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  • ASTROPHYSICS  (185)
  • SPACE VEHICLES
  • 1990-1994  (185)
  • 1970-1974
  • 1991  (185)
  • 1
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    An unusually strong Einstein ring in the radio source PKS1830 - 211 (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: High-resolution radio images of PKS1830 - 211 are obtained to study the possibility that the double structure is a gravitationally lensed object. The VLBI observations, taken from interferometric radiotelescope networks, reveal an elliptical ring that connects two bright spots of similar composition. Because the lens and the lensed object are closely aligned, and because of the structure of the two spots, the source is concluded to be a radio Einstein ring. The source is found to be close to the galactic plane, and the lens and the lensed object are extragalactic. The source is also found to be unusually bright, suggesting that it is aligned with a bright background source or amplified by some mechanism related to a source that is not so bright.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 352; 132-134
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  • 2
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    Chromospheric activity in Delta Scuti stars - The suspected variable Tau Cygni (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: High-resolution IUE spectra of the suspected variable Tau Cyg were obtained to search for a possible variability of the Mg II h, k double-peaked emission. The observations, spanning an interval of about 6.3 h, have shown flux excursions within or just near 15 percent, a value suggested as the detection limit of actual variations with IUE spectra. A variability, difficult to explain, could be present in the ratios Fk2v/Fk2r. The emission fluxes seem to be higher than those of the Delta Scuti variables Rho Pup and Beta Cas. This comparison could give some insights on the possible role of the convection on the pulsational and chromospheric activities of Tau Cyg. A positive correlation between the total emission fluxes and the rotational velocities of these stars was found.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 243; 2, Ma
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  • 3
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    Cs-135 - Ba-135: A new cosmochronometric constraint on the origin of the Earth and the astrophysical site of the origin of the solar system (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: It is argued that if Cs-135 was indeed present in the early solar system at the level inferred from evidence presented here, then two major conclusions follow. (1) A supernova contributed newly synthesized r-process matter into the protosolar reservoir within approx. 5 Ma of the Cs/Ba fractionation recorded in LEW 86010; (2) The strong Cs depletion in the bulk Earth reservoir (Cs-133/Ba-135 approx. 0.1) took place very early in solar system history. If this volatile loss was pre-accretionary, then the accretionary chronology of the Earth is not constrained. However, if it is a consequence of accretion, then the very tight time constraint of approx. less than 5 Ma (rel. to LEW 86010) is obtained for accretion of most of the Earth's mass.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Abstracts for the 54th Annual Meeting of the Meteoritical Society; p 8
    Format: application/pdf
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  • 4
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    Compositions of near-Earth asteroids (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The goal is to determine whether any of the near-earth asteroids contain water-bearing phyllosilicate (clay) minerals. If these minerals are present, they would provide a readily available source of water for propellant generation and use in life support systems. Telescopic detection of water on the near-earth asteroids is complicated because thermal emission from the asteroid itself masks the diagnostic absorption features for objects this close to the sun. Sophisticated thermal models are necessary to determine whether the absorption features are present. This year, development of these models was continued and more telescopic data to test the models was obtained.
