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  • 1
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    AR-39Ar-40 dating of basalts and rock breccias from Apollo 17 and the malvern achondrite (1977)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The principles and the potential of the Ar-39/Ar-40 dating technique are illustrated by means of results obtained for 12 Apollo 17 rocks. Emphasis is given to methodical problems and the geological interpretation of lunar rock ages. Often it is ambigious to associate a given lunar breccia with a certain formation, or a formation with a basin. In addition, large-scale events on the Moon have not necessarily reset radiometric clocks completely. One rock fragment has a well-defined plateau age of 4.28 b.y., but the ages of two Apollo 17 breccias define an upper limit for the formation age of the Serenitatis basin at 4.05 b.y. Ages derived from five mare basalts indicate cessation of mare volcanism at Taurus-Littrow approximately 3.78 b.y. ago. Ca/Ar-37 exposure ages show that Camelot Crater was formed by an impact approximately 95 m.y. ago. After a short summary of the lunar timetable as it stands at the end of the Apollo program, we report about Ar-39/Ar-40 and rare gas studies on the Malvern meteorite. This achondrite resembles lunar highland breccias in texture as well as in rare-gas patterns. It was strongly annealed at some time between 3.4 and 3.8 b.y. ago. The results indicate that very similar processes have occurred on the Moon and on achondritic parent bodies at comparable times, leading to impact breccias with strikingly similar features, including the retention of rare-gas isotopes from various sources.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, Pt. 2; p 525-540
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  • 2
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    A single-star interpretation of Nova Cygni 1975 (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Observational evidence has revealed that Nova Cygni 1975 is not a typical nova event. We suggest that Nova Cygni is to be understood, not in terms of a canonical close binary system, but essentially as a single star undergoing a thin-shell thermonuclear explosion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 208; Aug. 15
    Format: text
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  • 3
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    On the white dwarf HZ 43 as an extreme-ultraviolet source (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: It is confirmed by atmospheric modeling that both the visual continuum and the XUV spectrum (60 to 600 A) of HZ 43 can be fitted self-consistently with the emergent flux from a stellar atmosphere having an effective temperature of about 125,000 K and log g of at least 7. An examination of theoretical white-dwarf cooling sequences and estimates of the stellar luminosity indicate that the parameters of HZ 43 are consistent with a hot white dwarf of 0.6 to 1.2 solar masses. The age is estimated to be as short as 100,000 years, raising the possibility that the star may have ejected a planetary nebula or may be surrounded by an expanding H II region. It is concluded that the detection of a planetary nebula shell or an H II region around HZ 43 may provide an astrophysical test of the direct neutrino-electron interaction.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 206; June 15
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  • 4
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    The far-ultraviolet spectrum of Sirius B from Copernicus (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 207; July 1
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  • 5
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    Nonradial oscillations of neutron stars (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Linear, adiabatic, Newtonian, nonradial pulsation analyses have been performed for finite-temperature neutron star models with a fluid core, solid crust, and thin surface fluid 'ocean', including the effects of the neutron star crust. The pulsation equations are considered, including the spheroidal and toroidal modes. A local analysis is performed to provide information about the pulsation modes in the short-wavelength limit. Numerical calculations are made on the mode spectrum and systematic properties. Damping mechanisms are investigated, including gravitational radiation damping, neutrino emission damping, electromagnetic radiation from an oscillating stellar magnetic field, nonadiabatic effects, and internal friction and viscosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 325; 725-748
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  • 6
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    Neutrino pair energy deposition in supernovae (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The role of neutrino-antineutrino annihilation (producing an electron-positron pair) in delayed type II supernova explosions is investigated theoretically. The assumptions and analysis of Goodman et al. (1987) are examined in detail, with a focus on the need for a large density gradient at the edge of the neutrinosphere. It is found that the neutrino annihilation mechanism cannot contribute significantly to the energy of the explosion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 321; L129-L13
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  • 7
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    An independent method for determining the age of the universe (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An age of 9.3 + or - 2.0 Gyr is derived for the Galactic disk on the basis of comparisons between the sudden drop in the observed luminosity distribution and theoretical evolutionary white dwarf models and allowance for a mean prewhite-dwarf lifetime of 0.3 Gyr. To obtain the age of the universe, the time between the big bang and the first appearance of stars in the Galactic disk is added. The age of the universe is estimated to be 10.3 + or - 2.2 Gyr.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 315; L77-L81
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  • 8
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    Accretion disk oscillations - A local analysis in a disk of finite thickness (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Two types of oscillations are observed to occur in dwarf novae: 'coherent' and 'quasi-periodic' oscillations. These may be associated with the pulsation of the white dwarf or the accretion disk components of the dwarf nova. Here a local (short-wavelength) analysis is utilized to study the oscillation of a self-consistent, two-dimensional model of an accretion disk. The linearized equations describing adiabatic, inviscid, nonaxisymmetric oscillations are used to derive a fifth-order algebraic equation for the (complex) pulsation frequency of the disk. The solutions of this equation for various values of the wavevector k reveal that the disk is capable of supporting (1) a pair of high-frequency acoustic modes (p-modes); (2) a pair of intermediate-frequency modes which may share the characteristics of internal gravity waves (g-modes) and inertial waves; and (3) a mode associated with a dynamical instability (purely imaginary frequency). The role played by the shear in determining the stability or instability of these modes is also considered. Finally, the global oscillation frequencies of the disk are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 296; 529-539
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