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  • Other Sources  (1,815)
  • ASTRONOMY  (1,815)
  • 1990-1994  (1,815)
  • 1
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    Pulsar astrometry by using VLBI (PSR0329 between Kashima 26mPhi and Usuda 64mPhi) (1993)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Communications Research Laboratory (CRL) carried out a VLBI (Very Long Baseline Interferometer) experiment of the Pulsar 0329 plus 54 on November in 1992 between Kashima 26mPhi and Usuda 64mPhi. We got a correlation for it by using K-3 VLBI correlator which was developed by CRL. Though we observed a slow pulsar this time, we are going to make millisecond pulsar experiments by making good use of this result and by using K-4 correlator which is under developing in CRL. Its result will give us precise positions and proper motions of pulsars which are useful for obtaining precise pulsar timing.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center, The 24th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 65-72
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  • 2
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    Determination of the extragalactic-planetary frame tie from joint analysis of radio interferometric and lunar laser ranging measurements (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources provide the basis for defining an accurate non-rotating reference frame in terms of angular positions of the sources. Measurements of the distance from the Earth to the Moon and to the inner planets provide the basis for defining an inertial planetary ephemeris reference frame. The relative orientation, or frame tie, between these two reference frames is of interest for combining Earth orientation measurements, for comparing Earth orientation results with theories referred to the mean equator and equinox, and for determining the positions of the planets with respect to the extragalactic reference frame. This work presents an indirect determination of the extragalactic-planetary frame tie from a combined reduction of VLBI and Lunar Laser Ranging (LLR) observations. For this determination, data acquired by LLR tracking stations since 1969 have been analyzed and combined with 14 years of VLBI data acquired by NASA's Deep Space Network since 1978. The frame tie derived from this joint analysis, with an accuracy of 0.003 sec, is the most accurate determination obtained so far. This result, combined with a determination of the mean ecliptic (defined in the rotating sense), shows that the mean equinox of epoch J2000 is offset from the x-axis of the extragalactic frame adopted by the International Earth Rotation Service for astrometric and geodetic applications by 0.078 sec +/- 0.010 sec along the y-direction and y 0.019 sec +/- 0.001 sec. along the z-direction.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 287; 1; p. 279-289
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  • 3
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    Millimeter-wavelength observations of minor planets (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Bolometer observations at 250 GHz of fifteen minor planets have shown that the emissivity of these objects is close to unity. This results in an independent method to determine the absolute calibration scale of radio observations at mm wavelengths: Applying our results to Mars, the prime calibrator at this wavelength, gives a mean absolute disk temperature at mean solar distance of approximately 210 K. Further, the diameters of circularly symmetric asteroids can be determined or the surface area of asteroids can be estimated assuming some geometric constraints on their shape.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 287; 2; p. 641-646
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  • 4
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    Asymmetries in the Io plasma torus (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Using Ulysses radio wave data taken during the 1992 Jupiter encounter, we conclude that there are significant large and small spatial scale azimuthal asymmetries at high latitudes in the Io plasma torus. During a period of time near perijove when the spacecraft motion was predominantly in the azimuthal direction and was relatively fixed in both latitude and radial distance, inferred electron densities depart significantly from the common assumption of longitudinal symmetry. Specifically, electron plasma concentrations near 0 deg system III longitude (and 0400 LT) are greater than those near 180 deg (and 0000 LT). Superposed on this large-scale variation are regularly spaced density depletions, 30-50% in magnitude, and having a spatial periodicity of about 17 deg. Some of these depletions may drive various known radio and plasma wave sources by means of large B parallel electric potentials. The observations are compared with recent models and with the in-situ Voyager observations.
