Rapid progress in multi-wavelength observations of Seyfert Galaxies in recent years is providing evidence that X-ray emission in these objects may be produced by magnetic flares occurring above a cold accretion disk. Here we attempt to develop a physically consistent model of accretion disks producing radiation via magnetic flares as well as the optically thick intrinsic disk emission, and apply this model to observations of Active Galactic Nuclei (AGN) and Galactic Black Hole Candidates (GBHCs). The following issues are considered: (1) the pressure equilibrium in the flare region, (2) the reflection and reprocessing of the X-radiation from flares in the underlying disk, (3) the spectra of GBHCs in the context of the model, (4) and the generation of the flares by the disk--the energy budget of the corona. Our results show that: (1) The temperature of the disk atmosphere near active magnetic flares in AGN is in the range 1 - 3 x 10⁵ Kelvin, and that the material is relatively non-ionized. This temperature is in a good agreement with the observed rollover energy in the Big Blue Bump (BBB) of Seyfert 1 Galaxies. We thus suggest that the BBB is simply the X-rays from magnetic flares reprocessed into the X-ray skin of the accretion disk. (2) We suggest an explanation for the recently discovered X-ray Baldwin effect and the controversy over the existence of BBBs in quasars more luminous than typical Seyferts. (3) Due to an ionization instability and much higher X-ray incident flux, we found that the X-ray skin in GBHCs is nearly completely ionized. Using an approximate model to describe this effect, we calculated the reflected/reprocessed spectrum and the resulting corona spectrum simultaneously. We found that the spectrum of GBHCs in their hard state may be explained with this model, with basically the same parameters for magnetic flares as in the AGN case. (4) The magnetic energy transport is shown to be large enough to account for the observed amount of X-rays from Seyferts and GBHCs. We predict that X-ray spectra are hard for accretion rates below the gas-to-radiation transition, and that they are softer above this transition. (5) We collected our results into a diagram that shows how the observational appearance of accreting black holes changes with the accretion rate and the mass of the hole, and compared it with observations of AGN and GBHCs. Our conclusion is that the agreement between theory and observations is very encouraging and we suggest that the physics of magnetic flares is the physics that should be added to the standard accretion disk theory in order to produce a more realistic description of accretion flows with large angular momentum.

The main goal of this thesis is to study the properties of isolated early-type galaxies with the hope of learning about their formation and evolution. With this goal in mind, B and I optical, and Ks near infrared images of 4 different samples of early-type galaxies in contrasting galactic density environments have been secured with the Steward Observatory 90 inch and 61 inch telescopes. The 4 early-type galaxy samples consist of: a sample extracted from the Catalog of Isolated Galaxies of Karachentseva, a sample of isolated galaxies previously studied by Fasano and Bonoli, a sample of galaxies from the Hickson Compact Groups Catalog, and a sample of galaxies with detected ISM's. This data set is used to examine whether differences in the galactic environment are related to differences in key properties of early-type galaxies. Multi-color surface photometry analysis is performed on the 4 samples, and the results are used in several contexts. For most of the galaxies in the Karachentseva sample surface photometry is reported for the first time. Likewise, Ks data for most of the objects in this thesis have never been reported. The light profile of the galaxies are fitted with Sersic profile functions. In agreement with other investigations, it is found that the Sersic parameter, n is primarily dependent on the galaxy size, and does not seem to be strongly dependent on properties such as environment or ISM content. The (B - I) color index, ellipticity, position angle, and third and fourth-order Fourier coefficients are derived from the surface photometry. It is confirmed that the third-order coefficients signal the presence of dust, and that the coefficient of the cos(4θ) gives structural information of the galaxies. Furthermore, the subtraction of model ellipticals has revealed peculiarities in the morphology, such as disks, spiral arms, dust lanes, multiple nuclei, etc. The largest and most relevant sample in this investigation consists of 39 galaxies, and it contains ∼25% of the galaxies classified as ellipticals in the Karachentseva catalog. Only approximately one half of the galaxies classified as ellipticals in that catalog appear to be correctly classified, a result which may imply a reduction of the percentage of ellipticals in the Karachentseva catalog to ∼6% of the total population of Isolated Galaxies. A significant number of merger candidates has also been found among the isolated galaxies. It is argued that the fraction of merger candidates to isolated ellipticals can be used to constrain models for the evolution of compact groups into isolated galaxies. The results of CO(1-0) millimetric wavelength observations taken at the NRAO 12 M telescope, as well as submillimeter continuum emission from dust at the SMT are also presented.

