There are three principal aims of this work; firstly to derive the analytical expressions for the potential energy and the mutual gravitational attraction between two homogeneous or non-homogeneous oblate spheroids with coplanar equatorial planes; secondly, to construct and study the equations of motion of dynamical systems consisting of particles and rigid homogeneous spheroidal bodies whose equatorial planes are coplanar; thirdly, to investigate by numerical integration and compare the evolution of dynamical models of interacting galaxies. Two different types of dynamical models of galaxies were used in this work:(a) galaxies consisting of gravitating particles, (b) galaxies comprising of gravitationally interacting particles and heavy central rigid homogeneous oblate spheroids. Chapter (2) and appendices (4), (5), (6) and (7) are an account of the method used to derive the expressions for the potential energy and the mutual gravitational attraction between two rigid bodies bounded by spheroidal surfaces with coplanar equatorial planes, when the densities of the bodj.es are either constant or inversely proportional to the square of the radial distance from the centres of the bodies. These expressions were at first obtained in the form of non-elementary integrals over the complete elliptic integrals of the first and second kind, a result due to the fact that the common volume between two ellipsoids cannot be expressed in finite terms. The evaluation of these integrals was achieved with the aid of MacLaurin' s theorem by collapsing one of the spheroids to its confocal disc; their final form is that of rapidly convergent series in terms of the parameters which determine the shape and orientation of the spheroids. In the course of obtaining the expressions mentioned above we derived some other useful formulae, for example, the formulae giving the gravitational attraction between two homoeoids and the potential and force law of a non-homogeneous oblate spheroid. Having found the expressions for the gravitational potential and attraction between two spheroids we proceeded by constructing and solving the equations of motion of dynamical systems consisting of either particles or particles and rigid homogeneous oblate spheroids with coplanar equatorial planes [chapters (1) and (3), appendices (2) and (3)]. The solutions of the equations of motion - being non-algebraic - were obtained in the form of power series. In particular, for the first type of dynamical systems (particles only) they were found in the form of three different types of series. The first type is based on the development and implementation of generalized f and g series for the N-body problem, the second type is based on recurrent formulae used for the evaluation of the terms of the series and the last type of series is a power series in terms of ln ɼijτ/ɼij and polynomial of ɼijτ/ɼij. All the series mentioned above lend themselves easily, to numerical calculations since their convergence, which was analytically proved, is a rapid one. We concluded the present work by numerically integrating the equations of motion of dynamical models of pairs of interacting galaxies. The galaxies were of the types (a) and (b) mentioned previously. The numerical integration was performed with variable time steps in order to reduce computing time. A general method was developed for the precise evaluation of the length of the time step determined by the desired integration accuracy. The calculations were carried out to an extremely high degree of accuracy. The most significant of the results of the numerical experiments on the evolution of dynamical models of interacting galaxies were:(i) the development of long-lived spiral structure when galaxies of type (b) were lased even for intrinsic velocities and impact parameters so high that galaxies of type (a) were unable to produce such structure,(ii) the roughly periodic appearance and disappearance of the spiral structure,(iii) the fact that in the early stages of their evolution the dynamical models take up rather long-lived triaxial ellipsoidal shapes.

