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  • ASTROPHYSICS  (172)
  • 2015-2019
  • 1985-1989  (172)
  • 1980-1984
  • 1987  (172)
  • 1
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    X-rays from the radio halo of M87 (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: The Einstein Observatory and the VLA were used to scan the radio halo of the galaxy M87 to detect the presence, if any, of inverse Compton X-ray (ICX) emissions. The scans revealed a coincidence of an asymmetrical X-ray structure with a luminosity near 4 x 10 to the 41st ergs/sec and dominant symmetrical emission from the hot interstellar gas. The emission can be attributed to ICX if the magnetic field of the proposed halo varies between 3-8 times below equipartition levels of 2-5 micro-gauss, which would imply that the confinement is produced by an outside medium. The necessary characteristics of the confining mechanism are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 312; 101-110
    Format: text
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  • 2
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    Airborne and groundbased spectrophotometry of comet P/Halley from 5-13 micrometers (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Spectrophotometry of comet Halley from 5-13 microns was obtained from the Kuiper Airborne Observatory and from the Lick Observatory Nickel Telescope, revealing a strong broad emission band at 10 microns and a weak feature at 6.8 microns. The 10-micron band is identified with silicate materials, and the primary component of the silicate emission is suggested to be due to olivine. The 6.8 micron feature may be due either to carbonates or the C-H deformation mode in organic molecules. The data indicate that small particles are abundant in the coma and that the dust contains at least two physically separate components. Significant spatial and temporal variations are also noted in the spectrum.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2
    Format: text
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  • 3
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    Collisional and dynamical processes in moon and planet formation (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Research on a variety of dynamical processes relevant to the formation of planets, satellites and ring systems is discussed. The main focus is on studies of accretionary formation of early protoplanets using a numerical model, structures and evolution of ring systems and individual bodies within planetary rings, and theories of lunar origin.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 112-114
    Format: application/pdf
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  • 4
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    Molecular clouds and cloud cores in the inner Galaxy (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: A compilation of CO emission regions and their measured parameters is presented which represents a nearly complete accounting of the molecular clouds in the first quadrant of the Galaxy. Emission regions associated with radio H II regions have systematically brighter CO peaks that are a factor of two to three times larger and have twice the mean velocity dispersion as the general cloud population. Both the H II region clouds and the hot core regions have a Galactic distribution characteristic of a spiral arm population, whereas the colder clouds are much less confined in Galactic azimuthal angle. Virial masses are obtained for the large sample of clouds with assigned kinematic distances. The mean H2 density for a GMC of diameter 40 pc is 180/cm. For these clouds, a linear relationship is found between the H2 column density and the integrated CO emission. The variation in the Z-dispersion of clouds as a function of cloud mass suggests that more massive GMCs have smaller random velocities.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series (ISSN 0067-0049); 63; 821-915
    Format: text
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  • 5
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    Discovery of three new RS Canum Venaticorum-like counterparts to HEAO I X-ray sources (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: The identification of three high-latitude HEAO I Scanning Modulation Collimator X-ray sources with the chromospherically active RS CVn-like stars HD 113816, HD 146413, and HD 39576 is reported. Optical observations, including coude spectroscopy and broad-band and narrow band photoelectric photometry are presented. The Ca II emission strength of all three stars shows that they are chromospherically active. HD 146413 and HD 39576 exhibit variable X-ray emission in the 1-13 keV energy range, while HD 113816 is a softer and steadier source. The level of X-ray flux detected from these three stars is some one to two orders of magnitude higher than predicted empirically from the Ca II emission fluxes. It is proposed that this emission results from flarelike activity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 315; 273-285
    Format: text
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  • 6
