We present a data base of U,V photometric and structural properties for 642 spectroscopically confirmed members, V-band selected to Mᵥ = -18 mag, from three local Abell clusters: A85 (z = 0.055), A496 (z = 0.033) and A754 (z = 0.055). From our (U - V) half-light aperture colors and total model V-band magnitudes we construct precise color-magnitude diagrams for member galaxies out to ≳1 h⁻¹ Mpc. We measure well-defined color-magnitude relations (CMR) with low intrinsic scatter (σCMR ∼ 0.06-0.09 mag) in the cluster cores ( < 0.5h⁻¹ Mpc). We define three galaxy populations based on the relative color difference Δ(U - V) between the galaxies color and the best-fit CMR: (1) red sequence galaxies with Δ( U - V) ≥ -2σ(CMR); (2) intermediately blue (≡ bS0) galaxies with -2σ(CMR) > Δ(U - V) > -0.425 mag; and (3) blue (Butcher-Oemler ≡ B-O) galaxies with Δ( U - V) ≤ -0.425 mag. These color-magnitude cuts provide a rough galaxy age segregation assuming blueward deviations from the CMR represent mean stellar age differences. Red sequence members are the traditional cluster old, early-types (E/S0) and B-O galaxies have spiral-like colors; therefore, the bS0 population are assumed to be intermediate in age. We find a significant (∼10% in numbers) population of bS0 members in two local clusters (A85 and A754) . This is the first evidence for a quantitatively classified population of bS0 galaxies in clusters at < 1 Gyr look-back time. The bS0 populations exhibit the following characteristics: (1) Bulge-to-total morphologies intermediate between red sequence and B-O members. (2) Less morphological structure associated with star formation compared to normal, field spirals. (3) bS0 members are not found near the cluster cores which suggests more recent infall. (4) Lack of a significant color gradient which is different from both the cluster red sequence and field spirals. The observed bS0 properties are consistent with these galaxies being present-day examples midway through the predicted evolution of infalling, field spiral to red, cluster S0 via galaxy harassment and/or ram-pressure stripping. Therefore, the existence of these galaxies provides clear observational evidence for the present-day whereabouts of the blue galaxies once prevalent in rich clusters (the B-O effect) and for environmental based evolution of the cluster galaxy membership.

The possibility that some portion of the infrared (IR) radiation emanating from Active Galactic Nuclei (AGN's) may arise from disklike structures of ionized plasma accreting onto massive or supermassive black holes motivates the investigation of the effects on the observed radiation of the strong gravitational fields in the vicinity of the emitting particles. Numerous previous studies have been incomplete in several respects: (a) they have neglected to take into account the contribution to the observed specific power flux of radiation emitted from the underside of the disk and gravitationally lensed into the upper half-hemisphere; (b) they have considered only a limited range of observing positions and hole spins; (c) many have been restricted to examination of the steady state flux arising from homogeneous disks; (d) they have employed a methodology not readily extendible to the analysis of gravitational effects on radiation arising from more complicated physical systems (e.g., nonplanar ensembles of gaseous clouds). The present study develops, within the context of the optically thick, geometrically thin accretion disk model, a new method of complementary images. Fully taking into account the so-called first-orbit disk images, including the effects of disk self-occlusion, for the entire range of observing positions and hole spins, and for both homogeneous and thermally inhomogeneous disks, it applies this method to both steady state and time-dependent analyses in the paradigm case of the Galactic Center black hole candidate Sagittarius A*. Completely general results applicable to any similar black hole-accretion disk system are presented. An illustration is given of how the basic method, along with ancillary analytical devices such as that of extended images and computationally efficient techniques based on their properties, may be extended to the analysis of considerably more complicated physical systems, and tentative results for the case of the Broad Line Region (BLR) of quasar spectra are presented.

