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  • 1
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    Unknown
    In:  Other Sources
    Publication Date: 2011-08-17
    Description: Photometry in the UBV spectra was used to observe Aquila X-1. This X-ray source, usually producing flux on the order of 1-10% that of the Crab Nebula, often behaves in a manner resembling the behavior of galactic X-ray stars. A description of the calibration methods used in the observations is presented, with attention to photoelectric-photographic methods. These observations suggest a quiescent spectral class near Ko, i.e., a dwarf at a distance of 1.6 kpc. The more intense X-ray emissions are said to be generated from internal heating of the stellar atmosphere, with additional energy supplied by a low-mass companion star. This explaination is at variance with the semi-detached Roche model.
    Keywords: ASTROPHYSICS
    Type: Nature; 271; Feb. 16
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  • 2
    Publication Date: 2011-08-17
    Description: The problems of the generation and detection of gravitational waves and the difficulty of detecting the burst of gravitational radiation produced by a stellar collapse in our Galaxy, or in neighbouring clusters of galaxies where such collapses are expected to occur frequently, have been reviewed elsewhere. As stellar collapses, explosions, or supernovae are poorly understood, the values of the strength of these sources depend on uncertain assumptions. However, it is possible to make some independent estimates on semi-empirical grounds, using observed facts concerning the remnants of stellar evolution. These estimates, reported here, have serious weaknesses. They must involve oversimplified models and very crude standard calculations of the collapse and radiation processes. Also, because they are based on observed properties of stellar remnants, they say nothing about collapses which do not produce observable remnants. Although this selection may introduce a strong bias, these estimates deserve consideration because they are tied to real data.
    Keywords: ASTROPHYSICS
    Type: Nature; 283; Feb. 7
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  • 3
    Publication Date: 2019-06-27
    Description: The disk model of Shakura and Sunyaev (1973) and Novikov and Thorne (1973) is used to calculate temperature distributions and integrated spectral fluxes for disks around a typical white dwarf and a typical neutron star, under the assumption that each element of the disk locally radiates as a blackbody. In addition, the disks' integrated UBV colors are calculated using the grid colors for real model atmospheres calculated by Buser and Kurucz (1978) and the observed colors given by Allen (1973). In all the calculations the effect of radiation from one part of the disk on all the other parts is included.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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  • 4
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: The blue and red shift jitter observed in SS 433 is examined with a view to determining its sources. The jitter is characterized by a Delta-z rms amplitude of 0.01, corresponding to a 3000 km/sec Doppler velocity, which is larger than either the width or the error of measurement of the shifted lines. In addition, the amplitude of the jumps is not strongly dependent on the phase in the 164-day cycle, and the amplitudes of the jitter in the redshifted and blueshifted branches are comparable. It is shown that these features set strong constraints on models proposed for SS 433 by Sarazin et al. (1980), Katz (1980), and Van den Heuvel et al. (1980).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters; 23; 1, 19; 1982
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  • 5
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: Gamma-gamma pair production and annihilation in gamma-ray burst source regions are calculated. These processes do not produce effective collimation of the flux above pair production threshold, but when repeated approximately 1/alpha times, higher order processes soften the spectrum and permit escape of intense fluxes.
    Keywords: ASTROPHYSICS
    Type: Astronomy Express (ISSN 0265-5365); 1; 89-95
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  • 6
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    In:  Other Sources
    Publication Date: 2019-06-27
    Description: Some theoretical problems posed by the observations of SS 433 are considered. The monoenergetic beams point toward a gas-dynamic acceleration process. In this model the collimation implies that the acceleration occurs in a region of slab symmetry, possibly the surface layers of an accretion disk. The 164 day rotation of the beam pattern may be explained as a precession period.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 236
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  • 7
    Publication Date: 2019-06-27
    Description: Spherically symmetric, steady state accretion of an ionized hydrogen plasma onto a neutron star is considered for accretion rates which exceed a critical rate at which the Eddington limiting luminosity is produced. The coupled hydrodynamic and frequency integrated, radiative transfer equations are solved for accretion rates up to 10 times the nominal limit. Steady state solutions are presented that imply a multiplicity of different luminosity solutions for a single accretion rate in this 'supercritical' regime.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 236
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  • 8
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    In:  Other Sources
    Publication Date: 2019-06-27
    Description: Both HerX-1 and SS433 may contain accretion disks slaved to a precessing companion star. If so, it is possible to bound the effective viscosity in these disks. The results, in terms of the disk parameter alpha, are lower bounds of 0.01 for HerX-1 and of 0.1 for SS433.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters; 20; 4, 19; 1980
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  • 9
    Publication Date: 2019-06-28
    Description: High-precision digital spectra of the HDE 226868/Cygnus X-1 system have been obtained at a variety of orbital phases, using a Digicon photon counting array at the coude focus of the Lick Shane reflector. The spectra have been cross-correlated to search for evidence for the existence of a luminous stellar companion to HDE 226868, as has been suggested by several models where the secondary star is not a black hole. We find no evidence for such a star and place a lower limit on the difference between HDE 226868 and its companion of 4 magnitudes. This limit rules out all of the models for the Cygnus X-1 system calculated by Avni and Bahcall which include main-sequence stars as secondaries rather than black holes. A merit function generally useful for cross-correlation of digital spectra is described.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 240
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  • 10
    Publication Date: 2019-06-27
    Description: Data from a SAS 3 observation of Cygnus X-1 have been analyzed, assuming a simple shot-noise model for the time variability. The results confirm the suggestion of Sutherland, Weisskopf, and Kahn that the shot parameters are constant when the source is in its low state. The first significant measurement of the time sense of the shot-noise pulses was performed, with the result that the average pulse shape is time-symmetric, not asymmetric as has been previously assumed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 223
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