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  • Chemical Engineering  (826)
  • ASTRONOMY  (599)
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  • 1990-1994  (678)
  • 1980-1984  (685)
  • 1955-1959  (132)
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  • 1
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    BATSE gamma-ray burst line search. 1: Search for narrow lines in spectroscopy detector data (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Analysis of data from the Spectroscopy Detectors (SDs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO) has found no convincing line features in the spectra of gamma-ray bursts (GRBs) in almost 3 years of operation, in contrast to expectations based on results from other experiments. In this Letter we discuss the visual search for narrow lines in the SD data. The search has examined 192 bursts, of which approximately 18 were intense enough that lines similar to those seen by instruments on the Ginga satellite would have been visible between approximately 20 and approximately 100 keV. A simplified calculation shows that the BATSE and Ginga results are consistent at the 13% level.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 433; 2; p. L77-L80
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  • 2
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    Mitigation of adverse environmental effects on lunar-based astronomical instruments (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The galactic cosmic-ray flux incident on the moon was examined for its potential adverse impact on the performance of the large lunar telescope (LLT) proposed as a part of NASA's Space Exploration Initiative (SEI). Noise produced by the cosmic-ray flux in the charge coupled devices to be used as the primary photodetector in the telescope was estimated. It was calculated that approximately 2.5 m of regolith would provide the shielding necessary to reduce the noise to an acceptable level. Dust is an omnipresent environmental concern for any human-assisted or robotic scientific instruments deployed on the moon. The degree to which dust poses an operational risk to the telescope was examined. Three potential methods for reducing this risk were identified: locating scientific instruments at remote locations; utilizing a prepared, dust-free site for all rocket activities; and covering the optics during high-risk times.
    Keywords: ASTRONOMY
    Type: In: Engineering, construction, and operations in space III: Space '92; Proceedings of the 3rd International Conference, Denver, CO, May 31-June 4, 1992. Vol. 2 (A93-41976 17-12); p. 1832-1841.
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  • 3
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    An Occultation by Saturn's Rings on 1991 October 2-3 October 2-3 Observed with the Hubble Space Telescope (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An occultation of the star GSC 6323-01396 (V = 11.9) by Saturn's rings was observed with the High-Speed Photometer on the Hubble Space Telescope (HST) on 1991 October 2-3. This occultation occurred when Saturn was near a stationary point, so the apparent motion of Saturn relative to the star was dominated by the HST orbital motion (8 km/s). Data were recorded simultaneously at effective wavelengths of 3200 and 7500 A, with an integration time of 0.15 s. Fifteen segments of occultation data, totaling 6.8 h, were recorded in 13 successive orbits during the 20.0 h interval from UTC 1991 October 2, 19:35 until UTC 1991 October 3, 15:35. Occultations by 43 different features throughout the classical rings were unambiguously identified in the light curve, with a second occultation by 24 of them occurring due to spacecraft orbital parallax during this extremely slow event. Occultation times for features currently presumed circular were measured and employed in a geometrical model for the rings. This model, relating the observed occultation times to feature radii and longitudes, is presented here and is used in a least-squares fit for the pole direction and radius scale of Saturn's ring system.
    Keywords: ASTRONOMY
    Type: The Astronomical Journal (ISSN 0004-6256); 106; 6; p. 2544-2572
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  • 4
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    Flat-spectrum radio sources from the Parkes 2.7 GHz survey - A study of a complete sample (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A complete sample, taken from the Parkes 2.7 GHz catalog, of flat-spectrum radio sources with flux densities greater than 0.5 Jy is described. The sample covers all right ascensions and declinations for +10 deg to -45 deg, excluding the Galactic plane, and contains 403 sources. Attention is drawn to the advantages of radio surveys over optical surveys. The survey is used to highlight some selection effects found in optical surveys. How this sample can be used to give information on the early universe is discussed.
