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  • ASTROPHYSICS  (943)
  • 1985-1989  (943)
  • 1965-1969
  • 1950-1954
  • 1987  (943)
  • 1
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    Nucleus of comet Halley as a torque-free rigid rotator (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model for the rotation of the nucleus of comet Halley is proposed on the assumption that the nucleus is homogeneous and a torque-free rigid rotator. It spins about its long axis with a period of 7.4 days, while this axis precesses about a fixed direction with a period of 2.2 days. To satisfy the moments of inertia, the precession angle must be 77 deg. This model settles the major problems associated with the recent controversy about two rotation periods.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 325; 326-328
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  • 2
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    Pioneer 10 and 11 observations of waves upstream of interplanetary corotating shocks (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An extended region of enhanced magnetic field fluctuations is found upstream of some of the corotating shocks observed by Pioneer 10 and Pioneer 11 between 1 and 5 AU. This perturbed region is present when the corotating shock, generally quasi-perpendicular, becomes oblique or quasi-parallel due to a temporary out-of-spiral direction of the upstream magnetic field. The observed waves are almost not compressional. Their amplitude is a large fraction of the ambient field, and their frequency is around 1 mHz in the spacecraft frame. A brief discussion of the possible mechanisms of generation is given.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 285-290
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  • 3
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    Collisionless coupling in the AMPTE artificial comet (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Analysis of previously reported observations of the solar wind-barium interaction associated with the AMPTE artificial comet release of Dec. 27, 1984, is presented. On the basis of these results it is argued that solar wind couples momentum (and energy) to the barium ions through both laminar and turbulent processes. The laminar forces acting on the particles are the laminar electric and magnetic fields; the turbulent forces are associated with the intense electrostatic wave activity. This wave activity is shown to be caused by a cross-field solar wind proton-barium ion streaming instability. The observed wave frequencies and saturated amplitudes are consistent with the theoretical analysis.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 47-54
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  • 4
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    Are small diamonds thermodynamically stable in the interstellar medium? (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Very small diamond particles (50 A diameter) are shown to be thermodynamically stable with respect to similar sized graphite particles for reasonable values of the surface free energies of diamond and graphite. Small diamonds are likely to be stable against both thermal evaporation and chemical attack in the general interstellar medium. A few of the consequences of these conclusions are examined.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 139; 1, De
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  • 5
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    The ultraviolet variability of AY Ceti (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: AY Cet is a single-line binary comprised of a spotted G5 III primary and a white dwarf secondary. A series of UV spectra have been obtained with the IUE satellite on five different dates covering a substantial part of the optical cycle of the primary star. No evidence that the continuum or the Ly-alpha absorption line of the secondary star varied is found. There were significant changes in the strengths of the UV emission lines, but the variations were only weakly correlated with either the orbital phase of the binary or the rotational phase of the primary. The UV emission lines were especially strong near maximum visual brightness at a time when the starspot(s) on the primary was least visible. The enhanced line emission is attributed to a flare event on the primary, most likely at a high-latitude site close to the pole of this star. The UV radiative losses of this flare were comparable with those of flares previously observed on the RC CVn variables Lambda And and HR 1099.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 94; 1657-166
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  • 6
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    On the saturation of the refractive index structure function. II - Influence of the correlation length on astronomical 'seeing' (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A physical length scale in the wavefront corresponding to the parameter (r sub 0) characterizing the loss in detail in a long exposure image is identified, and the influence of the correlation scale of turbulence as r sub 0 approaches this scale is shown. Allowing for the effect of 2-point correlations in the fluctuations of the refractive index, Venkatakrishnan and Chatterjee (1987) proposed a modified law for the phase structure function. It is suggested that the departure of the phase structure function from the 5/3 power law for length scales in the wavefront approaching the correlation scale of turbulence may lead to better 'seeing' at longer wavelengths.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 229; 379-382
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  • 7
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    Microturbulence in the upper photosphere of Alpha Persei (F5 Ib) derived from ultraviolet spectral observations (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-resolution ultraviolet spectra of the moderate supergiant Alpha Per (F5 Ib) were studied to determine the dynamic state of its upper photosphere. It was found that the line-of-sight microturbulent velocity component in the region of origin of the UV spectrum is about 5 km/s, and is slightly smaller than the value derived from the visual spectrum. This is ascribed to dissipation of mechanical energy between the higher and lower layers where, respectively, the ultraviolet and visual light lines originate. Between these two levels, which are one scale height apart, the mechanical energy flux decreases to about 0.3 of its photospheric value. The consequent value for the (outward directed) turbulent acceleration is 24 cm/sec-squared, more than one half the observationally determined effective acceleration of gravity.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 185; 1-2,
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  • 8
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    Deconvolution of a pre-outburst picture of SN 1987A (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The block iterative method (Young 1971) of algebraic image restoration is applied to a photographic plate of the field around SN 1987A obtained 4 yr before outburst by Chu at the CTIO 4-m telescope. By setting appropriate constraints for the solution on a pixel-by-pixel basis, the image of a starfield centered on Sk -69 202, the precursor to the supernova, is restored. It is found that this star has two companions, which others (e.g., Walborn et al., 1987 and West et al., 1987) have also noted and designated as Star 2 and Star 3. Also found is marginal evidence for Star 4, a weak source at theta = 222 deg, r = 1.9 arcsec. Correction for the contributions of these companions yields an estimate of the magnitude for Sk -69 202 alone of V = 12.37.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 185; 1-2,
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  • 9
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    Helium diffusion in stars and the value of the cosmological constant (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effect of He diffusion on the evolution of stars is to speed it up by increasing the mean atomic weight at the center, thereby minimizing the apparent conflict between the great ages of globular clusters and the age of the universe, as arrived at via the Hubble constant. Attention is presently given to the consequences of work on this effect by Noerdlinger and Arrigo (1980) and Stringfellow et al. (1983), implying that Tayler's (1986) estimate for globular clusters of 16 Gyr should be reduced to 13 Gyr.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Quarterly Journal (ISSN 0035-8738); 28; 345
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  • 10
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    Particle acceleration and production of energetic photons in SN1987A (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A pulsar wind model for the acceleration of particles in SN1987A is discussed. The expected photon flux is investigated in terms of the spectrum of parent protons and electrons, the nature of the region in which they propagate after acceleration, and the magnetic field and radiation environment which determines the subsequent fate of produced photons. The model is found to produce observable signals if the spin period of the pulsar is 10 ms or less.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 329; 314-316
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  • 11
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    Observations of jets from low-luminosity stars. II - SVS 12, HH 30, near HL Tauri, and HH 34 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Spatially resolved spectral scans were obtained for four Herbig-Haro jets emanating from low-luminosity premain-sequence stars. There appears to be a general tendency for the excitation and electron density to diminish along these jets. For three jets, the electron density dependence is close to 1/r. HH 30's scattered stellar continuum showed much weaker Fe II lines in 1985 than in 1979, indicative of variable stellar activity. The most distant knot in HH 34's jet has the lowest excitation of any known HH object, with S II-line/H-alpha = 12.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 321; 846-854
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  • 12
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    The unusual radio outburst of Nova Vulpeculae 1984 No. 2 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Multifrequency radio monitoring of Nova Vulpeculae 1984 No. 2 has revealed a unique radio light curve, exhibiting a strong outburst which precedes the appearance of normal radio emission from the principal ejecta of the nova by at least 100 days. The early emission is extremely optically-thick and has brightness temperature in excess of 100,000 K. A model is discussed in which the radiation is produced by a strong shock propagating outward through the principal ejecta of the nova, as a result of an interaction with a later, high velocity wind from the central source. It is shown that the general features of the radio light curve can be explained by the presence of a central wind with a mass loss rate of about 0.00001 solar masses/yr, lasting for a period of 200 to 300 days after the optical outburst. The first radio map of nova ejecta shortly after outburst is presented. Comparison of the angular expansion rate to the ejection velocity implies a distance of 3.6 kpc, and preliminary analysis of the main outburst emission indicates a mass and kinetic energy of the ejecta respectively of about 0.0008 solar masses and 8 x 10 to the 45th erg.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 183; 1, Se
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  • 13
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    Observable properties of E0 triaxial galaxies - A test for triaxiality (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown that most triaxial galaxies oriented in space to appear as E0 galaxies should have observable rotation velocities. By projecting Levison and Richstone's (1987) triaxial models so that they look like E0s, it was found that v/sigma can be as large as 1.0. In a separate argument, the observed distribution of axial ratios of ellipticals was used to show that between 3 percent and 23 percent of E0 galaxies are intrinsically flattened systems. Thus, if elliptical galaxies are triaxial then some E0 galaxies should have observable rotation velocities.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 320; L93-L97
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  • 14
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    Polyoxymethylene in Comet Halley (1987)
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    Publication Date: 2011-08-19
    Description: It is shown that polyoxymethylene (POM) with n about four or five explains the mass spectrum obtained with the PICCA instrument during the Giotto encounter with Comet Halley. A sequence of processes is presented showing the likelihood that POM will form under interstellar conditions. A preliminary comet coma model that includes POM is presented which predicts a qualitatively correct spectral intensity behavior when compared with observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 320; L149-L15
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  • 15
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    Spectral signatures of jumps and turbulence in interplanetary speed and magnetic field data (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown here that, consistent with a suggestion of Burlaga and Mish (1987), the f exp -2 spectra in the magnitudes of the magnetic and velocity fields in the solar wind result from jumps due to various rapid changes in the time series for these quantities. If these jumps are removed from the data, the spectra of the resulting 'difference' time series have the f exp -5/3 form. It is concluded that f exp -2 spectra in these magnitudes arise from phase coherent structures that can be distinguished clearly from incoherent turbulent fluctuations.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 10
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  • 16
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    Light scattering in cometary dust comae (1987)
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    Publication Date: 2011-08-19
    Description: Single and multiple scattering calculations were performed for a spherically symmetric cometary atmosphere irradiated by a plane parallel source. It is suggested that the increased flux found for anisotropic phase functions is due to the effect of directional scattering in the forward sun-comet axis. The isotropic multiply scattered flux at the surface is shown to be an increasing function of the opacity (tau) for tau of less than about 2.5. At large tau values, the maximum in the downward directed scattered flux still increases, but occurs at a height of several radii above the nucleus, resulting in a reduction at the surface. Results suggest that, except in the vicinity of the sun-comet axis, the plane parallel geometry tends to underestimate the degree of scattering.
