Our society increasingly relies on spacecraft operations in the Earth's inner magnetosphere, particularly for communications. Long-duration high-intensity fluxes of relativistic electron are hazardous to spacecraft operational systems. Adverse effects of these energetic electrons on spacecraft has resulted in significant public interest and renewed efforts to advance our understanding and predictive capabilities of relativistic electron flux variations in the inner magnetosphere. The flux variations are especially dynamic during geomagnetically disturbed times. It is often observed that fluxes of relativistic electrons in the Earth's inner magnetosphere decrease by orders of magnitude, followed by a substantial enhancement of up to two orders of magnitude above the pre-storm levels. This work primarily focuses on the investigation of two physical processes for the relativistic electron flux variations: The fully-adiabatic effect and the delayed substorm injection mechanism. We simulate fully-adiabatic variations of electron fluxes for the special case of equatorially mirroring electrons using Rice magnetic field models and a quiet-time electron flux model. The storm-time electron fluxes can be obtained by fully-adiabatically evolving pre-storm fluxes using Liouville's theorem. Our study shows that the fully-adiabatic effect can cause a flux decrease of up to almost two orders of magnitude for Dst = -100 nT. We also simulate acceleration and injection of plasma sheet electrons during substorm dipolarization using a 3-D MHD field model. The test particle simulation shows that tens-of-keV plasma sheet electrons may be accelerated up to relativistic energies during a rapid substorm injection followed by a slow radial diffusion to the inner magnetosphere. Comparison with measurements shows that the mechanisms may contribute significantly to the observed flux variations.

Charge exchange of solar wind with the Martian exosphere is shown to have two-fold consequences. From the solar wind perspective, the thermal pressure is removed by charge exchange with Martian neutral particles. To maintain a constant total pressure in the flow, increase of magnetic field occurs and therefore accounts for the formation of the magnetic pileup boundary observed by the Mars Global Surveyor Magnetometer. To simulate this a fluid model is constructed and results from it are shown to successfully fit observations. On the other hand, the Martian exosphere is affected by the charge exchange, too. Compared to Venus, Mars has an ionosphere that is so dilute that charge exchange of solar wind should play an important role in the formation of a nonthermal Martian hydrogen exosphere component. In order to study quantitatively how the Martian exosphere is influenced by it, we develop a 3-dimensional Monte Carlo exosphere model in which effects of charge exchange with solar wind are isolated. Simulation results show the existence of that hot population does change the exospheric temperature structure greatly, and we also investigate the simulation results by calculating the contribution of the hot component to Ly-alpha emission and comparing it with data acquired by Mariners' ultraviolet spectrometers. Finally, it is concluded that charge exchange is important in the interaction between solar wind and Martian exosphere. Output of our models can be used in future modeling and data analysis for the coming Mars missions.

The most detailed study to date of the physical diagnostics and ionization structure of the core of M42 (the Orion Nebula) is presented using new long slit spectra and existing CCD imagery. Cospatial temperature and density diagnostics are presented for distances out to $\sim$5 arcminutes from the Trapezium and clearly show gradients in $T\sb{e}$ and $N\sb{e}.$ Temperatures are derived using S$\sp+,$ O$\sp+,$ N$\sp+,$ O$\sp{++}$ and the Balmer Discontinuity, T(Bac). Values for T(S$\sp+)$ in the range 11,000-14,500 K are presented and suggest shock heating at the ionization front as predicted by some models. A gradient in T(Bac) is derived with temperatures as low as 3000 K and is left open to interpretation. Density gradients for S$\sp+,$ O$\sp+$ and Cl$\sp{++}$ are also presented and are consistent with model predictions for an H scII region in the champagne phase of evolution. Using imagery we have constructed a picture of the core of Orion, including previously unknown features. Ratio maps show a high ionization cavity centered on the Trapezium and a low ionization region to the southwest. Ripples and bends in the background molecular cloud are detected. Further to the southwest the ionization begins to increase with distance, which is interpreted as the molecular cloud curving back toward the observer. Additional features in the imagery include a bar-like structure to the northeast of the Trapezium and a high density knot and ellipse of material believed to be a Herbig Haro object. Our diagnostics provide unprecedented detail as to the variation of temperature fluctuations with position. The mean square temperature fluctuation, $t\sp2,$ for the ions O$\sp{++}$ and N$\sp+$ is similar on a global scale, with a value in the range 0.03-0.05 for an assumed constant recombination temperature. Using a gradient in T(Bac) predicts $t\sp2$ values of 0.01-0.15 with values increasing outward. The ion S$\sp+$ gives unusually high values of $t\sp2$ and is not a reliable indicator of fluctuations in the H$\sp+$ zone since some of the (S II) emission arises from beyond the ionization front.

