Spectroscopic observations of 18 of the brighter Be and 0e stars in the Northern Hemisphere have been presented in this project. About 900 spectrograms were secured and measured using the more objective numerical technique (REDUCE and VCROSS) to obtain as many accurate radial velocities as possible for these stars. The analysis of these measurements has demonstrated clearly, that most of these early-type stars are indeed variable in radial velocity, while a real periodicity in the radial velocities of some of the programme stars is found. The long-term periodicities were attributed to the binary nature, while the short ones could be ascribed to the pulsation phenomenon. Orbital elements are determined for four newly discovered binary systems, and improved orbits are determined for four known binaries. Five other stars display short time-scale periodicity (less than 1.5 days) attributable to radial or non-radial pulsation, whilst three variables show little evidence for periodicity. Only two stars are found to have constant radial velocities. A brief summary of the properties of Be stars and all the available models to explain the Be phenomenon is presented in chapter one. Chapter two contains a brief description of the observing equipment and the techniques used. The reasons for selecting the programme stars are given in the same chapter. A complete explanation of the measuring technique used in this investigation is given in chapter three. In chapter four, all the analyses and the results for each star are given individually, while a discussion of previous work on these stars appears in the relevant sections. The final chapter contains a discussion of the results from this study together with an analysis of the energy distributions of the programme stars, compiled by the author from published fluxes and photometry from the ultraviolet to the infra-red parts of the electromagnetic spectrum. Some consideration of future work to be done on these types of stars is also given.

The development of an interactive data reduction and analysis system for astronomical spectra written in the FORTH computing language and operated on the Nova 820 minicomputer at the University Observatory, St. Andrews is discussed. Spectra of a number of B stars, many of which were obtained by the author at the South African Astronomical Observatory, were measured and reduced using this system. Equivalent widths of metal absorption lines are used to deduce the stars' fundamental photospheric parameters and abundances by comparison with the predictions of both non-LTE and line-blanketed LTE models. It is shown that effective temperatures derived with the line-blanketed LTE models are in good agreement with those found by other authors for near main sequence B stars using measurements of the integrated flux of the stars. Unblanketed non-LTE models give effective temperatures which are systematically high by approximately 7%, similar to the difference between blanketed and unblanketed LTE models. The major differences between the predictions for absorption lines using LTE and non-LTE models are due to the different level populations predicted and not to the different photospheric structures. The use of non-LTE models is found to reduce the microturbulence required to bring element abundances derived from strong lines into agreement with those found for weak lines but not to remove the need for the inclusion of microturbulence in the solutions for most B stars. An investigation of the suitability of the analysis of high resolution Michelson interferometry using Fourier decomposition techniques as a means of determining the broadening mechanisms and velocity fields in the photospheres of early A stars is made.

Spectra were obtained from several sources for a fine abundance analysis of the extreme helium-rich star HD 168476. The atmospheric parameters are found using theoretical models and abundances determined for the ions identified in the spectra. The star is found to have an effective temperature of 14000°K, log(surface gravity) of 1.5 and a microturbulent velocity of 10 km/s. Over 1400 lines are identified on the spectra ranging in wavelength from 3100A to 4925A and 5490A to 6585A, and about 530 lines are suitable for the abundance analysis. It is confirmed that helium, carbon, nitrogen and neon are overabundant, with hydrogen and oxygen underabundant. An ultraviolet spectrum of the star is also obtained and lines identified. In addition to the ions found in the visible region of the spectrum, neutral ions are also present, indicating the possibility of a cool outer shell to the star. Photometric and spectroscopic observations are made to study the light and radial velocity of the star, to determine if it is variable. Statistical tests showed that the star is variable in its V magnitude, and most probably in its colours, as well as being variable in its radial velocity. No period is found and it is suspected that the variability may be complex. Several theories for the causes of the variability are discussed and a possible origin for the extreme helium-rich nature of the star mentioned.

