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  • 1
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    Asteroid radar astrometry (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Measurements of time delay and Doppler frequency are reported for asteroid-radar echoes obtained at Arecibo and Goldstone during 1980-1990. Radar astrometry is presented for 23 near-earth asteroids and three mainbelt asteroids. These measurements, which are orthogonal to optical, angular-position measurements, and typically have a fractional precision between 10 to the -5th and 10 to the -8th, permit significant improvement in estimates of orbits and hence in the accuracy of prediction ephemerides. Estimates are also reported of radar cross-section and circular polarization ratio for all asteroids observed astrometrically during 1980-1990.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 102; 1490-150
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  • 2
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    Angular diameter measurements of stars (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Angular diameters determined with the Mark III Optical Interferometer are presented for 12 stars at wavelengths of 450 and 800 nm. The uniform disk diameters resulting from fits to the visibility observations have rms residuals of order 1 percent for the 800 nm measurements and less than 3 percent for the 450 nm measurements. The improvement over previous observations with this instrument is due to improved data analysis and the use of a wider range of baseline lengths. An analysis of the calibration systematics for the Mark III Optical Interferometer is included. There is good agreement between these measurements and previously published data. The changes in uniform disk diameter between wavelengths of 450 and 800 nm agree with models of stellar atmospheres.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 101; 2207-221
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  • 3
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    Spectroscopic binary orbits from ultraviolet radial velocities. VIII - LZ Cephei (HD 209481) (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present a study of the double-lined spectroscopic binary LZ Cep based on high-resolution IUE spectra. We determine the radial velocities by using a cross-correlation technique incorporating profile fitting; this allows measurements of velocity separations down to unusually small values. The final velocity curve has a small but significant eccentricity. By considering other constraints, we construct a model for the system, which correctly predicts the light curve; in the model, the secondary fills its critical equipotential lobe. The secondary is conspicuously overluminous for its mass, and must have reached its present configuration following a phase of case A mass transfer.
    Keywords: ASTRONOMY
    Type: The Observatory (ISSN 0029-7704); 111; 1103; p. 167-178.
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  • 4
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    Speckles in interstellar radio-wave scattering (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Observations of speckles in the scattering disk of the Vela pulsar are presented and speckle techniques for studying and circumventing scattering of radio waves by the turbulent interstellar plasma are discussed. The speckle pattern contains, in a hologrammatic fashion, complete information on the structure of the radio source as well as the distribution of the scattering material. Speckle observations of interstellar scattering of radio waves are difficult because of their characteristically short timescales and narrow bandwidths. Here, first observations are presented, taken at 13 cm wavelength with elements of the SHEVE VLBI network, of speckles in interstellar scattering.
    Keywords: ASTRONOMY
    Type: IAU Colloquium on Radio Interferometry: Theory, Techniques and Applications; Oct 08, 1990 - Oct 12, 1990; Socorro, NM; United States
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  • 5
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    The Gamma Ray Observatory - Viewing the violent universe (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An overview is given of the Gamma Ray Observatory (GRO) experimental satellite and the four instruments that permit the study of space phenomena from 0.03 to 30,000 MeV. The GRO comprises: (1) the Burst and Transient Source Experiment; (2) the Oriented Scintillation Spectrometer Experiment; (3) the Imaging Compton Telescope; and (4) the Energetic Gamma-Ray Experiment Telescope. The GRO is expected to provide data regarding the active galaxies, extragalactic diffuse radiation, the Galactic center, matter-antimatter annihilation, and gamma-ray emission from quasars.
    Keywords: ASTRONOMY
    Type: Space Congress; Apr 23, 1991 - Apr 26, 1991; Cocoa Beach, FL; United States
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  • 6
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    Image construction from the IRAS survey (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: IRAS survey data can be used successfully to produce images of extended objects. The major difficulties, i.e., nonuniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, have been resolved. The results of three different image construction techniques are compared: coaddition, constrained least-squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arcsecods, using 60 microns survey data is presented. This exceeds the telescope diffraction limit of about 1 minute of arc at this wavelength.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 248; 1 Au; 328-336
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  • 7
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    Locating very high energy gamma-ray sources with arcminute accuracy (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The angular accuracy of gamma-ray detectors is intrinsically limited by the physical processes involved in photon detection. Although a number of pointlike sources were detected by the COS B satellite, only two have been unambiguously identified by time signature with counterparts at longer wavelengths. By taking advantage of the extended longitudinal structure of VHE gamma-ray showers, measurements in the TeV energy range can pinpoint source coordinates to arcminute accuracy. This has now been demonstrated with new data analysis procedures applied to observations of the Crab Nebula using Cherenkov air shower imaging techniques. With two telescopes in coincidence, the individual event circular probable error will be 0.13 deg. The half-cone angle of the field of view is effectively 1 deg.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 377; L97-L100
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  • 8
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    Germanium detector vacuum encapsulation (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper describes an encapsulation technology that should significantly improve the viability of germanium gamma-ray detectors for a number of important applications. A specialized vacuum chamber has been constructed in which the detector and the encapsulating module are processed in high vacuum. Very high vacuum conductance is achieved within the valveless encapsulating module. The detector module is then sealed without breaking the chamber vacuum. The details of the vacuum chamber, valveless module, processing, and sealing method are presented.
    Keywords: ASTRONOMY
    Type: International Symposium on Gamma-Ray Line Astrophysics; Dec 10, 1990 - Dec 13, 1990; Paris; France
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  • 9
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    A search for primeval galaxies (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We are conducting a search for emission-line objects at large redshifts, ostensibly young and forming galaxies. Our method is to search for strong line emission, in particular Ly-alpha, using two techniques: a direct, narrow-band imaging search using a Fabry-Perot interferometer; and a serendipitous long-slit spectroscopic search. Assuming that none of the faint candidates found so far are actually primeval galaxies, we can set the strongest limits to date on the surface density of Ly-alpha-luminous primeval galaxies on the sky. Some of the faint emission line galaxies detected in our survey at z roughly 0.5 - 1 may be representative of the faint blue galaxy population detected in deep continuum imaging surveys.
    Keywords: ASTRONOMY
    Type: In: The space distribution of quasars; Proceedings of the Workshop, Victoria, Canada, June 3-5, 1991 (A93-28776 10-90); p. 354-357.
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  • 10
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    Radar and spacecraft ranging to Mercury between 1966 and 1988 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Improved solutions have been obtained for the orbit and equatorial cross-section of Mercury using radar ranging data spanning 22 years. These data have yielded new results on the precession of Mercury's perihelion and better limits on a possible time variation in the gravitational constant G.
    Keywords: ASTRONOMY
    Type: Astronomical Society of Australia, Proceedings (ISSN 0066-9997); 9; 2, 19
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