This work studies the dynamic behavior of solar energetic particles (SEPs, defined as protons and electrons with energies of 1 MeV to 1 GeV) by simulating their motion in model electromagnetic fields. Because of the hazards they pose to orbiting spacecraft and manned spaceflight operations, these species must be included in modern modeling efforts, including forthcoming space weather models. In this thesis, we describe an original computer program called the Solar Energetic Particle Tracer (SEPTR). As part of an operational computer model, SEPTR calculates the upper rigidity cutoffs for particles within an evolving magnetosphere. We use a feature of SEPTR to calculate late a global ionospheric grid of rigidity cutoffs using the DGRF 1980 magnetic field model. Rather than map rigidity space in order to find the cutoffs, we use an algorithm designed to locate the upper cutoff in a minimum of time, which is more appropriate for an operational model. Comparisons to similar calculations by Smart and Shea [1985] support the validity of our method. A second feature of SEPTR is the ability to use data of SEP or X-ray fluxes in order to generate differential energy spectra for magnetospheric protons. The rigidity cutoffs are then applied to the proton spectrum in order to provide a representation of the local flux. Because we calculate actual particle trajectories rather than making use of popular approximations, our code is ideal for studying the limitations of adiabatic theory. We examine the expansion of the first adiabatic invariant series in terms of ordering parameter, identify examples of non-adiabatic behavior, and specify a form of the first adiabatic invariant that is appropriate for full particle tracing. The dayside magnetopause frequently has a geometry with a minimum in magnetic field strength off the magnetic equatorial plane. This feature leads to particle drift paths that move into the Northern or Southern polar cusp. Our model suggests a possible concentration of energetic electrons in these regions as well as chaotic radial diffusion when the particle resumes equatorial mirroring.

We present high resolution, echelle spectroscopy of the close pre-main-sequence binary star systems DQ Tau and UZ Tau-E. Over a 16 day time interval we acquired 14 nights of spectra for DQ Tau and 12 nights of spectra for UZ Tau-E. This represents the entire orbital phase of DQ Tau, and 63 percent of that for UZ Tau-E. As expected, photospheric lines such as Li I lambda6707 clearly split into two components as the primary and secondary orbit one another, as did the permitted line He I lambda5876. Unlike the photospheric features, in both objects the forbidden lines of [O I] lambda6300, which has both a low-velocity and high-velocity component, and [O I] lambda5577, which has primarily a low-velocity component, retain the same shape throughout the orbit. Therefore these lines must originate outside of the immediate vicinity of the two stars and any gas that participates in the orbital motion of the stars.

The central star of the Helix Nebula, the closest planetary nebula, is ringed by hundreds of Cometary Knots. Presented here are images taken with WFPC2 of a field in the northern portion of the bright ring and some physical parameters and models derived from the data. The field of view contains more than thirty well formed Cometary Knots and reveals that the entire bright ring is composed of knot-like structures. The data is in three narrow emission line filters, H$\alpha$, (OIII) and (NII). Optical thickness to ionizing photons for the knots is established, physical properties such as density in the ionized portions of the knots and dust mass are determined and the beginning of a model to explain the detailed structure set forth.

We have studied the high velocity flows and related shock phenomena in the Orion Nebula. Hubble Space Telescope WF/PC and WFPC2 images have been used in morphological studies and proper motion studies of the objects of interest. The high spectral resolution echelle slit spectra have been obtained for the central Orion Nebula in order to study both high velocity flows associated with compact objects and large scale high velocity systems. A group of Herbig-Haro objects located to the north of the Trapezium cluster have been studied in detail. Their morphology, proper motions and motions along the line of sight have been investigated. A bow shock model has been applied to predict the emission line profiles of bow shocks and the resultant line profiles were compared with the observed spectra. The comparison was successful except there is a discrepancy for one of the objects. The possible origin and evolution of this group of objects have been discussed. Two Herbig-Haro objects(HH203/HH204) in the vicinity of $\theta\sp2$A have also been studied both through the HST images and slit spectra. The possible nature of HH203 was suggested by comparing the emission line image with bow shock model predicted emission in inhomogeneous density environment. The spectra of Knot C has been presented and the nature of this object was discussed. We also reported the discovery of a Herbig-Haro like object-HH269, which is located to the southwest of the Trapezium cluster. A slit spectra mapping of the vicinity of the Trapezium cluster and HH202 have been done. The high velocity flows associated with several "proplyds" have been studied. A 1$\sp\prime$ diameter "receding disk" near the Trapezium cluster was found in (OIII) line spectra. A couple of complicated extended high velocity systems were found near HH202. The spectra of this region were presented.

