We investigate a new interaction of globular clusters with galactic field stars. By dynamical friction, high-velocity field stars passing through individual globular clusters are decelerated. This frictional interaction contributes to cluster heating, and, in conjunction with disk shocking and other mechanisms, it helps regulate the evolution of globular clusters. Moreover, penetrating field stars with low relative velocities can even be captured by globular clusters. Our calculated rate of captures suggest that there is a substantial population of stars having an origin external to the globulars in which they now reside. Intriguing candidates for this "immigrant" population include some blue straggler stars and short-period pulsars.

In the large magnetic fields associated with highly magnetized neutron stars, the Compton cross section exhibits a resonance at the local cyclotron energy. In this work I describe applications of magnetic Compton scattering to models of both rotation powered and accretion powered pulsars. Radio pulsars are generally considered to be rapidly rotating, highly magnetized neutron stars. The rapid rotation coupled with the large magnetic field induces large electric fields that can accelerate electrons in the neutron star magnetosphere to large energies. I have produced a Monte Carlo code to model $\gamma$-ray emission from rotation powered pulsars utilizing pair cascades initiated by Comptonized photons. Previous polar cap $\gamma$-ray emission models have relied on pair cascades initiated by curvature radiation photons. This Monte Carlo model can reproduce the double peak pulse profiles often observed from rotation powered pulsars and explain the trend for harder spectra from slower pulsars. X-ray Pulsars are thought to be highly magnetized neutron stars accreting matter from an ordinary stellar companion. The accreting matter is channeled onto the neutron star polar cap by the magnetic field. This material produces a hot spot on the neutron star surface that emits X-rays. I have investigated the effects of radiation pressure due to these X-rays on the accreting material. The radiation pressure is greatly enhanced by the resonance in the magnetic Compton cross section. Because the electron cyclotron energy varies with distance from the neutron star, the energy dependent X-ray spectrum maps to a spatially varying radiation force. This force can exceed the force of gravity over a limited region of the X-ray pulsar magnetosphere. I postulate that when this occurs matter can be elevated above the neutron star surface outside the accretion column. This material will act as an energy dependent "lamp shade" that will produce pulse profiles that vary with photon energy. This model is capable of reproducing the energy dependent pulse profiles observed from the X-ray pulsars 4U 1626-67, 4U 1538-52, 4U 1907+09, and Vela X-1.

Narrow band filter images of the inner Orion nebula were taken by the the Hubble Space Telescope WF/PC in 1990 and 1991. Two data sets were reduced and astrometric solutions were obtained for the two fields with good accuracy. The three major emission line filters for the 1991 data were calibrated into absolute energy units. The continuum contribution was removed from the images, and the $\rm H\alpha$ contribution was removed from the (NII) images. Calibration constants were found to differ from predicted prelaunch values, and possible explanations were investigated. VLA and HST images of two compact sources near the center of the Orion Nebula were compared. The VLA and HST images are similar when the two are scaled to the same units. VLA images show a higher concentration of surface brightness, reflecting its better resolution; whereas, the HST images, due to greater sensitivity of the HST, showed extended cometary form. The positions of three Herbig-Haro objects on HST images were compared with ground based observations at various wavelengths. The basic agreement between these positional observations can be used to analyze the structure of these sources, because of the different excitation mechanism for each source.