    Keywords: ASTROPHYSICS
    Type: Earth, Moon, and Planets (ISSN 0167-9295); 39; 51-74
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  • 17
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    Count Bowell at record heliocentric distance (1987)
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    Publication Date: 2011-08-19
    Description: New observations of Comet Bowell at the record distance of 13.6 AU are presented. An extended coma is present, the size of which is consistent with the same slow expansion rate of roughly 1 m/s detected around perihelion. The cross-section of the solid grains within the central 10 arcsec of the coma has decreased by over an order of magnitude since 1980-84, which indicates that the coma production is declining. The decline began near R of roughly 10 AU, the same distance at which production began on the preperihelion leg. The coma at R of 10 AU or less may be formed by sublimation of CO2 or an ice of similar volatility from the nucleus.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 328; 506-509
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  • 18
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    Formation of large-scale structure from cosmic-string loops and cold dark matter (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Some results from a numerical simulation of the formation of large-scale structure from cosmic-string loops are presented. It is found that even though G x mu is required to be lower than 2 x 10 to the -6th (where mu is the mass per unit length of the string) to give a low enough autocorrelation amplitude, there is excessive power on smaller scales, so that galaxies would be more dense than observed. The large-scale structure does not include a filamentary or connected appearance and shares with more conventional models based on Gaussian perturbations the lack of cluster-cluster correlation at the mean cluster separation scale as well as excessively small bulk velocities at these scales.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 328; 691-694
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  • 19
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    Orbital eccentricity in classical novae (1987)
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    Publication Date: 2011-08-19
    Description: The effect on the orbital parameters of a classical nova of the ejection of mass during the nova explosion is considered. The most easily observable consequence is the generation of a small eccentricity in the orbit which leads to a luminosity modulation at a period just longer than the orbital period. Observation of such an effect would have implications not just for interpreting the dynamics of the explosion but also for measuring the secular effect of tidal interaction after the outburst.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 328; 505
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  • 20
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    Regularly pulsed neutrinos from supernova SN1987A? (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Some consequences of the 8.9 millisecond periodicity observed in neutrino events from SN1987A with the Kamiokonde and IMB experiments are discussed. Interpreting the apparent period as a rotation of a compact object would imply that the neutrino emission is anisotropic and that the neutrino mass, averaged over all observed flavors, is less than 0.2 eV/c-squared. It is also noted that P = 8.9 ms is a reasonable period for very young pulsars.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 328; 503
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  • 21
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    Nonspherical supernova remnants. IV - Sequential explosions in OB associations (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Multisupernova remnants, driven by sequential supernova explosions in OB associations, are modelled by means of two-dimensional hydrodynamical calculations. It is shown that due to the Rayleigh-Taylor instability the remnants quickly evolve into highly irregular structures. A critical evaluation of the multisupernova model as an explanation for supershells is given.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 182; 1, Au; 120-126
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  • 22
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    Evolutionary sequences for horizontal branch stars (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new grid of canonical evolutionary horizontal branch (HB) sequences is presented. Sequences are computed for each combination of the following helium and heavy-element abundances, respectively: Y(main sequence) = 0.20, 0.25, 0.30, and Z = 0.0001, 0.001, and 0.01. The results show that the bifurcation point at which the HB morphology changes from redward-evolving tracks to tracks with blueward loops shifts to higher effective temperatures with increasing helium abundance or metallicity. The sequences can be used to study in more detail how a number of HB properties such as the HB lifetime, the effective temperature at the bifurcation point in the track morphology, the luminosity dropoff of the blue HB, and the luminosity width of the red HB depend on the composition.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 65; 95-135
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  • 23
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    Shock processing of interstellar dust - Diamonds in the sky (1987)
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    Publication Date: 2011-08-19
    Description: The processing of interstellar dust grains by strong shock waves is studied, with the emphasis on the effects of grain-grain collisions. Such collisions provide the high pressures required to transform interstellar graphite and amorphous carbon grains into diamonds. Diamond metamorphism is as important for the destruction of such grains as vaporization and sputtering. It is calculated that about 5 percent of the C is expected to be in the form of 5-100 A diamonds in the interstellar medium. These results support the suggested interstellar origin for the recently discovered small meteoritic diamonds by providing a feasible interstellar formation mechanism.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 319; L109-L11
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  • 24
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    Quantized synchrotron radiation in strong magnetic fields (1987)
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    Publication Date: 2011-08-19
    Description: Spectra from electrons making synchrotron transitions in high magnetic fields are calculated using the exact quantum transition rates for Landau states up to n = 500, and the results are compared with spectra calculated from the classical formula and the asymptotic quantum formula. The behavior of the transition rates are examined at low and high harmonics as a function of the spin state of the electron. The calculations confirm those of Herold, Ruder, and Wunner (1982) for low Landau states, extending them to higher states and individual spin state transitions. The results also confirm the dominance of ground-state transitions at high field strengths noted by White (1976). Single particle emissivities for electrons with both spin-up and spin-down in the initial state are calculated using these transition rates. Spectra for thermal electron distributions at transrelativistic temperatures and for steady state injection of monoenergetic electrons with isotropic pitch angles are also presented.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 319; 939-950
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  • 25
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    Molecular and atomic clouds associated with infrared cirrus in Ursa Major (1987)
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    Publication Date: 2011-08-19
    Description: Observations of CO and H I revealed that in Ursa Major the high-latitude far-infrared 'cirrus' emission discovered by the Infrared Astronomical Satellite comes from molecular and atomic clouds. These clouds differ sufficiently from the large clouds in the Galactic plane so that the ratio of H2 column density to velocity-integrated CO radiation temperature, N(H2)/W(CO), derived from Galactic plane surveys, may not apply to them. On the assumption of a constant gas-to-dust ratio, it is argued that the cirrus emission in Ursa Major is a good mass tracer, since both the atomic and the molecular gas are probably optically thin at visual wavelengths, and the grains are heated not by local sources but by the background field of Galactic starlight. The N(H2)/W(CO) ratio thus derived for those diffuse clouds, is significantly lower than the ratio applicable to Galactic plane surveys.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 319; 723-729
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  • 26
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    Numerical simulation of the generation of turbulence from cometary ion pick-up (1987)
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    Publication Date: 2011-08-19
    Description: Observations of magnetic field fluctuations near Comet Halley have revealed a rapid development of a Kolmogoroff-like turbulence spectrum extending from below 0.01 Hz to above 0.1 Hz. Spectra obtained far from the comet have a strong peak in power near the Doppler-shifted ion-cyclotron frequency of singly ionized water. Closer to the comet, the spectrum at higher frequencies is enhanced in power level over the background solar wind spectrum by approximately an order of magnitude. The equations of incompressible MHD are solved using a two-dimensional 256 x 256 mode spectral method code to simulate this spectral evolution as an inertial range turbulent cascade. The initial conditions contained a constant magnetic field and a single coherent wave mode at a low wave number. The solar wind turbulence was modeled by a background noise spectrum having a Kolmogoroff spectral index. The coherent mode decayed into an inertial range spectrum with Kolmogoroff slope within a few eddy-turnover times. Both the time scale and the increase in power level of the turbulence seen in the simulation are in accord with the Giotto observations.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 860-863
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  • 27
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    IRAS observations of southern molecular clouds (1987)
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    Publication Date: 2011-08-19