The hard X-ray spectrum from black hole candidates, such as 1E1740.7-2942 and Cygnus X-1, has been attributed to an inner hot (Tₑ ≈ 10⁹ K) two-temperature disk which Comptonizes externally produced soft photons from the outer disk. We developed a natural extension of this model, wherein the innermost region of the two-temperature disk, is much hotter (Tₑ ≈ 5 x 10⁹ K) since it is shielded from the external photons and is forced to cool via bremsstrahlung self-comptonization. The emission from this region can account for the long term γ-ray variability in Cygnus X-1. The e⁺e⁻ pairs produced above the hot plasma give rise to the annihilation line observed in 1E1740.7-2942 and the residual pairs form the extended radio jets observed in this source. These early successes called for more detailed modeling of the hot disk. The effects of e⁺e⁻ pairs produced inside the disk were investigated using a better technique for the Comptonization process than what had been reported previously in the literature. This has important quantitative (but no qualitative implications) on the model. Another crucial effect is that of the proton thermal energy being advected to smaller radii. This makes the disk sensitive to the outer boundary conditions (i.e the structure of the transition zone between the outer cold disk and the inner hot region). To determine the physics of the transition region we have developed a scheme for the radiative cooling which is valid at all optical depths. The application of this scheme revealed that the transition region is an extended one. The disk has a hot two-temperature configuration even without the assumption that instabilities in the disk drive the cold disk to this stage (which has been doubted in the past). Moreover, the spectrum from the transition zone matches well with the observed X-ray spectrum of Cygnus X-1 and variations in the magnetic field can account for the two X-ray states. We conclude from this new self-consistent model that the soft X-ray photons observed arise from the cold disk, the X-ray continuum is produced in the transition zone, while the γ-rays and associated phenomena (like the e⁺e⁻ line and the radio jets) are due to the inner hot disk.

This thesis is an observational study of the impact of star formation on the interstellar medium. Emission from the ionized component of the interstellar gas is used to measure both the kinematics and the physical properties of the gas in 14 dwarf galaxies. The galaxies examined show emission from ionized gas outside the HII regions. This warm ionized medium has a substantial power requirement and often shows arcs and filaments on scales exceeding 100 pc. To determine the mix of physical processes exciting the gas, I measure optical emission-line ratios averaged over scales of 30-150 parsecs at thousands of locations within the galaxies. I find that, relative to HII regions, the spectrum of the diffuse ionized gas has stronger lines from low-ionization states of oxygen, nitrogen, and sulfur and weaker lines from highly ionized atoms. The HII-DIG spectral transition defines a narrow sequence in diagnostic-line-ratio diagrams which is distinct from the conventional HII-region excitation sequence. Photoionization modeling demonstrates that the HII-DIG sequence is driven primarily by a decrease in the relative density of ionizing photons to atoms--consistent with ionization by distant stellar clusters. The strength of the line emission from ionized He relative to that from ionized hydrogen implies stars of mass greater than 35 M(⊙) contribute to the ionizing continuum. A second excitation process, shocks with speeds from 60-100 km s⁻¹, is shown to contribute up to 50% of the emission from the lowest surface brightness gas. High-resolution, longslit spectra reveal organized gas flows on scales ranging from the resolution limit, about 20-100 km s⁻¹, to galactic-scale dimensions, roughly 1 kpc. Many of the expanding shells detected kinematically are coincident with arcs or filaments in the galaxy images, and the geometry of the larger bubbles is often polar rather than spherical. The simplest dynamical models for their growth imply ages from 1-20 Myr and require energies from 1 to more than 6000 supernovae. The extent, mass, and rotation of the neutral gas are compiled from the literature and used to argue that many of these bubbles breakthrough the HI disk and form galactic winds. A detailed study of I Zw 18 suggests such winds could have a strong influence on the chemical evolution of dwarfs. The total mass of gas escaping the galaxies is, however, not yet well-constrained and may be quite small.

