Saturn as a radio source
Magnetospheric radio emissions, Saturn electrostatic discharges, inferred source locations, and emission theories are addressed.
Kaiser, M. L.↗
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Basic experimental study of the coupling between flow instabilities and incident sound
Whether a solid trailing edge is required to produce efficient coupling between sound and instability waves in a shear layer was investigated. The differences found in the literature on the theoretical notions about receptivity, and a need to resolve them by way of well-planned experiments are discussed. Instability waves in the shear layer of a subsonic jet, excited by a point sound source located external to the jet, were first visualized using an ensemble averaging technique. Various means were adopted to shield the sound reaching the nozzle lip. It was found that the low frequency sound couples more efficiently at distances downstream of the nozzle. To substantiate the findings further, a supersonic screeching jet was tested such that it passed through a small opening in a baffle placed parallel to the exit plane. The measured feedback or screech frequencies and also the excited flow disturbances changed drastically on traversing the baffle axially thus providing a strong indication that a trailing edge is not necessary for efficient coupling between sound and flow.
Ahuja, K. K.↗
Multispacecraft observations of the harmonic structure of Pc 3-4 magnetic pulsations
Harmonically related Pc 3-4 pulsations (7-100 mHz) are observed simultaneously by the three geosynchronous satellites ATS 6, SMS 1, and SMS 2, which are separated 20 deg from one another. At a given instant the frequency of the same harmonic is different from one spacecraft to another and each spacecraft observes a decrease in the fundamental frequency as it moves from morning (15 mHz) to afternoon (10 mHz). This frequency behavior is explained in terms of standing Alfven waves, for which the frequency is determined by the local magnetic field and plasma density. Occurrence of harmonic Pc 3-4 waves only during daytime hours (0400-2000 LT) and their frequency characteristics suggest a broadband energy source located on the dayside. Possible azimuthal wave number m and azimuthal phase velocity V(phi) of the second through fourth harmonics are determined from an unusual interval during which identical harmonic frequencies were observed at SMS 1 and ATS 6. Under the assumption of tailward propagation of constant-phase fronts at the same velocity for all these harmonics, V(phi) of about 1700 km/s is obtained.
Takahashi, K.↗
Coating a Sphere With Evaporated Metal
In vacuum coating apparatus, metal evaporated onto sphere from small source located some distance away. Sphere held in path of metal vapor while rotated about axis that rocks back and forth. One tilting motion particularly easy to produce is sinusoidal rocking with frequency much lower than rotational frequency. Apparatus developed for coating single-crystal sapphire spheres with niobium.
Strayer, D. M.↗
Remanent magnetization model for the broken ridge satellite magnetic anomaly
A crustal model for the interpretation of the Broken Ridge satellite magnetic anomaly was constructed from bathymetric data assuming an Airy-type isostatic compensation. An average crustal magnetization of 6 A.m is required to account for the observed anomaly amplitudes provided that the whole crust is homogeneously magnetized. In contrast, a model representing only the topographic expression of the Broken Ridge, above the surrounding sea floor, requires a magnetization of the order of 40 A.m-1. Since this latter figure is much higher than is to be expected from studies of magnetic properties of oceanic rocks, it is concluded that the majority of the crustal volume of Broken Ridge is magnetized relatively uniformly. The direction of the source magnetization is consistent with an inclination shallower than the present geomagnetic field and close to that of an axial dipole. Since a more northerly source location for Broken Ridge is contrary to the paleolatitude data it is though that the magnetization represents a magnetization obtained by averaging the geomagnetic field direction over a sufficient time to remove secular variation effects. This pattern is indicative of viscous magnetization.
Johnson, B. D.↗
Detection of gamma-ray lines from the direction of the Crab Nebula
The Crab Nebula and its associated pulsar NP0531+21 were observed during a balloon flight of the Durham MK1 high resolution spectrometer on June 6, 1981. The data indicate two significant line features of energies of 404.7 and 1049.8 keV with intensities of (7.2 + or - 2.1) x 0.001 and (12.0 + or - 0.5) x 0.01/5. After subtracting instrumental resolution, the widths of these lines were determined to be (3.5 + or - 1.4) keV and (6.3 + or - 1.6) keV at 404.7 and 1049.8 keV respectively. A third line at 78.8 keV was detected as a transient event with a peak intensity of (1.1 + or - 0.3) x 0.01 photons sq cm/s and a width 1.5 keV. It is shown that all three line features are consistent with a point source located at the Crab.