    Description: A report is given of a project to use IRAS Band 3 (60 microns) and Band 4 (100 microns) observations to investigate the far-infrared properties of southern galactic molecular clouds. A method by which dust temperature and total gas column density can be estimated is presented. Results are tabulated for 65 prominent southern far-infrared sources. The dust temperatures are closely grouped between 30 and 50 K, while the column densities range between 2 x 10 to the 20th and 10 to the 22nd/sq cm. Maps of dust temperature and gas column density have been generated for two fields containing far-infrared sources to illustrate the effectiveness of this form of presentation.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 227; 1013-102
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  • 28
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    X-ray spectra and atmospheric structures of bursting neutron stars (1987)
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    Publication Date: 2011-08-19
    Description: Atmospheric structures and emitted X-ray spectra of bursting neutron stars are investigated. Theoretical curves are fitted to observational ones on the color temperature vs. luminosity diagram and two relations among mass, radius, and distance of the bursters are obtained. The fit of the theoretical curve to observations is statistically acceptable. Two possible sets of mass, radius, and distance to the X-ray bursts source MXB 1636-536 are derived, taking into account absorption lines at 4.1 keV, theoretical mass-radius relations of neutron star models, and the distance to the Galactic center. If the absorption line is due to Cr XX III, then M = 1.7-2.0 solar masses, R = 11-12 km, and d = 6.3-6.7 kpc, and if it is due to Fe XXV, then M = 1.8-2.1 solar masses, R = 8-10 km, and d = 5.8-6,4 kpc. The distance to the Galactic center is almost the same as that to MXB 1636-536.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of Japan, Publications (ISSN 0004-6264); 39; 2, 19; 287-308
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  • 29
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    Optical and UV spectroscopy of the black hole binary candidate LMC X-1 (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Both further optical spectroscopy of the binary star identified with LMC X-1, obtained between 1983 and 1985, and a series of IUE UV spectra taken during a 5 day interval in 1984 are presented. The optical data are used to refine the orbital period to 4.2288 days, and improved orbital parameters are derived. The velocity of the optical emission lines is antiphased with the absorption lines and has twice the velocity amplitude. These new results support the estimates of the masses in the system given earlier. The most probable component masses are approximately 20 solar masses for the primary and near 6 solar masses (for the x-ray star), suggesting the the latter may be a black hole. The UV spectra show very weak, low-velocity stellar-wind lines. It is suggested that much of the surrounding medium is highly ionized by the X-ray flux. The 'nonwind' UV spectral lines and the UV continuum temperature are consistent with the optical data, indicating a late O type star of M(bol) = -8.5. There is a weak modulation of absorption-line strengths with orbital phase, suggestive of a lack of axisymmetry in the X-irradiation of the primary star and indicative of a fairly low orbital inclination.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 94; 340-344
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    The hydrogen coverage of interstellar PAHs (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a UV photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense UV fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments.
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    Photometric light curves for seven rapidly-rotating K dwarfs in the Pleiades and Alpha Persei clusters (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Light curves and period estimates were obtained for several Pleiades and Alpha Persei cluster K dwarfs which were identified as rapid rotators in earlier spectroscopic studies. A few of the stars have previously-published light curves, making it possible to study the long-term variability of the light-curve shapes. The general cause of the photometric variability observed for these stars is an asymmetric distribution of photospheric inhomogeneities (starspots). The presence of these inhomogeneities combined with the rotation of the star lead to the light curves observed. The photometric periods derived are thus identified with the rotation period of the star, making it possible to estimate equatorial rotational velocities for these K dwarfs. These data are of particular importance because the clusters are sufficiently young that stars of this mass should have just arrived on the main sequence. These data could be used to estimate the temperatures and sizes of the spot groups necessary to produce the observed light curves for these stars.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 471-481
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    Modeling the Milky Way in the infrared (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The spatial distribution of stars in the Milky Way is modeled using an exponential disk with the addition of a de Vaucouleurs (1958, 1977, and 1979) R exp 1/4 spheroid. The present model is compared to 2-2.5-micron star counts and surface-brightness data and to IRAS 12-micron source counts. The data are consistent with a flattened bulge; it is maintained that a fraction of the bulge population has a considerable infrared excess.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 453-460
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  • 33
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    Evolutionary models of interstellar chemistry (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The goal of evolutionary models of interstellar chemistry is to understand how interstellar clouds came to be the way they are, how they will change with time, and to place them in an evolutionary sequence with other celestial objects such as stars. An improved Mark II version of an earlier model of chemistry in dynamically evolving clouds is presented. The Mark II model suggests that the conventional elemental C/O ratio less than one can explain the observed abundances of CI and the nondetection of O2 in dense clouds. Coupled chemical-dynamical models seem to have the potential to generate many observable discriminators of the evolutionary tracks. This is exciting, because, in general, purely dynamical models do not yield enough verifiable discriminators of the predicted tracks.
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    Optical observations related to the molecular chemistry in diffuse interstellar clouds (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations, which have been published since 1979, of molecular species in diffuse clouds are discussed. Particular attention is given to the ultraviolet measurements of CO with the Copernicus and IUE satellites and to ground-based optical measurements of CH, CH(+), CN, and 02. These data encompass large enough samples to test the chemical schemes expected to occur in diffuse clouds. Upper limits for other species (e.g., H2O, H2O(+), and C3) place restrictions on the pathways for molecular production. Moreover, analysis of the rotational distribution of the C2 molecule results in the determination of the physical conditions of the cloud. These parameters, including density, temperature, and the intensity of the radiation field, are necessary for modeling the chemistry.
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    The fate of the earth in the red giant envelope of the sun (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effect on the earth of entering the red giant envelope of the future sun is studied. Employing a 30-zone red giant model, the earth orbital decay timescale, neglecting ablation/vaporization, is determined to be of the order of 200 years, rendering earth survival impossible. The effects of ablation/vaporization processes are found to increase the ballistic coefficient of earth, thereby setting the 200-year decay timescale as an upper limit.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 178; 1-2,
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  • 36
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    Thermal diffusion in partially ionized gases - The case of unequal temperatures (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Previous calculations of thermal diffusion coefficients in partially ionized gases are extended to the case of unequal neutral and ion temperatures and/or temperature gradients. Formulas are derived for the general case of a major gas as well as for minor atoms and ions. Strong enhancements of minor-ion thermal diffusion coefficients over their values in the fully ionized gas are found when the degree of ionization in the main gas is relatively low. However, compared to the case of equal temperatures, the enhancements are less strong when the neutrals are cooler than the ions. The specific case of the H-H(+) mixture, which is important in the study of solar and stellar atmospheres, is discussed as an application.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 178; 1-2,; 286-291
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  • 37
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    A search for sinusoidal gravitational radiation in the period range 30-2000 seconds (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Since condensed massive objects in binary systems should generate observable periodic gravitational radiation, a large fraction of which may appear in one harmonic of the orbital frequency, monochromatic Doppler frequency perturbations were searched for at about 9000 discrete frequencies in the 0.0005-0.0333-Hz band using predetection data taken with the Pioneer 11 spacecraft. The results of the search are presented, and formal sensitivities for the possible signals are discussed. The results are interpreted as observational thresholds for possible incident gravitational wave trains having polarization states and propagation directions that are a priori unknown.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 536-541
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  • 38
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    The nucleus of comet P/Arend-Rigaux (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Simultaneous broadband visual and infrared photometry of comet P/Arend-Rigaux is reported. Its VJHK colors are similar to other periodic comets and the class D asteroids. The visual flux decreased by 0.5 mag within 2 hr, while the thermal flux at 10 microns continued to decrease by 0.7 mag over 3 hr. These observations are consistent with thermal models of a nucleus with a geometric albedo of 0.03 and equivalent radii of 5.1 and 3.8 km.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 94; 169-173
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  • 39