Photometric and spectroscopic observations have been made of northern hemisphere early type stars at intermediate galactic latitudes. Stellar distances, the corresponding distances from the galactic plane and the interstellar reddening along the lines of sight have been derived. The available published data was used to support the observational results. The HI spiral features seem to have corresponding optical counterparts, and the agreement between the two patterns is remarkably good. The neutral hydrogen kinematic distances depart from the stellar distances. This can be explained in terms of the density wave theory, with a small modification which may be the result of a non-zero distance from the galactic plane. The Local Arm extends to about 500pc above the galactic plane and the Perseus Arm to 1 kpc. Thus it seems that the interpretation of intermediate latitude high and intermediate velocity features, as vertical extensions to the spiral arms in the galactic plane, may be correct. Stellar and interstellar calcium radial velocities suggest that these intermediate latitude spiral features adhere closely to differential galactic rotation, and that the small departures from this motion exhibit a significant correlation with the predictions of the density wave theory. Published proper motions are used together with the stellar radial velocities to derive the components of the stellar space motions with respect to their local standards of rest. In cases where the component normal to the galactic plane was significantly different from zero, the dynamical lifetime was calculated on the assumption that the star was formed in the galactic plane. These were found to be compatible with the evolutionary lifetimes for only half of the stars considered, suggesting that about 50% of intermediate latitude OB stars were formed in or near the galactic plane and subsequently ejected from it. The remainder seem to have been formed at considerable distances from the galactic plane, and a scheme for explaining this is proposed. This scheme also explains the apparent asymmetry between the northern and southern galactic hemispheres. A few interesting high velocity stars and OB star associations are also considered.

Although relative ground based stellar photometry has been an established investigative technique for many years, there have been very few programmes which have provided absolute stellar fluxes and indeed where such results have been published, they have been derived mainly from spectro-photometric data for a few bright stars. Such measurements are essential for the confirmation of model atmosphere calculations and for those models relating to early type stars, it is essential to extend such observations well into what is known as the vacuum ultraviolet region, i.e. below 3000A. The measurements are technically very difficult because of the need to use balloon or rocket platforms and when this work was started in 1962, only a very few observations had been conducted by the Naval Research Laboratory in Washington using very simple photometers with no absolute calibration. Under the auspices of a Senior Research Fellowship (the first in Scotland), held at the Royal Observatory, Edinburgh, the author proposed to the newly formed European Space Research Organisation, a number of stellar investigations aimed at obtaining absolute stellar fluxes in the region 1200Å - 2800Å. This thesis gives an account of almost a decade spent in developing the techniques of rocket astronomy and absolute calibration in the vacuum ultraviolet. Since no other European groups were engaged in similar studies, it was necessary for the author to essentially begin at the very beginning and a substantial period was spent in designing and testing optical systems which would withstand a typical Skylark Rocket launch. Systems of this type had never been flown before and many hours of vibration testing were necessary to ensure a satisfactory optical and mechanical configuration. The choice of a suitable ultraviolet detector was not easy and a substantial part of the early laboratory research was aimed at evaluating commercially available detectors and in the end an entirely new range of photo-multipliers was developed as a co-operative venture between the author and E.M.I. Hayes, Middlesex, resulting in a commercially saleable product. Wavelength isolation techniques were developed and the use of reflective mirror surfaces was successfully pioneered. A complete range of rocket-borne electronic systems was developed including solid state electrometers and high voltage power supplies. The techniques for encapsulating photomultipliers to withstand the rocket environment and the mounting of large optical mirrors were successfully developed and over fifty telescopes constructed and launched. The problems of calibrating on an absolute basis these rocket borne telescopes of large aperture were investigated and a network of traceable sub-standards was developed which ensured comparison with other (American) data. Highly stable microwave sources were developed and detectors calibrated at several national laboratories. These techniques were eventually used in the calibration of the T.D.I. S2/68 satellite experiment. The problem of integration of the payloads at centres throughout Europe was successfully overcome and the development of range facilities undertaken. Seven fully instrumented Skylarks were proposed and launched with a total of twenty photometers out of fifty-five photometers actually observing the Sky. The remainder having failed to produce any data due to rocket failure. During the period of the investigation, i.e. (1962-1970) the author obtained the first absolute stellar fluxes above the Earth's atmosphere and the total observations obtained equalled that obtained by all the other U.S. Groups including the satellite results of A. Smith. The results were compared with current model atmosphere calculations and showed that if blanketed models were used, the results would be to within ±0.25 magnitude in the region 1400Å-2800Å. The results also showed that it was possible to establish an absolute calibration network which was capable of not only permitting inter-comparison between the author's photometers, but also with other rocket groups, a situation that had hitherto been impossible. These results were the only stellar data to be obtained by any Group within the ESRO rocket programme. No other European results were obtained during that period.