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    Radio emission from RS CVn binaries. II - Polarization and spectral properties (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Multiepoch radio observations of circular polarization and spectral characteristics of several close, late-type stellar binaries are reported. The median luminosity of four well-studied systems ranged from 16.2 to 17.1 ergs/s/Hz. For individual systems, the fractional circular polarization decreases with increasing luminosity, particularly at frequencies above 5 GHz. Eclipsing binaries have significantly lower average circular polarization compared with noneclipsing systems. Helicity reversal is almost always observed between 1.4 and 4.9 GHz for systems with high orbital inclination. Comparison with ten years of previously published polarization observations for two RS CVn stellar systems show that the same helicity occurs at a given frequency for a given source, indicating a very stable, large-scale magnetic field geometry. These spectral and polarization characteristics strongly support a model of inhomogeneous gyrosynchrotron emission arising from electrons with power law energy spectra interacting with inhomogeneous magnetic fields.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 93; 1220-122
    Format: text
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  • 7
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    Infrared emission from P/Halley's dust coma during March 1986 (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Photometry at 2-20 microns of the inner dust coma of comet Halley was obtained at the NASA IRTF on March 6.85, 12.8, 13.75, 17.7, and 24.8. Positions offset 10 arcsec were measured as well as the central brightness. The strength of the 10 micron emission feature was observed to vary with location in the coma. The infrared emission is in general agreement with the dust size distribution measured from the Vega and Giotto spacecraft. March 6.8, 17.7, and 24.8 corresponded to strong dust jet activity. The strength of the 10 micron silicate emission is shown to be a sensitive indicator of grain size and thus of jet activity. Dust production rate on March 13.75, 6 hr before Giotto encounter, was about 10 to the 7th gm/s.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2
    Format: text
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  • 8
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    An X-ray survey for pre-main-sequence stars in the Taurus-Auriga and Perseus molecular cloud complexes (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Seventy-five fields from the Einstein X-Ray Observatory IPC detector between 3h and 5h right ascension and 15 deg and 35 deg declination are examined to search for X-ray-emitting low-mass pre-main-sequence (PMS) stars. Six such stars were previously found; they appear to be similar to T Tauri stars but without dense circumstellar envelopes or winds. Finding charts are presented for 59 X-ray sources that may be PMS stars. While some are likely to be spurious X-ray sources, chance coincidences with unrelated stars, or non-PMS stellar sources such as RS CVn type binaries, approximately half are probably X-ray-selected PMS stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 94; 1251-125
    Format: text
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  • 9
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    A detailed investigation of proposed gas-phase syntheses of ammonia in dense interstellar clouds (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: The initial reactions of the Herbst and Klemperer (1973) and the Dalgarno (1974) schemes (I and II, respectively) for the gas-phase synthesis of ammonia in dense interstellar clouds were investigated. The rate of the slightly endothermic reaction between N(+) and H2 to yield NH(+) and H (scheme I) under interstellar conditions was reinvestigated under thermal and nonthermal conditions based on laboratory data. It was found that the relative importance of this reaction in synthesizing ammonia is determined by how the laboratory data at low temperature are interpreted. On the other hand, the exothermic reaction between N and H3(+) to form NH2(+) + H (scheme II) was calculated to possess significant activation energy and, therefore, to have a negligible rate coefficient under interstellar conditions. Consequently, this reaction cannot take place appreciably in interstellar clouds.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 321; 898-906
    Format: text
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  • 10
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    Far-infrared measurements of N/O in H II regions - Evidence for enhanced CN process nucleosynthesis in the inner Galaxy (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Measurements of the far-infrared lines of forbidden O III 51.8 microns, 88.4 microns, and forbidden N III 57.3 microns are presented for 13 H II regions covering a wide range in Galactocentric distance. These lines are used to measure the variation of N(2+)/O(2+) with Galactic radius from the center out to 12 kpc. It is argued that this ratio is indicative of the elemental ratio N/O. It is shown that the line flux ratio 57.3 microns forbidden N III/51.7 microns forbidden O III is nearly equal to the N(2+)/O(2+) abundance ratio and is only weakly dependent on nebular conditions. The derived N(2+)/O(2+) values show an inverse correlation with distance from the Galactic center. N(2+)/O(2+) tends to increase as the H II region electron temperature decreases, a behavior consistent with a model of Galactic enrichment in which N-14 is secondary to primary O-16, a scenario that is the natural result of CN processing.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 320; 573-585
    Format: text
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