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    The distribution of rotational velocities for low-mass stars in the Pleiades (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The available spectral type and color data for late-type Pleiades members have been reanalyzed, and new reddening estimates are obtained. New photometry for a small number of stars and a compilation of H-alpha equivalent widths for Pleiades dwarfs are presented. These data are used to examine the location of the rapid rotators in color-magnitude diagrams and the correlation between chromospheric activity and rotation. It is shown that the wide range of angular momenta exhibited by Pleiades K and M dwarfs is not necessarily produced by a combination of main-sequence spin-downs and a large age spread; it can also result from a plausible spread in initial angular momenta, coupled with initial main-sequence spin-down rates that are only weakly dependent on rotation. The new reddening estimates confirm Breger's (1985) finding of large extinctions confined to a small region in the southern portion of the Merope nebula.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 337-355
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  • 40
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    Forbidden coronal iron-like emission in the Puppis A shock front - The effect of inhomogeneities (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: CCD images of the shock front at the eastern rim of Pup A, obtained in the forbidden lines of Fe X (6374 A) and Fe XIV (5303 A), are reported and compared to Einstein high-resolution-image soft X-ray data. The observed part of the remnant is complex, containing density irregularities. Optical and X-ray data are consistent in showing a nearly flat gradient of ionization temperature behind the shock. To determine conditions in the shock, scans of surface brightness across it in the optical lines were compared to surface brightnesses predicted by idealized Sedov models. It was not possible to match both the red and green line scans by a simple, single-component model, and the failure is ascribed to the presence of the density inhomogeneities. This result has important implications for the determination of SNR shock-front models by fitting X-ray data with Sedov models.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 370-378
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  • 41
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    Inhomogeneous cosmology. III - Primordial gravitational waves and dust (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper, the properties of a special class of inhomogeneous cosmological models and the interaction of the inhomogeneities with the evolution of the background geometry and matter are studied. The cosmological model is chosen so that the initial inhomogeneities evolve into 'plane' gravitational waves propagating through a smooth Bianchi I dust background. It is shown how the inhomogeneities interact with matter, 3 K radiation, and the background geometry, causing the expansion to slow down in some regions and speed up in others. It is also shown how the gravitational waves can produce a 'dragging of the inertial frame' which will affect the observed distribution of matter and 3 K radiation. In particular, this frame-dragging effect can account for a major fraction of the obsserved dipole component between the 3 K background radiation and the rest frame of global matter, an effect usually assumed to have been produced by large-scale local motion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 1-14
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  • 42
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    Studies of calcium emission stars. I - HD 158393 a giant star in a binary system (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: HD 158393 is a giant star of spectral type late G or early K which has moderately strong Ca II H and K emission cores. UBVRIJHK photometry and IUE spectra reveal a companion of type F0-F2, luminosity class IV or V. Radial velocity data yield an orbit with a period of 31 day. The K and F stars have nearly equal mass, with a minimum value of 1.7 solar masses if i of less than 72 deg is adopted, as required by the absence of eclipses. The strong Ca II emission indicates the enhanced chromospheric activity which is typical of giant stars in a binary system of this period, and the light is variable in a 31-day period, indicative of synchronous rotation as well as on a long time-scale. Analysis of the 31-day light period by fitting a spot model indicates the presence of two spots in 1975 and 1976; the major spot appears to have been present throughout the observing period (1973-1981). The potential confusion caused by the presence of the second spot for part of the observing period emphasizes the importance of fitting a model if the photometric period is to be understood in terms of the synchronous rotation. The two spots showed different periods and were at different latitudes, suggesting differential rotation of the giant star.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 226; 813-827
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  • 43
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    Measurement of the He II radiation field in planetary nebulae through Bowen fluorescence (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Excitation of O III by He II is treated for sources over a useful range of densities to give accurate predictions of Bowen/non-Bowen line ratios. These are applied to recent observations of planetary nebulae to show that Bowen excitation increases monotonically with excitation class, and to deduce other important consequences.
    Keywords: ASTROPHYSICS
    Type: Physica Scripta (ISSN 0031-8949); 35; 6, Ju; 778
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  • 44
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    Possible models for the high-energy transient GB790107 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The properties of the high-energy transient GB790107 place severe constraints on the viability of models proposed for typical gamma-ray burst events as applied to this soft gamma-ray repeater. Here, the various models proposed for gamma-ray bursts are reviewed. It is shown that a model involving a comet cloud around a neutron star is consistent with the observational data.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 327; 398-400
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  • 45
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    Mass outflows associated with young stellar objects (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Properties of optical and molecular outflows associated with young stellar objects are discussed with emphasis placed on new results concerning outflow energetics, collimating structures, and the relationship between the outflow properties and the magnetic field geometry characterizing the host molecular clouds. Particular consideration is given to the IRAS observations of YSO mass outflows, which reveal extended far-IR emission associated with high-velocity molecular gas and in which a number of disk-like structures associated with YSO outflow sources were resolved. The disk axes appeared to lie along the direction of molecular outflows or stellar jets. The mass outflows showed a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds, suggesting that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.
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  • 46
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    Double layers and plasma-wave resistivity in extragalactic jets - Cavity formation and radio-wave emission (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Current driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur in extragalactic jets for estimated values of the carried currents. Strong plasma double layers, however, may exist within self-maintained density cavities. The relativistic double-layer-emitted electron and ion beams drive plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.
    Keywords: ASTROPHYSICS
    Type: Laser and Particle Beams (ISSN 0263-0346); 5; 169-175
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  • 47
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    Elemental abundance analyses with coadded DAO spectrograms. I - The field horizontal-branch stars HD-64488, 109995 and 161817 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is possible to improve the quality of elemental-abundance analyses by using higher-S/N data than has been the practice at high resolution. The procedures developed at the Dominion Astrophysical Observatory to coadd high-dispersion coude spectrograms are used with a minimum of 10 6.5-A/mm IIa-O spectrograms of each of three field hoorizontal-branch (FHB) A stars to increase the S/N of the photographic data over a considerable wavelength region. Fine analyses of the sharp-lined prototype FHB stars HD 109995 and 161817 show an internal consistency which justifies this effort. Their photospheric elemental abundances are similar to those of Population II globular cluster giants. As their photometric and spectrophotometric properties are similar to blue HB stars in such clusters, they are confirmed to be the brighter analogs of such stars. HD 64488, which is photometrically and spectrophotometrically similar to the FHB stars, is found to be metal-poor (Fe/H = -1) with much broader lines (v sin i = 147 km/s). The implications of the abundance anomalies of all three stars are discussed.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 226; 581-600
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  • 48
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    Surface brightness profiles of 10 comets (1987)
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    Publication Date: 2011-08-19
    Description: CCD photometric observations of the comae of 10 comets, obtained at the 4-m and 2.1-m telescopes at KPNO during 1985-1986 using filters centered at 700.5, 650.0, or 546.0 nm, are reported. The data are presented in extensive tables and graphs and characterized in detail. The radial surface brightness profiles are shown to be steeper than predicted by an idealized spherically symmetric steady-state comet model, the steepness increasing with the projected distance from the nucleus. These profiles are attributed, on the basis of Monte Carlo simulations, to imperfect coupling between the sublimated gas and the optically dominant grains of the coma.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 992-1001
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  • 49