In Part 1, a background to the project is provided by summarizing the general properties of Miras. A section is devoted to describing pulsating variables from a theoretical viewpoint, and this is followed by a discussion of past photometric work. Finally, a comparison is made between the theory and observations of Miras, which points out the well- known incompatibilities between the two approaches. Part 2 begins by underlining the desirability of observing Miras in UBVRI, and then goes on to describe the mechanical design of the St. Andrews ten colour, two photo multiplier, automated photometer. This photometer was designed as a general user instrument for the South African Astronomical Observatory, where the observing programme was carried out between May 1973 and October 1974. The photometric characteristics of Miras are then reconsidered, and the adopted ten colour photometric system, which adds five 200 Å wide filters to UBVRI, is described. The procedures used for obtaining the observations, and the reduction methods are summarized, along with the likely sources of error. This is followed by the analysis of the results, which consists mainly of a description of the properties of the various two-colour diagrams, particular emphasis being placed on those such as (V-R, R-l) and (V, R-I) which show unexpectedly narrow sequences. In addition, considerable attention is directed at the scatter in the (U-B, R-I) diagram, and also at the interesting R Aqr system. The data are then considered from the period-luminosity- colour viewpoint, enabling a discussion of absolute magnitudes and the value of the pulsation constant, as well as an investigation, of the possible harmonic relationships between Miras of differing periods. Finally, an attempt is made to place the Me Miras in the (M[sub]bol, log Te) diagram, and the conclusion is drawn that the discrepancies between theory and observation can probably be mostly attributed to the methods of interpretation of the latter.

Surface photometry is one area of extragalactic studies in which information is urgently needed by optical as well as radio astronomers. The aim of this thesis is to supply some of the photometric parameters for 48 galaxies in two international colour systems. The reader will notice that descriptions are included of many detailed aspects of the work and little attention is paid to the more basic problems. This is because the discussion of the basic problems in photo-graphic photometry of galaxies formed the contents of an M.Sc. thesis. Volume one is devoted to a detailed description of the methods used for the reduction techniques together with a discussion of the results, while volumes two and three contain the photometric data. In the first volume, the first chapter is concerned with previous investigations and the following chapter contains detailed descriptions of the instruments and methods used in the preliminary plate reductions. The subject of isophotometry is dealt with in the third chapter, while in the fourth and fifth chapters respectively, mention is made of the reduction techniques, together with conclusions which may be deduced from the photometric data. This information is given in volume two for those galaxies with NGC catalogue numbers from 4189 to 4459, while the data for objects from NGC 4461 to NGC 4762 are listed in the third volume of the thesis.

We investigate stellar models for main-sequence and horizontal-branch stars constructed using the Carson opacities and make comparisons with models based on the Cox-Stewart opacities. A Henyey code based on the prescription of Kippenhahn et al (1967) is used for most of the calculations of stellar structure and evolution. In the equation of state we treat ionisation equilibrium and non-relativistic degeneracy for separate temperature-density regimes. The opacity is obtained by 4-dimensional linear interpolation in the Carson opacity tables. Nuclear energy generation rates are taken from Fowler et al (1975) and neutrino losses from the approximation due to Beaudet et al (1967). Electron-screening factors are from Reeves (1965). The standard local mixing-length theory of Bohm-Vitense (1958) is used to treat non-adiabatic convection, although some models are calculated with modifications due to Deupree et al (1979, 1980). We neglect semi convection. The Carson opacities have only a small effect on the position of ZAHB models, but this may be metallicity dependent. The drop in the hydrogen- shell luminosity due to the helium-core expansion during HB evolution is greater than that obtained with the Cox-Stewart opacities. Allowing for the inclusion of semi convection and convective overshooting, we find that adoption of the Carson opacities leads to a reduction of approximately 25% in the HB lifetimes. For a given range of values for the masses and envelope helium abundances of stars on a synthetic HB, the width in effective temperature is increased, and in luminosity the width is decreased. The dependence of the core luminosity on the falling core helium abundance is increased by approximately 16%. Studies of main-sequence stars lead to agreement with Stothers' (1974a, 1974b, 1976) results for homogeneous models constructed with the Carson opacities. The evolution of main-sequence stars of intermediate mass is unaffected by the change in the opacity. Two evolutionary sequences (for 1 Mo stars) suggest that the main-sequence lifetimes of low mass stars may be reduced by as much as 30%. Combined with a shift in the ZAMS position this will move isochrones for low mass stars towards lower effective temperatures and densities. If studies of red-giant evolution indicate little change in the luminosity level of the horizontal branch, globular cluster ages determined from the position of the main-sequence turnoff point may be substantially reduced (possibly by as much as 50%). This could save a conflict between observed values for globular cluster ages and a value for the Hubble constant of 90. Studies of the apsidal motion constant, k2, for evolved MS stars shows that the discrepancy between observed values of k1 for eclipsing binary systems and theoretical values obtained from homogeneous stellar models may be resolved by considering the evolution of the binary components. CO Lac is an exception to this result, but analysis of the observations suggests that a redetermination of the orbital semi-amplitudes may resolve the conflict.

