No description available.

Using a state of the art galaxy formation software package, GCD+, we model the formation and evolution of galaxies which resemble our own Galaxy, the Milky Way. The simulations include gravity, gas dynamics, radiative gas cooling, star formation and stellar evolution, tracing the production of several elements and the subsequent pollution of the interstellar medium. The simulations are compared with observations in order to unravel the details of the Milky Way's formation. Several unresolved issues regarding the Galaxy's evolution are specifically addressed. In our first study, limits are placed on the mass contribution of white dwarfs to the dark matter halo which envelopes the Milky Way. We obtain this result by comparing the abundances of carbon and nitrogen produced by a white dwarf-progenitor-dominated halo with the abundances observed in the present day halo. Our results are inconsistent with a white dwarf component in the halo 5% (by mass), however mass fractions of ~1-2% cannot be ruled out. In combination with other studies, this result suggests that the dark matter in the Milky Way is probably non-baryonic. The second component of this thesis probes the dynamical signatures of the formation of the stellar halo. By tracing the halo stars in our simulation, we identify a group of high-eccentricity stars that can be traced to now-disrupted satellites that were accreted by the host galaxy. By comparing the phase space distribution of these stars in our simulations to observed high-eccentricity stars in the solar neighbourhood, we find devidence that such a group of stars - a 'stellar stream' - exists locally in our own Galaxy. Our next set of simulations demonstrate the importance of strong energy feedback from supernova explosions to the regulation of star formation. Strong feedback ensures that the building blocks of galaxy formation remain gas-rich at early epochs. We demonstrate that this process is necessary to reproduce the observed low mass and low metallicity of the stellar halo of the Milky Way. Our simulated galaxy is shown to have a thick disk component similar to that observed in the Milky Way through an abrupt discontinuity in the velocity dispersion-versus-age relation for solar neighbourhood stars. This final study suggests that the thick disk forms in a chaotic merging period during the Galaxy's formation. Our thick disk formation scenario is shown to be consistent with observed properties of the thick disk of the Milky Way.

No description available.

Thesis (Ph.D.) - Swinburne University of Technology, 2004. / A dissertation presented in fulfillment of the requirements for the degree of Doctor of Philosophy, Swinburne University of Technology - 2004. Typescript. Includes bibliographical references (p. 111-122).

Thesis--Northwestern University, 1968.

Thesis (Ph. D.)--Rhodes University, 1998. / Includes bibliographical references (p. 183-197).

Academical dissertation, Lund. / Issued also without series note. "List of errata": 3d prelim. leaf. Bibliography: p. [B47]-B61.

Rede--Groningen (Aanvaarding van het ambt van hoogleraar) 1958.

Thesis--Groningen. / Without thesis statement.

Photoelectric scanner observations are combined with infrared photometry in the JHKL bands to give interstellar extinction curves by the colour difference method for 25 reddened stars in the Southern Milky Way. The observed stars are distributed from galactic longitude ℓ^II = 260°; through the Galactic Centre to ℓ^II = 30°. The scanner data ranges in wavelength from 3A80 to 5240 A with a resolution of 40 A in the second order of diffraction, and from 5080 to 8040 A with a resolution of 80 A in the first order. The infrared photometry extends the wavelength coverage to 3.5 µ. The normalized extinction curves show appreciable variations from star to star which are not apparently related to galactic structure. In several cases stars quite close together in the sky show appreciably different curves, suggesting that fluctuations in the grain size distribution may be occurring on a fairly localized scale. Using a graphite-iron-silicate grain model, extinction curves computed from the Mie theory are fitted to the observational data. This provides a theoretical basis for extrapolation of the curves to λ ⁻¹=0, allowing the ratio of total to selective extinction, R, to be deduced. R varies between 2.6 and 3.5 for 22 stars lying within 10° of the galactic plane, and between 3.8 and 4.3 for 3 stars in Upper Scorpius. One of the Upper Scorpius stars studied, HD 147889, lies in an HII region near the centre of the p Oph complex of dust and nebulosity, A variable extinction analysis applied to members of the Sco OB-2 association indicates an increase in the value of R for stars lying towards nebulosity in the complex; for these stars alone a result of R = 4.2 ± 0.5 is derived, whilst for the remainder, R = 3.3 ± 0.3. The distance modulus of the association is deduced to be 6.1 ± 0.1, which is in good agreement with the kinematical value. The scanner extinction curves contain considerable broadband structure. In particular, a depressed region between wavenumbers 1.6 and 1.97 µ⁻¹ is a common feature of the curves. A similar depression was noted by Whiteoak in the extinction curves of Northern Milky Way stars. Its depth correlates well with reddening, suggesting that the feature originates in the grains. The extinction curve of HD 147889 shows a -1 cusp-like depression at 1.97 µ⁻¹ which divides the curve into two distinct sections. The ratio of the 4430 A diffuse interstellar band height to colour excess shows signs of systematic variation with longitude for stars whose reddening occurs mainly in the local spiral arm.