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    Solar cycle study of interplanetary Lyman-alpha variations - Pioneer Venus Orbiter sky background results (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: PVO observations of the interplanetary Ly-alpha (IPL) background, obtained over an entire solar cycle (SC) from 1979 to 1985, are compiled and analyzed statistically, along with data from other instruments and earlier solar cycles. The results are presented in extensive tables and graphs and characterized in detail. Findings reported include SC variation of 1.8 for the longitudinally averaged IPL intensity (in agreement with the variation of the 27-d disk-averaged integrated solar Ly-alpha flux), yearly averaged ecliptic H-atom lifetime at 1 AU equal to 1.0 Ms at solar minimum and 1.5 Ms at solar maximum, interplanetary H density equal to 0.07 + or - 0.01/cu cm, and interplanetary H/He within the heliopause but far from the sun of 7 + or - 3.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 964-986
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  • 50
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    The C-12/C-13 isotope ratio of the interstellar medium in the neighborhood of the sun (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Data from observations of Xi Per, P Cyg, 20 Tau, and 23 Tau, obtained at 4232 and 3957 A using a coude spectrograph and a 1872-element reticon on the 3-m Shane telescope at Lick Observatory during 1984-1985, are combined with data on Zeta Oph (Hawkins et al., 1985) and used to estimate the C isotope ratio of the ISM near the sun. The results are presented in extensive tables and graphs and characterized in detail. The (C-12)H(+)/(C-13)H(+) abundance ratios toward the five stars are found to agree to within 12 percent and shown to be representative of the C-12/C-13 ratios in the gas, strongly indicating that the local ISM is homogeneous. The difference between the ISM ratio (43 + or - 4) and the solar-system value (89) is attributed to the chemical evolution of the ISM in the 4.9 Gyr since the formation of the sun.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 926-950
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    Gamma-ray burst localization by HEAO 3 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relative response of the five segments of the HEAO 3 gamma-ray-spectroscope anticoincidence shield (a 6.62-cm-thick 33.1-cm-OD 27.4-cm-high CsI cylinder) is used to estimate the directions of gamma-ray bursts on February 13, 1980 and September 29, 1979. The operation of the instrument and the data-analysis procedures are described, and the results are presented graphically. The 1980 event is located in an error box centered on alpha = 104.5 deg and delta = -15 deg (error box A of Atteia et al., 1987). The position of the 1979 event (alpha = 75 deg and delta = 40 deg) is shown to be consistent with ISEE 3 and Pioneer Venus Orbiter arrival times.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 846-851
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  • 52
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    Does lower Omega allow a resolution of the large-scale structure problem? (1987)
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    Publication Date: 2011-08-19
    Description: The intermediate angular scale anisotropy of the cosmic microwave background, peculiar velocities, density correlations, and mass fluctuations for both neutrino and baryon-dominated universes with Omega less than one are evaluated. The large coherence length associated with a low-Omega, hot dark matter-dominated universe provides substantial density fluctuations on scales up to 100 Mpc: there is a range of acceptable models that are capable of producing large voids and superclusters of galaxies and the clustering of galaxy clusters, with Omega roughly 0.3, without violating any observational constraint. Low-Omega, cold dark matter-dominated cosmologies are also examined. All of these models may be reconciled with the inflationary requirement of a flat universe by introducing a cosmological constant 1-Omega.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 564-575
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    Are the virial masses of clusters smaller than we think? (1987)
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    Publication Date: 2011-08-19
    Description: The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30 percent thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 593-600
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  • 54
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    On the polarization, compression and nonoscillatory behavior of hydromagnetic waves associated with pickup ions (1987)
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    Publication Date: 2011-08-19
    Description: Solution of the kinetic dispersion equation shows that heavy pickup ions with large perpendicular energies excite a new hydromagnetic wave mode with maximum growth, high (magnetic field and mass density) compression ratios, and almost linear polarization coexisting slightly away 6-15 deg from parallel propagation. The mode arises from the coupling of the heavy ion beam to the modified left-hand wave dispersion caused by the multiion nature of the medium. The ion beam can also bring about nonoscillatory, purely growing structures distinct from the mirror wave through the coupling of a counter-streaming left-hand mode to a costreaming right-hand wave. The free energy source parameters are varied to determine their relative influence and define the domain of existence of the instability. Its characteristics may prove helpful in the interpretation of recent cometary (Halley and Giacobini-Zinner) and artificial release (AMPTE) observations.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 495-498
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  • 55
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    Redshifts of low-X-ray luminosity clusters of galaxies (1987)
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    Publication Date: 2011-08-19
    Description: Measurements of redshifts and velocity dispersions are presented for Abell clusters A539, A1185, and A1228, and the southern clusters S1840-623, S1904-618, S1908-566, and S2000-561. All these clusters have reported X-ray luminosities or upper limits. Finding charts for the clusters are presented, and the measured heliocentric redshifts are given along with redshifts obtained by other investigators. Comments are made about each cluster. The technique used to derive the redshifts is summarized.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 93; 1350-135
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    Are the Galactic-bulge X-ray sources magnetized? (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper attempts to demonstrate that a better understanding of Galactic-bulge X-ray sources can be achieved if their magnetic moments are assumed to have the same values as those of young pulsars. It is argued that most of the matter leaving the inner edge of the accretion disk can reach the neutron star's surface in the form of massive clumps in quasi-Keplerian orbits. As a result, most of the accretion flow covers a broad equatorial belt rather than the polar caps, and the star shines as an almost unpulsed source. The liberation of half of the accretion power before the surface is reached can lead to the reported UHE pulses and bright infrared bursts. Spasmodic accretion is discussed as a model for gamma-ray bursts, and the observed low-energy X-ray absorption features are considered as an indication of strong magnetic fields shifted to lower energies during super-Eddington outbursts.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 177; 1-2,
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    Ion composition and upstream solar wind observations at comet Giacobini-Zinner (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The observations by the ion composition instrument (ICI) on the ICE spacecraft made during the encounter with comet P/Giacobini-Zinner (Ogilvie et al., 1986) are discussed in detail. Solar wind He-4(2+) kinetic temperatures, densities, and velocities before, during, and after the encounter are presented. These data combined with He-4(2+) velocity distributions provide evidence for the existence of a thick diffuse shock. Relative abundances of water group ions and CO(+) are derived along with an estimate of the abundance of an ion with M/Q = 24 + or - 1 amu/e. The ICI data are compared with electron data from two other experiments (Bame et al., 1986; Meyer-Vernet et al., 1986) and found to be in reasonable agreement in the region outside the tail. Spectroscopic data for several neutral and ionic species are compared with the ICI results for the water group ions and CO(+). The spectroscopic data are also used to eliminate Mg(+) and CN(+) as candidates for the M/Q = 24 peak. The two most likely candidates are C2(+) and Na(+), but neither photoionization of parent neutrals nor sputtering from dust grains is sufficient to explain the observed abundance relative to H2O(+).
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 39-46
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    Properties of a large-scale interplanetary loop structure as deduced from low-energy proton anisotropy and magnetic field measurements (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Correlated particle and magnetic field measurements by the ISEE 3 spacecraft are presented for the loop structure behind the interplanetary traveling shock event of Nov. 12, 1978. Following the passage of the turbulent shock region, strong bidirectional streaming of low-energy protons is observed for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magnetic field, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, a value of 3 AU is derived for the mean free path during the passage of the closed loop. It is inferred from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 6-14
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    A 1.6 MHz survey of the galactic background radio emission (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations of the galactic radio emission at 1.6 MHz have been made during the current solar activity minimum using a radio telescope with a beamwidth of 25 deg. The radiation intensity was mapped for six declinations between -12 and -72 degrees and from 1000 to 0500 hours R.A.
    Keywords: ASTROPHYSICS
    Type: Australian Journal of Physics (ISSN 0004-9506); 40; 5, 19; 705-708
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    Long-term cycles in cosmic X-ray sources (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Data on long-term cycles in galactic X-ray sources are reviewed, and classes of variations are identified including precessional activity, recurrent outbursts in Population II sources, and Be/neutron star flare cycles. Cycles of 30-300 days have been found in LMC X-4, Her X-1, SS433, and Cyg X-1 which represent cyclic variations in both the inner and outer parts of the accretion disk. Quasi-periodic cycles with periods ranging from 1/2 to 2 years have been noted in several low-mass X-ray binaries. It is suggested that periodic outbursts in the Be/neutron star systems may result from variable mass transfer in a wide eccentric orbit.
