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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Spatial distribution of cosmic rays in magnetic cycles of the Sun

The space-time distribution of cosmic ray (CR) density is determined from the solution of the anisotropic diffusion equation. The boundary problem is solved in a quasistationary axisymmetric case, taking into account the delay of cosmic rays relative to the cyclic variations of solar activity. The specificty of the modulation model is the use of the empirical dependence of the free path of particles for scattering on the observed latitudinal distribution of solar activity. Another specific feature of the model is an account of an additional effect due to the drift of charged particles towards the helio-equator plane or backward, depending on the direction of the total magnetic field of the Sun.

Alania, M. V.↗
NASA NTRS1984

The multiple modes of interaction of the solar wind with a comet as it approaches the sun

A quasi-steady one-dimensional hydrodynamic model is used to study the various modes of interaction between the solar wind and a medium-bright water-dominated comet approaching the sun. It is found through a series of calculations that at large heliocentric distances (greater than 5 AU) the solar wind penetrates to the surface of the comet. As mass loading reaches a critical value, a standing shock wave is created in the solar wind upstream from the cometary nucleus, and as distance decreases, the cometary atmosphere becomes dense enough to stand off the solar wind ahead of the nuclear surface. It is shown that the present scenario of solar wind/comet interaction is qualitatively valid for comets with different sizes, chemical compositions and optical properties.

Mendis, D. A.↗
NASA NTRS1985

The graviton luminosity of the sun and other stars

Graviton production in electron-electron (e-e) and electron-ion (e-z) scattering is evaluated in the Born approximation. The calculation is compared with that for photon production, that is, Coulomb quadrupole bremsstrahlung, and a number of results are taken over from that problem. Application is made to the sun, and it is found that for the solar plasma the main contribution to the graviton luminosity comes from the central core at r/R approximately 0.1. The total luminosity (Lg) in gravitons is about 7.9 x 10 to the 14th ergs/s, close to an earlier estimate by Weinberg (1965, 1972); about 33 percent of the total results from e-e collisions with the rest from e-z collisions (mainly e-p and e-alpha). Approximate corrections to Born formulas are evaluated, and this Lg includes the associated (approximately + or - 10 percent, respectively) modification. The quantum-mechanical aspects of the solar Lg problem are discussed, and it is shown why a previous classical calculation overestimated Lg by about an order of magnitude. Production of gravitons in binary collisions in other types of stars is discussed briefly. It is found that Lg varies very little along the main sequence. White dwarfs have a typical graviton luminosity LWD approximately 10 to the 19th ergs/s, while neutron stars have LNS approximately 10 to the 25th ergs/s; these estimates are very rough.

Gould, R. J.↗
NASA NTRS1985

Cometary impacts, molecular clouds, and the motion of the sun perpendicular to the galactic plane

The stochastic nature of the mass extinction model of Rampino and Stothers (1984), based on the vertical oscillation of the solar system about the plane of the Galaxy, can accommodate a few events with large phase discrepancies. The degree of modulation is crucial in that it depends on the scale height of the population of molecular clouds relative to the amplitude of the solar system and tends to zero if this ratio is large and encounters are entirely random. Here data are presented here from CO surveys of molecular clouds both within and beyond the solar circle which permit explicit calculation of the strength of the modulation. The cloud layer near the sun it too extended and, as a consequence, the modulation of cloud encounters is too weak for a statistically significant period to be extracted from the nine extinctions analyzed by Rampino and Stothers.

Thaddeus, P.↗
NASA NTRS1985

Periodic orbits of the general three-body problem for the sun-Jupiter-Saturn system

Two families of symmetric periodic orbits of the planar, general, three-body problem are presented. The masses of the three bodies include ratios equal to the sun-Jupiter-Saturn system and the periods of the orbits of Jupiter and Saturn are in a 2:5 resonance. The (linear) stability of the orbits are studied in relation to eccentricity and mass variations. The generation of the two families of periodic orbits follows a systematic approach and employs (numerical) continuation from periodic orbits of the first and second kind in the circular restricted problem to the elliptic restricted problem and from the circular and elliptic problems to the general problem through bifurcation phenomena relating the three dynamical systems. The approach also provides insight into the evolutionary process of periodic orbits continued from the restricted problems to the general problem.

