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  • 1
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    Pulsed high-energy gamma-rays from the radio pulsar PSR1706-44 (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Gamma radiation above 100 MeV in energy has been detected from the radio pulsar PSR1706-44. The gamma emission forms a single broad peak within the pulsar period of 102 ms, in contrast to the two narrow peaks seen in the other three known high-energy gamma-ray pulsars. The emission mechanism in all cases is probably the same, the differences arising from the geometry of the magnetic and rotation axes and the line of sight. Gamma-ray emission accounts for as much as 1 percent of the total neutron star spindown energy in these pulsars, much more than emerges at optical or radio frequencies. Thus, study of this emission is important in understanding pulsar emission and evolution.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 359; 6396; p. 615, 616.
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  • 2
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    Major outburst of periodic Comet Halley at a heliocentric distance of 14 AU (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The properties and evolution of the major outburst experienced by Comet Halley at 14 AU during February-March 1991 are studied. It is found that the observed halo is a segment of a conical surface populated by solid particles ejected from a localized, temporarily activated region on the sunlit hemisphere of the spinning nucleus. The total mass of the ejecta was at least 10 exp 12 g and CO was probably the prime driver, accelerating the smallest grains to a terminal velocity of about 45 m/s. The mass loading of the gas flow by particulate matter is enormous, with the mass production rate exceeding the expected production rate of CO by a factor of several tens.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 263; 1-2; p. 367-386.
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  • 3
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    Manifestations of dynamo driven large-scale magnetic field in accretion disks of compact objects (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A turbulent dynamo nonlinear theory of turbulence was developed that shows that in the compact objects of accretion disks, the generated large-scale magnetic field (when the generation takes place) has a practically toroidal configuration. Its energy density can be much higher than turbulent pulsations energy density, and it becomes comparable with the thermal energy density of the medium. On this basis, the manifestations to which the large-scale magnetic field can lead at the accretion onto black holes and gravimagnetic rotators, respectively, are presented.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 46-54
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  • 4
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    The galactic distribution (in radius and Z) of interstellar molecular hydrogen (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Observations of the galactic longitude and latitude distributions of gamma = 2.6 mm CO emission are presented. Analysis of this spectral line data yields the large scale distribution of molecular clouds in the galactic disk and their z-distribution out of the disk. Strong maxima in the number of molecular clouds occur in the galactic nucleus and at galactic radii 4-8 kpc. The peak at 4-8 kpc correlates well with a region of enhanced 100 Mev gamma ray emissivity. This correlation strongly supports the conclusion that the gamma rays are produced as a result of cosmic ray interactions in molecular H2 clouds rather than HI. One important implication of this is that the interstellar magnetic field lines to which cosmic rays are confined must therefore not be excluded from these dense clouds. The width of the cloud layer perpendicular to galactic plane between half density points is 105 + or - 15 pc near the 5.5 kpc peak. The total mass of molecular gas in the interior of the galaxy exceeds that of atomic hydrogen.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 163-176
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  • 5
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    Cometary activity, discrete outgassing areas, and dust-jet formation (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Conceptual models for various types of features observed in cometary comae (jets, spirals, halos, fans, etc.), their computer simulation, and the hydrodynamic models for jet formation are critically reviewed, and evidence for anisotropic, strongly collimated flows of ejecta emanating from discrete active regions (vents) on the rotating cometary nuclei is presented. Techniques employed to generate synthetic comet images that simulate the features observed are described, and their relevance to the primary objects of coma-morphology studies is discussed. Modeling of temporal variations in the water emission from discrete active regions suggests that production curves asymmetric with respect to perihelion should be commonplace. Critical comparisons with the activity profiles of Enke's comet and with light curves of disappearing comets and comets that undergo outbursts are presented. Recent developments in the understanding of the processes that cause the nongravitational perturbations of cometary motions are reviewed, and the observed discontinuities are identified with the birth of new sources and/or deactivation of old vents.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 2 (A93-13551 02-90); p. 769-823.
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  • 6
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    Nucleus of comet Halley as a torque-free rigid rotator (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model for the rotation of the nucleus of comet Halley is proposed on the assumption that the nucleus is homogeneous and a torque-free rigid rotator. It spins about its long axis with a period of 7.4 days, while this axis precesses about a fixed direction with a period of 2.2 days. To satisfy the moments of inertia, the precession angle must be 77 deg. This model settles the major problems associated with the recent controversy about two rotation periods.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 325; 326-328
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  • 7
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    Thermal-infrared and visual imaging of comet Giacobini-Zinner (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Thermal-infrared and visual images obtained simultaneously of comet Giacobini-Zinner on UT 1985 August 4.4 are presented. The 10.8-micron map, which spans several arc minutes with 8-arcsec resolution, is the first ground-based infrared image of a comet. Considerable spatial structure is evident in the map, including a curved dust tail consisting primarily of dust grains larger than 100 microns. The width of this large-grain tail implies that these grains depart the nucleus with velocities less than 3 m/s. The distribution of grain albedo is determined for the central 1 arcmin. It is speculated that an observed increase in the albedo by a factor of 2 with distance from the nucleus and prolonged radius vector results from the confinement to the orbital plane of large fluffy grains previously considered for GZ by others; the lower albedo of this dust could result from multiple internal scattering increasing the probability of absorption of incident light. It is estimated that dust was departing the nucleus at the rate of about 8 x 10 to the 5th g/s, comparable to that derived for many other comets.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 310; L61-L65
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  • 8
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    Nucleus studies of Comet Halley (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Early results from, and research initiatives warranted by, the earth-based observations of Halley's near-nucleus and related phenomena are reviewed. Where appropriate, this information is combined with spacecraft data obtained by the various flight projects. The basic objective is to gain a greater insight into the nature of the comet's nucleus and its environment.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 5; 12, 1; 307-316
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  • 9
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    Coma morphology and dust-emission pattern of periodic Comet Halley. IV - Spin vector refinement and map of discrete dust sources for 1910 (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A hypothetical continuous ejection of dust from discrete emission sources on the sunlit hemisphere of a rotating comet nucleus is tested against 34 digitally processed plates of Comet Halley over the May 5-June 6, 1910 period, as well as the reported projected lengths of six antisunward jets observed between May 14 and June 6, 1910. A map of the comet's nucleus is presented of whose 13 discrete dust sources only two can be modeled as point-like regions. Attention is given to curious cases of 'chain' activation in which the sources that intersect one another on the surface emit dust sequentially, in successive rotations.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 92; 462-482
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  • 10
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    Composition of comet Halley dust particles from Giotto observations (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Mass spectra of cometary dust particles measured by the PIA dust particle analyzer aboard the Giotto spacecraft show some unexpected and striking features. First, small particles below 10 to the -14th g are much more abundant than anticipated by models. Second, most of the particles are rich in light elements such as H, C, N, and O, suggesting the validity of models that describe the cometary dust as including organic material. Third, the light elements specifically seem to have a low ratio of mass to volume. Three examples of original mass spectra showing typical compositions are given; these have been measured, and are compared with a computer-simulated mass spectrum.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 321; 336
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