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  • Analytical Chemistry and Spectroscopy  (849)
  • ASTROPHYSICS  (566)
  • Biochemistry and Biotechnology
  • 1980-1984  (1,667)
  • 1980  (1,667)
Collection
Keywords
Publisher
Years
  • 1980-1984  (1,667)
Year
  • 1
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    The effect of rotation on the hydrodynamics of stellar collapse (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: ASTROPHYSICS
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  • 2
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    Fragmentation in rotating isothermal protostellar clouds (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The paper reports results of an extensive set of three-dimensional hydrodynamic calculations performed to investigate the susceptibility of rotating clouds to gravitational fragmentation; only isothermal collapse sequences were considered. It is found that rotating isothermal gas clouds are unstable to fragmentation under a wide range of conditions. The degree of instability and the mode (ring vs. blob) of fragmentation is sensitive to alpha, but insensitive to beta. The initial amplitude of a perturbation does not appear to be crucial; fragmentation should occur eventually even for low-amplitude initial NAPs.
    Keywords: ASTROPHYSICS
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  • 3
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    Spectroscopic and polarimetric observations of NGC 1333 and the surrounding dark cloud complex (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Spectroscopy and polarimetry of several very red stars, noted on Near Infrared Photographic Sky Survey photographs in the region of NGC 1333, have yielded a 'map' suggesting the extent of polarization arising from a two-cloud structure in the region. Spectral types and color indices of the stars make it possible to infer that grain radii in the clouds exceed typical interstellar medium values and, further, that they increase with optical depth into the cloud. The present observations indicate that the cloud structure is far more extensive than previously realized.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 85; Dec. 198
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  • 4
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    Collapse and equilibrium of rotating, adiabatic clouds (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A numerical hydrodynamics computer code analysis of the collapse and establishment of equilibrium of adiabatic gas clouds restricted to axial symmetry found that the clouds are originally uniform in density and rotation. The method can compare the dynamic collapse and approach to equilibrium with the data on incompressible uniformly rotating equilibrium clouds and on equilibrium structures of differentially rotating polytropes. It is concluded that the stellar formation theory indicates that the low alpha fragments produced at the termination of the dynamic isothermal collapse phase of interstellar clouds may undergo significant dynamic collapse in an adiabatic regime leading to transitory ring formation and additional fragmentation on a smaller scale.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
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  • 5
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    Comparisons of interstellar CH/+/ and H2 (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Copernicus observations of H2 toward stars in the Pleiades and 23 Orionis have been obtained because of their importance in understanding the formation of interstellar CH(+). No model of CH(+) equilibrium seems to agree very well with these observations; in particular, the suggestions that CH(+) is formed either from collisions between vibrationally excited H2 and C(+) or from radiative association of C(+) and H2 can apparently be excluded. These data do suggest that there is a correlation between the amounts of rotationally excited H2 and CH(+) which are present. Observations of the Pleiades also help interpretations of the reflection nebulae near these stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
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  • 6
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    Axial rotation, tangled magnetic fields, and theoretical models of very massive stars (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A simple method of computing theoretical models of very massive stars endowed with fast axial rotation and tangled magnetic fields is described and used in the present paper. Both of the two perturbing (nongravitational) forces induce changes in the luminosity and radius that are studied as functions of zero-age chemical composition, opacity, and evolutionary state of the interior. The central condensation of the star is found to have a significant influence on shifts of the upper main-sequence band in the H-R diagram if the perturbing force is concentrated in the stellar envelope (but not if the perturbing force is distributed so as to be approximately proportional to gravity everywhere); the layers of the envelope that contribute most heavily to the central condensation lie approximately at a radius fraction of r/R = 0.5. It is shown that fast uniform rotation and intense envelope magnetic fields lead to probably the largest possible shifts of the main-sequence band in the H-R diagram that rotation and magnetic fields can induce. These displacements are, however, too small to account for the total width of the observed main-sequence band at luminosities brighter than log (L/solar luminosity) = 4.5.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
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  • 7
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    The evolution of supernova remnants in different galactic environments and its effects on supernova statistics (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is shown that only a small fraction of the many supernovae in the Galaxy produces observable supernova remnants; this fraction, which is found to depend weakly on the lower mass limit of the SN progenitors, and more strongly on the specific characteristics of the associated interstellar medium, decreases from about 15% near the galactic center to 10% at R(gal) of about 10 kpc and drops nearly to zero for R(gal) greater than 15 kpc. Whether an SNR is detectable is determined by the density of the ambient interstellar medium in which it is embedded; it is found that SNRs are detectable only above some critical density (about 0.1 per cu cm). The presence of large low-density superbubble cavities around stellar associations due to the combined effects of stellar winds and supernova shells strongly suggests that a large portion of the detectable SNRs must have runaway stars as their progenitors.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
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  • 8
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    The unique cosmic event of 1979 March 5 (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The transient gamma-ray burst observed on March 5, 1979 by the nine spacecraft forming the interplanetary gamma-ray burst network is discussed. Measurements reveal the event to be unlike any previously observed gamma-ray burst or X-ray burster, with a maximum intensity greater than several thousandths erg/sq cm per sec, a rise time of less than 200 microsec, a narrow and featureless initial spike and a regular 8-sec oscillation with a compound pulse shape. The source of the transient has been localized to a region including the supernova remnant N 49 in the Large Magellanic Cloud, at a distance of 55 pc, and a ratio of X-ray point-source steady state to transient emission of less than 10 to the -9th was obtained. The identification of the burst source with the supernova remnant at that distance would require an enormous source output if it was radiated isotropically, and substantially less if beaming is present. Alternatively, the event could be explained by a nearby, invisible neutron star.
    Keywords: ASTROPHYSICS
    Type: Comments on Modern Physics; vol. 9
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  • 9
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    On the phase-locked polarization variations in Cygnus X-1 (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The paper presents data on the accumulated V-band orbital phase curves of polarization in Cygnus X-1 which disagree with the analysis of Simmons, Aspin, and Brown (1980). No curves which conform to the canonical model were observed, and a noncanonical structure is indicated by F tests on third, fourth, and fifth harmonics, which have a probability of 0.85 as a group. The fifth harmonic has a probability of 0.99; in contrast, the fundamental harmonic has a probability of only 0.6, which is below the detection threshold. Therefore, major conclusions of Simmons et al based on a nonsymmetrical canonical model assuming that fundamental harmonics are present, but harmonics with n greater than 2 are absent, are unacceptable. Analysis of the author's data by Simmons et al is criticized on the grounds that he did not take into account the cumulative aspects of the data and did not recognize the need to average out the random noise generated by Cygnus X-1 over many orbital cycles.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 91; 1-2,; Nov. 198
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  • 10
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    The X-ray structure of two rich galaxy clusters and its implications for the detectability of microwave diminutions (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The X-ray observations of the galaxy clusters Abell 2319 and 576 show a reduced temperature of the microwave background due to the Suniaev-Zeldovich effect. The X-ray maps indicate smooth emission in these clusters concentrated toward the optical center; the surface brightness in the 1-3 keV band falls with the inverse square of radius outside a small core, and fits the Hubble's law of optical surface brightness of elliptical galaxies. The low temperature indicates that in A576 (1) the core radius of the gravitational potential is two to three times larger than inferred from galaxy counts, (2) the temperature rises with radius over most of the cluster and falls to zero at large radii, and (3) the gas does not obey the equation of state.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 241
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