Kwok, J. H.↗
NASA NTRS1986

Retractable Sun Shade

Window-shade type spring roller contains blanket, taken up by rotating cylindrical frame and held by frame over area to be shaded. Blanket made of tough, opaque polyimide material. Readily unfurled by mechanism to protect space it encloses from Sun. Blanket forms arched canopy over space and allows full access to it from below. When shading not needed, retracted mechanism stores blanket compactly. Developed for protecting sensitive Space Shuttle payloads from direct sunlight while cargo-bay doors open. Adapted to shading of greenhouses, swimming pools, and boats.

Frank, A.↗
NASA NTRS1985

An unbiased X-ray sampling of stars within 25 parsecs of the Sun

A search of all of the Einstein Observatory IPC and HRI fields for untargeted stars in the Woolley, et al., Catalogue of the nearby stars is reported. Optical data and IPC coordinates, flux density F sub x, and luminosity L sub x, or upper limits, are tabulated for 126 single or blended systems, and HRI results for a few of them. IPC luminosity functions are derived for the systems, for 193 individual stars in the systems (with L sub x shared equally among blended components), and for 63 individual M dwarfs. These stars have relatively large X-ray flux densities that are free of interstellar extinction, because they are nearby, but they are otherwise unbiased with respect to the X-ray properties that are found in a defined small space around the Sun.

Johnson, H. M.↗
NASA NTRS1986

The Sun at high spatial resolution: The physics of small spatial structures in a magnetized medium

An attempt is made to provide a perspective on the problem of spatial structuring on scales smaller than can presently be directly and regularly observed from the ground or with which current space-based instrumentation can be anticipated. There is abundant evidence from both observations and theory that such spatial structuring of the solar outer atmosphere is ubiquitous not only on the observed scales, but also on spatial scales down to (at least) the subarcsecond range. This is not to say that the results to be obtained from observations on these small scales can be anticipated: quite the opposite. What is clear instead is that many of the classic problems of coronal and chromospheric activity - involving the basic dissipative nature of magnetized plasmas - will be seen from a novel perspective at these scales, and that there are reasons for believing that dynamical processes of importance to activity on presently-resolved scales will themselves begin to be resolved on the sub-arcsecond level. Since the Sun is the only astrophysical laboratory for which there is any hope of studying these processes in any detail, this observatioinal opportunity is an exciting prospect for any student of magnetic activity in astrophysics.

Rosner, R. T.↗
NASA NTRS1986

Boundary conditions on the early Sun from ancient cosmogenic neon in meteorites

Isotopic analysis of neon from individual grains of the meteorites Murchison (CM) and Kapoeta (howardite) shows large enrichments of cosmogenic neon in grains with solar flare tracks. The quantity of this component is incompatible with galactic cosmic ray or solar cosmic ray irradiation under present conditions and is attributed to irradiation by energetic flares from an early active Sun. Handpicked grains from each meteorite were grouped according to the presence or absence of solar flare heavy ion tracks, and these four samples were analyzed with an ion counting noble gas mass spectrometer.

Hohenberg, C. M.↗
NASA NTRS1986

Particle acceleration by the sun

A review is given of the analysis of new observations of energetic particles and energetic secondary emissions obtained over the solar maxium (approx. 1980) by the Solar Maximum mission, Hinotori, the international Sun-Earth Explorer, Helios, Explorer satellites, and Voyager spacecraft. Solar energetic particle events observed in space, He(3)- rich events, solar gamma rays and neutrons, and solar neutrinos are discussed.

Lin, R. P.↗
NASA NTRS1986

Precompaction irradiation effects: Particles from an early active sun?

Two recent studies have shown that solar flare irradiated grains from Murchison and Kapoeta have excess spallogenic Ne-21 compared to unirradiated grains, indicating large precompaction particle irradiation effects. The quantity of cosmogenic neon in these grains presents serious difficulties for either galactic cosmic ray or normal solar flare sources. In the first study it was suggested that the effect might be the result of exposure to an early active sun. The more recent experiment both confirms the earlier results and provides constraints on the characteristic energy spectrum on the irradiation. The first results were obtained from Murchison olivines and Kapoeta pyroxenes by mass spectrometric analysis of sets of grains selected on the basis of the presence or absence of solar flare particle tracks. In the second work plagioclase feldspar grains from Kapoeta were studied.