Owens, A.↗
A coded aperture imaging system optimized for hard X-ray and gamma ray astronomy
A coded aperture imaging system was designed for the Gamma-Ray imaging spectrometer (GRIS). The system is optimized for imaging 511 keV positron-annihilation photons. For a galactic center 511-keV source strength of 0.001 sq/s, the source location accuracy is expected to be + or - 0.2 deg.
Gehrels, N.↗
The Gamma-Ray Imaging Spectrometer (GRIS): A new balloon-borne experiment for gamma-ray line astronomy
High resolution gamma-ray spectroscopy is a relatively new field that holds great promise for further understanding of high energy astrophysical processes. When the high resolution gamma-ray spectrometer (GRSE) was removed from the GRO payload, a balloon program was initiated to permit continued development and improvement of instrumentation in this field, as well as continued scientific observations. The Gamma-Ray Imaging Spectrometer (GRIS) is one of the experiments selected as part of this program. The instrument contains a number of new and innovative features that are expected to produce a significant improvement in source location accuracy and sensitivity over previous balloon and satellite experiments.
Teegarden, B. J.↗
GeV gamma-ray astronomy telescopes with high angular resolution
Gamma-ray telescopes flown on satellites have poor angular resolution with typical point source error circles of a few square degrees. It is shown that a major improvement in angular resolution for the detection of gamma-rays in the GeV region can be obtained with a single crystal as converter. The electron produced by a gamma ray incident at a small angle to a major crystal axis or plane is captured into channeling and radiates gamma rays. The channeling radiation and the electron-positron pair can be detected and yield point source locations with a precision of 5 arcseconds at 10 GeV. This is an improvement of three orders of magnitude on the angular precision of telescopes sensitive to gamma-rays above 50 MeV flown on Satellites.
Mcbreen, B.↗
The wave pattern produced by a point source on a rotating disk
It is pointed out that the boundary layer on a rotating disk is important in stability theory because it provides a particularly simple way to study the important phenomenon of crossflow instability. This type of instability is responsible for early transition on sweptback wings. Mack and Kendall (1983) have studied the wave patterns formed by harmonic point sources in a Blasius boundary layer on the basis that the source uniformly excites all oblique normal modes of the source frequency. The calculation procedure for planar boundary layers was modified to fit the different geometry of the rotating disk and the lack of an axis of symmetry. Calculations were performed of the wave pattern produced by a zero-frequency point source located at the Reynolds number of the artificial roughness element in an experiment conducted by Wilkinson and Malik (1983). The results provided in the present investigation confirm that the experimental wave pattern is a superposition of the complete azimuthal wavenumber spectrum of zero-frequency normal modes with uniform initial amplitude and phase.
Mack, L. M.↗
Radio emissions from the planets earth, Jupiter, and Saturn
The present investigation is concerned with a comparison of the general observable properties of the radio emission from the earth, Jupiter, and Saturn. Attention is given to typical dynamo spectra, average power, average sense of circular polarization, external control of radio emission, source locations, and emission efficiencies. A data summary regarding planetary radio observations is presented in a table. The polarization of northern hemisphere emission for the three planets is considered along with possibilities regarding the total radiated power of the Uranus radio emission.
Kaiser, M. L.↗
Suprathermal H(+) and He(2+) in the distant geomagnetic tail ISEE-3 observations
Preliminary ISEE 3 observations of suprathermal H(+) and He(2+) in the distant geomagnetic tail are summarized, with an emphasis on their energy spectra and composition. Regions found near earth are duplicated in the distant tail, but with various regions more intermixed and less distinct. The H(+) and He(2+) energy spectra in all regions and at all geocentric distances for which observations exist are on average not power laws but are well represented by a given expression. The He(2+)/H(+) ratio of 0.03 to 0.07 in the plasma sheet shows no systematic variation with geocentric distance and is two to three times lower than in the other regions. Well-directed, strong, tailward flows distinguish the near bow-shock/magnetosheath region from the geomagnetic tail and plasma sheet where anisotropies are generally smaller and the flow direction more variable although still tailward, indicating source locations at less than 60 earth radii most of the time.