An optical study of the HII region populations evident in three galaxies, M101, M51 and NGC 4449, has been made. Using narrow-band filters, emission line imagery has been taken using a CCD focal-reducing camera, at wavelengths covering the emission from H $\alpha,$ H $\beta,$ (O III) $\lambda$5007 and (S II) $\lambda\lambda$6716+6731. Using several identification techniques to spatially select the HII regions, emission line properties have been derived for 625 HII regions in M101, 465 in M51 and 163 in NGC 4449, making this the most complete study of its kind to date. Several trends have been discovered concerning the properties of the HII regions with radial position within their galaxy. M101 exhibits a large gradient in excitation, and oxygen abundance, as well as a gradient in the line-of-sight reddening. No positional variation in the derived ionization parameter for each HII region was found. Local variations in the effective collapse density for neutral gas have been detected for both M101 and M51. No such analysis was possible for NGC 4449 due to a lack of available data. M51 shows systematic emission variations only in the brightest cores of its largest HII regions, an effect attributed to a larger influence of the local ISM on the properties of the fainter, and more obscured, HII regions. M51 exhibits a spiral pattern that does not follow a single mathematical description, departing most dramatically at the corotation radius. A variation in the evolutionary time from peak local compression to peak star formation with radius has been detected for one of the arms in the galaxy, but not the other. NGC 4449 displays no systematic variations in the derived emission properties of its HII region population. This is attributed to a star formation mechanism that is independent of the radial ordinate, contrasting with the spiral density wave mechanism dominant in spiral galaxies. Unprecedented deep CCD imagery of this galaxy is presented, revealing the complicated structure of ionized filaments between the HII regions. The emission properties of these filaments are studied.

The Comet Rendezvous and Asteroid Flyby Mission (CRAF) will include, as one of its complement of thirteen scientific instruments, a plasma electron analyzer capable of providing 3-dimensional measurements of the energy and angular distribution of electrons in the solar wind, asteroidal and cometary environments. After initial instrument selection, mission planners at JPL suggested that an instrument capable of performing angular scanning electronically rather than mechanically be investigated. This thesis describes the development of the redesigned CRAF plasma electron detector, consisting of an electronic scanning component, called the "elevation analyzer", and an energy analyzing component based on the Soft Particle Spectrometer (SPS). The numerical simulation of each component's operation--consisting of ray-tracing particles through the electrostatic field of each analyzer and collecting statistics on those particles successfully transmitted--is used to determine the energy and angular response functions of each component and the design dimensions that optimize these responses.

Gamma-ray bursts (GRBs) remain one of the most inexplicable astrophysical phenomena observed today. While counterparts at other wavelengths would provide the best clues as to the nature of GRBs, none have been observed. To supplement studies on GRB distribution and population statistics, temporal morphologies, and spectral line searches, we focus on the analysis of GRB continuum spectral evolution. Previous spectral evolution studies have shown a variety of patterns: most individual pulses show a hard-to-soft evolution, but studies of both the SIGNE and BATSE GRB databases reveal several other patterns, including hardness-intensity tracking, soft-to-hard, static, and chaotic spectral evolution. This type of analysis attempts to identify spectral evolution signatures that can discriminate between different physical scenarios or different GRB subpopulations based on temporal profile, duration, intensity, or spatial distribution. Contrary to most studies that use only one model and one parameter to characterize spectral evolution, several models are used here. Statistically equivalent models are shown to give consistent physical results. I verify the variety of spectral evolution patterns present in GRBs, and investigate how the actual shape of the spectrum evolves, following multi-parameter spectral fits in time. Different spectral evolution patterns exist simultaneously in multiple parameters. Hardness-intensity correlations in pulse and over burst decay phases are quantitatively examined: correlation is often significant, but the relation between hardness and intensity is non-unique. Hardness-intensity lag-times are found to correlate to the rise-time of the hardness profile. Comparisons of double-pulse GRBs reveals a variety of results, including the implication that late-emitting pulses are less affected by early emission.

