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.
During both Voyager encounters with the saturnian system, the Planetary Radio Astronomy experiment detected strong discrete episodic bursts of radio emission, termed Saturn electrostatic discharges (SED). An examination of Voyager 2 photopolarimeter data now reveals a narrow feature (possibly a gap) in Saturn's B ring. A single, unique object appears to be responsible for both the SED and this feature.
Observations and theories of particle acceleration in solar flares are reviewed. The most direct signatures of particle acceleration in flares are gamma rays, X-rays and radio emissions produced by the energetic particles in the solar atmosphere and energetic particles detected in interplanetary space and in the Earth's atmosphere. The implication of these observations are discussed. Stochastic and shock acceleration as well as acceleration in direct electric fields are considered. Interplanetary particle propagation is discussed and an overview of the highlights of both current and promising future research is presented.
Detection of several absorption recombination radio lines of carbon at 26 MHz in Cas A direction resulted in an attempt to select similar situations (a gas cloud projection on the intense source of the nonthermal radio emission) that are promising for detecting lines of such a kind. Recommendations are given for observations to be made.
Magnetospheric radio emissions, Saturn electrostatic discharges, inferred source locations, and emission theories are addressed.
A few interplanetary electron density scales which were derived from the analysis of interplanetary solar radio burst are discussed and compared to a model derived from 1974 to 1980 Helios 1 and 2 in situ density observations made in the 0.3 to 1.0 AU range. The Helios densities were normalized to 1976 with the aid of IMP and ISEE data at 1 AU, and were then sorted into 0.1 AU bins and logarithmically averaged within each bin. The best fit to these 1976-normalized, bin averages is N(R(AU)) = 6.1 R(-2.10)/cu cm. This model is in rather good agreement with the solar burst determination if the radiation is assumed to be on the second harmonic of the plasma frequency. This analysis also suggests that the radio emissions tend to be produced in regions denser than the average where the density gradient decreases faster with distance than the observed R(-2.10).
Results are presented of optical mapping of 29 QSOs, together with results of VLA observations of 16 of the optically observed objects. Principal results are that QSOs to z = 0.45 have extended nebulosity, the average ratio of nuclear to fuzz luminosity, corrected for resolution, is about 0.5, some 8 times higher than Seyfert I values, the average fuzz luminosity is -21.5, fainter than giant ellipticals, and fuzz morphology does not resemble E or S galaxies, but is very similar to Seyfert I's to similar luminosity limits. In some cases, indications of spiral structure are seen, and a large fraction of asymmetrical morphology is noted. In the QSO 0241 + 622, steep spectrum radio emission is found displaced from the central source exactly along the minor optical axis.
It is suggested that the absorbing characteristics of sulfuric acid vapor appear to reconcile what had been thought to be an inconsistency among measurements and deductions regarding the constituents of the Venus atmosphere and radio occultation, radar reflection, and radio emission measurements of its opacity. Laboratory measurements of sulfuric acid, sulfur dioxide, water vapor, and carbon dioxide are used to model relative contributions to opacity as a function of height in a way that is consistent with observations of the constituents and absorbing properties of the atmosphere. It is concluded that sulfuric acid vapor is likely to be the principal microwave absorber in the 30-50 km altitude range of the middle atmosphere of Venus.
A discussion is presented of the constraints imposed by X-ray, UV and optical observations on the absorbing material in the Seyfert 1.5 galaxy NGC 4151, comparing said observations with both photoionization model predictions of broad line region clouds and models of the narrow line region gas. The weakness of both semiforbidden C III 1909 and the broad component of H-alpha relative to C IV 1549, in conjunction with the absence of an absorption Balmer jump, indicate a broad line region ionization parameter that is greater in NGC 4151 than in QSO clouds by a factor of 30. The present calculations suggest that narrow line region clouds have a composition similar to extragalactic giant H II regions, with the H line spectrum showing that dust is mixed with narrow line region gas. It is hypothesized that broad line region clouds are likely to be in a radiatively driven wind, and it is shown that such clouds are opaque to radio emission.
Radio, optical and X-ray observations are presented of the peculiar radio galaxy 3C 433, a Seyfert 2 object with luminosity an order of magnitude greater than that expected from its complex, shell-type morphology. Observations conducted at 6 and 12 cm with the VLA and at 21 cm with the Westerbork telescope show a striking asymmetry between the northern and southern radio emissions, and an overall X-shaped morphology. Optical observations using the Video Camera and High Gain Video Spectrometer on the 4-m telescope and the Intensified Image Dissector Scanner on the 2.1-m telescope at Kitt Peak confirm the identification of the source with a pair of bright galaxies. Observations in the X-ray from the Einstein Observatory IPC reveal an unresolved source at the position of 3C 433, as well as two serendipitous X-ray sources. The observations may be used to explain the overall structure of the source either in terms of tidal torquing or precessing models of double galaxies; however, it is argued that the tidal torquing model requires fewer assumptions to account for the brightness asymmetry.