    Keywords: ASTRONOMY
    Type: Australian Journal of Physics (ISSN 0004-9506); 43; 2, 19
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  • 5
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    Evidence for material between Saturn's A and F rings from the Voyager 2 photopolarimeter experiment (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The region in the Saturn system between the F ring and the outer edge of the A ring is an area that appears, in images from the imaging experiment, to be virtually devoid of material except for three small satellites. Near the orbit of 1980S28, Atlas - the innermost satellite - the Voyager Photopolarimeter Stellar Occultation data show a discontinuity in count rate which marks a boundary between the tenuous material near the outer edge of the A ring and the orbit of Atlas. The data pertaining to this region have been examined with the aid of statistics and models generated from other similar ring structures. It is concluded that the discontinuity is real, implying the existence of tenuous material of normal optical depth of 0.01 to 0.006 in this region.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 60; 409-415
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  • 6
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    High-resolution observations of the QSO 3C 345 at 1.3 centimeters (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: High-resolution VLBI observations made at a frequency of 22.235 GHz of the quasar 3C 345 are discussed. Antennas located at the Crimean Astrophysical Observatory, USSR; Onsala, Sweden; Effelsberg, West Germany; and the Haystack Observatory, Massachusetts were employed at 4-min integration times to provide baselines ranging up to 5.5 x 10 to the 8th wavelengths. About 40% of the total flux density of 7.85 Jy, observed in November 1977, and 8.05 Jy, observed in October 1978, is found to originate in an unresolved component of the quasar core in a region less than 0.1 milliarcsec in diameter. The elongated jet-like component of the quasar is observed to contain several peaks of emission extending up to 6 milliarsec from the core which decreased in extent between the two observations.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 243
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  • 7
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    IUE observations of dust albedo in nebulae (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The wavelength dependence of the effective albedo of the dust at several positions near the Hourglass region of M8 was determined. Accurate estimates of the contribution of the continuous gas emission can be made using the region 1400A to 1600A. The main uncertainty results from the peculiar extinction of the exciting star, Herschel 36, and the possibility that extinction between the star and the reflecting portions of the nebula exists and needs to be corrected for. The albedo for some planetaries such as NGC 6543 were also investigated. The main uncertainty here is estimating instrumental contributions to the scattering in observing these small objects.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center Advan. in Ultraviolet Astron.; p 405-408
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  • 8
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    Centaurus A, the core of the problem (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The bright, peculiar elliptical galaxy Centaurus A (NGC 5128, PKS 1322-427) was one of the first extragalactic radio sources to be optically identified (Bolton et al. 1949). At a distance of 4 Mpc, Centaurus A is the closest active radio galaxy and affords the highest linear imaging resolution (1 mas approximately equal to 0.02 pc) and hence the best prospects for studying an active nucleus close to the central radio source. We present the results of multi-epoch, 8.4-GHz, very long baseline interferometry (VLBI), imaging observations of the nucleus made over the past three years. The nucleus possesses a core-jet structure where the inner portion of the jet shows apparent linear motion with a velocity substantially less than the speed of light.
    Keywords: ASTRONOMY
    Type: Australian Journal of Physics (ISSN 0004-9506); 47; 5; p. 619-624
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  • 9
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    The NASA - Arc 10/20 micron camera (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-04-02
    Description: A new infrared camera (AIR Camera) has been developed at NASA - Ames Research Center for observations from ground-based telescopes. The heart of the camera is a Hughes 58 x 62 pixel Arsenic-doped Silicon detector array that has the spectral sensitivity range to allow observations in both the 10 and 20 micron atmospheric windows.
    Keywords: ASTRONOMY
    Type: Experimental Astronomy (ISSN 0922-6435); 3; 1-4; p. 173-174
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  • 10
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    The in-flight calibration of the Hubble Space Telescope fine guidance sensors (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Hubble Space Telescope (HST) fine guidance sensors are unique in the precision and performance levels being attempted; spacecraft control and astrometric research at the near milliarcsecond level are the ultimate goals. The inflight calibration of the sensors is presented, describing both the algorithms being used as well as the results achieved to date. The calibration items of principal interest are optical distortion, sensor magnification, and relative alignments. Calibration accuracies at the 20 milliarcsecond level have been achieved for specific data sets for optical distortion parameters. Unexpected variations occurring from Dec. 1990 - May 1991 in the magnification and alignment parameters are currently under investigation. Plans are being developed for new data acquisitions and reductions that should substantially improve HST pointing performance.
    Keywords: ASTRONOMY
    Type: ESA, Spacecraft Flight Dynamics; p 239-244
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