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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Periodic escape of relativistic electrons from the Jovian magnetosphere

We adopt a model in which the Jovian magnetospheric tail is forced open by plasma that is accelerated out of the ionosphere by the centrifugal force of corotation. Any longitudinal asymmetry that exists in the ionospheric plasma source and/or the planetary magnetic field will cause a diurnal variation in the radial extent of the trapping region for energetic electrons. This diurnal variation in the extent of the particle trapping region can result in a time-dependent loss of relativistic electrons from the Jovian magnetosphere, modulated at the planetary rotation period. The diurnal trapping process may be relevant to the observation of electron pulses in interplanetary space during the Pioneer 10 approach to Jupiter.

Hill, T. W.↗
NASA NTRS1976

Solar particle emission

A variety of flare-associated and recurrent solar particle events are analyzed using the technique of 'mapping' the fluxes back to the estimated high coronal longitude of the interplanetary field line passing through the spacecraft. Often it is possible to separate temporal from spatial effects as well as those of coronal and interplanetary propagation. Considerable regularity appears in the coronal injection profiles deduced during events in 1969, 1972 and 1973, implying extended acceleration of protons about 0.3-7.5 MeV, helium and medium nuclei about 1 MeV/nuc and relativistic electrons. Clear associations are found in 1973 among energetic particle injection profiles, solar wind stream sources, and low coronal magnetic structure.

Roelof, E. C.↗
NASA NTRS1977

Analysis of magnetic fields using variational principles and CELAS2 elements

Prospective techniques for analyzing magnetic fields using NASTRAN are reviewed. A variational principle utilizing a vector potential function is presented which has as its Euler equations, the required field equations and boundary conditions for static magnetic fields including current sources. The need for an addition to this variational principle of a constraint condition is discussed. Some results using the Lagrange multiplier method to apply the constraint and CELAS2 elements to simulate the matrices are given. Practical considerations of using large numbers of CELAS2 elements are discussed.

Frye, J. W.↗
NASA NTRS1977

Accretion flows in binary X-ray systems

Recent developments in the study of accretion flows in binary X-ray systems are reviewed, concentrating on issues concerning the gas flows rather than the radiation mechanisms. A model for Her X-1 is presented which illustrates the main structures expected to exist in the case where mass transfer is by Roche-lobe overflow and the X-ray source is a rotating magnetized neutron star. A model for Cyg X-1 is given which shows the accretion-flow structures to be expected if the compact object is a black hole, including an accretion wake and a very small accretion disk around the black hole. Physical parameters of the accretion flows in these two instances are examined along with some scale lengths that may be derived from these parameters by dimensional analysis. Detailed attention is given to neutron-star magnetospheres (for slow, intermediate, and fast rotators), accretion-disk structure, accretion from stellar winds, and the relationship between X-rays and the gas dynamics of accretion flows. It is suggested that accretion flows in binary X-ray systems be observed directly by means of high-resolution UV and X-ray spectroscopy.

Mccray, R.↗
NASA NTRS1981

Directionality effects in the transfer of X-rays from a magnetized atmosphere: Beam pulse shape

A formalism is presented for radiation transfer in two normal polarization modes in finite and semiinfinite plane parallel uniform atmospheres with a magnetic field perpendicular to the surface and arbitrary propagation angles. This method is based on the coupled integral equations of transfer, including emission, absorption, and scattering. Calculations are performed for atmosphere parameters typical of X-ray pulsars. The directionality of the escaping radiation is investigated for several cases, varying the input distributions. Theoretical pencil beam profiles and X-ray pulse shapes are obtained assuming the radiation is emitted from the polar caps of spinning neutron stars. Implications for realistic models of accreting magnetized X-ray sources are briefly discussed.

Meszaros, P.↗
NASA NTRS1982

Microwaves and hard X-rays from solar flares - Multithermal and nonthermal interpretations

It is generally accepted that the hard X rays and centimeter-wavelength (microwave) radio emission from impulsive solar flares come from a common source. The present investigation is concerned with the development of a model for impulsive hard X rays and microwaves under the assumption that they arise from the same distribution of electrons, possibly, but not necessarily, from the same volume of space. An examination is conducted of a model in which the hard X rays and microwaves are produced in a homogeneous volume by a power-law electron distribution (nonthermal model). An investigation is also performed of a multithermal model in which the hard X rays and microwaves come from an inhomogeneous source, a nest of magnetic arches in which the highest temperature electrons are confined to a small core, and where, away from the core, the temperature decreases. It is found that more or less satisfactory models can be constructed using either multithermal or nonthermal, power-law electron distributions.

