SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The area in the vicinity of the H II region W3 is mapped at an effective wavelength of 69 microns with high angular resolution (1 min) using the 102-cm balloon-borne telescope. The main continuum source, W3, shows a partially resolved complex structure with a FWHM size of 1.8 min. The radio sources W3(OH) and G133.8 + 1.4 are also observed as well as three faint sources not associated with known radio emission.
The geometry and electron gyrofrequency were calculated for both the North and South feet of the Io-threaded flux tube at several altitudes as a function of sub-Io longitude for various multipole field models. The models predict a maximum surface gyrofrequency equal to the observed high frequency limit of the decameter-wave radio emission (DAM) and tend to favor a mechanism involving transverse propagation from a source in the Northern hemisphere. Calculations indicate that the beaming pattern of the emission may be determined by reflection from the ionosphere rather than by inherent beaming from the source region.
A model is presented that suggests that plasma sheaths form between the ionospheric plasma moving with Io and the ambient plasma corotating with Jupiter. Potentials across these sheaths could be as high as 580 kV which is the motional emf across Io's ionosphere. Electrons and ions can be accelerated across these sheaths. The sheaths may exist at the top of the Io ionosphere with characteristic thicknesses of 1/4 kilometers. The model is consistent with the Pioneer observations of 0.15 MeV electrons at the inner edge of Io's L-shell and the enhanced number density of low-energy protons at the outer edge. Ion sputtering of the Io surface is discussed and may explain the presence of atomic hydrogen and sodium in the vicinity of Io. Also these accelerated particles may be important to the formation of the Io ionosphere. High electron flux which may lead to decametric radio emissions, Jovian atmospheric heating and optical and X-ray emissions is also discussed.
Included in this discussion of findings regarding the planet Jupiter are atmospheric characteristics, weather, the magnetosphere, radiation belts, radio emission, natural satellites, possible origins, the Great Red Spot, the interior and the possibility of life.
This review summarizes both the direct spacecraft observations of nonrelativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the sun and in the interplanetary medium. These observations bear on the basic astrophysical process of particle acceleration in tenuous plasmas. We find that in many small solar flares, the nearly 5-100 keV electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. These electrons may produce the other flare electromagnetic emissions through their interactions with the solar atmosphere. In large proton flares these electrons may provide the energy to eject material from the sun and to create a shock wave which could accelerate nuclei and electrons to much higher energies.
The NASA Goddard Space Flight Center radio astronomy experiment on Helios, identified as Experiment 5c, has sixteen observing frequencies over the range of 26.5 to 3000 kHz. The antenna consists of two extendible 15-m booms, forming an electric dipole, two high-impedance preamplifiers located at the root of the booms, and the 16-channel radiometer. Important information about propagation conditions, such as absorption, scattering and refraction, are expected from observations of radio emission regions at distances between 1 and 0,3 AU.
The UV Ceti-type stars, YZ Canis Minoris, AD Leonis, and Wolf 424 AB, were monitored for 57.8 hours from January 15 to February 22, 1974, using the 1000-foot (305-m) radio telescope at Arecibo, Puerto Rico, and the 91-cm or 76-cm reflector at McDonald Observatory. Radio observations were made at frequencies of 430, 318, and 196 MHz, and optical monitoring was done in the Johnson U or B band, the Stromgren u band, or white light. During the period of simultaneous observations, 62 optical flares were detected. A total of 13 RF flares were independently identified, of which 10 reached maximum flux within 10 min of the peak time of an optical flare. Using times of optical-flare events as reference data, an additional 15 cases of radio enhancements associated with optical flares are identified. The most probable delay interval between the optical-flare maximum and 318-MHz radio peak was found to be 0 to 5 min, with the optical flare occurring first. Aside from this statistical delay of peak occurrence and a general tendency for radio and optical flares to be associated, no systematic correlations of optical and radio amplitudes or morphology were found. The possible consequences of the radio emission's being due to a coherent process are discussed.
This paper presents an analysis of observations of large intensities of low-energy protons deep within the Jovian magnetosphere which were made by Pioneer 10 with an electrostatic plasma analyzer having an energy range from 108 eV to 4.80 keV. A proton density profile plotted against the earth-received time of the satellite signals reveals four significant plasma features: (1) a 'plasmasphere' with relatively high proton densities, located inside the flux tubes of Io at 6 Jupiter radii and extending toward the planet to at least 2.8 radii; (2) a 'plasmapause', on which Io's flux tubes are positioned; (3) a sparse sporadic zone beyond Io, extending out to 8 Jupiter radii; and (4) a ring current beginning at 8 radii, which extends outward in the form of a thin plasma disk and in which Europa is embedded. The thermal energies of the protons in each zone are determined, and it is suggested that Jupiter's ionosphere is the source of these protons. It is noted that the relationship of Io to the 'plasmapause' is probably of fundamental importance to that satellite's modulation of Jovian decametric radio emissions.
