations taken of GK Per over a 41 day period during a dwarf nova outburst in 1996. We have confirmed the white dwarf spin period of 351s but find no evidence of any quasi-periodic oscillations around the 5 - 6ks period. During the outburst, the spin pulse changes from a complex, low-amplitude (~ 14%), double-peaked shape to a high-amplitude (~61%), flat-bottomed quasi-sinusoid at the peak of the outburst. Spectral fits indicate that the absorption and X-ray flux both increase during the outburst, and that it is not possible to reproduce the X-ray spin pulse with only changes in the absorption. Using the model developed here, we have reproduced the quiescent and outburst lightcurves of GK Per and find that the observed changes in the lightcurve morphology are consistent with an increase in the accretion disc mass transfer rate by a factor of f'V 16. We also suggest that the observed lightcurves are consistent with X-ray emission from complete accretion rings around either one or both poles if the dipole axis is inclined to the spin axis by ~ 5.50 , and is offset from the centre of the white dwarf by ~ 0.12 Rwd. NGC 6633 is a young, open cluster with a similar age to the Hyades and Praesepe, but probably a lower metallicity. We present the results of ROSATHRI observations of an optically selected catalogue of likely members of NGC 6633. Eight out of fifty-one NGC 6633 members have been detected, with main-sequence spectral types A to G, above a threshold X-ray luminosity of ~ 6 -12 x 1028ergs-1• We find that NGC 6633 does not contain cool stars which are as X-ray luminous as the most active objects in the Hyades and that the median X-ray luminosity of F-G stars in NGC 6633 is less than that in the Hyades, but probably greater than in Praesepe. However, when X-ray activity is expressed as the X-ray to bolometric flux ratio we find that NGC 6633 and the Hyades are very similar and display similar peak levels of coronal activity. We attribute this discrepancy to a number of possible wide binary systems with higher X-ray (and bolometric) luminosities in the Hyades sample and either a low metallicity in NGC 6633, which makes its cool stars both X-ray and bolometrically less luminous at the same colour, or that the distance to NGC 6633 has been underestimated, which would decrease stellar X-ray luminosities without changing X-ray to bolometric flux ratios. We have highlighted the need for a model that can be used to calculate the iron Ka line profiles detected in intermediate polars that result from Comptonisation of photons trapped by resonance scattering. Such a model may yield information about the structure of the post-shock accretion columns and in particular details about the transition to optical thickness. Monte Carlo simulations are an ideal candidate because of the complexities involved in solving the equations of radiative transfer in the accretion columns of intermediate polars. We present the theoretical background necessary to construct such a model and the initial implementation of a framework upon which more complicated models may be built.

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