We present detailed spectroscopic and multiband photometric observations of the nearby galaxy M82 in order to study the high-velocity outflows observed in such galaxies as a property of the energetic starburst phenomena associated with their nuclei. The high spatial and kinematic resolution of our observations has allowed us to perform photometric analysis of H$\alpha$, (N II), and (O III) spectral lines at roughly one hundred thousand positions across the extent of the galaxy. The observed velocities of the H$\alpha$-emitting gas in M82 suggest a bipolar outflow of material along the minor axis at a projected velocity of $\sim$300 km/s, fueled by the bright nuclear starburst regions in the galaxy's disk. All three spectral lines show double components in the centers of the outflowing lobes, with the H$\alpha$ line split by $\sim$300 km/s over a region almost a kiloparsec in size. We argue for a model in which the optical emission is radiated by denser ambient material on the surface of "bubbles" that have been evacuated by a hot wind ($\sim$10$\sp8$ K) visible at x-ray wavelengths. The outflow is confined to a cylinder within 350 pc of the disk, but flares outward in a cone beyond that point. The optical line-emitting filaments consist of both gas that has been entrained from the disk by the outflow and material already present in the halo of M82. Although the detailed structure of the bubbles is complex, we confirm the major predictions of galactic wind hydrodynamical simulations. Line ratio maps reveal high (N II) /H$\alpha$ in the disk, suggesting the presence of a diffuse ionized medium (DIM) similar to that seen in NGC 891 and other star forming galaxies. The halo of M82 is also observed in emission lines, but only as dust-scattered disk radiation. We conclude that M82 has an active star-forming disk, a dusty scattering halo, and a bipolar starburst-driven wind.

The Magnetospheric Specification Model (MSM) calculates electron and ion fluxes that may endanger spacecraft. This thesis is to evaluate the electron flux levels specified by the MSM by comparison with the Garrett model output and spacecraft observations for the large magnetic storm of April 1988. The MSM is a magnetospheric physics model which uses ground-based and satellite data as input. The Garrett model, on the other hand, is a statistical model based on average geosynchronous electron fluxes. The MSM flux enhancement predictions are in better temporal agreement than the other model. The largest error of the MSM is associated with flux dropouts which are observed by the spacecraft but not predicted by the MSM. The other possible error sources are (1) the MSM does not properly represent extreme thinning of the plasma sheet, (2) the MSM tends to overestimate the convection electric field.

The purpose of this thesis is to study an evolving system of SUperNOva CONdensateS (SUNOCONS) within the Interstellar Medium (ISM). This is done via a Monte Carlo process where refractory dust grains formed within supernova remnants are subjected to the processes of sputtering and collisional fragmentation in the diffuse phase and accretion within the cold molecular cloud phase. In order to record chemical detail, we take each new particle to consist of a superrefractory core plus a more massive refractory mantle. The particles are allowed to transfer to and fro between the different phases of the ISM until either the particles are destroyed or the program finishes. The resulting chemical and size spectrum(s) are then applied to various astrophysical problems with the following results: (1) after six thousand million years roughly 10 to 20% by mass of the most refractory material (Al$\sb2$O$\sb3$) survives the rigors of the ISM intact, which leaves open the possibility that 'fossilized' isotopically anomalous material may have been present within the primordial solar nebula. (2) structured or layered refractory dust grains within our model cannot explain the observed interstellar depletions of refractory material. (3) fragmentation due to grain-grain collisions in the diffuse phase plus the accretion of material in the molecular cloud phase can under certain circumstances cause a bimodal distribution in grain size.

I propose here an interesting historical scenario for galaxy formation that may find application to the problems of dwarf irregular galaxies in general and of I Zw18 in particular. My purpose is to present calculations of the C:N:O ratios within this simple model in an attempt to explain the apparent paradox, that characterizes I Zw18, of having very low concentrations of C, N and O in HII regions of a current starburst (some forty times smaller than solar) and yet having nearly solar ratios for C/O and N/O. I first calculate concentrations in a hot ambient medium that suffers a "Hubble-like flow" wind in a galaxy that has experienced several bursts of star formation. This hot matrix contains HI clouds whose collisions initiate the starbursts. The ambient gas which is found to have large and variable X$\sb{\rm O}$, X$\sb{\rm C}$ and X$\sb{\rm N}$ concentrations, is mixed very slowly into the clouds, so that today a few percent of the cloud mass has been gathered from the hot medium by admixing, resulting in cloud concentrations comparable to those found in I Zw18. Different assumptions were tried for the details of the galactic history. The resulting ratios of the abundances in the clouds were found to be insensitive to these details.