    Keywords: ASTROPHYSICS
    Type: Space Science Reviews (ISSN 0038-6308); 45; 3-4,
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    Determination of the masses of elliptical galaxies and clusters of galaxies with AXAF (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The procedures to be used in the determination of the mass and mass distribution of elliptical galaxies and clusters of galaxies, using spatially resolved X-ray spectra of galaxies and clusters of galaxies to be obtained by the imaging spectrometers on AXAF, are described. The procedures utilize the unique AXAF features of large band width, large field of view, high angular resolution, long exposure times, and the availability of sophisticated AXAF instrumentation. The techniques described involve the measurement of the surface brightness and temperature profiles of the hot gas trapped in the potential wells of these systems. Then, by using the equation of hydrostatic equilibrium, which relates the total mass inside a given radius to the size, absolute temperature, density gradient, and temperature profile, it will be possible to infer the mass distribution in these objects to large physical scales.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters and Communications (ISSN 0888-6512); 26; 1-2,
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  • 62
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    Primeval galaxies and cold dark matter (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In the context of the cold dark matter theory for the large-scale matter distribution, the onset of galaxy formation is a gradual process, with star formation being initiated at z = about 10 and reaching a peak for luminous galaxies at z = about 1. The mass function of galaxy cores matches the observed quasar luminosity function at z = 2-3. Primeval galaxies are envisaged as a collection of many interacting and merging clumps, attaining a peak luminosity that is an order of magnitude below that achieved in models in which galaxy formation is initiated abruptly. Hence, ongoing searches for primeval galaxies would not necessarily have been successful unless they are designed to find moderately low-luminosity, low-surface-brigtness extended objects at low redshift.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 323; L107-L11
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    The relative amounts of stars and interstellar matter in the local Milky Way (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper considers the balance between star formation and mass loss from evolved stars in the region within 1 kpc of the sun. There is considerably more mass in stars than in the interstellar medium, and more material is being incorporated into new stars than is being returned by evolved stars. In the simplest interpretation of the data, it appears that unless there is some infall of new interstellar gas, the era of substantial star formation out of interstellar gas will be over in a few (perhaps 3) billion years.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 1123-112
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    Modeling Halley before and after the encounters (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Numerical models developed prior to the 1986 spacecraft flybys at comet P/Halley described anticipated dust and gas environments. Predicted values for gas production, for dynamic ranges of gas and dust experiments, and for likely spacecraft effects were matched during the flybys well within expected margins; in particular the dust-impact-generated attitude disturbance experienced by Giotto several seconds before closest approach was within the envelope of expectations from the models. Three major areas are identified in which 1986 results for Halley might be used to improve the models, namely (1) gas production values from earth-based and in situ observations, (2) dust flux and fluence values in the coma from three spacecraft, and (3) dust size distributions from the in situ data which require the presence of numerous particles at masses less than 10 to the -17th kg.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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    The dust distribution within the inner coma of comet P/Halley 1982i - Encounter by Giotto's impact detectors (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Analyses are presented of Giotto's Dust Impact Detection System experiment measurements of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on March 13 and 14, 1986. Ground-based CCD imagery of the inner coma dust continuum at the time of the encounter are used to derive the area of grains intercepted by Giotto. Data obtained at large masses show clear evidence of a decrease in the mass distribution index at these masses within the coma; it is shown that such a value of the mass index can furnish sufficient mass for consistency with an observed deceleration.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,; 719-741
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    The spectral behavior of P/Halley at large heliocentric distance in light of the Giotto/Vega results (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents the results of the preperihelion spectroscopic observations of the P/Halley comet, conducted with the Mayall 4 m telescope/CRYOCAM combination on Kitt Peak when the comet was between 8.8 and 5.6 AU from the sun. The V magnitudes and the (g - r) and (V - R) color indices, derived from the five spectra obtained between October 10, 1983, and February 4, 1984, showed a trend to increasing redness with decreasing heliocentric distance. However, the (V - R) color of the comet while near 8 AU was anomalous in that it was significantly bluer than the sun. Tentative interpretation of this phenomenon is presented.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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    Study of the isotopic features of Swan bands in comets (1987)
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    Publication Date: 2011-08-19
    Description: It is shown from a detailed statistical equilibrium calculation of the (C-12)(C-13) molecule that the interpretation of the observed intensities of Swan bands of the normal and the isotopic molecule of C2 in terms of the abundance ratio of C-12 and C-13 is a reasonable one. The synthetic profile of some isotopic features in the (0.0) Swan band is compared with the observed profiles for comet West.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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    Some diatomic molecules from comet P/Halley's UV spectra near spacecraft flybys (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The abundances of diatomic molecules seen in the UV both give clues to the parent compounds and help unravel the gas and ion mass spectrometry. From IUE spectra of comet Halley, upper limits on SH and CS(+) column densities and estimates of probable NO, S2, and SO are found. In particular, judged from the 226-nm gamma band, NO was relatively abundant at 2-8 x 10 to the 13th/sq cm on March 9-14. The production rate of S2 was around 1 x 10 to the 27th molecules/s at that time, but both showed day-to-day variability by 2-3 times.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,; 329-332
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    Cometary MHD and chemistry (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An MHD and chemical comet-coma model was developed, applying the computer program of Huebner (1985) for the detailed chemical evolution of a spherically expanding coma and the program of Schmidt and Wegman (1982) and Wegman (1987) for the MHD flow of plasma and magnetic field in a comet to the Giotto-mission data on the ion abundances measured by the HIS ion mass spectrometer. The physics and chemistry of the coma are modeled in great detail, including photoprocesses, gas-phase chemical kinetics, energy balance with a separate electron temperature, multifluid hydrodynamics with a transition to free molecular flow, fast-streaming atomic and molecular hydrogen, counter and cross streaming of the ionized species relative to the neutral species in the coma-solar wind interaction region with momentum exchange by elastic collisions, mass-loading through ion pick-up, and Lorentz forces of the advected magnetic field. The results, both inside and outside of the contact surface, are discussed and compared with the relevant HIS ion mass spectra.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,; 339-350
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    Unusual characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies are examined using a model of solar wind permeated by dilute drifting ring distributions of electrons and oxygen ions with finite thermal spreads. The model has parameters compatible with the ICE observations at the Giacobini-Zinner comet. It is shown that cometary newborn ions with large perpendicular energies can excite a wave mode with rest frame frequencies in the order of the heavy ion cyclotron frequency, Omega(i), and unusual propagation characteristics at small obliquity angles. For parallel propagation, the mode is left-hand circularly polarized, might be unstable in a frequency range containing Omega(i), and moves in the direction of the newborn ion drift along the static magnetic field.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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    Structure and dynamics of the plasma tail of comet P/Halley. I - Knot event on December 31, 1985 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: On the basis of about 500 photographs of comet Halley taken by many observers, Saito et al. (1986) classified the detected disturbances of the plasma tail as outstanding rays, streamer, helix, kink, arcade, and disconnection event (DE). In this paper, the interaction of the solar wind with the plasma tail of Comet P/Halley is examined by using results of observations by the Sakigake spacecraft of the December 31, 1985 event, which included various disturbances and one DE-like knot. On the basis of twenty photographs taken on December 31 by Japanese astronomers, the dynamic pressure model proposed by Saito et al. (1986) is examined, and the mechnism of the knot event that appeared in the plasma tail of the comet on December 31, is explained.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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  • 72
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    Low-frequency magnetic field fluctuations in comet P/Halley's magnetosheath - Giotto observations (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The interaction region between comets and the solar wind is characterized by large amplitude, low frequency magnetic field fluctuations, both within the upstream region as well as in the magnetosheath. Magnetosheath observations of the magnetic field experiment onboard Giotto indicate values of delta B/B equal to about O(1). Power spectral peaks appear at frequencies of 10mHz with the spectrum exhibiting a power law dependence with an exponent of the order 2. Radial variation of the fluctuation level does not clearly increase with decreasing distance from the cometary nucleus as observed by the magnetometer onboard Vega-1 and as expected from quasi-linear theory. The entrance into the cometary bow shock is furthermore characterized by an order of magnitude increase of the fluctuation level, both on the in- and outbound pass of Giotto.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,; 65-68
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    Cometesimals in the inner solar system (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Spectra obtained by the ultraviolet spectrometer on the Voyager 2 spacecraft between 1 and 2.5 AU are shown to provide evidence for a very large number of 'cometesimals' with radii between a few meters and a few tens of meters in the neighborhood of the earth. The evidence consists of a component in the interplanetary Lyman-alpha radiation that decreases rapidly with heliocentric distance. It is proposed that the source consists of cometesimals which are ice-coated, porous, low-density refractory boulders that may be the building blocks of ordinary comet nuclei. It is shown that the cometesimals required to produce the observed Lyman-alpha emission can also account for all the lunar craters with diameters between 200 m and 1500 m produced during the phase 3200 million years at sites such as Mare Tranquillitatis.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 330; 548-550
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    A non-thermal axially symmetric radio wake towards the Galactic centre (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A highly unusual radio source lying within 1 deg of the Galactic center has been discovered whose 'cometary' morphology suggests that it is a wake produced by a radio source moving supersonically with respect to the ambient interstellar medium. Maps of the source are shown, and its characteristics are discussed. Two possible models which might explain the wake are suggested.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 330; 455-458
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    Constraints on possible precursor AGN sources of the cosmic X-ray background (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New limits on small-scale surface brightness fluctuations of the residual cosmic X-ray background are used to reevaluate the conjecture that unresolved precursor AGN sources could be the origin of the flux. The large number of these predominantly X-ray-emitting objects thereby required imposes that their lifetime be longer than previously considered. Attention is drawn to the fact that the reduction in the effective Eddington luminosity limit for such sources due to electron-positron pair opacity could have the effect of increasing their lifetime to an appropriate level.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 322; L1-L4
