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  • ASTROPHYSICS  (13)
  • SPACE SCIENCES  (10)
  • 2010-2014
  • 1980-1984  (3)
  • 1975-1979  (10)
  • 1970-1974  (10)
  • 1950-1954
  • 1
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    NGC 1275 /3C 84/ - Similar structure in the optical and 3-mm radio variations (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Optical and 3.3-mm data for the Seyfert galaxy NGC 1275 (3C 84) are compared. Similarities exist between the variations at the two wavelengths with regard to amplitude, time scale, and interval between events. The question is raised whether these similarities may be the result of a common triggering mechanism.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific; vol. 91
    Format: text
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  • 2
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    High-resolution X-ray observations of the Cassiopeia A supernova remnant with the Einstein Observatory (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Cas A was observed with the imaging detectors on the Einstein X-ray Observatory. The mass of the expanding shell due to the interaction of the blast wave and the ambient medium is determined. This indicates that Cas A is probably not in the free expansion phase, but has not yet reached the adiabatic phase of expansion. Detailed comparison of X-ray, optical, and radio images shows various degrees of correlation, indicating that several processes for emission are present. An upper limit of 1,500,000 K is established for any stellar remnant that is below the expected temperature of a neutron star by a factor of about 5. The total mass of the SNR is found to be 10-30 solar masses
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 234
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  • 3
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    Neutron star envelopes (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is pointed out that the separate study of neutron star envelopes is a valuable technique for gaining insights into neutron star cooling calculations. It is shown that, to an excellent approximation, the temperature at the inner boundary of the envelope, T sub b, is a function only of T sub s to the 4th power over g sub s, where T sub s is the effective temperature and g sub s is the surface gravity. This result makes it possible to investigate very simply the effects of general relativity and of opacity changes on the T sub b - T sub s relation and to compare calculations by different workers, even though they use different neutron star models. It is also shown that the most important opacity source for obtaining a reliable T sub b - T sub s relation is the conductive opacity of matter when the ions are liquid. Calculations are presented in which particular attention is given to this region and the best available opacities are used.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 259
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  • 4
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    Structure of neutron star envelopes (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The envelopes of nonmagnetic neutron stars are studied using the best available opacities and equation of state. The general relativistic equations of the structure and evolution of nonmagnetic neutron stars are discussed, and it is shown that they can be reduced to a single equation for calculating the thermal structure of neutron star envelopes. The physical input needed to solve the thermal structure equation is investigated and the numerical results of envelope model calculations are presented. It is shown that the thermal structure of neutron star envelopes is determined by the single parameter T(s) to the 4th/g(s), where T(s) is the effective surface temperature and g(s) the surface gravity of the star. This result is used to derive a number of other scaling relations, and the effects of general relativity on the envelope thermal structure are examined in detail. The results of a sensitivity analysis of the regional opacity needed to obtain a reliable relationship between the temperatures of the inner and outer boundaries of the envelope is presented.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 272; Sept. 1
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  • 5
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    Sensitivity of model calculations to uncertain inputs, with an application to neutron star envelopes (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A method is given for determining the sensitivity of certain types of calculations to the uncertainties in the input physics or model parameters; this method is applicable to problems that involve solutions to coupled, ordinary differential equations. In particular the sensitivity of calculations of the thermal structure of neutron star envelopes to uncertainties in the opacity and equation of state is examined. It is found that the uncertainties in the relationship between the surface and interior temperatures of a neutron star are due almost entirely to the imprecision in the values of the conductive opacity in the region where the ions form a liquid; here the conductive opacity is, for the most part, due to the scattering of electrons from ions.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 204; Aug. 198
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  • 6
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    Synchrotron sources. II - Pulsars and compact extragalactic objects. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Discussion of some limitations on synchrotron models for optical pulsars and compact extragalactic objects. Using the results of a previous paper, it is shown that several existing models for the pulsar NP 0532 are inconsistent with the measured time variations and polarization of the optical emission. The possibility that the low-frequency falloffs in some extragalactic objects (PKS 2134 + 004, OQ 208, and NGC 1068) could be due to emission from particles with small pitch angles, absorption by a thermal plasma, or synchrotron self-absorption is also considered. It is found that radiation by particles with small pitch angles could explain the radio emission from PKS 2134 + 004 and OQ 208, but this process is inconsistent with the observations of NGC 1068. The absorption interpretations cannot account for the turnover in the spectrum of PKS 2134 + 004.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 183; July 15
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  • 7
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    Synchrotron sources. I - Extension of theory for small pitch angles. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Some of the features of synchrotron radiation are examined which occur when relativistic particles move at small pitch angles in a magnetic field. The emission from individual particles is computed. The general properties of the emission from distributions of particles with small pitch angles is discussed, and the emissivities and degrees of polarization for several specific source models are presented. For sources which mainly contain particles with small pitch angles, the degree of circular polarization will normally be high, whereas, if the magnetic field is somewhat irregular, the degree of linear polarization will be small. If the particle distribution also has a low-energy cutoff, the emissivity will vary linearly with frequency at low frequencies.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 183; July 15
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  • 8
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    Some aspects of cosmic synchrotron sources (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Synchrotron emission is considered from individual particles which have small pitch angles and the general properties of synchrotron sources which mainly contain such particles, as well as the emissivities and degrees of circular polarization for specific source distributions. The limitation of synchrotron source models for optical pulsars and compact extragalactic objects are discussed, and it is shown that several existing models for the pulsar NP 0532 are inconsistent with the measured time variations and polarizations of the optical emission. Discussion is made also of whether the low frequency falloffs in the extragalactic objects PKS 2134 + 004, OQ 208, and NGC 1068 is due to emission from particles with small pitch angles or absorption by a thermal plasma or synchrotron self-absorption. It is concluded that the absorption interpretations cannot account for the turnover in the spectrum of PKS 2134 + 004. Measurements of polarization, angular structure, and X-ray flux are also described.
    Keywords: SPACE SCIENCES
    Type: NASA-CR-131526 , SUIPR-435
    Format: application/pdf
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  • 9
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    The generation of gravitational radiation by escaping supernova neutrinos (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Formulae for the gravitational radiation due to the anisotropic axisymmetric emission of neutrinos from a small source are derived. We find that a burst of neutrinos released anisotropically from a supernova will generate a burst of gravitational radiation that may be comparable in amplitude and energy to the gravitational radiation generated by the fluid motion in the collapse of the supernova core.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 223
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  • 10
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    Effects of primordial fluctuations on the abundances of light elements (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Some of the effects of primordial inhomogeneities on the production of H-2, He-3, and Li-7 are investigated. For the most part, temperature fluctuations have only small effects on the abundances. The density fluctuations are modeled by a unimodal distribution so that the Universe is characterized by the mean density and the relative amplitude of the density variations. It has been found that the constraint which H-2 production imposes on the mean mass density is eased somewhat by allowing for density inhomogeneities. However, unless the composition of the interstellar matter is atypical of most of the matter in the Universe, the mass density will be at least a factor of 3 below the critical density. For reasonable estimates of the pregalactic abundances, sufficient He-3 and Li-7 cannot be produced in the same model universe. Production of both Li-7 and H-2 requires large-amplitude primordial fluctuations, while sufficient He-3 and H-2 can be formed in very low-density, fairly homogeneous universes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 197; Apr. 15
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