Gloeckler, G.↗
Saturn as a radio source
Magnetospheric radio emissions, Saturn electrostatic discharges, inferred source locations, and emission theories are addressed.
Kaiser, M.L.↗
A summary of whistlers observed by Voyager 1 at Jupiter
We summarize the Voyager 1 observations of whistlers at Jupiter in order to provide a basis for further analyses of the density profile of the Io plasma torus as well as to support studies of atmospheric lightning at Jupiter. All the whistlers detected by Voyager 1 fell into three general regions in the torus at radial distances ranging beteen 5 and 6 R sub J. An analysis of the broadband wave amplitudes measured by the Voyayer 1 plasma wave instrument and estimates of the peak whistler amplitudes imply the grouping of whistlers was due to variations in the sensitivity of the receiver to whistlers and not to variations in the source or propagation paths of the whistlers. The whistler dispersions are presented in statistical form for each of the three groups of events and analyzed in view of the structure of the Io plasma torus as determined by plasma probe measurements. The results of these analyses give source locations for the whistlers at the foot of the magnetic field lines threading the torus in both hemispheres and over a range of longitudes.
Kurth, W. S.↗
Opening of the magnetic field lines in a fast rotating magnetosphere, with an application to Jupiter
A simple model of a magnetosphere rotating around a rotating Jupiter-like object with a spin-aligned dipolar moment mu is considered. A low-energy plasma is released by inner sources located beyond the corotation radius and is diffused outward through closed lines. The lines form a closed thin equatorial disk, maintaining a quasi-static balance between the centrifugal force and the magnetic tension. Solutions are obtained for the analytical equations characterizing the plasma in the closed region; the structure of the magnetic field outside the disk; and the self-consistent value of the critical radius r sub zero. The analytical solutions are compared to the observed properties of the Jovian magnetosphere, and the results are discussed in detail.
Aly, J. J.↗
Optical observations of new X-ray emitting cataclysmic variables
Two X-ray emitting cataclysmic variables were discovered as a result of a program to identify faint X-ray sources located by the HEAO-A3 modulation collimator experiment. The objects, H0534-581 and 1H0542-407, have similar high excitation spectra with intense emission lines showing broad and narrow components. Photometry shows that H0534-581 and 1H0542-407 have average magnitudes of V=14.9 and 15.7 respectively, leading to Lx/Lopt ratios of 1.5 (typical of dwarf novae in quiescence). While pronounced variability of delta B or = 1.5 mag is observed from both systems, there is no clear evidence for repeatable orbital periods between 1 and 4 hr.
Tuohy, I. R.↗
The detailed intensity distribution of the AKR emission cone
The detailed intensity distribution of auroral kilometric radiation (AKR) at frequencies near the spectral peak of 200 kHz and below, over the entire northern hemisphere at large radial distances, is presented based on 3.5 years of IMP 6 data and four years of Hawkeye data. The time-averaged intensity of the AKR emission cone at frequencies from 178 to 100 kHz is found to be nearly uniform. Evidence contradicts a 'hollow cone' structure. The solid angles for the AKR emission cones studied are in good agreement with previously published results, and there is good agreement with previously determined AKR source location. The time-averaged picture of the AKR emission pattern at 178 kHz is representative of the instantaneous AKR emission. Present theories for the generation and propagation of AKR appear insufficient to explain the observed illumination pattern.
Green, J. L.↗
An imaging proportional counter for a 0.1 to 10 keV X-ray telescope
A xenon multiwire position-sensitive proportional counter (PSPC) with a high degree of long-term stability has been constructed and tested in detail. It is suitable for a 0.1 to 10 keV X-ray telescope such as AXAF, which it would share with detectors having better spatial and spectral resolution. Compared to other detectors, the larger format, higher quantum efficiency, and lower background of the PSPC makes it generally the most useful instrument for observations of diffuse cosmic X-ray sources and associations of sources more extended than a few tenths of a degree in diameter. Given the good spatial linearity, the systematic uncertainty for source locations is finer than an arcsecond. The spatial resolution varies as 0.3 mm/exp 0.5 (keV) over the range 0.2-4 keV, in accordance with theoretical limits determined by the size and the number of electrons in the primary charge cloud.
Gorenstein, P.↗