Caffee, M. W.↗
NASA NTRS1985

A sun-aligned arc observed by DMSP and AE-C

On May 12, 1977, 8 minutes after a DMSP satellite photographed a sun-aligned auroral arc in the southern polar cap, AE-C crossed over the same arc. Precipitating electrons were observed with a peak energy flux of 0.94 erg per sq cm s but with no clear monoenergetic beam, and coincident ion precipitation was measured at energies of a few keV. A very sharp ion convection reversal was found coincident with the particle precipitation and embedded in a region of constant antisunward flow. Magnetic field data indicate that the arc occurred during the recovery phase of a weak magnetic storm, with the IMF in a toward sector and the Z component nearly zero. The data are consistent with a source of particles at altitudes of the order of 5-8 R(E) on field lines containing the plasma sheet boundary layer. The electron spectra do not indicate the existence of an electrostatic potential along the magnetic field lines projecting from the arc. The electrodynamic properties associated with the arc appear to be consistent with a simple model in which field-aligned currents are required along any boundary where the horizontal ionospheric current diverges.

Hoffman, R. A.↗
NASA NTRS1985

The visibility of type III radio bursts originating behind the sun

More than 95 percent of the solar type III bursts observed by the two Voyager spacecraft when they were in the solar hemisphere opposite the earth were also recorded by ISEE-3, and 10 of 21 type III bursts whose electron streams were directed toward the earth were recorded on the far side of the sun by Voyager. It is presently suggested that the reason for this widespread visibility is a high degree of radio wave scattering that originates at or near the local plasma frequency. Such other observed features of solar bursts as large apparent source heights may be explained by the strong scattering.

Dulk, G. A.↗
NASA NTRS1985

Radio emission from the sun and stars

Radio astronomy of the sun has reached a high level of maturity, while radio astronomy of the stars is now a burgeoning new field of study. The present review is mainly concerned with radiation which is emitted by 'normal' stars, defined here to include those appearing on classical Hertzsprung-Russell diagrams. The mechanisms for both steady, quiescent emission and intense, strongly varying outbursts are discussed. Included are discussions of bremsstrahlung, gyrosynchrotron emission, electron-cyclotron masers, and plasma radiation. The manifestation of these mechanisms in various kinds of solar radiation are considered along with stellar manifestations.

Dulk, G. A.↗
NASA NTRS1986

S V line ratios in the sun

In the present prediction of level populations and emission line intensity ratios for electron densities and temperatures appropriate to the sun, on the basis of new atomic data for S V, the electron impact collision rates for spin-forbidden transitions, and the intercombination transition spontaneous radiative rate, are noted to be substantially larger than previously ascertained. The S V intensity ratio is shown to be a useful electron density diagnostic for log N(e) greater than 11.5 ratios deduced from observations obtained with a slit spectrograph aboard Skylab generally agree with the theoretical values presented.

Dufton, P. L.↗
NASA NTRS1986

Formation of the sun and its planets

Aspects of star formation are considered, taking into account those observations and models which have a relation to the formation of the solar system. Attention is given to the galactic structure, the stellar properties, planetary indications, interstellar clouds, observations of forming stars, the conditions for cloud collapse, models of star formation, the modeling of secondary features, and aspects of dynamical evolution. Aspects of cosmochemistry are also explored. Questions of chronology are discussed along with nuclide variations, chemical variations among chondritic meteorites, and chemical variations among differentiated objects. A description of planet formation is provided, taking into consideration, gas-dust interaction, sun and accretion disk dynamics, planetesimal swarms, planet-disk interactions, planetary systems, terrestrial planet formation, and gaseous protoplanet contraction.

Kaula, W. M.↗
NASA NTRS1986

An unbiased X-ray sampling of stars within 25 parsecs of the sun

A search of all of the Einstein Laboratory IPC and HRI fields for untargeted stars in the Woolley, et al., Catalogue of the nearby stars is reported. Optical data and IPC coordinates, flux density F sub x, and luminosity L sub x, or upper limits, are tabulated for 126 single or blended systems, and HRI results for a few of them. IPC luminosity functions are derived for the systems, for 193 individual stars in the systems (with L sub x shared equally among blended components), and for 63 individual M dwarfs. These stars have relatively large X-ray flux densities that are free of interstellar extinction, because they are nearby, but they are otherwise unbiased with respect to the X-ray properties that are found in a defined small space around the sun.

Johnson, H. M.↗