The lines of sight to QSOs are powerful probes of large-scale structure from redshifts corresponding to the most distant QSOs to the local universe. In this thesis, spectroscopy of QSO pairs and groups are used to study superclustering at high redshift and to estimate the tranverse dimensions of the Lyα absorbers. We present high resolution (∼30km s⁻¹) echelle spectra obtained with the CTIO 4-m telescope of the wide QSO pair Tol 1037—2704 (z(em) = 2.193) and Tol 1038—2712 (z(em) = 2.331), as well as two neighboring quasars. The quasars exhibit a large number of apparently correlated C IV absorption systems over a narrow redshift range 1.48 ≤ 2 ≤ 2.15 which is thought to be produced by an intervening supercluster. The velocity correlation function of C IV absorbers distributed among the four lines of sight show significant clustering signal on comoving scales out to ∼30 h⁻¹ Mpc at redshift z ∼ 2 (h ≡ H₀/100 km s⁻¹ Mpc⁻¹; q₀ = 0.5). The spatial correlation function shows a marginally significant peak on scales of < 18h⁻¹ Mpc. The clustering amplitude on these scales is larger than that predicted by current theories of the formation of large scale structure. We present spectroscopy of three close pairs of quasars with angular separations 10" to 2' in order to measure the sizes of the Lyα forest absorbers from scales of a few tens of kpc out to hundreds of kpc. Ground-based estimates of the pair Q1343+2640.A (z(em) = 2.029) and B (z(em) = 2.031) imply a characteristic radius of the Lyα absorbers of ∼100 h⁻¹ kpc at z ≃ 2. Ultraviolet FOS spectra of the pair Q0107—025A (z(em) = 0.956) and B (z(em) = 0.952) in the redshift range 0.5 < 2 < 0.9 show a number of Lyα absorption features common to both spectra as well as several features which are not in common, and imply characteristic radii of 400 h⁻¹ kpc to bigger than 1 h⁻¹ Mpc. Furthermore, the rms velocity difference between the common systems between the two lines of sight is only about 100 km s⁻¹ These measurements lead to a picture of absorbing clouds that are larger in extent than previously thought and surprisingly quiescent. Using a new statistical technique, we tested the relative likelihood of three geometric models, namely, spherical absorbers, with and without a distribution in size, as well as filamentary and disk-like absorbers. Spherical absorbers with uniform radius cannot represent the observations and are ruled out. Randomly-inclined disks and filaments match the data comparably, with disks being slightly favored over filaments. Our results are in remarkable agreement with hydrodynamical simulations in which the Lyα absorption is found to arise in diverse structures with coherence lengths as great as 1 Mpc. Finally, we present FOS observations of a second pair of quasars, LB 9605 (z(em) = 1.834) and LB 9612 (z(em) = 1.898), over the redshift range 1.1 < z < 1.7 from which we placed an 95% confidence upper limit on the radii of the Lyα absorbers of 280 h⁻¹ kpc. The estimates span the redshift range 0.5 < z < 2, corresponding to roughly a third of the age of the universe, and provide tantalizing evidence for evolutionary growth in the size of the Lyα absorbers

The star formation history of galaxies is the primary influence on galaxy evolution, and hence the evolution of almost all the visible matter in the universe. In this dissertation, I present studies of the star formation history of galaxies which have come from two distinct perspectives: the study of galaxies that have unusual star formation histories, and the search within the general galaxy population for galaxies with unusual star formation histories. A spectrophotometric atlas of 40 merging and strongly interacting galaxies is obtained and analyzed in order to examine their stellar populations and star formation histories. Within the sample, the subsample of 10 ultraluminous IRAS systems is compared with the optically selected subsample. The population of objects in the sample with anomalously strong Balmer absorption lines, a spectral signature indicative of post-starburst evolution, is examined and compared with distant "E+A galaxies" which have similar spectrophotometric properties. Spectrophotometry across the entire optical wavelength range is obtained and analyzed for a sample of 8 E+A galaxies, ranging in redshift from 0.09 ≤ z ≤ 0.54. The method of stellar population modeling, widely used with only minor variations in the astronomical community, is examined and its strengths and limitations are discussed.