Thesis (Ph.D.) - University of Maryland. / "Dissertation directed by Professor Doug Currie, Department of Physics." Includes bibliographical references (p. 260-269).

Located at 2 pc, the L7.5+ T0.5 dwarfs system WISE J104915.57-531906.1 (Luhman 16 AB) is the third closest system known to Earth, making it a key benchmark for detailed investigation of brown dwarf atmospheric properties, thermal evolution, multiplicity, and planet-hosting frequency. In the first study of this series - based on a multicycle Hubble Space Telescope (HST) program - we provide an overview of the project and present improved estimates of positions, proper motions, annual parallax, mass ratio, and the current best assessment of the orbital parameters of the A-B pair. Our HST observations encompass the apparent periastron of the binary at 220.5 +/- 0.2 mas at epoch 2016.402. Although our data seem to be inconsistent with recent ground-based astrometric measurements, we also exclude the presence of third bodies down to Neptune masses and periods longer than a year.

We have followed up the three Y0 dwarfs WISEPA J041022.71+150248.5, WISEPA J173835.53+273258.9 and WISEPC J205628.90+145953.3 using the United Kingdom Infrared Telescope Wide Field Camera. We find parallaxes that are more consistent and accurate than previously published values. We estimate absolute magnitudes in photometric passbands from Y to W3 and find them to be consistent between the three Y0 dwarfs indicating that the inherent cosmic absolute magnitude spread of these objects is small. We examine the Mauna Kea Observatory system J magnitudes over the 4 yr time line and find small but significant monotonic variations. Finally, we estimate physical parameters from a comparison of spectra and parallax to equilibrium and non-equilibrium models finding values consistent with solar metallicity, an effective temperature of 450-475 K and log g of 4.0-4.5.

We present Astrometry.net, a system for automatically recognizing and astrometrically calibrating astronomical images, using the information in the image pixels alone. The system is based on the geometric hashing approach in computer vision: We use the geometric relationships between low-level features (stars and galaxies), which are relatively indistinctive, to create geometric features that are distinctive enough that we can recognize images that cover less than one-millionth of the area of the sky. The geometric features are used to generate rapidly hypotheses about the location---the pointing, scale, and rotation---of an image on the sky. Each hypothesis is then evaluated in a Bayesian decision theory framework in order to ensure that most correct hypotheses are accepted while false hypotheses are almost never accepted. The feature-matching process is accelerated by using a new fast and space-efficient kd-tree implementation. The Astrometry.net system is available via a web interface, and the software is released under an open-source license. It is being used by hundreds of individual astronomers and several large-scale projects, so we have at least partially achieved our goal of helping ``to organize, annotate and make searchable all the world's astronomical information.''

We present Astrometry.net, a system for automatically recognizing and astrometrically calibrating astronomical images, using the information in the image pixels alone. The system is based on the geometric hashing approach in computer vision: We use the geometric relationships between low-level features (stars and galaxies), which are relatively indistinctive, to create geometric features that are distinctive enough that we can recognize images that cover less than one-millionth of the area of the sky. The geometric features are used to generate rapidly hypotheses about the location---the pointing, scale, and rotation---of an image on the sky. Each hypothesis is then evaluated in a Bayesian decision theory framework in order to ensure that most correct hypotheses are accepted while false hypotheses are almost never accepted. The feature-matching process is accelerated by using a new fast and space-efficient kd-tree implementation. The Astrometry.net system is available via a web interface, and the software is released under an open-source license. It is being used by hundreds of individual astronomers and several large-scale projects, so we have at least partially achieved our goal of helping ``to organize, annotate and make searchable all the world's astronomical information.''

Thesis (M.Sc)--University of Western Sydney, Nepean, 1995. / Includes bibliography.

Thesis (Ph.D.) - Universidad de Valencia, 1999. / Introductory pages in Spanish. Thesis is in English. Includes subject index, pages 177 - 178.