Dulk, G. A.↗
NASA NTRS1983

Jupiter's magnetic field and magnetosphere

Among the planets of the solar system, Jupiter is unique in connection with its size and its large magnetic moment, second only to the sun's. The Jovian magnetic field was first detected indirectly by radio astronomers who postulated its existence to explain observations of nonthermal radio emissions from Jupiter at decimetric and decametric wavelengths. Since the early radio astronomical studies of the Jovian magnetosphere, four spacecraft have flown by the planet at close distances and have provided in situ information about the geometry of the magnetic field and its strength. The Jovian magnetosphere is described in terms of three principal regions. The inner magnetosphere is the region where the magnetic field created by sources internal to the planet dominates. The region in which the equatorial currents flow is denoted as the middle magnetosphere. In the outer magnetosphere, the field has a large southward component and exhibits large temporal and/or spatial variations in magnitude and direction in response to changes in solar wind pressure.

Acuna, M. H.↗
NASA NTRS1984

Electron-positron pair equilibrium in strongly magnetized plasmas

Steady states of thermal electron-positron pair plasmas at mildly relativistic temperatures and in strong magnetic fields are investigated. The pair density in steady-state equilibrium, where pair production balances annihilation, is found as a function of temperature, magnetic field strength and source size, by a numerical calculation which includes pair production attenuation and Compton scattering of the photons. It is found that there is a maximum pair density for each value of temperature and field strength, and also a source size above which optically thin equilibrium states do not exist.

Harding, A. K.↗
NASA NTRS1985

What determines the location of satellites and planets?

The discrete structural pattern in the distribution of the satellites and planets around their primaries has since its discovery been thought to hold the key to the origin and evolution of the solar system. Different attempts to rationalize this distribution are reviewed with emphasis on theories with foundation in verifiable physical processes. Foremost among these is the band structure theory, which relates the emplacement of interstellar dust and gas source material around the magnetized primarily to the critical velocity for ionization of the four major interstellar gas components. The uncertainties, that are inevitable in all reconstructions, are in this theory compensated by the support from precise manifestations of the 2/3 effect in the Saturnian ring system and in the asteroid belt, and by the reproduction of related phenomena in laboratory and space experiments.

Arrhenius, G.↗
NASA NTRS1986

Tandem-Mirror Ion Source

Improved ion source produces beam of ions at any kinetic energy from 1 to 1,000 eV, with little spread in energy or angle. Such ion beams useful in studies of surface properties of materials, surface etching, deposition, and development of plasma-diagnostic instrumentation. Tandemmirror ion source uses electrostatic and magnetic fields to keep electrons in ionization chamber and assure uniform output ion beam having low divergence in energy and angle.

Biddle, A.↗
NASA NTRS1986

X-rays from the magnetic white dwarf PG 1658 + 441

X-ray emission has been detected from PG 1658 + 441, a hot, isolated, magnetic white dwarf. The source was first detected in an Einstein IPC observation and was later identified in an Exosat channel multiplier array observation. Both imaging observations were motivated by an attempt to find the optical counterpart to the HEAO 1 soft X-ray source H1659 + 44. Spectral analysis, however, indicates that H1659 + 44 and PG 1658 + 441 are unrelated. The broad-band spectrum of this DA white dwarf can be explained as emission from a homogeneous, high-gravity, pure hydrogen atmosphere with a temperature near 28,000 K. The observations of PG 1658 + 441 support the suggestion that a correlation exists between temperature and helium abundance in white dwarf atmospheres.

Pravdo, S. H.↗
NASA NTRS1986

Radio emission from binary stars

Radio emission from binary star systems; characteristics of the binary systems inferred from the radio observations; and the reasons for the activity are reviewed. Binary stars with two main sequence stars, with one normal star and a white dwarf, and those containing a neutron star or a black hole are described. Energy may be directly available as matter falls into the potential well of a compact object. Electromagnetic induction effects may occur due to relative motions of magnetic fields and matter. By enforcing rapid rotation, binaries can induce strong dynamo action and hence generate free energy in the form of intense, complex, evolving magnetic fields. Whatever the source of energy, the observations at radio and X-ray wavelengths demonstrate that electrons are accelerated to high energies (mildly relativistic and, ultrarelativistic). Observed or inferred radio brightness temperatures range up to 10 to the 15th power K or more, implying coherent emission for sources brighter than 10 billion K.

