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  • 1
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    Testing general relativity: Progress, problems, and prospects (1971)
    In:  CASI
    Details
    Publication Date: 2005-11-30
    Description: The results from ground-based experimental testing are presented. Prospects for improving these experiments are discussed. Radar echo time delays, perihelion advance and solar oblateness, time variation of the gravitational constant, and radio wave deflection are considered. Ground-based and spacecraft techniques are compared on an accuracy vs. cost basis.
    Keywords: GEOPHYSICS
    Type: JPL Proc. of the Conf. on Exptl. Tests of Gravitation Theories; p 136-147
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  • 2
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    A high-resolution radio image of a young supernova (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A VLBI radio images of the bright supernova 1986J, which occurred in the galaxy NGC891 at a distance of about 12 Mpc, is presented. No detailed image of any supernova or remnant has been obtained before so soon after the explosion. The image shows a shell of emission with jetlike protrusions. Analysis of the images should advance understanding of the dynamics of the expanding debris, the dissipation of energy into the surrounding circumstellar medium, and the evolution of the supernova into the remnant.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 350; 212-214
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  • 3
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    Radar observations of Comet Halley (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Five nights of Arecibo radar observations of Comet Halley are reported which reveal a feature in the overall average spectrum which, though weak, seems consistent with being an echo from the comet. The large radar cross section and large bandwidth of the feature suggest that the echo is predominantly from large grains which have been ejected from the nucleus. Extrapolation of the dust particle size distribution to large grain sizes gives a sufficient number of grains to account for the echo. The lack of a detectable echo from the nucleus, combined with estimates of its size and rotation rate from spacecraft encounters and other data, indicate that the nucleus has a surface of relatively high porosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 338; 1094-110
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  • 4
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    Supernova 1987A - A radiosphere resolved with VLBI five days after the neutrino burst (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The results of VLBI observations of SN1987A are reported. No emission from the supernova above a level of about 20 percent of the supernova's total flux density was detected, although signals were detected from two calibrator sources with amplitudes roughly equal to those determined in earlier VLBI observations. It is inferred that the supernova's radiosphere was resolved, and a lower bound on the radiosphere's radius of 2.2 mas is estimated from an epoch 5.2 days after the neutrino burst. Given the photometric data from the supernova, a distance to the LMC of 50 + or - 5 kpc, and an apparent expansion velocity that varied systematically with time from 18,000-16,000 km/s, as estimated from the blue-shifted H-alpha absorption lines on the days preceding the observations, it is concluded that 5.2 days after the neutrino burst the supernova's radiosphere was at least 2.5 times larger than the inferred blackbody photosphere, and at least as large as the H-alpha line-forming region.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 412-415
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  • 5
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    Constraining proposed combinations of ice history and Earth rheology using VLBI determined baseline length rates in North America (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We predict the present-day rates of change of the lengths of 19 North American baselines due to the glacial isostatic adjustment process. Contrary to previously published research, we find that the three dimensional motion of each of the sites defining a baseline, rather than only the radial motions of these sites, needs to be considered to obtain an accurate estimate of the rate of change of the baseline length. Predictions are generated using a suite of Earth models and late Pleistocene ice histories, these include specific combinations of the two which have been proposed in the literature as satisfying a variety of rebound related geophysical observations from the North American region. A number of these published models are shown to predict rates which differ significantly from the VLBI observations.
    Keywords: GEOPHYSICS
    Type: Smithsonian Astrophysical Observatory, Measurement and Interpretation of Crustal Deformation Rates Associated with Postglacial Rebound; 4 p
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  • 6
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    VLBI observations of the compact components in M82 (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: VLBI observations at 2.3 and 8.4 GHz of 15 compact components in M82, obtained on May 19, 1983, are examined. Angular sizes and linear sizes of the compact sources in M82 are estimated; it is detected that most of the compact sources studied have linear sizes in excess of 0.3 pc. The brightness distribution of the strongest of the 15 compact sources, 41.9 + 58, is investigated; two dominant, elongated components oriented at an angle of about 20 deg and having maximum dimensions of 10-30 mas are observed.
    Keywords: ASTROPHYSICS
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  • 7
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    Principles of very-long-baseline interferometry (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The basic principles of very-long-baseline interferometry as related to its use in the determination of vector baselines, polar motion, and earth rotation are presented. Aspects relevant to geodetic applications that involve observations of extragalactic radio sources are covered. The instrumentation used in these observations and the basic observables and their simplest interpretation are described. Complications of the interpretation due to the various geophysical 'signals' and nongeophysical 'noise' that affect the observables are considered.
    Keywords: GEOPHYSICS
    Type: Ohio State Univ. Appl. of Geodesy to Geodyn., an Intern. Symp.; p 29-33
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  • 8
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    Comparison of earth rotation as inferred from radio interferometric, laser ranging and astrometric observations (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results of measurements of the earth's rotation vector for a 400-day period from late September 1980 to December 1981, for which date from VLBI, satellite laser ranging (SLR), and lunar laser ranging (LLR) were available, are compared. The acquisition of the data and their evaluation are described. VLBI, SLR, and classical astrometric determinations of the X-parameter required to describe the location of the rotation pole on the earth's surface are shown, and VLBI, LLR, and classical astrometric determinations of the angle of rotation about this pole (UT1) are presented. The results indicate that VLBI and SLR, at their present stages of development, yield standard errors under 20 cm in the determinations of X, about twofold smaller than obtained from classical measurements, and that VLBI and LLR yield determination of UT1 with standard errors less than 40 cm, somewhat smaller than that of the corresponding determinations from classical observations. Methods for improving these types of intercomparisons are suggested.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 302; April 7
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  • 9
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    Geodesy by radio interferometry - Intercontinental distance determinations with subdecimeter precision (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Analysis of very-long-baseline interferometer (VLBI) observations yielded estimates of the distances between three radio telescopes in the United States and one in Sweden, with formal standard errors of a few centimeters: Westford, Massachusetts-Onsala, Sweden: 5,599,714.66 + or - 0.03 m; Green Bank, West Virginia-Onsala, Sweden: 6,319,317.75 + or - 0.03 m; and Owens Valley, California-Onsala, Sweden: 7,914,131.19 + or - 0.04 m, where the earth-fixed reference points are defined in each case with respect to the axes of the telescopes. The actual standard errors are difficult to estimate reliably but are probably not greater than twice the formal errors.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Mar. 10
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  • 10
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    Time-dependent radio fine structure of the compact sources NRAO 150 and 4C 39.25 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Very long baseline interferometer observations at 7.85 GHz have been used to probe the milliarcsecond structure of the unidentified, very compact radio source NRAO 150 and QSO 4 C 39.25. NRAO 150 exhibited no structural variations from 1972 to the end of 1974. A model with two circular Gaussian components fits the data well. NRAO 150 had a flux density of 7.6 plus or minus 0.5 Jy in the compact component; 4 C 39.25 showed a two-component structure, the components having a separation of (2.02 plus or minus 0.05 arc sec) x 10 to the -3rd power. The upper bound on the speed of transverse separation is 0.0001 arc sec per year or less than 2.7 c. From the spectrum there are also indications of a third, larger component.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 86; 3, Ju; June 198
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