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  • 1
    Electronic Resource
    Electronic Resource
    Oscillatory Model for Radio Source 3 C 273 (1964)
    [s.l.] : Nature Publishing Group
    Nature 201 (1964), S. 1016-1016 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Smith and Hoffleit4 have examined the luminosity history of the object and found that its brightness underwent rather drastic changes during the past eighty years. The light curve exhibits fluctuations of a time-scale of the order ten years, on which occasional light flashes are superimposed. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2011016a0
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  • 2
    Electronic Resource
    Electronic Resource
    Excitation of Lunar Luminescence by Solar Protons (1964)
    [s.l.] : Nature Publishing Group
    Nature 202 (1964), S. 1097-1098 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] After this discovery, Kopal and Rackham2'3 observed on the night of November 1.-2, 1963, twice a red glow in the Kepler region of the Moon. These observations were made through narrow passband interference niters centred at 6725 A in the red, and at 5450 A in the green. The red photographs showed a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2021097a0
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetoturbulent Energy and Stability of Supermassive Stars (1965)
    [s.l.] : Nature Publishing Group
    Nature 207 (1965), S. 1345-1346 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE discovery and subsequent investigation of the quasi-stellar radio objects, or 'quasars', have aroused great interest by many investigators1-5. The observed luminosities are of the order of 1046 ergs sec-1 and their lifetimes fall in the range of 103-106 years. Hoyle and Fowler6 proposed that a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2071345a0
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  • 4
    Electronic Resource
    Electronic Resource
    Rapidly rotating polytropes in the post-Newtonian approximation to general relativity (1971)
    Springer
    Astrophysics and space science 12 (1971), S. 58-82 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The study of uniformly polytropes with axial symmetry is extended to include all rotational terms of order Ω4, where Ω is the angular velocity, consistently within the first post-Newtonian approximation to general relativity. The equilibrium structure is determined by treating the effects of rotation and post-Newtonian gravitation as independent perturbations on the classical polytropic structure. The perturbation effects are characterized by a rotation parameter υ = Ω2/2πGϱ c and a relativity parameter, σ =p c /ϱ c C 2 , wherep c and ϱc are the central pressure and density respectively. The solution to the structural problem is obtained by following Chandrasekhar's series expansion technique and is complete to the post-Newtonian rotation terms of orderσυ 2. The critical rotation parameterv c , which characterizes the configuration with maximum uniform rotation, is accurately evaluated as a function of σ. Numerical values for all the structural parameters needed to determine the equilibrium configurations are presented for polytropes with indicesn=1, 1.5, 2, 2 5, 3, and 3.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656138
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  • 5
    Electronic Resource
    Electronic Resource
    Rapidly rotating supermassive stars in the first post-Newtonian approximation to general relativity (1971)
    Springer
    Astrophysics and space science 12 (1971), S. 83-97 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structure and stability of rapidly uniformly rotating supermassive stars is investigated using the full post-Newtonian equations of hydrodynamics. The standard model of a supermassive star, a polytrope of index three, is adopted. All rotation terms up to and including those of order Ω4, where Ω is the angular velocity, are retained. The effects of rotation and post-Newtonian gravitation on the classical configuration are explicitly evaluated and shown to be very small. The dynamical stability of the model is treated by using the binding energy approach. The most massive objects are found to be dynamically unstable when σ=1/c 2.p c /ϱ c ≳ 2.2 × 10−3, wherep c andϱ c are the central pressure and density, respectively. Hence, the higher-order terms considered in this analysis do not appreciably alter the previously known stability limits. The maximum mass that can be stabilized by uniform rotation in the hydrogen-burning phase is found to be 2.9×106 M ⊙, whereM ⊙ is the solar mass. The corresponding nuclear-generated luminosity of ∼6×1044 erg/sec−1 is too small for the model to be applicable to the quasi-stellar objects. The maximum kinetic energy of a uniformly rotating supermassive star is found to be 3×10−5 Mc 2, whereM is the mass of the star. Masses in excess of 1010 M ⊙ are required if an adequate store of kinetic energy is to be made available to a pulsar like QSO. However such large masses have rotation periods in excess of 100 yr and thus could not account for any short term periodic variability. It is concluded then that the uniformly rotating supermassive star does not provide a suitable base for a model of a QSO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656139
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  • 6
    Electronic Resource
    Electronic Resource
    The structure of rapidly rotating relaxed globular clusters (1971)
    Springer