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    Prospects for gamma-ray line observations of individual supernovae (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The gamma-ray line emission from individual type I and type II supernovae are studied using numerical simulations and photon propagation codes to predict the flux levels and line shapes. For both types, the gamma ray lines with the highest flux from an individual event are the 0.847 and 1.238 MeV lines from the Ni-56 to Co-56 to Fe-56 decay chain. For type I supernovae, the 0.847 MeV line peaks at about 70 days after event onset. The historical record indicates an approximate discovery rate of once in 10 years for balloon-borne instruments, once in two to three years for the Gamma-Ray Observatory, and once in one to two years for a proposed space mission. The 0.847 MeV line flux from type II supernovae peaks at about 600 days after event onset at a low level which restricts observations to the events in the Galaxy and its nearest neighbors. The expected line shape is narrower than for type I supernovae.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 215-233
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    Cosmic string wakes (1987)
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    Publication Date: 2011-08-19
    Description: Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 1-19
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    Light echoes - Type II supernovae (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Type II supernovae (SNs) light curves show a remarkable range of shapes. Data have been collected for the 12 Type II SNs that have light curve information for more than four months past maximum. Contrary to previous reports, it is found that (1) the decay rate after 100 days past maximum varies by almost an order of magnitude and (2) the light curve shapes are not bimodally distributed, but actually form a continuum. In addition, it is found that the extinctions to the SNs are related to the light curve shapes. This implies that the absorbing dust is local to the SNs. The dust is likely to be part of a circumstellar shell emitted by the SN progenitor that Dwek (1983) has used to explain infrared echoes. The optical depth of the shell can get quite large. In such cases, it is found that the photons scattered and delayed by reflection off dust grains will dominate the light curve several months after peak brightness. This 'light echo' offers a straightforward explanation of the diversity of Type II SN light curves.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 323; L51-L54
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    Light echoes - Supernovae 1987A and 1986G (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The sudden brilliance of a supernova (SN) eruption will be reflected on surrounding dust grains to create a phantom nebula. The paper presents a series of calculations in which the apparent brightness of this 'light echo' is predicted for a variety of situations where the dust is part of the interstellar medium (ISM). It is found that the supernova 1987 A will have a very bright echo off the ISM that may perhaps be visible with binoculars for many years. At a time of 400 days past maximum, the SN 1986G is found to be 2.7 mag brighter than would be predicted by an extrapolation of its light curve. This unique property has an easy explanation as a light echo off the dust in the dust lane of Cen A.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 323; L47-L49
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    Early-universe thermal production of not-so-invisible axions (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is found that, for Peccei-Quinn symmetry-breaking scales of less than about 4 x 10 to the 8th GeV (corresponding to axion masses of greater than about 0.03 eV) thermal production of axions in the early universe (via the Primakoff and photoproduction processes) dominates coherent production by a factor of about 1200/m sub a/(1 eV)/ exp 2.175. The photon luminosity from the decays of these relic axions leads to an upper limit to the axion mass of order 2-5 eV. If the axion mass saturates this bound, relic axion decays may well be detectable.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 59; 2489-249
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    Ultraviolet interstellar extinction toward NGC 6530 and the intrinsic energy distribution of 9 Sagittarii and HD 165052 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ultraviolet interstellar extinction curve is determined toward 12 early B main-sequence stars and one O8 V star in NGC 6530. The extinction is found to be uniform across the cluster. At short wavelengths, the extinction curve of NGC 6530 falls below the average Galactic curve by a full magnitude, indicating that the population of small grains relative to larger grains is lower than normal. Longward of 2830 A the curve is almost coincident with the mean Galactic curve. The 2175 A feature is narrower than the average. The derived extinction curve is used to deredden the observed fluxes of two early O-type stars in NGC 6530:9 Sgr and HD 165052. The intrinsic continua are compared to model atmospheres in the region 1200-8200 A. The LTE, line-blanketed models of Kurucz (1979) fit the observations better than the non-LTE, unblanketed models of Mihalas (1972) suggesting that line-blanketing effects are more important than the non-LTE effects in the atmospheres of these stars. The temperatures of the models that best fit the observations are lower than the Zanstra temperatures and the temperatures estimated from the strengths of the He I and He II lines, by 10,000 to 20,000 K.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 949-959
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    The effect of decay of the amplitude of oscillation on random process models for QPO X-ray stars (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Random process models provide a useful mathematical framework for analysis of the quasi-periodic oscillations (QPO) recently discovered in the X-ray emission from certain luminous Galactic X-ray stars. In this paper, consideration is given to the effects of the power spectrum of the decay of the amplitude of oscillation that is expected in some physical models for the QPO phenomena. The resulting changes in the power spectrum depend on the ratio of the decay time of the amplitude of oscillation to the lifetime of the shot envelope. For values of this ratio less than about 10, it is found that incoherent QPO peaks in the power spectrum are significantly reduced in height and total power and are broadened in width, making them more difficult to detect. Coherent terms in the power spectrum, if present, are reduced in height and total power, but their width is unaffected. The red noise component remains unchanged. The present results are applied to the beat-frequency modulated accretion model in order to set constraints on the physical properties of the boundary layer between the inner edge of the accretion disk and the neutron star magnetosphere.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 831-837
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  • 83
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    The infrared diagnostic of a dusty plasma with applications to supernova remnants (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IRAS observations of infrared emission from supernova remnants constitute the first observational evidence of shock-heated dust in the interstellar medium. These observations can provide valuable information on the morphology of supernova remnants, and on their interaction with the ambient interstellar medium. In particular, they can be used to study the physical condition and the cooling rate of dusty astrophysical plasmas. In this paper, consideration is given to the possibilities and limitations of using the infrared observations as a diagnostic for the shocked gas, and as a means of determining remnant parameters. The paper presents improved calculations for the cooling rate of a dusty plasma by means of gas-grain collisions, and the equilibrium temperature of the dust for a variety of plasma conditions. These results are then used to define the density-temperature parameter space of the plasma, which, given its infrared spectrum, should be occupied by the observed remnant. This constraint can be used to estimate distances to supernova remnants and to set limits on various parameters that determine their evolution. The analysis is applied to the remnants Cas A and the Cygnus Loop.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 812-821
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  • 84
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    OH megamasers in high-luminosity IRAS galaxies (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: OH megamaser emission and H I and CO profiles from the distant infrared galaxies IRAS 10173 + 0828, III Zw 035, and Zw 475.056 are reported. The OH isotropic luminosities at 1667 MHz are 463, 534, and 6.6 solar luminosities, respectively. Far-infrared pumping efficiencies of the OH greater than 1 percent are found in IRAS 10173 + 0828 and III Zw 035. These two galaxies show anomalously large 1667/1665 MHz emission line ratios. OH megamasers reside in the nuclei of superluminous far-infrared galaxies that have a high content of molecular gas, high efficiency of star formation, and in some instances, a striking deficiency of atomic hydrogen.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 688-693
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  • 85
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    The linear filaments of the radio arc near the Galactic center (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-resolution radio continuum VLA images of a segment of the Galactic center arc centered at G0.16-0.15 at wavelengths of both 6 and 20 cm are presented. In this segment, the highest multiplicity of filaments, the largest degree of linear polarization, and a maximum rotation measure of -5500 rad/sq m between wavelengths 6.166 and 6.363 cm are found. The large 'helical segments' which surround the filamentary system are also shown and discussed. Based on a number of intriguing characteristics of the filamentary system, including the helical component and possible twisting of some of the filaments, a picture is considered in which the geometry of the magnetic structure is that of a cylindrically symmetric, force-free field anchored to the halo of the Galaxy. An analogy with solar flare filaments is used to discuss some aspects of the Galactic center filaments.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 322; 721-728
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  • 86
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    The evolution of topography on a comet (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The evolution of cometary surface topography is presently modeled in terms of a focusing of thermal energy due to topographical concavity. The model encompasses incident sunlight, shadowing, molecular sublimation, and mutual radiative heating by the walls of a circle-segment cross section trench, which has a 'lensing' effect. After a large number of perihelion passages, the net effect of trench bottom sublimation losses will be the accentuation of topographical concavities. The comet surface sublimation, comet-splitting, and comet surface jet-formation consequences of this model are discussed.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 72; 128-134
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  • 87
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    The variation of protons, alpha particles, and the magnetic field across the bow shock of Comet Halley (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Data from the Ion Mass Spectrometer and the magnetometer on the Giotto spacecraft are used to examine the structure of the inbound crossing of the Comet Halley bow shock on March 13, 1986. It is found that the velocity decrease, the field strength increase, and the heating of picked up cometary protons occurred over a broad region corresponding to several heavy-ion gyroradii. The solar-wind protons and alphas, on the other hand, were compressed and heated at a narrow structure on the leading edge of the broad shock region.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 995-998
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  • 88
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    Circumstellar interaction and a pulsar nebula in the supenova 1986j (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown here that the circumstellar interaction model for radio supernovae provides an adequate fit to the existing data on supernova SN1986j. The model implies a time of explosion of about January 1983 and provides a guide for the future evolution of the radio source. A shell-like source structure is expected. The model, together with VLBI observations of the radio source, implies a shock velocity of about 10,000 km/s and a presupernova mass loss rate of about 0.0001 solar mass/yr for a wind velocity of 10 km/s. The time behavior of the optical flux and its high luminosity suggest that a central pulsar nebula is the energy source. The required properties are comparable to those expected in the early phases of the Crab nebula.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 329; 611
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  • 89
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    Comets and their composition (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent theoretical and observational studies of comets are reviewed, with an emphasis on in situ data from spacecraft encounters with P/Giacobini-Zinner (September 1985) and P/Halley (March 1986). Topics addressed include clues on the origin and permanence of the Oort cometary cloud, observations of cometary nuclei far from the sun, the Halley nucleus, compositional and physical data from comae studies, and the parent molecules in comet ices. Also discussed are quantitative analyses of coma production; special features in the tail of P/Giacobini-Zinner; and proposals for (1) observations to detect distant giant comets, (2) high-resolution spectroscopic studies of comae, and (3) additional spacecraft missions such as the NASA Comet Rendezvous and Asteroid Flyby.
