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  • ASTROPHYSICS  (1.144)
  • 1980-1984  (1.144)
  • 1925-1929
  • 1983  (578)
  • 1980  (566)
  • 1
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    X-ray spectra of young supernova remnants (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Einstein solid-state-spectrometer (SSS) spectra are presented for the Crab Nebula, Cas A, SN 1006, the Tycho SNR, and the Kepler SNR. The history of X-ray observations of SNRs is reviewed; the SSS instrument is briefly characterized; a reduction technique which accounts for all background sources in the 0.5-4.5-keV band is applied; and the physical models of SNRs constructed to reproduce the refined spectra are discussed. The limitations of the modeling methods and the need for further observations, especially of localized regions, are indicated.
    Schlagwort(e): ASTROPHYSICS
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  • 2
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    Magnetic topology and the heating of extended chromospheres (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: New data indicate that red giants are surrounded by geometrically thick chromospheres of several stellar radii extent. Such chromospheres occur among stars which apparently lack coronae. Maintenance of this extended warm region may require non-compressional wave heating of a magnetic character, and this may provide a crucial clue to the mechanism of rapid mass loss from red giant stars.
    Schlagwort(e): ASTROPHYSICS
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  • 3
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    A note on the oxygen gradient in NGC 628 (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Kitt Peak 2.1-m telescope and Intensified Image Dissector Scanner have been used to gather spectrophotometric data in the 3600-5200 A spectral region for five H II regions in the spiral galaxy NGC 628. The Pagel et al (1979) technique was then applied to determine the relative number abundances of O to H in each of the H II regions. An examination of the abundance values obtained as a function of the radial coordinate yields an O gradient of -0.05 + or - 0.03 dex/kpc.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 986-988
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  • 4
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    Testing for a cosmological influence on local physics using atomic and gravitational clocks (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The existence of a possible influence of the large-scale structure of the universe on local physics is discussed. A particular realization of such an influence is discussed in terms of the behavior in time of atomic and gravitational clocks. Two natural categories of metric theories embodying a cosmic infuence exist. The first category has geodesic equations of motion in atomic units, while the second category has geodesic equations of motion in gravitational units. Equations of motion for test bodies are derived for both categories of theories in the appropriate parametrized post-Newtonian limit and are applied to the Solar System. Ranging data to the Viking lander on Mars are of sufficient precision to reveal (1) if such a cosmological influence exists at the level of Hubble's constant, and (2) which category of theories is appropriate for a descripton of the phenomenon.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 28; 1822-182
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  • 5
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    Observations of NGC 7027 from 5.2 to 7.5 microns - The detection of Ni II and additional dust features (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: NGC 7027 was observed with a multichannel grating spectrometer from 5.2 to 7.5 microns at a spectral resolving power of 120-200. Two new dust emission features are resolved at 5.62 and 6.95 microns, and for the first time the Ni II fine-structure line at 6.64 microns is detected. It is shown that a single molecular dust constituent might account for six of the nine observed dust features between 2 and 14 microns. The strength of the Ni II line indicates either that Ni is not depleted in the neutral gas, or that the line is formed at high density.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 666-670
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  • 6
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    A new calibration of the extragalactic distance scale using Cepheids and RR Lyrae stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Visual absolute magnitudes of classical Cepheids, metal-poor RR Lyrae stars and short-period type II Cepheids have been determined with very high precision by combining a large number of old and new astrophysical data. Five independent methods (four observational and one theoretical) have been successfully used: (1) secular and statistical parallaxes; (2) moving-group parallaxes; (3) cluster main-sequence fitting; (4) the Baade-Wesselink method and its modifications; and (5) light-curve and velocity-curve fitting (the theoretical method). With these five adopted methods, the zero point of the galactic and extragalactic distance scale can be set on a relatively firm and self-consistent basis. Classical Cepheids and RR Lyrae stars now provide essentially identical distances to nearby galaxies: the distance modulus to the Large Magellanic Cloud is 18.5 and to the Small Magellanic Cloud is 18.8, both with an uncertainty of 0.1. The distance to the center of our Galaxy is 8.6 plus or minus 0.5 kiloparsecs. The major uncertainty in these values lies in the correction for interstellar extinction.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 20-30
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  • 7
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    On the line profile coefficient for stimulated emission (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is pointed out that the line profile coefficients for spontaneous and stimulated emission are identical in low-intensity radiation fields. In more intense radiation fields, however, the stimulated emission profiles in the radiative transfer equation and in the rate equations for the atomic level populations may differ from each other, owing to their different physical nature. A seeming discrepancy between the stimulated emission profiles of the usual semi-classical aproach and a recent quantum mechanical approach by Cooper et al. (1982), which should also be valid for intense 'broadband' fields, is discussed and shown to have negligible consequences for low-intensity radiation fields.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 127; 1, Oc; 224-226
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  • 8
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    Observational tests of baryon symmetric cosmology (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observational evidence for Baryon symmetric (matter/antimatter) cosmology and future observational tests are reviewed. The most significant consequences of Baryon symmetric cosmology lie in the prediction of an observable cosmic background of gamma radiation from the decay of Pi(O)-mesons produced in nucleon-antinucleon annihilations. Equations for the prediction of the gamma ray background spectrum for the case of high redshifts are presented. The theoretical and observational plots of the background spectrum are shown to be in good agreement. Measurements of cosmic ray antiprotons and the use of high energy neutrino astronomy to look for antimatter elsewhere in the universe are also addressed. Previously announced in STAR as N83-10996
    Schlagwort(e): ASTROPHYSICS
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  • 9
