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  • ASTROPHYSICS  (1,248)
  • 1990-1994  (1,248)
  • 1992  (1,248)
  • 1
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    On the decay of the magnetic fields of single radio pulsars (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We investigate the statistical evidence for the decay of the magnetic field of single radio pulsars. We perform population syntheses for different assumed values for the time scale of field decay using a Monte Carlo method. We allow for the selection effects in pulsar surveys and compare the synthesized populations with the observed pulsars. We take account of the finite scale height of the distribution in the Galaxy of free electrons, which determine the dispersion measure and hence the apparent distance of radio pulsars. Our simulations give much better agreement with the observations if the time scale for the field decay is assumed to be longer than the typical active life time of a radio pulsar. This indicates that no significant field decay occurs in single radio pulsars.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); p. 198-212.
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  • 2
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    Diagnostics of disk-magnetosphere interaction in neutron star binaries (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The interaction between the magnetospheres of accreting neutron stars and accretion disks plays at key role in determining the properties of many accretion-powered neutron star X-ray sources and the recycled binary and millisecond rotation-powered pulsars. Here we show that the behavior of the horizontal branch quasi-periodic intensity oscillations in low mass X-ray binaries and the correlation between the magnetic fields and periods of binary and millisecond pulsars are sensitive probes of the state of the inner disk.
    Keywords: ASTROPHYSICS
    Type: ; : Problems in the ae
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  • 3
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    COBE DMR results and implications (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This lecture presents early results obtained from the first six months of measurements of the Cosmic Microwave Background (CMB) by Differential Microwave Radiometers (DMR) aboard COBE and discusses significant cosmological implications. The DMR maps show the dipole anisotropy and some galactic emission but otherwise a spatially smooth early universe. The measurements are sufficiently precise that we must pay careful attention to potential systematic errors. Maps of galactic and local emission such as those produced by the FIRAS and DIRBE instruments will be needed to identify foregrounds from extragalactic emission and thus to interpret the results in terms of events in the early universe. The current DMR results are significant for Cosmology.
    Keywords: ASTROPHYSICS
    Type: In: The infrared and submillimetre sky after COBE; Proceedings of the NATO Advanced Study Institute, Les Houches, France, Mar. 20-30, 1991 (A93-51701 22-90); p. 331-344.
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  • 4
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    The origin of the extremely metal-poor post-AGB stars (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Certain A-F supergiants show almost solar photospheric abundances of C, N, O, S, and Zn, while Fe, Mg, Ca, Si, Cr, and other elements are more than two orders of magnitude below solar. We suggest that the present photosphere was originally solar in composition; the missing elements were incorporated into dust grains that were separated from the atmosphere. The heavy-element-depleted gas comprises the present photosphere. There are two possible mechanisms by which this process might take place: capture by the presently visible star of the depleted gas from a binary companions, or the rapid termination of a vigorous stellar wind in a single star, so that the grains are blown outward through the expanding envelope. Besides the abundance peculiarities, the hypothesis explains why some objects have carbon-rich dust outside of an oxygen rich photosphere, why these stars have the rather narrow range of (T(eff), log g) near (7000 K, 1.0), and why some might have a great deal of circumstellar dust while others have little. Perhaps the most serious objection to the hypothesis is the possible presence of stellar winds observed in the winds of the peculiar post-AGB stars themselves.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 259; 2; p. L39-L42.
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  • 5
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    Particle acceleration at comets (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper compares calculated and measured energy spectra of implanted H(+) and O(+) ions on the assumption that the pickup geometry is quasi-parallel and about 1 percent of the waves generated by the cometary pickup process propagates backward (towards the comet). The model provides a good description of the implanted O(+) and H(+) energy distribution near the pickup energies.
    Keywords: ASTROPHYSICS
    Type: In: Particle acceleration in cosmic plasmas; Proceedings of the Workshop, Bartol Research Inst., Newark, DE, Dec. 4-6, 1991 (A93-39976 16-93); p. 267-272.
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  • 6
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    Constraints on dark matter from intergalactic radiation (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Several of the dark matter candidates that have been proposed are believed to be unstable to decay, which would contribute photons to the radiation field between galaxies. The main candidates of this type are light neutrinos and axions, primordial mini-black holes, and a nonzero 'vacuum' energy. All of these can be constrained in nature by observational data on the extragalactic background light and the microwave background radiation. Black holes and the vacuum can be ruled out as significant contributors to the 'missing mass'. Light axions are also unlikely candidates; however, those with extremely small rest energies (the so-called 'invisible' axions) remain feasible. Light neutrinos, like those proposed by Sciama, are marginally viable. In general, we believe that the intergalactic radiation field is an important way of constraining all types of dark matter.
    Keywords: ASTROPHYSICS
    Type: Vistas in Astronomy (ISSN 0083-6656); 35; p. 439-478.
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  • 7
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    Non-linear effects of QED multiple-photon processes on cyclotron spectra (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The relativistic magnetic resonant multiple-photon processes are discussed up to order alpha(f)exp 2, in particular two-photon scattering and two-photon emission. The latter also contributes to the opacity and photon production, although more weakly than the scattering. These processes are nonlinear in the radiation field, and therefore the transfer depends sensitively on the cross sections. We show model spectra including three cyclotron harmonics for the accreting pulsar Her X-1 and the gamma-ray burster GB880205. The lines are highly polarized, and their depth is sensitive to the polarization treatment.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 369-376.
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  • 8
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    Polarization cancellation in the two-component winds from Wolf-Rayet stars (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: In this paper we explore the possibility that there can be at least partial cancellation of the equatorial disk polarization as a result of scattering from the electrons that are present in the strong polar wind of WR stars. In order to achieve the cancellation necessary to explain the wavelength-dependent polarization, the polar wind must have a mass-loss rate that is near the maximum that is supported by radiation-driven wind theory. In addition, we find that it is possible to derive important new information regarding the relative column masses of the polar and equatorial winds.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 401; 1; p. 311-316.
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  • 9
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    Hydrodynamical evolution of coalescing binary neutron stars (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The hydrodynamics of the final merging of two neutron stars and the corresponding gravitational wave emission is studied in detail. Various test calculations are presented, including the compressible Roche and Darwin problems and the head-on collision of two polytropes. A complete coalescence calculation is presented for the simplest case of two identical neutron stars, represented by Gamma = 2 polytropes, in a circular orbit, with their spins aligned and synchronized with the orbital rotation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 401; 1; p. 226-245.
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  • 10
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    Radio continuum and radio recombination line observations of Sagittarius B1 and G0.6-0.0 (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Continuum emission and H110-alpha recombination line emission from Sgr B1 and G0.6-0.0 have been observed using the VLA. It is shown that Sgr B1 is a region of great complexity, both spatially and kinematically. The continuum observations show that this region is dominated by many extended features rather than compact sources. On the other hand, Sgr B2 is dominated by several ultracompact H II regions. The two regions may be in different stages of evolution, with Sgr B1 being older, perhaps by as much as 0 exp 6 yrs. The recombination line study shows that Sgr B1 is composed of two distinct kinematic regions, a simple western one and a more complex eastern one. G0.6-0.0 is a region composed of at least four ultracompact H II regions that is situated between Sgr B1 and Sgr B2. There is an arc of ionized gas that lies to the east and to the south of these compact regions. The velocity of G0.6-0.0 is intermediate between those of Sgr B1 and Sgr B2. These facts strengthen the argument that these regions are physically associated.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 401; 1; p. 168-181.
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