Many groups are trying to find faint stellar companions using a variety of techniques. The most obvious is to take long exposure pictures. Here adaptive optics (AO) is useful in correcting the blurring effects of the atmosphere. Starlight is concentrated into a tighter peak and less energy is put into the surrounding halo. Another method is to look for periodic decreases in a star's irradiance due to a planet blocking some of the light as it crosses in front of the star or transits. The most productive technique so far has been to look for periodic doppler shifts in the light coming from a candidate star, i.e. radial velocity searches. Several large planets have been found this way. This dissertation explores aspects of these three methods. The ability to detect a companion amid noise depends on the properties of the noise. While theoretical expectations exist for the properties of the halo produced by an AO system, experimental studies are few. The temporal and spatial characteristics of the halo produced by the AO system at the Starfire Optical Range are explored from the viewpoint of searching for faint stellar companions. We set limiting companion magnitudes for stars imaged while searching for brown dwarfs. The primary limitation to ground based transit searches is scintillation, irradiance fluctuations due to atmospheric turbulence. We explore reduction of this noise via differencing signals from binary stars. Theory is extended to include temporal and angular separation effects simultaneously. Evaluation of the derived equations and simulations demonstrate the benefits and limitations. Finally the design of an echelle spectrograph for use on the 6.5 m MMT or the Magellan telescope that is well suited to radial velocity searches for planets is presented. It has throughput between 10% and 18%, resolution of 200,000 per pixel and can sample the entire 0.31 to 1.1 μm range at once. This is accomplished by avoiding metallic reflections whenever possible and by using a mosaic of CCDs fit to the curved focal surface of a Schmidt camera. Efficient simultaneous observation of many spectral lines makes this a powerful instrument for radial velocity companion searches.

Beam profiles from the Infrared Astronomical Satellite (IRAS) at 60 and 100μm and for both hot and cold sources are analyzed using Fourier techniques to check the efficiency of the short wavelength blockage in the 60 and 100μm filters. Comparison of these power spectra with the expected passbands and an estimate of the noise supports the hypothesis that the 100μm filters have a short wavelength leak of 14.3 ± 3.6%, but that there is no detectable leak in the 60μm filters. Following decrement of the 100μm flux by 14.3%, stellar atmosphere models are anchored at 12μm to the IRAS flux measurements for 33 chosen stars and predicted flux measurements at 25, 60 and 100μm are computed. Comparison of these predictions with those measured by IRAS shows that the IRAS measurements are overestimated at 25 and 60μm and underestimated at 100μm with regard to atmospheric models.

Impact crater scaling laws are used to predict the diameter and amount of melt produced in impacts on quartz sand of projectiles with mass from 100 gm to 100 kg and velocity from 20-40 km/sec. A one dimensional cooling model incorporating conduction, change of phase, and radiation is used to predict the cooling history of the crater. Several possible initial distributions (exposed to surface, shallow or moderate burial by cooler material) of the impact melt are considered. Infrared spectra are calculated for the modeled surface temperature distribution at several times during the cooling. The impact IR signature is prominent in the wavelength range 1.5-6 μ against the lunar nightside background. The optimum wavelength for detecting the smallest accessible impact is between 3 and 4 μ. It is found that the maximum signal strength is dependent on the initial distribution of melt as well as impact energy. The duration of the signal above a minimum detectability threshold is proportional to impact energy with only modest dependence on the initial melt distribution. Basic design requirements and capabilities for sensors to detect the impact signature from lunar orbit and earth orbit are considered. The lunar orbiting sensor can detect impacts as small as ∼50 gm. With a field of view covering ∼640000 km² a rate of approximately 2 events per week might be expected. An earth orbiting sensor could detect impacts of ∼100 gm at the sub earth point. Larger impacts could be detected closer to the lunar limb. Monitoring a large fraction of the nighttime hemisphere visible from earth orbit the observable event rate is similar to that from the lunar orbiter. Ground based observation at wavelengths between 2 and 2.4 μ could detect ∼2 kg impacts with an event rate estimated at 1 per 400 hours observing time.

The Infrared Astronomical Satellite (IRAS) Serendipitous Survey Catalog (SSC) was constructed from pointed observations made by the satellite when it was in Additional Observations (AO), i.e., non-survey, mode. Analysis of the SSC shows that it contains a higher percentage of sources which have been detected only at 60mum than are found in the IRAS Point Source Catalog (PSC). This could reflect the existence of a large population of faint extragalactic (galaxian) objects due to the increased sensitivity of the SSC relative to the PSC, especially in the 60 mum band, or simply be a result of spurious sources in the SSC. Inspection of cirrus contamination over each AO showed that it had little or no effect on the high 60 mum-only source count. An automated optical identification program presented here indicated that 60 mum-only sources were as likely to have optical counterparts as all other sources, and more likely than randomly-placed artificial sources. The SSC sources studied had, on average, one more optical source found nearby than did artificial data: probably the optical counterpart to the IRAS source. These results support the validity of the 60 mum-only sources and the SSC in general.