Rice University has been developing a gamma ray telescope to be used for the detection of spectral gamma ray lines from Type I supernovae within one megaparsec in the energy range from 100 keV to 10 MeV. The detector is an actively shielded array of 121 0.5$\sp{\prime\prime}$ x 0.5$\sp{\prime\prime}$ x 2.0$\sp{\prime\prime}$ NaI(Tl) crystals, each optically separated from the remainder of the array independently viewed. Inflight calibration of the 121 individual PMTs will be handled by an on board computer in conjunction with LEDs attached to the crystals. The active shield is constructed of individual blocks viewed separately by one or more photomultiplier tubes acting in anticoincidence with the central detector, providing excellent isolation from non-source gamma ray detections. The telescope uses a coded aperture approach yielding an overall geometrical spatial resolution of 2.6$\sp\circ$ x 2.6$\sp\circ$ FWHM. The energy resolution of the detector is expected to be 12% FWHM at 0.661 MeV. Simulations of the detector/shield assembly yield a projected sensitivity of 1 $\times$ 10$\sp{-4}$ photons cm$\sp{-2}$ sec$\sp{-1}$ for a 3 sigma detection at 1 MeV. (Abstract shortened with permission of author.)

Presented are the results of an empirical study of the scattering of starlight in the UV and optical continuum by dust in Orion, plus the distribution of the ionic species of CNO across the face of the nebula. Spectra from the IUE have been combined with ground-based spectrophotometry and CCD imagery. This study of M42 is the most extensive to date. The distribution of dust and its effects on the scattering of starlight are examined. The variation of scattered light with distance and wavelength has been parameterized and a functional relationship determined. Abundances for ionic species of carbon, oxygen and nitrogen have been calculated. Several results were uncovered. The C/H abundance in Orion must be lowered by a factor of 3-5 compared to past results. The C/H abundance is constant across the inner 5 arcmin of the nebula as is the C/O ratio.

The motion of a charged particle in a multipole magnetic field has three adiabatic invariants associated with it. The first is that the magnetic flux through the particle's cyclotron orbit about a field line is constant. An equivalent statement is that the magnetic moment of the particle due to its cyclotron motion is constant. The second adiabatic invariant states that the integral of the particle's parallel momentum between its two mirror points is constant. The third adiabatic invariant says that the magnetic flux through a surface connected to the longitudinal invariant surface and passing through the magnetic axis is constant. In this thesis I have examined the relationship between the magnetic moments from the first and third invariants. For a particle in the equatorial plane of a dipole field, the ratio of the magnetic moment from the third invariant to that from the first invariant is 3/2.

We have studied Hubble Space Telescope images of the Orion Nebula. Many fine scale features of the nebula and compact objects embedded in the nebula were found. Some of the compact objects were resolved or partially resolved, and exhibit comet or elongated shapes. We propose that those compact objects associated with infrared sources are protoplanetary systems. Many high ionization, high velocity bow shock structures were found in the region where the protoplanetary disk systems are concentrated. High resolution spectra of (S III) $\lambda$ 6312 A line were obtained to study the kinematic properties of the S$\sp{++}$ ions. Four velocity systems were found. Three of them were explained. The first two arise in the main and the foreground layer of the nebula, respectively. The third one results from the reflection of the first system by dust particles inside or around the nebula. An east-west velocity gradient was found for the main emission. We also studied the turbulent motion of the S$\sp{++}$ ions. The results do not agree with predictions of the available turbulence model of H II regions. High resolution (N II) $\lambda\lambda$ 6548, 6583 A, (S II) $\lambda\lambda$ 6716, 6731 A, H$\alpha$, He $\lambda$ 5876 A, and (O I) $\lambda$ 6300 A, and (S III) $\lambda$ 6312 A spectra of the nebula were obtained to study the characteristic motions of their corresponding ions. The results are consistent with those of previous detailed studies of O$\sp+$, O$\sp{++}$, and S$\sp{++}$ ions, indicating the existence of an emission from the foreground lid. Combined with results of previous emission and absorption line studies, we conclude that the line-of-sight structure of the nebula can be approximated as two emitting layers. One litter is the main body of the nebula lying at the near side of the molecular cloud OMC-1, the other is the layer at the far side of the foreground neutral lid. The gas lying in between these two layers is very tenuous. We introduced a method for modeling the geometry of the nebula. The method utilizes a density map and an H I recombination emission map of the nebula. It was applied to the main emitting layer of the nebula, which was the first attempt to quantitatively model the geometry of a nebula. The results indicate that the method is quite successful. The model geometry shows some of the features expected and improves our understanding of the prominent features observed in the nebula.