Spectroscopic observations of some of the brighter W Ursae Majoris type contact binaries in the northern hemisphere have been obtained at a medium dispersion of 20-30 Å/mm. A computer program has been developed to process and analyse these spectra using modem digital reduction techniques in order to obtain more accurate spectroscopic data for such systems. Radial velocity measurements have provided spectroscopic mass ratios which have been compared with the values derived from light curve synthesis. The improved mass ratios have removed the discrepancy which existed between the spectroscopic and photometric values in most of the systems observed. The application of spectrum deconvolution techniques has revealed an asymmetry in the structure of two W subclass systems shown by the variation in the strength of the primary components' spectral lines. Measurement, of the relative line strengths of the two components has provided further evidence for the presence of extensive magnetic starspots on the surface of the primary component of these systems.

A survey of early-type stars at intermediate galactic latitudes was carried out in the southern hemisphere winters of 1970 and 1971. The observing programme was limited to negative declinations and covered a range in right ascension of approximately 12h to 20h. At the Royal Observatory, Cape Town, in 1970, UBV photoelectric measurements were made of 56 stars for which no UBV data existed and 20 stars which had been observed on one or two previous occasions, the intention being to obtain four separate measures of each star. In 19711 the Bochum University telescope at the E.S.O. site in Chile was used for H/3 photoelectric photometry of over 200 intermediate and high latitude stars. Shortly afterwards, spectra for radial velocity determination and MK classification were obtained with the two-prism spectrograph and 74" reflector of Radcliffe Observatory, Pretoria. Work was concentrated upon some 60 stars not previously observed with spectroscopic equipment and selected on the basis of blue colour or possible high luminosity from photometric considerations. A few southern standard stars and stars from earlier Radcliffe programmes were re-observed as control or overlap stars. Chapters II - IV describe the observational procedures and reduction methods. Tables in chapter V contain results from the 1970-71 programmes plus UBV and spectroscopic data for intermediate and high latitude stars from various other sources. The remaining chapters are concerned with analysis and discussion of the observations. Chapter VI summarises some optical and radio determinations of the spiral structure of the Galaxy and compares the spatial distribution of the programme stars with these results. The possibility that early-type stars may be formed well away from the galactic plane is considered by comparison of kinematic and evolutionary lifetimes of some stars at appreciable distances from the plane. In chapter VII, intermediate and high latitude stars are shown to participate in the differential rotation of the Galaxy and detailed analysis of the space motions of a number of high velocity stars leads to the conclusion that some may .have sufficient energy to escape from the galactic system. The radial velocities of interstellar Ca II lines are shown in chapter VIII to be as expected for material in the solar neighbourhood involved in differential galactic rotation. An apparent deviation from circular motion reported by observers investigating H II regions is also present in the Ca II gas. Constants in the cosecant equation of interstellar reddening are re-determined and show an apparently significant difference between northern and southern galactic hemispheres. Appendix I describes attempts to simulate the effect of filters in order to explain the curvature in the transformations from instrumental to standard photometric systems. Appendix II gives details of the method used to compute stellar space velocities from proper motions and radial velocities and includes a short Fortran IV programme which implements the operations described.