The Orion Nebula (NGC 1976, M 42) is an H II region composed of a slowly expanding thin zone of photoionized gas on the facing side of the Orion Molecular Cloud. The Orion Nebula is also a famous star formation region in which numerous jets and shocks arise from many young stars. Creating bipolar jets to shed excess angular momentum is an essential process in star formation. The jets interact with the interstellar medium or with wakes of previously passing jets and subsequently form shocks. These shocks can be observed with optical or near infrared emission lines and are called Herbig-Haro (HH) objects. The purpose of the present study was to catalog and study the HH objects in the Orion Nebula, and hence, this will help us understand how stars form in a molecular cloud and then evolve in an H II region. We measured the proper motions (tangential velocities) and radial velocities of the HH objects with the highest possible accuracy. By combining the results of the proper-motion and radial velocity measurements, we could obtain the spatial (three-dimensional) motions of the HH objects, which gave us the opportunity to discover the true physical nature of the HH objects in the Orion Nebula. We were able to measure the proper motions of the HH objects with a 10 km s-1 accuracy using the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) images in [S II], [N II], Halpha, and [O III], taken 4 to 6 years apart. This is the first study dedicated to measuring the proper motions of HH objects in the Orion Nebula covering the complete range of ionization states. A shock consists of a shock front followed by a collisional excitation zone and a cooling zone in which [O III], [N II], and [S II] emission layers form. Halpha emission comes directly from the collisional excitation zone. The presence of [O III], [N II], or [S II] emissions is a good indicator of the strength of a shock. We identified all the HH flows in the northwest and southeast regions of the Orion Nebula and found two new bipolar objects. We confirmed that the major HH flows in the northwest region were created by an explosive event which took place approximately 1000 years ago. We also found a new HH flow moving toward the northeast in the southwest region of the Orion Nebula. The proper motion of HH 202 was measured with high accuracy for the first time, and the result indicates that HH 202 and HH 203/204 may have emanated from the same unknown origin. (Abstract shortened by UMI.)

Two auroras sampled nearly simultaneously at high and low altitudes along a field line by the Dynamics Explorer (DE) spacecraft have been used to study auroral electrodynamics. Electric fields plotted as a function of invariant latitude show that the large-scale features are essentially the same at high and low altitudes outside the auroral acceleration region. Parallel electric fields associated with parallel currents are such as to filter out the small-scale structure in the high-altitude electric field pattern. From the magnetic field measurements, we find that there is a return current region embedded between two auroral arc structures. The latitude shift between the high-altitude and low-altitude return current regions indicates that the auroral arcs are moving equatorward with a velocity of about 250 m/s. Collisionless plasma kinetic theory (Knight, 1973) has been used to predict the relationship between the upward parallel current and the parallel potential drop. The DE 1/DE 2 pair offers a unique Opportunity to test this relationship because the DE 1 spacecraft can measure high altitude plasma parameters without contamination from auroral heating. Using measured values of J$\sb{\Vert}$ (mapped to the surface) and $\Phi\sb{\Vert}$, the ratio of J$\sb{\Vert}$/e$\Phi\sb{\Vert}$ varies considerably but with a mean value about 0.5$\sim$2.2 $\times$ 10$\sp{-9}$ mho/m$\sp2$. Suprathermal electron bursts are also observed in the diffuse aurora at the same invariant latitudes, both at high and at low altitudes. Thus we suggest that these "bursts" are more properly described as a spatial rather than temporal phenomenon. Observations of upflowing ionospheric ions are obtained by both DE 1 and DE 2 over the nightside auroral regions. At low altitudes, the mean value of the net upward ion number flux is of the order of 10$\sp9$ cm$\sp{-2}$ s$\sp{-1}$. The ionosphere is predominantly O$\sp+$, and the ions with energies greater than 5 eV are a only very small fraction (less than 1%) of the total ion population. At high altitudes, the upflowing ions are accelerated and heated (with characteristic energies of hundreds of eV). Comparing upflowing fluxes at high and low altitudes yields an estimated height of the bottom of the auroral acceleration region of 1100-1400 km.

Optical observations of the nuclei of 10 S0 Markarian galaxies and two non-Markarian early type galaxies have been obtained with the McDonald Observatory 2.7m telescope. The spectra of 7 Markarian galaxies show deep Balmer absorption lines and stellar-like continua. The nuclear spectra of UGC 01157, 04902, 06570, and 12618 show strong (O II), (O III), and H$\beta$ emission lines analogous to normal H II regions. None of the galaxy continua show a featureless non-thermal component or (O I) $\lambda$ 6300 line emission typical of LINER activity. The continua of UGC 02093 and 07933 are similar to normal early type galaxies. Composite model spectra with decreasing birthrates, IMF exponents of $-1$, $-2.5$, and $-4$, and solar metallicity have been constructed from observed stellar spectra. Comparison of CaH + H$\varepsilon$ to CaK absorption line flux ratios measured in 5 star-burst galaxies to single star-bust episode models implies stellar population ages greater than 5 $\times$ 10$\sp9$ years.