This document describes the Imager for Mars Pathfinder (IMP) calibration targets and outlines a procedure for their use in first-order spectrophotometric image calibration. The Mars Pathfinder mission and landing site are discussed, as are previous observations of Mars. Bidirectional reflectance theory relevant to target design and usage as well as planetary surface measurement will be developed in the context of spectrophotometric image calibration. The design, fabrication, and characterization of the calibration targets is discussed, including an inversion for model parameters using two independent data sets. A procedure detailing first-order spectrophotometric calibration of IMP images is introduced, suitable for rapid scientific analysis necessary during the early landed phase of the mission. The procedure is applied to an image dataset to demonstrate its effectiveness, and possible uses of this procedure on Mars are described. Finally, improvements to the theory, target characterization, and calibration procedure, are discussed in the context of long-term scientific study and the minimization of errors.

The Magellan radar imager detected approximately 60 dark (i.e. low backscatter cross section) parabola-shaped features on the surface of Venus; each parabola is oriented with the open end toward the west and envelopes an impact crater near its "focus." In this thesis, I use a model of parabola formation to fit the 58 Venusian parabolas observed to date, as well as 9 circular features that are similar to the parabolas. I achieve good results for ∼65% of the 41 parabolas that meet the conditions for the model to apply. As a result of modeling the parabolas, I derive a quantitative description of the distribution of small (∼1 cm to ∼1 μm in diameter) impact ejecta over a planetary surface. My results agree well with the distribution of fine impact ejecta derived for the Terrestrial impact crater Chicxulub. In addition, these results lead to a method for estimating the quantity of fine-grained material available on Venus for surface transport processes such as saltation.

This thesis presents an exploration of various aspects relating to the formation and evolution of structure in the Universe. It focuses on two main observables which provide information on two distinct epochs of the Universe: Part I analyses the Cosmic Microwave Background (CMB) which is used to test early Universe theories and validate current methods for cosmological parameters estimation; Part II analyses the distribution, history and content of local galaxies with a view to learn about type Ia supernovae progenitors, assembly of stellar mass in galaxies and galaxy evolution. In Part I, a search for signs of non-Gaussianity in theWilkinson Microwave Anisotropy Probe is conducted, using the two-point correlation function of peaks (hot and cold spots) in the temperature field. A clear deviation from Gaussianity is found in both data releases, which is associated with cold spots, the southern hemisphere, large-scales and the galactic plane. The results indicate that the presence of un-subtracted foregrounds in the data are a more likely explanation for this signal than a cosmological origin, but the latter cannot be excluded. Part I further explores the two-point correlation function of temperature peaks as an estimator to constrain fNL, a specific type of non-Gaussianity. Using sets of non-Gaussian simulated maps with the correct cosmology and resolution, this thesis explores how accurately one can hope to constrain fNL when data from the upcoming CMB experiment Planck is available. Part II presents a novel method developed to extract the star formation history of a galaxy from its spectrum: VErsatile SPectral Analysis (VESPA). VESPA dynamically adapts the number of parameters it recovers from each spectrum to each galaxy, only recovering as much information as the data warrant. This insures the recovered solutions are dominated by the signal, not the noise, and allows robust recovery of star formation and metallicity histories and up to two dust extinction values per galaxy. VESPA was applied to the fifth data release of the Sloan Digital Sky Survey (SDSS) to construct a catalogue of histories for nearly half a million galaxies. Part II also explores how this catalogue can provide important information about the formation of structure in the local Universe. Specifically, this thesis: shows evidence for the presence of a short-lived progenitor to SNIa and explores VESPA’s potential role in future Dark Energy SNIa experiments; explores how changes in the Initial Mass Function affect stellar mass estimates and its consequences; and by using estimates of the galaxy mass function as a function of redshift (calculated using both the spectral fossil record and instantaneous star formation rate methods) explores the possibility of putting constraints on the merger history of present-day galaxies.