The bright hydrogen-deficient binary Upsilon Sgr has been studied in detail in the areas of radial velocities, flux distribution, temperature, surface gravity, composition and mass loss using the analysis of spectroscopic data. From IUE high resolution spectra the primary radial velocity orbit has been confirmed (K1 = 47.3±0.8kms−1) and the secondary radial velocity curve determined for the first time (K2 = 29.7±1.7kms−1). The orbit has been constrained to an inclination of 65 - 78°. The masses of the primary and secondary are then 3.0 ± 0.3 and 4.8 ± 0.5M☉ respectively, with an orbital separation of 230±20R☉.The primary is expected to fill its Roche Lobe at a radius of ~60R☉.Using all the available photometry and line-blanketed hydrogen-deficient model atmospheres the primary effective temperature has been determined to be 11,800±500K. IUE spectra were used to determine an extinction of E[sub]B-v = 0.20±0.05 leading to a distance of ~1400pc and a luminosity of 61,000(+11,000)/(-5,000) L☉. The long standing problem of the flux distribution has been mostly solved and little of the UV flux shortward of 1400 Å comes from a hot bright secondary. The same model atmospheres and a high resolution CCD/echelle spectrum was used to confirm the temperature (Teff= 11,750±750K) and to obtain a surface gravity of log g = 1.5±0.5. υ Sgr is ~ 99.6% helium, 0.016% H with CNO abundances indicative of advanced evolution and high main sequence mass. From profile fitting of the UV resonance lines of C, N and Si the mass-loss rate from υ Sgr is at least 2.5 x10−1°M☉yr−1. The upper limit to the mass-loss rate is 1.0 x10 −5M☉yr−1 from the lack of observed changes in the orbital parameters. The mass of the primary component and the low likely mass-loss rate indicate that the primary component will not be able to shed enough material before core collapse, an event that will be classed as a type Ib supernova. This is the first solid evidence that hydrogen-deficient binaries are progenitors of these objects although other candidates are not ruled out. The other known hydrogen-deficient binaries (KS Per, LSS 1922 and LSS 4300) have had their temperatures (12,500±500K, 12,000±500K, 12,000±1,000K) and interstellar extinctions (0.55± 0.05, 0.80±0.05, 0.90±0.10) re-determined from a flux distribution analysis. Mass-loss rates from 6 O stars, 3 Extreme Helium stars and 2 sdO stars have also been determined. The O and EHe results broadly agree with the previous determinations. Results for the 2 sdO stars, BD H-37° 1977 and BD +37 ° 442, are presented from profile fitting for the first time and indicate a mass-loss rate slightly higher than for the EHe stars.

W Ursae Majoris-type (W UMa-type) variable stars are contact eclipsing binary stars whose evolution is unknown. Modelling to determine the physical parameters of as many W UMa-type variable stars as possible might provide some insight as to how these contact binaries form and evolve. The All Sky Automated Survey (ASAS) has discovered over ve thousand of these systems. Using data from the ASAS and from the Wide Angle Search for Planets (SuperWASP) project, models of selected ASAS contact binaries are being created to determine their physical parameters. Some W UMa-type variable stars are known to undergo changes in orbital period. For selected ASAS contact binaries, a period analysis has been performed using SuperWASP data to determine if the systems are undergoing changes in orbital period. Results of the modelling and period analyses of selected systems are presented. / Thesis (M. Sc. (Astronomy))