Burke and Franklin (1955) discovered radio emissions from Jupiter at 22.2 MHz. Subsequent observations established the strong control of the decametric emissions by the satellite Io. The Voyager encounters with Jupiter in 1979 have resulted in a dramatic increase in detailed knowledge of the plasma properties of the Jovian magnetosphere. The Io plasma torus is discussed, taking into account the Voyager plasma science experiment, positive-ion temperatures in the torus, electron distribution functions in the torus, elementary-charge concentrations in the torus, positive-ion composition in the torus, and plasma velocities in the torus. The Io flux tube is considered along with the middle magnetosphere and the outer magnetosphere. Attention is given to the sources of plasma, aspects of diffusive transport, questions of inertial loading, and the existence of nonazimuthal flow velocities in the middle magnetosphere.
VLBI 2.3 GHz observations of a strong radio flare of the binary star system Circinus X-1 indicate a radio source flaring component angular size of 0.0015-0.015 arcsec. This is equivalent to a linear size of 15-150 AU at the 10 kpc distance of Circinus X-1, although interstellar medium scattering may have enlarged the apparent angular source size. Since the radio source quiescent component, observed prior to the flare, had an angular size greater than 0.2 arcsec (equivalent to more than 2000 AU at 10 kpc), the quiescent radio emission comes from a region much larger than that proposed in recent models for Circinus X-1. The quiescent component appears to be variable on a time scale of years, and is probably fueled by the Circinus X-1 binary system.
Characterizations of the Saturn magnetospheric activities that have been made possible through data gathered by means of the Pioneer 11 and Voyagers 1 and 2 flybys are reviewed. The spacecraft data confirmed the presence of a Saturn magnetosphere, which features inward diffusion and energization of trapped energetic particles as well as cosmic ray albedo neutron decay as a source of inner belt protons. A dense plasma was identified in the region covering the outer magnetosphere to the magnetopause, which extends outward 17.3-23.6 Saturn radii on the sunward side and from 30.3-70 radii on the far side, according to the satellite measurements. Characteristics of the particle populations and behaviors of the outer magnetosphere, the slot region, the inner magnetosphere, and the ring region are reviewed, as are those of the magnetic field, the solar wind-magnetospheric interaction, and the Titan-magnetospheric interaction are described. Further investigation of the longitudinal asymmetry of decimetric radio emissions from Saturn is recommended.
Type III radio storms are observed by the radio experiment on board the International Sun Earth Explorer 3 out to 0.5-0.8 AU from the Sun, at a rate of 2 to 3 storms per solar rotation near solar maximum. They correlate with the type I and type III radio storms observed at higher frequencies, originating closer to the Sun. They are associated with an almost continuous injection of suprathermal electrons into the interplanetary medium. Some of the properties of the regions where the particles propagate are discussed, using the radio emission as a tracer.
The type 2 radio burst was identified as a shock propagating through solar corona. Radio emission from shocks travelling through the interplanetary (IP) medium was observed. Using the drift rates of IP type II bursts the velocity characteristics of eleven shocks were investigated. It is indicated that shocks in the IP medium undergo acceleration before decelerating and that the slower shocks take longer to attain their maximum velocity.
The energetic particles and the electric, magnetic, and electromagnetic fields associated with the Earth, the Sun, the Moon, the planets, comets, and the interplanetary medium are examined. Matters under current investigation are following: energetic particles trapped in the Earth's magnetic field, origin and propagation of very low frequency radio waves and electrostatic, the magnetospheres of Jupiter, Saturn and prospectively Uranus and Neptune, diffusion of energetic particles in Saturn's magnetosphere, radio emissions from Jupiter and Saturn, solar modulation and the heliocentric radial dependence of the intensity of galactic cosmic rays, interplanetary propagation and acceleration of energetic particles, the theory of wave phenomena in turbulent plasmas, and basic wave-particle-chemical processes in the ionospheric plasma.
The Cosmic Background Explorer (COBE) satellite, its instruments, and its scientific mission are discussed. The COBE radiometer is considered, and measurement of galactic radio emission with masers is reviewed. Extragalactic radiation and zodiacal dust are mentioned briefly.
Five of the extreme ultraviolet channels (L-alpha, L-beta, He I, He II, Fe XV) measuring irradiance fluctuations on board the AE-E satellite between 1977 and 1980 have been studied in detail. It is shown that the daily variations correspond very closely to the daily variations in solar radio emission (F10.7), but that the UV data are afflicted with serious and to date unrecognized calibration changes during the period of operation of the instruments. In order to correct for these changes, a statistical analysis is carried out, and a set of corrections to the raw data is suggested. The resulting, now uniform, data are then compared with rocket measurements (L-alpha) and data acquired onboard the AE-C satellite (L-beta). Finally the remaining discrepancies are discussed. After concluding that they are below the overall level of uncertainties, a first-order 10-year run of EUV irradiances derived from F10.7 data is proposed. This estimate includes the ratio of irradiance levels between the maxima of solar cycles 20 and 21 and the intervening minimum.
The results of extragalactic observations made with the imaging proportional counter (IPC) on board the Einstein Observatory satellite are reported. Quasars were found to be strong X ray sources with correlations between the X ray and optical luminosities; strong radio emissions also correlated well with X ray luminosities. The data indicate that the ratio of the X ray and optical luminosities is inversely proportional to the optical luminosity. Active galactic nuclei are also strong X ray sources. A continuity exists between the X ray behavior of Seyfert galaxies and quasars, while BL Lac objects exhibit X ray variability exceeding that of quasars, although some BL Lac objects may be quasars. The X ray data revealed evolutionary phases in galactic cluster structures.