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  • 1
    Publication Date: 2018-12-01
    Description: The abundances of elements and of He-3 in 90 solar electron events have been examined. It is found that the events fall into two distinct groups based upon their F/C ratio. Events in the F-rich group frequently have high He-3/He-4 ratios and are associated with type III and type V radio bursts in the parent flare. The F-poor events are associated with type IV bursts. These results on individual events support the conclusions of earlier work done with daily-averaged abundances.
    Keywords: SPACE RADIATION
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  • 2
    Publication Date: 2011-08-24
    Description: The Advanced Composition Explorer (ACE) was recently selected as one of two new Explorer-class missions to be developed for launch during the mid-1990s. ACE will observe particles of solar, interplanetary, interstellar, and Galactic origins, spanning the energy range from that of the solar wind to Galactic cosmic ray energies. Definitive studies will be made of the abundance of nearly all isotopes from H to Zn, with exploratory isotope studies extending to Zr. The scientific objectives, instrumentation, spacecraft, and mission approach that were defined for ACE during the Phase-A study period are summarized.
    Keywords: ASTRONAUTICS (GENERAL)
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  • 3
    Publication Date: 2018-12-01
    Description: The Energetic Particle: Acceleration, Composition and Transport (EPACT) experiment for the WIND spacecraft to be launched in late 1992 is presented. This experiment is designed to study the acceleration, composition and transport of a wide variety of energetic particle populations, including particles accelerated in interplanetary shocks, particles from solar flares, the anomalous component, and the Galactic cosmic rays.
    Keywords: SPACE RADIATION
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  • 4
    Publication Date: 2011-08-24
    Description: We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 He-3 rich events, with He-3/He-4 is greater than 0.1, observed by the International Sun Earth Explorer (ISEE) 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to approximately 1000 events/yr on the solar disk at solar maximum. Thus the resonant plasma processes that enhance He-3 and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of He-3 in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10(exp 10) atoms/cu cm. He-3/He-4 may decrease in very large impulsive events because of depletion of He-3 in the source region. The event-to-event variations in He-3/He-4, H/He-4, e/p, and Fe/C are uncorrelated in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, He-4, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor approximately 2.5 and Fe by a factor approximately 7. This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of approximately 3-5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A approximately 0.43), and Fe has Q/A approximately 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 90; 2; p. 649-667
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  • 5
    Publication Date: 2011-08-16
    Description: Corotating proton and electron streams are the dominant type of low-energy (i.e., 0.1-10 MeV per nucleon) particle event observed at 1 AU. The radial dependence of these events has been studied between 1 and 4 AU using essentially identical low-energy detector systems on IMP-7, Pioneer-10, and Pioneer-11. It had been expected that at a given energy, the intensity of these streams would decrease rapidly with heliocentric distance due to the effects of interplanetary adiabatic deceleration. Instead, it is observed that from event to event, the intensity either remains roughly constant or increases significantly (more than an order of magnitude) between 1 and 4 AU. It appears that interplanetary acceleration processes are the most plausible explanation. Several possible acceleration models are discussed.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; 203; Feb. 1
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  • 6
    Publication Date: 2011-08-19
    Description: H, He, and O cosmic-ray energy spectra obtained in the outer heliosphere by the Voyager 2 and Pioneer 10 spacecraft during the most recent periods of declining solar activity are presented graphically and analyzed. The recovery of high-rigidity particles is shown to be significantly delayed relative to that of the low-rigidity particles. This finding and the demodulated source spectra are attributed to the presence of singly ionized anomalous He and O, as predicted by Fisk et al. (1974).
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 333; L109-L11
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  • 7
    Publication Date: 2011-08-19
    Description: Ambient solar atmospheric abundances derived from gamma-ray spectroscopy are compared with observations of solar energetic particles. Agreement is found between the gamma-ray-derived Ne/O ratio and the corresponding mean ratio for He-3-rich flares. Both of these values are significantly higher than inferred coronal Ne/O ratios. It is suggested that the mean Ne/O ratio in He-3-rich flares reflects the composition of the flare plasma rather than the acceleration process.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 332; L87-L91
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  • 8
    Publication Date: 2011-08-19
    Description: A comparison between proton events and coronal mass ejections (CMEs) based on nearly three years of observations around the recent maximum of solar activity is presented. Peak proton fluxes are found to correlate with both the speeds and the angular sizes of the associated CMEs. It is shown that CME speeds do not significantly correlate with CME angular sizes, so that peak proton fluxes are correlated with two independent CME parameters. With larger angular sizes, CMEs are more likely to be loops and fans rather than jets and spikes and are more likely to intersect the ecliptic.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 9683-969
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  • 9
    Publication Date: 2011-08-24
    Description: A ground-based optical telescope system has been constructed with the capability to locate fast optical transients that may be associated with gamma-ray bursts (GRBs). The instrument has been integrated and operated during a shakedown period at GSFC, Maryland. Results of 35 hours of 'state mode' data are presented. The telescope has the proven capability to slew to any point on the night sky within 1.0 sec, track that position with better than one arcsecond stability, and image a 9 x 12 arcmin field of view with 1 arcsec angular resolution with 1.5 sec time resolution. The telescope-CCD camera system has a sensitivity of 13th magnitude for transients and 14th mag for field stars. In the 35 hr of operation many single frame transients of instrumental and optical origin have been observed; no two-sequential frame astrophysical transients have been identified. The combined rate of instrumental transients (predominantly sea-level muons) is 7.2/hr and of optical transients (satellite glints, airplane strobe lights, and meteors) is 5.1/hr. The RMT will operate in conjunction with the MIT Explosive Transient Camera survey instrument at Kitt Peak National Observatory, Tucson. The RMT is now being installed at Kitt Peak. Full operation will begin this summer.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Robotic telescopes in the 1990s; Proceedings of the Symposium, 103rd Annual Meeting of the Astronomical Society of the Pacific, Univ. of Wyoming, Laramie, June 22-24, 1991, 1991 (A93-36457 14-89); p. 137-150.
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  • 10
    Publication Date: 2011-08-24
    Description: The Solar, Anomalous, and Magnetospheric Particle Explorer SAMPEX will carry out energetic particle studies of outstanding scientific questions in the fields of space plasma physics, solar physics, magnetospheric and middle atmospheric physics, and cosmic ray physics. SAMPEX will measure the electron and ion composition of energetic particle populations from about 0.4 MeV/nucleon to hundreds of MeV/nucleon from a zenith-pointing small satellite in near-polar orbit. While over the magnetic poles, the instruments will study the composition of anomalous cosmic rays, solar energetic particles, and Galactic cosmic rays. At lower magnetic latitudes, geomagnetic cutoff effects will allow determination of the ionization state of these particles at energies much higher than can be studied from interplanetary spacecraft. At subauroral latitudes, SAMPEX will also observe precipitating relativistic magnetospheric electrons, which undergo important intertactions within the middle atmosphere.
    Keywords: ASTRONAUTICS (GENERAL)
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