<p> The observation of gravitational waves from compact stars (neutron and quark stars) is a promising method of determining their internal composition. This research presents the details and results for calculations of some of the principal modes of compact star oscillations, by which they radiate gravitational waves. These are: the <i>f</i>-modes, <i>p</i>-modes, and <i>g</i>-modes. We find that for the same stellar mass, the <i> f</i>-modes for quark stars are higher in frequency than for neutron stars. The <i>p</i>-mode frequency of quark stars decrease with stellar mass, displaying an opposite trend to that of neutron stars. Two-component models were also considered. A core-ocean model was examined for a neutron star, using a polytropic equation of state (EOS), and a core-crust model for a quark star, using a bag model EOS. We find that <i>g</i>-mode oscillations in neutron star oceans depend on the dominant chemical species of the ocean as well as the mass of the underlying core. The addition of a solid crust onto a quark star increases the frequencies, attributable to shear stresses between the core and crust. These results pave the way to model and contrast the gravitational wave signals emitted by oscillating compact stars.</p>

<p> The Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H &amp; K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H &amp; K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H &amp; K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar <i>S</i>-index to be 5&ndash;9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude ~12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun&rsquo;s are rare in stars of approximately the solar mass, and that the proper conditions may be restricted to a relatively narrow range of rotation rates.</p>

Two problems of galactic dynamics are studied. The first is the self-consistent problem of building equilibrium models for galaxies with an axis of symmetry. We consider models in which the distribution function f of stars in phase space depends on the two classical integrals, the total energy E, and the angular momentum about the symmetry axis J in axisymmetric systems or the magnitude of the angular momentum vector L in spherical systems. We have found a new analytic method which can be used to solve these equations generally. It gives f as a complex contour integral, which is an analogue of Eddington's (1916) solution for isotropic spherical galaxies, and is directly derived from the density. We have shown rigorously that our solution satisfies the integral solution, and have used it to obtain new distribution functions of three different systems. Among the axisymmetric systems that we have considered are the "flattened" isochrone (Evans et al 1990), Satoh's $n=\infty$ model (1980), generalized Hernquist models, and a family of models for which the density as a function of the potential and axial radial distance is only known implicitly. For spherical systems we have devised a method of constructing models with prescribed anisotropy parameter defined by Binney (1980). The distribution functions of these models can be found by the contour integral method which also provides some new simplified solutions. / The second part of the dissertation concerns the potential-density relation on a flat disk. We have greatly simplified Lynden-Bell's results (1989) and found some large families of potential-density pairs using our simplification. In particular, we have found a complete set for the whole family of Kalnajs-Mestel disks (Evans & de Zeeuw 1992), of which the isochrone disk is a special case. We have also adapted our simplified method to find two new biorthogonal potential-density sets. One is related to Gaussian disks (Toomre 1963) and the other to general Toomre (1963) disk models, and both should be useful for the analyses of these disks. The latter includes Clutton-Brock's (1972) set as a special case. (Abstract shortened by UMI.) / Source: Dissertation Abstracts International, Volume: 54-09, Section: B, page: 4714. / Major Professor: Christopher Hunter. / Thesis (Ph.D.)--The Florida State University, 1993.

Source: Dissertation Abstracts International, Volume: 40-09, Section: B, page: 4340. / Thesis (Ph.D.)--The Florida State University, 1979.

Source: Dissertation Abstracts International, Volume: 35-12, Section: B, page: 5746. / Thesis (Ph.D.)--The Florida State University, 1974.