Radio emissions were measured by the Hawkeye 1 satellite at low altitudes over the Southern Hemisphere along the auroral field lines, in the region where the intense nightside auroral kilometric radiation is believed to be generated. These measurements provide new evidence on the mode of propagation and origin of the auroral kilometric radiation. At low altitudes the auroral kilometric radiation is consistently observed to have a low frequency cutoff at the local electron gyrofrequency, f(-) sub g. Since the electron plasma frequency, f(-) sub p, is usually much smaller than f(-) sub g in the region where these observations are obtained, this cutoff corresponds closely with the propagation cutoff for the right-hand mode of propagation. These observations, therefore, provide a strong indication that the auroral kilometric radiation is right-hand polarized in agreement with previous conclusions made on the basis of the angular distribution of this radiation.
The paper summarizes discussions held between solar physicists and plasma physicists on the interface between solar and plasma physics, with emphasis placed on the question of what laboratory experiments, or computer experiments, could be pursued to test proposed mechanisms involved in solar phenomena. Major areas discussed include nonthermal plasma on the sun, spectroscopic data needed in solar plasma diagnostics, types of magnetic field structures in the sun's atmosphere, the possibility of MHD phenomena involved in solar eruptive phenomena, the role of non-MHD instabilities in energy release in solar flares, particle acceleration in solar flares, shock waves in the sun's atmosphere, and mechanisms of radio emission from the sun.
A high-field triaxial fluxgate magnetometer was mounted on Pioneer 11 to measure the main magnetic field of Jupiter. It is found that this planetary magnetic field is more complex than that indicated by the results of the Pioneer 10 vector helium magnetometer. At distances less than 3 Jupiter radii, the magnetic field is observed to increase more rapidly than an inverse-cubed distance law associated with any simple dipole model. Contributions from higher-order multipoles are significant, with the quadrupole and octupole being 24 and 21 percent of the dipole moment, respectively. Implications of the results for the study of trapped particles, planetary radio emission, and planetary interiors are discussed. Major conclusions are that the deviation of the main planetary magnetic field from a simple dipole leads to distortion of the L shells of the charged particles and to warping of the magnetic equator. Enhanced absorption effects associated with Amalthea and Io are predicted.
Plasma wave electric field measurements with the solar orbiting Helios spacecraft have shown that intense (approximately 10 millivolts per meter) electron plasma oscillations occur in association with type III solar radio bursts. These observations confirm the basic mechanism, proposed in 1958, that type III radio emissions are produced by intense electron plasma oscillations excited in the solar corona by electrons ejected from a solar flare.
A combined theoretical and observational approach is used to construct models of the inner corona applicable to quiet open-field regions and coronal holes. These models, extending from the top of the transition region at about 1.003 solar radii out to 3 solar radii, are calculated by employing parameters that describe the coronal geometry and heating. Thermal conductivity, heating, radiative losses, and solar-wind convection are included in the full energy-balance equation, which is integrated to obtain density and temperature models; the unknown heating term is parameterized in terms of the mechanical flux incident at the base and the characteristic scale height for the dissipation of this flux; and boundary conditions at the base are fixed by EUV-derived models of the transition region. Two representative models, one for a coronal hole and one for a quiet region, are examined in detail as illustrative examples of the technique used. It is noted that the models obtained predict most of the pertinent observations reasonably well but significantly overestimate the radio emission at 80 and 160 MHz and significantly underestimate the intensity of the Fe XV line at 284 A, especially in coronal holes.
A study based on data from Hawkeye 1, Imp 6 and Imp 8 satellites has shown that the intense kilometric radio emissions generated over the nightside auroral regions are beamed into a cone-shaped region whose axis of symmetry is tilted away from the magnetic axis of the earth, toward evenings, by about 20 deg. The solid angle of this emission cone increases systematically with increasing frequency, varying from about 1.1 sr at 56.2 kHz to about 3.5 sr at 178 kHz.
A selection of infrared variable stars was studied at wavelength 2.7 microns during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. The correlation of 2.7 micron and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 microns.
An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.
Gamma ray data favor a cosmic ray propagation halo comparable with the thickness of the primary radio emission disk of our Galaxy and the halo seen around NGC891.
A review is presented of current experimental and theoretical knowledge of plasma waves in the solar wind, with comments on the scientific importance of obtaining plasma wave measurements in the region near the sun with the solar probe. The waves discussed include the acoustic waves and shocks which are thought to be the primary source for heating the solar corona, Alfven waves, ion-cyclotron waves, whistler-mode turbulence, ion-acoustic waves, and electron plasma oscillations associated with solar radio emissions. A discussion is presented of the types of measurements which would be needed to study these waves on the solar probe, the constraints imposed on the spacecraft and the research and development which would be needed to provide the necessary instrumentation.