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  • Polymer and Materials Science  (3,130)
  • ASTROPHYSICS  (709)
  • 1985-1989  (3,839)
  • 1975-1979
  • 1985  (3,839)
Collection
Keywords
Publisher
Years
  • 1985-1989  (3,839)
  • 1975-1979
Year
  • 1
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    Meteoritic evidence that graphite is rare in the interstellar medium (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Carbonaceous material from several distinct astrophysical environments that has been identified in primitive meteorites is discussed. Most of this material is not well crystallized graphite, but ranges from kerogenlike macromolecular organic matter to poorly graphitized carbon. Of the small fraction of the carbonaceous material which is graphite, most may have resulted from the graphitization of macromolecular precursors in the solar nebula. Since graphite is more stable than those precursors, preexisting interstellar graphite should have survived in meteorites to at least the same extent as did other forms of carbon. It is concluded from this dearth of graphite that graphitic carbon was not a major component of the interstellar dust at the time of the formation of the solar system.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 318; 166-168
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Observational studies of the symbiotic stars. III High-dispersion IUE and H-alpha observations of EG Andromedae (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: High-dispersion IUE and optical spectra are presented for the symbiotic star EG Andromedae (HD 4174). Remarkable emission-line strength and profile variations are confirmed for the S IV, O IV, C IV, and He II ultraviolet lines as well as H-alpha. Accurate cross-correlation absorption-line velocities determined from Ti I, Ca I, and Fe I features convincingly demonstrate that EG And is a single-lined spectroscopic binary. The velocity curve suggests that the photometric ephemeris reported by Smith in 1980 should be revised by a redefinition of zero phase by about 0.08 of a period. The primary of the system may be similar to the central star of a planetary nebula embedded in a dense nebula with a mild stellar wind. The behavior of the emission lines is interpreted to indicate that the primary and its surrounding nebula suffer a partial eclipse by the cool giant secondary.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 295; 620-627
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  • 3
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    The geometric extent of C II (UV 0.01) emitting regions around luminous, late-type stars (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A method is presented by which the geometric extent of the chromospheres around late-type stars can be estimated from measurements of the total emission-line flux and line ratios within the C II (UV 0.01) multiplet. Application of this technique to a sample of 15 late-type stars indicates a clear difference in the radial extent of the chromospheres around coronal and noncoronal stars. The former stars appear to have very thin chromospheres (of no more than 0.1 percent of the photospheric radius), while the latter stars have chromospheres extending, on average, out to 2.5 photospheric radii. This, in principle, provides information for understanding structural differences between late-type giant and supergiant stars with and without coronae, and could lead to an understanding of the mass-loss mechanisms involved.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 289; 676-680
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  • 4
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    Rotational modulation of chromospheric emission in cool giants and 'hybrid' stars (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Archival data from the International Ultraviolet Explorer have been used to study temporal variations of the Mg II h and k emission lines in eight late-type giants. Evidence is presented that the variations are periodic in nature. It is argued that the periodicities can be interpreted in terms of rotation. It is found that the four fastest rotators in the sample are 'hybrid' stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 288; 310-328
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  • 5
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    Magnetism of nakhlites and chassignites (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Hysteresis measurements on three shergottite and two nakhlite meteorites indicate single domain grain size behavior for the highly shocked Shergotty, Zagami, and EETA 79001 meteorites, with more multidomain-like behavior for the unshocked Nakhla and Governador Valadares meteorites. High viscosity and initial susceptibility for Antarctic shergottite ALHA 7705 indicate the presence of superparamagnetic grains in this specimen. Thermomagnetic analysis indicate Shergotty and Zagami as the least initially oxidized, while EETA 79001 appears to be the most oxidized. Cooling of the meteorite samples from high temperature in air results in a substantial increase in magnetization due to the production of magnetite through oxidation exsolution of titanomagnetite. However, vacuum heating substantially suppresses this process, and in the case of EETA 79001 and Nakhla, results in a rehomogenization of the titanomagnetite grains. Remanence measurements on several subsamples of Shergotty and Zagami meteorites reveal a large variation in intensity that does not seem related to the abundance of remanence carriers. The other meteorites carry only weak remanence, suggesting weak magnetizing fields as the source of their magnetic signal. The meteorites' weak field environment is consistent with Martian or asteroidal body origin but inconsistent with terrestrial origin.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-176518 , NAS 1.26:176518
    Format: application/pdf
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  • 6
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    Extended atmospheres of outer planet satellites and comets (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The new cometary hydrogen particle-trajectory model, completed last year, has been used successfully to analyze observations of Comet P/Giacobini-Zinner. The Pioneer Venus Orbiter Ultraviolet Spectrometer observed the comet at 1216 A (hydrogen Lyman-a) on 11 September 1985 when the comet was 1.03 AU from the Sun and 1.09 AU from Venus. The analysis implies a production rate at 1.03 AU 2.3 x 10 to the 28th power/sec of the water molecules which photodissociate to produce the observed hydrogen. An upper limit for the H2O production rate of Comet P/Halley of 5 x 10 to the 28th power/sec at 2.60 AU was also obtained from the Pioneer Venus instrument.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-176398 , NAS 1.26:176398
    Format: application/pdf
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  • 7
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    Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The analysis of observed brightness profiles for the C2 radical in comets with Haser's model implies that the parent scale length varies as the square of the heliocentric distance. The use of new Haser scale lengths for C2 and CN determined under this project appears to explain the apparent drop in the C2-to-CN ratio with increasing heliocentric distance.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-176242 , NAS 1.26:176242
    Format: application/pdf
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  • 8
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    Accretion disk electrodynamics (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Accretion disk electrodynamic phenomena are separable into two classes: (1) disks and coronas with turbulent magnetic fields; (2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an alpha-omega dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.
    Keywords: ASTROPHYSICS
    Type: Unstable current systems and plasma instabilities in astrophysics; Aug 08, 1983 - Aug 11, 1983; College Park, MD
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    NASA TECHNICAL REPORTS
  • 9
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    Patchy reconnection and magnetic ropes in astrophysical plasmas (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The formation of flux ropes in the magnetosphere of Venus due to velocity shear is examined in order to infer the properties of flux ropes in the earth magnetosphere. Observational data obtained by the International Sun-Earth Explorer (ISEE) spacecraft for the geometry of directed flows in the earth magnetosheath are compared with magnetometer measurements carried out on board Pioneer Venus Orbiter, and the results are discussed in detail. It is shown that the velocity shear is the dominant element shaping the magnetic structure of the magnetosheaths.
    Keywords: ASTROPHYSICS
    Type: Unstable current systems and plasma instabilities in astrophysics; Aug 08, 1983 - Aug 11, 1983; College Park, MD
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  • 10
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    Unstable current systems and plasma instabilities in astrophysics; Proceedings of the 107th Symposium, University of Maryland, College Park, August 8-11, 1983 (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Among the topics discussed are: magnetic field reconnection in cosmic plasmas; energy dissipation mechanisms in the solar corona; and the acceleration of runaway electrons and Joule heating in solar flares. Consideration is also given to: the nonlinear evolution of the resistive tearing mode; anomalous transport in current sheets; equilibrium and instability in extragalactic jets; and magnetic field reconnection in differentially rotating accretion disks. Among additional topics discussed are: the creation of high energy electron tails by lower hybrid waves and its connection with type-II and type-III bursts; beam current systems in solar flares; and the spatio-temporal features of microwave emissions of active regions and flares.
    Keywords: ASTROPHYSICS
    Type: Unstable current systems and plasma instabilities in astrophysics; Aug 08, 1983 - Aug 11, 1983; College Park, MD
    Format: text
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