    Keywords: ASTROPHYSICS
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  • 90
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    First polymer in space identified in Comet Halley (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The heavy-ion mass spectrum obtained in the inner coma of Comet Halley with the PICCA instrument on the Giotto spacecraft has been examined. Short polymer chains of polyoxymethylene and their decay products are identified as the source for the spectrum with six mass peaks between about 45 and 120 atomic mass units. The properties of polyoxymethylene are consistent with many of the unexpected observations in the coma.
    Keywords: ASTROPHYSICS
    Type: Science (ISSN 0036-8075); 237; 628-630
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  • 91
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    Reexamination of the SAS 2 Cygnus X-3 data (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent observations of Cygnus X-3 have shown marked variability of the radiation on short time scales. In particular, the bursts lasting on the order of 10 minutes, seen in both the infrared and very high energy (greater than 10 to the 11th eV) gamma-ray regions, and the time-variations on many scales at high energies, have stimulated a reanalysis of the March 6 to 13, 1973 SAS 2 high-energy gamma-ray data. Although a clear periodicity in the E greater 35 MeV gamma radiation is observed at the 4.79 hr period seen in X-rays, there is no evidence for major variations of the radiation from one day to the next, and no statistically significant evidence for bursts on the 10-minute time scale seen in the infrared or very high energy ranges. If the excess observed had been predominantly in the form of ten minute bursts even at a rate as high as two/day, a clearly significant set of bursts would have been seen.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 319; 362-366
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  • 92
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    Second-overtone models of RR Lyrae stars (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Linear models of RR Lyrae stars pulsating in the second overtone indicate that this mode is self-excited only for rather low luminosities if the masses are normal. An unstable second-overtone model has been selected from the linear survey and has been followed up to limiting amplitude by using a nonlinear hydrodynamical computer program. Deep splitting of the main light peak in the theoretical light curve occurs but does not resemble any observed feature. Moreover, the distribution of periods of RR Lyrae stars in globular clusters can be accounted for adequately by fundamental-mode and first-overtone pulsation. It is concluded that second-overtone pulsators probably do not exist among RR Lyrae stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 319; 260-263
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  • 93
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    The H I distribution in clouds within galaxies (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An interpretation is given for the relatively flat distribution of atomic hydrogen as a function of radius within the visible disks of spiral galaxies and the existence of a correlation between H I surface density and morphological class of spiral galaxy. The H I is mostly contained in constant column density envelopes of molecular clouds. The clouds have a two-dimensional filling factor of unity when a galaxy is viewed face on. The column density of the cloud envelopes depends on the ratio of flux of H2 dissociating radiation in the ambient medium to envelope gas density. The flat H I profiles imply the gas density and pressure follow the ultraviolet ambient flux on kiloparsec scales throughout a given galaxy. Later-type galaxies have larger ultraviolet surface brightnesses, as deduced from the H-alpha surface brightnesses. Therefore, thicker protective H I envelopes develop in late-type spirals.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 319; 76-83
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  • 94
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    New CO and HCN sources associated with IRAS carbon stars (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Emission of CO and HCN was detected in 22 out of a sample of 53 IRAS sources classified as unidentified carbon-rich objects. The sample was selected according to the presence of the silicon carbide feature as revealed by low-resolution spectra. The molecular line widths indicate that the CO and HCN emission arises from the circumstellar envelopes of very highly evolved stars undergoing mass loss. The visible stars tend to be deficient in CO as compared with unidentified sources. Most the detected CO and HCN IRAS stars are distinct and thick-shelled objects, but their infrared and CO luminosities are similar to those of IRC + 102156 AFGL and IRC-CO evolved stars. The 12 micron flux seems to be a good indicator of the distance, hence a guide for molecular searches.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 180; 1-2,
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  • 95
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    Physical processes and infrared emission from the Cassiopeia A supernova remnant (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IRAS 12-100 micron data on the Cas A remnant are presented, and various physical mechanisms and astrophysical sites that may contribute to the observed infrared emission are analyzed. The contributions of various sources of infrared emission to the IRAS fluxes are found to be small. The residual infrared emission is attributed to thermal emission from dust which is swept up by the expanding supernova blast wave and collisionally heated by the postshock X-ray emitting gas. The calculations are consistent with a shock velocity of 1800 km/s and a preshock gas density of about 2/cu cm. The mass of the swept-up gas is about 0.6 solar mass. An excess of 12 micron thermal emission in the spectrum of Cas A suggests the presence of very small particles in the preshocked gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 315; 571-579
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  • 96
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    On the acceleration of charged particles at relativistic shock fronts (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The diffusive acceleration of highly relativistic particles at a shock is reconsidered. Using the same physical assumptions as Blandford and Ostriker (1978), but dropping the restriction to nonrelativistic shock velocities, the authors find approximate solutions of the particle kinetic equation by generalizing the diffusion approximation to higher order terms in the anisotropy of the particle distribution. The general solution of the transport equation on either side of the shock is constructed, which involves the solution of an eigenvalue problem. By matching the two solutions at the shock, the spectral index of the resulting power law is found by taking into account a sufficiently large number of eigenfunctions. Low-order truncation corresponds to the standard diffusion approximation and to a somewhat more general method described by Peacock (1981). In addition to the energy spectrum, the method yields the angular distribution of the particles and its spatial dependence.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 315; 425-433
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  • 97
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    Interstellar problems and matrix solutions (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The application of the matrix isolation technique to interstellar problems is described. Following a brief discussion of the interstellar medium (ISM), three areas are reviewed in which matrix experiments are particularly well suited to contribute the information which is sorely needed to further understanding of the ISM. The first involves the measurement of the spectroscopic properties of reactive species. The second is the determination of reaction rates and the elucidation of reaction pathways involving atoms, radicals, and ions which are likely to interact on grain surfaces and in grain mantles. The third entails the determiantion of the spectroscopic, photochemical, and photophysical properties of interstellar and cometary ice analogs. Significant, but limited, progress has been made in these three areas, and a tremendous amount of work is required to fully address the variety of unique chemical and spectroscopic questions posed by the astronomical observations.
    Keywords: ASTROPHYSICS
    Type: Journal of Molecular Structure (ISSN 0022-2860); 157; 255-273
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  • 98
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    Optical region elemental abundance analyses of B and A stars. VII - The metallic-lined star 32 Aquarii (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the metallic-lined (Am) star 32 Aquarii consistent with previous papers of this series. Its pattern of abundance anomalies is not identical with those of the hot Am stars although there are definite similarities. Changes of up to order 1 dex are foundly by comparison with the previous analysis by Smith. Slightly better agreement is found with the recent analyses of singly-ionized rare earth lines by Magazzu and Cowley. Results are also presented for a model selected on the basis of photometric indices according to the formula of Moon and Dworetsky.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics Supplement Series (ISSN 0365-0138); 70; 1, Ju; 49-56
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  • 99
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    Torsion as a source of expansion in a Bianchi type-I universe in the self-consistent Einstein-Cartan theory of a perfect fluid with spin density (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.
    Keywords: ASTROPHYSICS
    Type: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 35; 2302-230
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  • 100
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    Heliospheric shocks (excluding planetary bow shocks) (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A summary of advances made during 1983-1985 in the theory of collisionless heliospheric shocks is presented (with reference to the latest observations of slow shocks in the geomagnetic tail) together with a summary of recently developed simulations of shock structure and shock propagation. Consideration is also given to the theoretical basis for the production of energetic particles by shocks in the solar wind and the corona. Finally, satellite-based observations related to interplanetary and coronal shocks and to heliospheric boundary shock are discussed.
    Keywords: ASTROPHYSICS
    Type: Reviews of Geophysics (ISSN 8755-1209); 25; 697-710
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