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  • 1
    Electronic Resource
    Electronic Resource
    Neutral atmospheres of comets: A distributed source model (1974)
    Springer
    Astrophysics and space science 26 (1974), S. 153-166 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is argued that the typical nuclear region of a comet, under a variety of circumstances, consists of a central icy nucleus surrounded by an extended icy halo of grains forming a supplementary source for the observed atmospheric constituents. A complete hydrodynamic description of a neutral atmosphere corresponding to such a distributed source model when the predominant ‘parent-molecule’ is H2O is given, and numerical results corresponding to two different velocity distributions of the icy halo consistent with smaller and larger grains are computed. The applicability and relevance of these models are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642630
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  • 2
    Electronic Resource
    Electronic Resource
    On the interpretation of the observed cometary scintillations (1975)
    Springer
    Astrophysics and space science 35 (1975), S. L1 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00644837
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  • 3
    Electronic Resource
    Electronic Resource
    Composition of cometary dust: The case against silicates (1975)
    Springer
    Astrophysics and space science 37 (1975), S. L13 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is argued that the infrared emission including 10 and 18 μ features observed in recent comets is unlikely to be due to silicates. The vaporization temperature of the emitting material ∼500 K is consistent with emission by crystalline polyformaldehyde.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00640371
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  • 4
    Electronic Resource
    Electronic Resource
    A proto-planetary contribution to interstellar dust (1975)
    Springer
    Astrophysics and space science 38 (1975), S. L13 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is argued that a significant mass fraction of interstellar dust might be formed in protoplanetary particle streams. Some astrophysical and cosmogonic consequences are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647152
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  • 5
    Electronic Resource
    Electronic Resource
    The neutral atmospheres of comets (1976)
    Springer
    Astrophysics and space science 39 (1976), S. 335-385 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we have endeavored to critically evaluate our present understanding of cometary atmospheres. Following a brief introduction of the significance of the study of cometary atmospheres (Section 1), the relevant photometric and spectroscopic observations are summarized in Section 2. The interaction with the solar radiation, with regard to both the excitation of the observed species as well as the dissociation of stable molecules evaporating from the nucleus, is considered in Sections 3 and 4. The gas phase chemistry likely to take place in the dense inner coma is next considered in Section 5. The exospheric and hydrodynamic models of the expanding cometary atmosphere are considered in detail in Section 6, and both their limitations as well as possible improvements are discussed. The observed chemical composition of the neutral atmosphere and the inferred chemical composition of the volatile component of the nucleus, together with possible variations between different classes of comets is next considered in Section 7, and their possible cosmogonic significance is discussed. In conclusion, some of the important directions in which future research should progress, in order to provide more complete and secure knowledge of cometary atmospheres, are stressed (Section 8).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648334
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  • 6
    Electronic Resource
    Electronic Resource
    Dust in cosmic plasma environments (1979)
    Springer
    Astrophysics and space science 65 (1979), S. 5-12 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Cosmic dust is invariably immersed in a plasma and a radiative environment. Consequently, it is charged to some electrostatic potential which depends on the properties of the environment as well as the nature of the dust. This charging affects the physical and dynamical properties of the dust. In this paper the basic aspects of this dust-plasma interaction in several cosmic environments — including planetary magnetospheres, the heliosphere and the interstellar medium — are discussed. The physical and dynamical consequences of the interaction, as well as the pertinent observational evidence, are reviewed. Finally, the importance of the surface charge during the condensation process in plasma environments is stressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00643484
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  • 7
    Electronic Resource
    Electronic Resource
    On the acceleration of interstellar grains (1976)
    Springer
    Astrophysics and space science 42 (1976), S. L11 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Dust grains of radiir g ≲3×10−6 cm, injected into the intercloud medium at speeds in the range 107–108 cm s−1, may be stochastically accelerated to speeds ∼0.1c due to scattering by irregularities in the galactic magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01225975