    Keywords: ASTROPHYSICS
    Type: NASA Space Engineering Research Center for Utilization of Local Planetary Resources; 8 p
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  • 5
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    Preliminary spectral observations of the Galaxy with a 7 deg beam by the Cosmic Background Explorer (COBE) (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The FIR absolute spectrophotometer (FIRAS) on the Cosmic Background Explorer (COBE) has carried out the first all-sky spectral line survey in the FIR region, as well as mapping spectra of the Galactic dust distribution at below 100 microns. Lines of forbidden C I, C II, and N II, as well as of CO are all clearly detected. The mean line intensities are interpreted in terms of the heating and cooling of the multiple phases of the interstellar gas. In addition, an average spectrum of the galaxy is constructed and searched for weak lines. The spectrum of the galaxy observed by FIRAS has two major components: a continuous spectrum due to interstellar dust heated by starlight, and a line spectrum dominated by the strong 158-micron line from singly ionized carbon, with a spatial distribution similar to the dust distribution, and a luminosity of 0.3 percent of the dust luminosity. There are in addition moderately strong 122- and 205.3-micron lines, identified as coming from singly-ionized nitrogen. Maps of the emission by dust and forbidden C II and N II are presented.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 381; 200-209
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  • 6
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    Were small galaxies once the dominant cosmological population? (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Redshifts and K magnitudes have been obtained for a small but complete sample of 22 galaxies with B magnitudes down to 24. In the luminosity range B = 23-24, the B-band galaxy counts are dominated by a population of small blue galaxies at z roughly 0.25, which may collectively contain as much baryonic matter as the normal galaxies. It is possible either that these earlier galaxies have undergone merging to create the present galaxy population, or that they represent a quite different galactic population which has now faded or disappeared. Either possibility has considerable implications for understanding of galaxy formation.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 354; 460
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  • 7
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    IDE spatio-temporal impact fluxes and high time-resolution studies of multi-impact events and long-lived debris clouds (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: During the first 12 months of the Long Duration Exposure Facility (LDEF) mission, the Interplanetary Dust Experiment (IDE) recorded over 15,000 total impacts on six orthogonal faces with a time resolution on the order of 15 to 20 seconds. When combined with the orbital data and the stabilized configuration of the spacecraft, this permits a detailed analysis of the micro-particulate environment. The functional status of each of the 459 detectors was monitored every 2.4 hours, and post-flight analyses of these data has now permitted an evaluation of the effective active detection area as a function of time, panel by panel and separately for the two sensitivity levels. Thus, total impacts were transformed into areal fluxes, and are presented here for the first time. Also discussed are possible effects of these fluxes on previously announced results: apparent debris events, meteor stream detections, and beta meteoroids in observationally significant numbers.
    Keywords: ASTROPHYSICS
    Type: First LDEF Post-Retrieval Symposium Abstracts; p 41
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  • 8
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    First results from the Goddard High-Resolution Spectrograph - The Galactic halo and the Ly-alpha forest at low redshift in 3C 273 (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results of initial spectroscopy using the Goddard High-Resolution Spectrograph and the Hubble Space Telescope on the bright low-redshift quasar 3C 273 are presented. Absorption lines produced by gas in the disk and halo of the Galaxy from numerous neutral and weakly ionized atoms and also from highly ionized atoms are detected. The detection of N v provides additional strong support for the existence of gas with T about 200,000 K at large distances away from the disk of the Galaxy. Ten absorption lines with EW greater than 50 mA, and four possible lines with EW between 25 and 50 mA, are also found in the region between 1235 and 1406 A. These cannot be identified with any lines in the galactic interstellar medium and must therefore all be Ly-alpha systems at very low redshifts. This number of lines is 5-10 times larger than expected from a simple extrapolation of the high-redshift evolution derived from ground-based observations and is consistent with no evolution in cloud properties since z = 2.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 377; L21-L24
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  • 9
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    Report of the Ionosphere-Thermosphere-Mesosphere Panel (1991)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: The scientific objectives and mission concept that emerged from the discussions of this panel are presented. The overall scientific theme of this report is the investigation of the ionosphere, thermosphere, and mesosphere (near Earth space environment) as a global, dynamic, and coupled system. Among the specific goals of this area of research are: (1) understanding the consequences of transition between turbulent and laminar flow and collisional and collisionless media; (2) understanding the thermospheric/mesospheric coupling due to gravity wave, tidal, and trace constituent transport processes; (3) understanding the electrodynamical coupling between the thermosphere/ionosphere and magnetosphere; (4) understanding the coupling processes between small scale plasma structures; and (5) determining the real-time evolution of the global ionosphere electric field in response to solar wind and magnetosphere coupling.
    Keywords: ASTROPHYSICS
    Type: Space Physics Strategy-Implementation Study. Volume 1: Goals, Objectives, Strategy. A Report to the Space Physics Subcommittee of the Space Science and Applications Advisory Committee; p 39-48
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  • 10
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    Inhomogeneous structure in the chromospheres of dwarf M stars (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Linear combinations of observed spectra of the H-alpha and Ca-II resonance and IR lines from the chromospheres of a quiet (Gl 1) and an active (Gl 735) dwarf-M star are compared with the corresponding spectra from a star of intermediate activity (Gl 887). It is shown that the intermediate spectra cannot be explained as a simple juxtaposition of the extreme chromospheric states. It is concluded that the range of observed strengths of chromospheric activity indicators in dwarf-M stars is due, at least in part, to changes in the radial structure of the chromospheric heating function and not to changes in the area filling factor.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 253; 575-578
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