Using Images of the Orion Nebula from the Hubble Space Telescope and calibrated ground based images, we were able to recalibrate three narrow band HST filters, namely F656N, F658N and F502N. The results show that the first two filter profiles had kept the same shape as that published in the Wide Field Planetary Camera 1 (WFPC1) handbook but had decreased in overall transparency by about 40% each. Results for the F502N filter indicate that the profile had remained unchanged but had shifted towards the lower wavelength side by 2.9A. Using the new profiles, we investigated the 'wrong-sided' brightness phenomenon displayed in the SW portion of the Orion Bright Bar. It was concluded that the anomaly is not an artifact of filter contamination but is real and the result of a geometric effect. In short, it is due to a 'bump' in the nebula.

Jupiter's magnetosphere does not rigidly rotate with the System III angular rate. There is a corotation lag as a function of distance in the Jovian magnetosphere. The dominant rotational component, aside from System III, is a 3% longer period (System IV). System IV could be interpreted as a sideband of System III being amplitude-modulated by the 14.1-day period. Whether System IV is an independent Jovian coordinate or just a sideband is investigated in this thesis. The 9.64 hour period does not appear in periodogram analyses of EUV data from Voyager 2 and nKOM data from Voyager 1 and 2. Therefore, it is concluded that System IV is not a sideband and it is independent of System III. Through harmonic filtering, a signal with a 12.5-day period in the EUV data is found. It is suggested that the 12.5-day period is a solar-wind effect. (Abstract shortened with permission of autor.)

Calculations have been made of the new Rice University gamma ray astronomical telescope, over the energy interval 0.1 MeV-5.0MeV. A computer program, ACCEPT, was used and simulations performed on the Rice University's AS-9000 mainframe. For gamma ray fluxes at 3.5 g cm$\sp{-2}$ atmospheric depth over Palestine, Texas, efficiency curves for the principal detector have been obtained. Energy deposition profiles have been calculated and compared to previous simulations and observations. The study shows the simulation code ACCEPT to be more machine dependent than previously believed.

In this work I investigate the possibility of Type II supernovae being the origin for positrons producing observed annihilation radiation observed toward the Galactic center. It was my contention that the decay of $\sp{56}$Co coupled with falling densities would allow for the production and extended existence of positrons in the supernova outflow. Supernova 1987A has prompted many people to construct models of supernova outflow. I use the results of two existing models as the initial conditions in my models. I have created both an analytic and a computer model for the survival of positrons. These models show that while Type II supernovae fall short of the needed production of surviving positrons, the lower densities existing in Type I supernovae may be a more promising source.

This thesis is a theoretical study about the Earth's tail plasma sheet with regard to two aspects: the equilibrium structure for the anisotropic pressure, and the ideal-MHD ballooning stability. By adopting a stretched magnetotail model where ion motions are generally nonadiabatic, and assuming that the anisotropy resides only in the electron pressure tensor, it is shown that the magnetic field lines with $\rm p\sb\perp > p\sb\Vert$ are less stretched than the isotropic cases. As the parallel pressure p$\sb\Vert$ exceeds the perpendicular pressure p$\sb\perp$ approaching the conventional marginal firehose limit, $\rm p\sb\Vert = p{\sb\perp}$ + B$\sp2$/$\mu\sb0$, the magnetic field lines are more and more stretched. It is also shown that the current density is highly enhanced at the same limit, a situation that might be subject to a microscopic instability. However, we also emphasize that such an enhancement in the current density is heavily localized near the z = 0 plane, and thus it is unclear if such a microscopic instability can significantly alter the global configuration of the tail. It is further argued, in terms of the radius of the field curvature versus the particle's gyroradius, that the conventional adiabatic description of electrons may become questionable, very close to the conventional marginal firehose limit. To study the ideal-MHD ballooning mode, we first adopt a hard ionospheric boundary condition where the perturbation is required to vanish at the ionospheric foot points. For such a hard boundary condition, an "untypical" magnetic field configuration is found to be unstable to a ballooning mode that is antisymmetric about the equatorial plane while most of the "typical" tail plasma-sheet configurations are stable against the ideal-MHD ballooning mode. The unstable magnetic field model, however, does not look like the average observation-based model, but rather resembles some of the characteristics of the steady-state magnetic field models by Hau (1989, 1991). In addition, a physical argument is presented to show that the hard ionospheric boundary condition is the most appropriate simple boundary condition for the Earth's plasma sheet.

This thesis aims to compute the mean age of interstellar dust particles using a sputtering and recycling model originally formulated by Liffman and Clayton. The ages of the particles are evaluated after a period of 6 $\times$ 10$\sp9$ years, deemed here to be the age of our Galaxy, when the Solar System formed. I find a correlation between resulting particle sizes and their mean age. The consequence of this correlation is that if interstellar particles can be sorted dynamically by size, then the conglomerations of these size populations as dust grains will be composed of matter that is of differing ages. This age variation in grains of differing sizes will produce isotopic variations, or anomalies, due to the time dependent nature of secondary versus primary nucleosynthesis. The most important example of such an observed anomaly is the 5% enrichment of $\sp{16}$O in inclusions of Al$\sb2$O$\sb3$ in meteorite structures relative to the abundance of $\sp{16}$O in the solar gas. (Abstract shortened with permission of author.)