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.

In order to obtain a better understanding of auroral processes, statistical models have been formulated that characterize the spatial dependences of the aurora. These efforts include the Hardy probability model, the Hardy average model, and the Evans average model. Each differs in its technical approach but all three attempt to characterize electron energy fluxes at any given location in the auroral zone. In an attempt to describe the limitations of each model and perhaps make suggestions on how one can improve them, we reduced a six month sampling of DMSP-F2 electron precipitation data and averaged values over four second time intervals. Then each model generated a flux value for comparison against these satellite measurements so that Chi-square tests could be performed. Also the mean values for the whole six month period were calculated in order to determine the normalcy of the period tested. It is hoped that the knowledge gained through this endeavor will improve the accuracy of the Magnetospheric Specification Model's forecasts of the fluxes that endanger spacecraft.

We present a model describing the morphology and physical processes in NGC 6888, a 'wind-blown' nebula around the WN6 star HD192163. CCD imagery with the Palomar 1.5m revealed distinct morphological features that were further probed with spectrophotometry using the KPNO #2 telescope + Intensified Reticon Scanner. Distinctions in morphology in (O III) compared to H$\alpha$ led to a parametrization into two physical systems: (1). An inner ionized shell observable in all the emission lines, with (N II) T$\sb{\rm e}$ = 8000 $\sp\circ$K, (O III) T$\sb{\rm e}$ = 14,000 $\sp\circ$K and (S II) N$\sb{\rm e}$ = 400 cm$\sp{-3.}$, (2) The (O III) bubble and rim, visible only in (O III) and characterized by a higher (O III) T$\sb{\rm e}$ = 50,000 $\sp\circ$K. The nebula is found to have 5-10 M$\sb\bigodot$ of ionized mass. An extrapolation of (O III) $\lambda$5007 fluxes to IR emission line intensities led to revised values of neutral mass $\sim$40 M$\sb\bigodot$ for the nebula. Of this 3-6 M$\sb\bigodot$ is found to be enriched mass, 0.5 M$\sb\bigodot$ contributed by stellar wind mass loss and wind swept ISM mass is determined to be $\sim$20-60 M$\sb\bigodot$. Photoionization models demonstrate that the shell is enriched in N and He and depleted in O compared to Galactic H II regions. These results collectively indicate a scenario that is a combination of several physical processes. A slow wind ejected in an asymmetric fashion from the star is swept up by a fast stellar wind together with the ambient medium, creating the ionized shell. This interaction also creates Rayleigh Taylor instabilities which are determined to be plausible formation mechanisms for the observed knots. The hot gas ($\sim$ 10$\sp7 \sp\circ$K) penetrates the nebular material in the NW and SE as there is less ejecta pressure opposing it along the polar axis, and creates the observed (O III) bubbles in the NW and lattice in the SE.

Recent observations have discovered pervasive, low-ionization gas with unusual excitation in the halos of nearby spiral galaxies. This has led to speculation concerning the excitation mechanisms operating at high galactic latitudes, including exotic processes involving nonequilibrium physics, local grain destruction and decaying dark matter. We demonstrate that the excitation conditions of the diffuse ionized media (DIMs) in several such objects, NGC 891, the Galaxy and NGC 1068, can be understood in terms of photoionization by the dominant radiation fields in their halos, if proper consideration is given to the spatial distributions of their stellar populations, the relative importance of nuclear continuum sources and subsequent radiative transfer. Estimation of the stellar populations in NGC 891 and the Galaxy indicates that OB stars, and the central stars of planetary nebulae dominate the excitation of their DIMs. Photoionization models require local DIM electron densities of order unity to reproduce the observed emission characteristics of the high-$\vert z\vert$ gas. The DIM filling factor in NGC 891 is therefore restricted to the range 10$\sp{-3.5}\ \sbsp{\sim}{<}\ \phi\ \sbsp{\sim}{<}\ 10\sp{-1.5}$, while in the Galaxy $\phi\ \sbsp{\sim}{<}\ 10\sp{-1.2}$ is suggested. Ionization equilibrium indicates that only $\sim$5% of the total number of ionizing photons from OB stars escape the neutral disk, highlighting the importance of radiative transfer through the multiphase ISM. The DIM in NGC 1068 demonstrates a bipolar asymmetry common among active galaxies, with high-excitation emission confined to two diametric sectors aligned along the radio jet axis and low-excitation emission uniformly distributed over the disk. We show that this bipolar morphology can be understood using the developing picture of NGC 1068, in which its burried Type 1 Seyfert nucleus is visible only through scattered polarized light. The DIM excitation is therefore anisotropic, with high-excitation gas along the jet axis photoionized by direct nuclear continuum and low-excitation gas away from the axis, illuminated by indirect nuclear emission scattered into it. Photoionization models using power-law continua, indicate that the filling factor of this DIM is restricted to the range $10\sp{-5} \ \sbsp{\sim}{<}\ \phi\ \sbsp{\sim}{<}\ 10\sp{-4}$ in order to reproduce the observed DIM emission characteristics.

The temporal and spatial relationships between hard X-ray and UV emission in solar flares provide stringent restrictions on the physical processes responsible for solar flare emission. In this thesis, we present results from a detailed analysis of temporal profiles and spatially resolved hard X-ray images from RHESSI alongside high cadence observations of the UV continuum from TRACE for two solar flares: A C6.5 flare from 16 July 2002 06:38--06:43 UT and an M8.5 flare from 17 July 2002 07:00--07:05 UT. For both flares we find a significant temporal correlation between the UV and hard X-ray emission over the duration of both events. In the spatial analysis for the 16 July 2002 event, we note a significant spatial separation between the correlated UV sources and their hard X-ray counterparts leading to a complex flare topology invoking loop-loop interactions. We suggest a three-dimensional reconnection scenario in an attempt to address the spatial discrepancy in the hard X-ray and UV correlated emission.

We use the unprecedented spectral and spatial resolution of RHESSI to explore the behavior of electrons and their associated currents in solar flares. Spectral images are used to determine an estimate of the effective surface area for the different independent substructures within each event. The incident electron spectra at those flaring footpoints are derived from the RHESSI photon spectra. We find that, over a wide range of flare X-ray magnitudes, the integrated photon flux above 20 keV asymptotically approaches a limiting value, suggesting a saturation of the photon production in flares. The inferred particle fluxes in the beam, together with this saturation limit, are used to determine the energy loss mechanism dominating the energetic particle transport in solar flares.

This thesis presents two-dimensional hydrodynamic disk simulations with embedded protoplanets, emphasizing the non-linear dynamics in the co-orbital region. In particular, it demonstrates how a protoplanetary disk responds to embedded low mass planets at the inviscid limit. Since the potential vorticity (PV) flow is not conserved, due to the spiral shocks and possibly boundary layer effects emanating from the planet, the PV profile develops inflection points which eventually render the flow unstable. Vortices are produced in association with the potential vorticity minima. Born in the separatrix region, these vortices experience close encounters with the planet, consequently exerting strong torques on the planet. The existence of these vortices, if confirmed, have important implications on planetary migration rates. The formation of vortices is discussed in more detail and a key parameter is found which depends solely on planet mass and sound speed. With this key parameter, one can predict the disk evolution, PV growth rates, and threshold conditions for forming vortices in the co-orbital region. An analytical estimate for the change of PV due to shocks is compared to the actual change in PV in the hydrodynamic simulations. They match well except in the inner region where vortices form. In addition, extensive resolution tests were carried out but uncertainties remain about the physics of this particular region.