    Astrophysics and space science 12 (1971), S. 47-57 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A model of rapidly rotating globular clusters is constructed assuming uniform angular velocity and a truncated Maxwellian distribution in the stellar velocities. Since the first-order theory developed by Woolley and Dickens becomes inaccurate for rapid rotation, a small-mass envelope is fitted to their models by the method of Monaghan and Roxburgh. A comparison is made of the critical values derived by the two methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656137
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  • 7
    Electronic Resource
    Electronic Resource
    On non-adiabatic oscillations of gaseous systems in hydromagnetics (1973)
    Springer
    Astrophysics and space science 24 (1973), S. 105-115 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The general variational principle obtained by Unno for the study of stellar stability is extended to include the effects of magnetic fields in the general case where the perturbations are nonadiabatic. The unperturbed configuration is non-rotating, but internal motions are possible. A general stability equation is derived, using the modified variational principle. In the simplest case, this equation is identical to the one derived by Unno except for the appearance of magnetic terms in one of the coefficients (through the Lorentz force). If dissipation is neglected, the characteristic equation reduces to the one derived by Frieman and Rotenberg in the stationary case and by Kovetz in the static case. The stability of magnetic stars against homologous oscillations is examined and the usual result for the dynamical mode is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648678
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  • 8
    Electronic Resource
    Electronic Resource
    Heating of the solar chromosphere and corona (1976)
    Springer
    Astrophysics and space science 43 (1976), S. 187-197 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The generalized inhomogeneous wave equation that governs magnetoacoustic, vortical and thermal motions in compressible fluids and that thus is applicable to the problem of the heating of the solar chromosphere and corona is obtained. The effects of kinematic and bulk viscosity, heat conduction, Joule dissipation and magnetic diffusivity are included. Under the usual assumptions, the generalized wave equation reduces to the well-known equations of Lighthill, Kulsrud, Phillips and others. The major problems encountered in applying Lighthill's mechanism to sound generation in turbulent media are reviewed for both the subsonic and supersonic cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00640565
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  • 9
    Electronic Resource
    Electronic Resource
    Nonlinear coupling between pulsation and convection in late type stars (1976)
    Springer
    Astrophysics and space science 45 (1976), S. 175-190 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A simple idealized nonlinear model applicable to long period variable stars has been formulated that assumes the convective envelope ofM giants is composed of giant convection cells, which are comparable in size to the stellar radius. The simplicity of this model essentially constitutes a physical analog to the strong dynamic coupling that occurs if the convective envelope of the star undergoes both modes of motion. As shown implicitly in the time scales associated with these motions, the coupling produces asymmetrical fluctuations of the entire star, the mean velocity of which is comparable to the escape velocity of the star at particular values of the ratio of the pulsation and convection time scales. It is suggested that this can account for the mass loss from late type stars, and the circumstellar dust shells that are associated extensively with long period variables. For critical values of the pulsation and convection time scales, the solutions correspond to the rapid expansion of the entire convective envelope, and is the basis of a new mechanism that simulates the manner in which pulsating stars ballistically accelerate their convective shells to form planetary nebulae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642153
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  • 10
    Electronic Resource
    Electronic Resource
    The equilibrium and stability of magnetopolytropes (1969)
    Springer
    Astrophysics and space science 4 (1969), S. 255-274 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The theory of the oscillations of axisymmetric gaseous configurations with a prevalent magnetic field is presented. The virial tensor method is used to obtain the nine second harmonic modes of oscillations of the system. It is found that out of the nine modes, three are neutral, four are non-radial, and two are coupled. For the Prendergast spherical model it is found that one of the coupled modes is radial and the other non-radial. Both the radial and the non-radial modes obtained in this case agree with the corresponding formulae obtained byChandrasekhar andLimber (1954) andWoltjer (1962). The equilibrium structure of gaseous polytropes with toroidal magnetic fields is also investigated in detail for values of the polytropic indexn=1, 1.5, 2, 3 and 3.5. For this model the components of the moment of intertia and potential energy tensors together with the non-zero components of the supermatrix potential are obtained. The final results in terms of the effect of weak toroidal magnetic fields on the characteristic frequencies of distorted polytropes are presented in the form of tables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00661818
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