    Keywords: ASTRONOMY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A9; p. 17,205-17,210
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  • 5
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    Multiwaveband study of a major X-ray outburst from the Be/X-ray transient system A 1118-616 (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Be/X-ray binary system A 118-616 has been observed to undergo a major outburst in January 1992 by the Burst and Transient Source Experiment (BATSE) all-sky monitor on the Compton Gamma Ray Observatory. Ground-based optical and IR observations, supported by UV observations obtained under an IUE Target of Opportunity program, have provided us with an excellent multiwavelength study of this system to complement the X-ray data set. The results from this campaign are presented showing the details of the X-ray timing studies, the very strong H-alpha emission and the bright IR excess from the Be star's circumstellar disk (the fuel for the accretion process). Implications for the physics of the system are discussed.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 289; 3; p. 784-794
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  • 6
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    LMC stellar X-ray sources observed with ROSAT. 1: X-ray data and search for optical counterparts (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Observations of Einstein Large Magellanic Cloud (LMC) X-ray point sources have been made with ROSAT's High-Resolution Imager to obtain accurate positions from which to search for optical counterparts. This paper is the first in a series reporting results of the ROSAT observations and subsequent optical observations. It includes the X-ray positions and fluxes, information about variability, optical finding charts for each source, a list of identified counterparts, and information about candidates which have been observed spectroscopically in each of the fields. Sixteen point sources were measured at a greater than 3 sigma level, while 15 other sources were either extended or less significant detections. About 50% of the sources are serendipitous detections (not found in previous surveys). More than half of the X-ray sources are variable. Sixteen of the sources have been optically identified or confirmed: six with foreground cool stars, four with Seyfert galaxies, two with signal-to-noise ratio (SNR) in the LMC, and four with peculiar hot LMC stars. Presumably the latter are all binaries, although only one (CAL 83) has been previously studied in detail.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 106; 702; p. 843-857
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  • 7
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    Galileo infrared imaging spectrometry measurements at the Moon (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Imaging spectrometer observations were made of the surface of the Moon during the December 1990 flyby of the Earth-Moon system by the Galileo spacecraft. This article documents this data set and presents analyses of some of the data. The near infrared mapping spectrometer (NIMS) investigation obtained 17 separate mosaics of the Moon in 408 spectral channels between about 0.7 and 5.2 micrometers. The instrument was originally designed to operate in orbit about Jupiter and therefore saturates at many spectral channels for most measurement situations at 1 AU. However, sufficient measurements were made of the Moon to verify the proper operation of the instrument and to demonstrate its capabilities. Analysis of these data show that the NIMS worked as expected and produced measurements consistent with previous ground-based telescopic studies. These are the first imaging spectrometer measurements of this type from space for the Moon, and they illustrate several major points concerning this type of observation and about the NIMS capabilities specifically. Of major importance are the difference between framing and scanning instruments and the effects of the spacecraft and the scan platform on the performance of such and experiment. The science return of subsequent NIMS and other investigation measurements will be significantly enhanced by the experience and results gained.
    Keywords: ASTRONOMY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; E3; p. 5,587-5,600
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  • 8
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    Ultraviolet spectra and geometric albedos of 45 asteroids (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Spectral reflectances and geometic albedos between 2300 and 3250 A are determined for 45 asteroids from data acquired by the International Ultraviolet Explorer satellite. The geometric albedos are consistently low, ranging from approximately 0.02 for C-type asteroids to approximately 0.08 for M-type asteroids. An exception is the single E-type asteroid (44 Nysa) with a geometric albedo of 0.3 at 2950 A. We find that the three major asteroid taxonomic classes persist into the UV. The taxonomic classes are distinguished primarily by their albedos, but S types are generally redder than C or M types. The first ultraviolet phase curved of asteroids are presented.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 112; 2; p. 496-512
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  • 9
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    Correcting the distortion of images taken with the ultraviolet imaging telescope (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Ultraviolet Imaging Telescope (UIT) cameras include two-stage magnetically focused image intensifiers that introduce small but significant geometrical distortions into the data. These distortions, which create positional offsets as large as 25 arcsec at the field edges, are corrected by the procedure described here to 2-3 arcsec, approximately the resolution of the images. The distortion is measured by comparing and correcting UIT images to digitized Guidestar survey plates of the same fields. Two-dimensional third-order polynomials are used to model the distortion. The models assume that the distortion is an instrumental effect, independent of mission elapsed time and target, and that the effect of distortion is an instrumental effect, independent of mission elapsed time and target, and that the effect of distortion in the center of each field is minimal. The models are used to improve computed astrometric plate solutions and to remove the geometric distortion while transforming the image to a standard north-up, ease-left orientation.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 106; 705; p. 1151-1156
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  • 10
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    Lightcurves and phase relations of asteroid 55 Pandora (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Photoelectric observations of the asteroid 55 Pandora were carried out in Feb. - Mar. 1989 (6 nights) in range of phase angles Delta alpha = (2.5 - 1.4) deg, and in Sep. - Nov. 1991 (15 nights) Delta alpha = (0.5 - 16.3) deg. Average amplitudes of lightcurves in these oppositions are 0.22 m and 0.10 m, respectively. The value of linear phase coefficients and the absence of spike-effect of alpha less than 2 deg indicate that Pandora is a typical M-asteroid and the high albedo measured by IRAS-satellite is not real.
    Keywords: ASTRONOMY
    Type: Astronomicheskii Vestnik (ISSN 0320-930X); 27; 3; p. 75-80
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