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  • 8
    Electronic Resource
    Electronic Resource
    The ionospheres and plasma tails of comets (1977)
    Springer
    Space science reviews 20 (1977), S. 145-190 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The present understanding of cometary ionospheres and plasma tails is critically evaluated. Following a brief introduction of the significance of the study of cometary ionospheres and tails (Section 1), the observational statistics and spectroscopic observations are summarized in Sections 2 and 3. The complicated and time varying morphology of the plasma tail and the ionosphere as revealed both by photographs as well as visual drawings is discussed in Section 4. The evidence for a strong comet-solar wind interaction, the possible nature of this interaction and also the use of comets as probes of the solar wind are considered in the next 3 sections (5, 6, 7). This is followed by a discussion of the various processes so far proposed for the ionization of cometary gases and their limitations (Section 8). Hydrodynamic models of the solar wind-comet interaction, which refers essentially to the region outside the tangential discontinuity, are presented and evaluated in Section 9. A discussion of the ion chemistry and structure of the region inside the tangential discontinuity (which is here referred to as the cometary ionosphere) follows in Section 10. The largely indirect evidence for the existence of substantial magnetic fields in cometary ionospheres and type 1 tails is evaluated and their likely origin is considered in Section 11. The associated electric currents; their size and closure as well as their importance as sources of ionization in the inner coma are also discussed. Finally in Section 12, some of the directions in which future research should progress, in order to provide a more complete and secure knowledge of cometary ionospheres and plasma tails, are stressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02186863
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  • 9
    Electronic Resource
    Electronic Resource
    Monochromatic brightness variations of comets (1977)
    Springer
    Earth, moon and planets 17 (1977), S. 359-372 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A class of comets, of which Comet Kohoutek (1973f) is typical, show total as well as monochromatic brightness asymmetries about perihelion. They are fainter after perihelion than before at the same heliocentric distance. A model of the cometary nucleus consisting of a growing non-volatile dust mantle surrounding a volatile icy core is used to discuss this phenomenon. Numerical results are obtained for Comet Kohoutek (1973f). It is found that dust mantles of thickness in the range of 10–75 cm can be grown by perihelion passage for various values of the thermal conductivity of the dust if there is no substantial dust blow-off by the sublimating volatiles. The thermal conductivity of the dust mantle is quite small and is dominated by ‘radiative conductivity’ for heliocentric distances ≲ 2 AU. Since the radiative conductivity is larger for larger grain size, the thickest mantle corresponds to coarsest matrix. The strong insulation provided by the growing dust layer progressively suppresses the surface temperature of the volatile core below its quasi-equilibrium value had there been no mantle. As a consequence the production rate of the ‘parent-molecules’ as well as the monochromatic brightness of their ‘daughter’ products increases less steeply than in the mantleless case, as the comet approaches perihelion. Furthermore, there are significant monochromatic brightness asymmetries about perihelion, which are enhanced if there is a greater dust blow-off before perihelion than after, as is believed to be the case with Comet Kohoutek (1973f). Estimates of this asymmetry of 1 × 2 magnitudes for the OH brightness at a heliocentric distance × 1 AU are consistent with the rather limited observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00562645
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  • 10
    Electronic Resource
    Electronic Resource
    A note on the total mass of comets in the solar system (1986)
    Springer
    Earth, moon and planets 36 (1986), S. 187-190 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The assumption that the very low albedo determined for Halley's comet is typical of all short period comets, taken together with the assumption that the average sizes of long and short period comets are approximately equal, leads to an increase in the total mass of comets in the solar system by almost two orders of magnitude. If gravitational ejection from the Uranus - Neptune zone during the later phases of planet formation is indeed responsible for the classical Oort cloud between 104–1015 AU, then the mass of comets in this transplanetary region during cosmogonie times has to exceed the combined masses of Uranus and Neptune by over an order of magnitude. Furthermore, if the recent arguments for as many as 1014 comets in an ‘inner’ Oort cloud between ~40− 104AU are valid, then the total mass of comets in the solar system approaches 2% of a solar mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00057610
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