Thesis (Ph.D.) - University of St Andrews, January 2009.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1956. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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.

Faint blue stars situated out of the galactic plane have been studied using a variety of techniques. Stromgren photometry has been obtained for a number of these stars and classifications derived from the photometry. An interference filter centred at 3775 A near the Balmer discontinuity has been used in conjunction with the Stromgren filters. Observation of Stromgren standard stars, bright B stars and faint blue stars have been used to study the behaviour of the colours (u-38) and (38-b). Reddening-free parameters [u-38] and [38-b] have been evaluated and [38-b] is found to be linearly related to the Crawford Hβ index for B-type dwarfs, giants and supergiants. This relationship has been used to derive absolute magnitudes and distances for faint apparently normal B stars. [38-b] allows this work to be done at fainter magnitudes than possible with Hβ photometry. A filter pair centred on the HeII λ4686 line has been used to study 0-type stars including 0 subdwarfs. The resulting index is strongly correlated with the equivalent width of the Hell line and has a range of 0ᵐ.13. It is possible to separate sd0, 0 and 0f stars using this index. Although the index is correlated with absolute magnitude for 0 and 0f stars, the detailed behaviour precludes the accurate determination of absolute magnitude for dwarfs and giants. Theoretical indices have been computed from the models of Kudritzki and agree well with the results for stars with high helium abundance. These computations suggest that it is possible to separate sdO and DO stars with this system. The results have also been compared with the work of Auer and Mihalas. 30 A/mm image tube spectra have been used for Ealmer line width measurement and radial velocity determination. The line widths were used to estimate surface gravities for faint blue stars in conjunction with temperatures determined from the Stromgren [u-b] index. The results indicate that 30 A/mm image tube spectra can be used successfully for surface gravity determination. 75 A/mm image tube spectra have been used for spectral classification as a check on the classification provided by Stromgren photometry. The kinematics of certain subdwarfs and main sequence stars at high galactic latitude have been considered. Proper motions have been employed as a check for subluminosity using appropriate absolute magnitudes. Galactic orbits have been computed using the Schmidt model of the galactic force field. Several B-type dwarfs and subdwarfs were found to have been ejected from the galactic plane at high velocity. Thirty percent of the stars previously classified as normal dwarfs were found to be subluminous. The evolutionary implications of these results are discussed.

Thesis (Ph.D.) - University of St Andrews, May 2008.

No description available.

Thesis (Ph.D.)--Texas Christian University, 2008. / Title from dissertation title page (viewed Mar. 23, 2009). Includes abstract. Includes bibliographical references.

No description available.

In the last few decades, the emergence of large-scale infrared surveys has led to a revolution in the study of star formation. In particular, NASA’s Spitzer Space Telescope has recently carried out mid- and far-infrared observations of numerous star formation regions with unprecedented resolution and sensitivity, and has uncovered thousands of forming stars. In combination with present and future large-scale near-infrared and sub-mm surveys, spectral energy distributions from near-infrared to mm wavelengths will be available for these thousands of young stars. Never before has there been such a wealth of multi-wavelength data for so many young stars. Traditional techniques for studying the physical properties of young stars through their spectral energy distributions have usually focused either on the analysis of many sources using simple observational diagnostics such as colours or spectral indices, or on the analysis of a few sources through the detailed modelling of their full spectral energy distributions. The work presented in the first part of this thesis aims to bridge these two techniques through the efficient modelling of the spectral energy distributions of many young stars. In particular, the technique developed for this work makes it straightforward to find out how well different physical parameters are constrained, whether any parameters are degenerate, and whether additional data would resolve the degeneracies. In the second part of this thesis, a census of intrinsically red sources observed by Spitzer in the Galactic plane is presented, including a catalogue of over 11,000 likely young stellar objects. This sample of sources is the largest uniformly selected sample of young stars to date, and effectively provides a map of the sites of star formation in the mid-plane of the Milky-Way. In parallel, this census has uncovered over 7,000 candidate asymptotic giant branch stars, of which over 1,000 are variable at 4.5 or 8.0 microns.

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