Dulk, George A.↗
NASA NTRS1986

Magnetic connection for Saturn's rings and atmosphere

Latitudinal variations in images of Saturn's disk, upper atmospheric temperatures, and ionospheric electron densities are found in magnetic conjugacy with features in Saturn's ring plane. It is proposed that these latitudinal variations are the result of a variable influx of water transported along magnetic field lines from sources in Saturn's ring plane. These features are thus the surface expression of an electromagnetic erosion mechanism which transports water (in the form of high charge-to-mass ratio particles) from the rings to the atmosphere.

Connerney, J. E. P.↗
NASA NTRS1987

Crustal geologic studies with Magsat and surface magnetic data

The contributions during the last quadrennium are discussed, which involved both Magsat and aeromagnetic data, including new techniques for interpreting this data, specific intended to understand the connection between magnetic anomalies and the magnetic mineralogy of their sources.

Mayhew, Michael A.↗
NASA NTRS1987

Kinetic aspects of magnetotail dynamics - Observations

The observed kinetic (as opposed to fluid) aspects of particle behavior in the geomagnetic tail are discussed. Such behavior has been observed from thermal plasma energies to energies a few MeV or more. The importance of recognizing and analyzing the kinetic behavior of tail particles is that it provides a powerful diagnostic tool for inferring the state of the local and remote environment and the mechanisms responsible for observed tail dynamics, and a way of determining when fluid analyses (relying upon moments such as bulk velocity and temperature) may be misleading. Thus kinetic analyses provide a valuable complement to fluid-dynamics-based studies of the collective behavior of geomagnetic tail particles. Observed kinetic effects can be analyzed to examine spatial gradients; convection electric fields, distances to source regions, source-region characteristics, magnetic-field topology, heating/acceleration mechanism, boundary characteristics, and remote mechanisms affecting local particle distributions.

Mitchell, D. G.↗
NASA NTRS1989

Transient coronal extreme ultraviolet emission before and during the impulsive phase of a solar flare

Transient coronal EUV emission, recorded in an emission line of Fe XI at 180.4 A, has been observed prior to and during the initial stages of a solar flare. This emission provides direct evidence of the interactions between the lower corona and the chromosphere during flare initiation. The first EUV enhancement was correlated with activation and eruption of a filament, extended over a distance of about 120,000 km, and had an emission maximum at the site of filament disruption. A moving source of EUV emission also appeared along the trajectory of the erupting filament as it accelerated through the low corona. The mass of this source is estimated to be greater than that of the initial filament or surrounding corona, implying an additional mass ejection from the chromosphere. EUV emission during the impulsive phase of the flare consisted of transient sources along the photospheric magnetic neutral line, with intervening regions of lesser intensity that are interpreted as transient coronal loops below the erupting filament.

Neupert, Werner M.↗
NASA NTRS1991

Geomagnetic activity associated with earth passage of interplanetary shock disturbances and coronal mass ejections

Coronal mass ejection events (CMEs) are important occasional sources of plasma and magnetic field in the solar wind at 1 AU, accounting for approximately 10 percent of all solar wind measurements in the ecliptic plane during the last solar activity maximum. Using a recently appreciated capability for distinguishing CMEs in solar wind data in the form of counterstreaming solar wind electron events, this paper explores the overall effectiveness of shock wave disturbances and CMFs in general in stimulating geomagnetic activity. The study is confined to the interval from mid-August 1978 through mid-October 1982, spanning the last solar activity maximum, when ISEE 3 was in orbit about the L1 Lagrange point 220 Re upstream from earth. It is found that all but one of the 37 largest geomagnetic storms in that era were associated with earth passage of CMEs and/or shock disturbances, with the large majority of these storms (27 out of 37) being associated with interplanetary events where earth encountered both a shock and the CME driving the shock (shock/CME events). Although CMEs and/or shock disturbances were increasingly the cause of geomagnetic activity as the level of geomagnetic activity increased, many smaller geomagnetic disturbances were unrelated to these events.

Gosling, J. T.↗