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    Interacting binary stars - Freaks or rosetta stones (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Attention is given to semidetached binaries of the Algol type and to related interacting systems, such as Beta Lyrae and the W Serpentis stars. A brief description is given of observational problems. The basic properties of the Algol variables are satisfactorily explained by means of evolutionary models that assume considerable mass transfer between the components. It is pointed out that ultraviolet spectra obtained with the IUE satellite corroborate the view that the present subgiant secondary component was initially the more massive star and that it has been stripped of a large fraction of its mass so that the deep layers affected by CNO processing are now denuded. It is believed that the present-day 'classical' Algols must have undergone a phase of rapid mass transfer in the past and that Beta Lyrae and the W Serpentis stars are probably closer to that stage than ordinary Algols. Around the accreting star a complex structure is formed, and an induced stellar wind may blow a large part of the transferred matter out of the system.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society of Canada, Journal (ISSN 0035-872X); 77; 283-304
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  • 10
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    What causes the buoyancy reversal in compressible convection? (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The problem posed by the existence of a negative buoyancy work region at the top of cellular type convection in a deeply stratified superadiabatic layer (Massaguer and Zahn, 1980) is addressed. It is approached by studying two-dimensional cellular compressible convection with different physical parameters. The results suggest that a large viscosity, together with density stratification, is responsible for the buoyancy reversal. The numerical results obtained are analyzed. It is pointed out, however, that in an astrophysical situation a fluid involved in convection will generally have very small viscosity. It is therefore thought unlikely that buoyancy reversal occurs in this way.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 2, Se; 453-457
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  • 11
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    On a vibronic origin for the diffuse band spectrum (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Duley (1982) has proposed that many of the diffuse interstellar bands in the wavelength interval 542-677 nm arise from vibronic transitions of Cr (3+) ions in MgO grains. No explanation has been offered for the fact that as many as 85 of the possible 108 transitions of this system have not been observed in the interstellar medium. Moreover, the relative intensities of the diffuse bands which are observed appear to be inconsistent with their assignment. It is therefore concluded that this model is not consistent with the observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 1, Se
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  • 12
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    A note on the composition and structure of interstellar grains (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The plausibility of relatively pure diatomic oxide crystals forming in the expanding atmospheres of cool stars is commented on, and the likelihood of SiO grains condensing is discussed on the basis of laboratory nucleation experiments. Results of annealing experiments are used to consider the further evolution of silicon oxide and silicate grains. The evidence shows that SiO solids form only when SiO condenses directly onto surfaces, and that the probability of pure crystalline SiO grains forming is rather small.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 1, Se
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  • 13
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    Planetary nebulae and stellar evolution (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Newly defined characteristics of planetary nebulae (PN) derived from analysis of a photometric survey of 57 PN are reported. The data were combined with measurements of 27 other PN made since 1918 and were found to indicate core masses ranging from 0.55-1.0 solar mass. N/O elemental abundance ratios observed were correlated with the planetary nuclei masses, and were in direct proportion. IUE data on PN that overlapped a large part of the survey indicated that the PN in the galactic disk are more massive than PN in the halo. It is suggested that PN evolve into white dwarfs, a hypothesis supported by astrometric solutions for three nearby visual binaries featuring white dwarfs with well-determined masses. It is noted, however, that PN with masses exceeding one solar mass have been sighted in the Magellanic Clouds.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 305; 670
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  • 14
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    Two new possible planetary nebulae (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Two new possible planetary nebulae have been identified using the Parker, Gull, and Kirshner (1979) emission-line survey of the galactic plane. Both objects exhibit very strong forbidden O III lambda 5007 line emission, a symmetrical morphology, and a faint blue central star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 614-618
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  • 15
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    Ultraviolet observations of M1-2 (= VV 8) (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: First IUE spectrograms of the peculiar emission-line object M1-2 (= VV 8) are presented. In the wavelength region 1150-3200 A this object is characterized by emission lines superposed on a moderately strong continuum. Some ultraviolet and optical properties of M1-2 are discussed in the context of symbiotic stars and protoplanetary and planetary nebulae. An E(B-V) extinction of 0.37 mag is obtained from the ratio of the He II flux at 1640 and 4686 A and is compared with values derived from other parameters. The ultraviolet observations suggest that M1-2 is a young, high-density planetary nebula of excitation class 5 or 6 with characteristics similar to IC 4997.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 275; 628-635
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  • 16
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    The origin of the Gum nebula (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Obsrvations and theoretical investigations of the Gum nebula (GN) since about 1971 are reviewed. Direct observations of the GN, the Vela X supernova remnant (SNR), the Vela pulsar, and other stars in or near the GN are discussed with those of related phenomena such as the radio loops and known SNRs; the emphasis is on studies of the interstellar absorption lines, the evidence for hot gas in the GN, and the extended diffuse emission. The four basic models proposed for the GN are considered: a fossil Stromgren sphere, an old SNR, an H II region, or a superbubble. The GN physical parameters predicted by each model are listed in a table and compared. A minimum explanation which attributes the 36 x 36-deg filamentary structure and the 125-pc radius structure to the action of the stellar winds from Zeta Pup and Gamma-2 Vel (and perhaps the effect of a Vel X supernova explosion 20,000 years ago) is found most appropriate, at least until the questions of the net expansion rate of the GN (about 20 km/sec or about zero?) and the existence of the diffuse emission beyond the filamentary structure are resolved by observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Comments on Modern Physics, Part C - Comments on Astrophysics (ISSN 0146-2970); 10; 1-14
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  • 17
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    Electron velocity distributions near interplantary shocks (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Previous work on electron heating mechanisms operating at the supercritical earth's bow shock is extended to the generally lower Mach number interplanetary shocks. This is done by studying electron velocity distributions observed both upstream and downstream of interplanetary shocks observed by ISEE 3 between August 1978 and December 1979. It is found that perpendicular heating accompanied by little or no parallel heating occurs at the weaker shocks but that parallel heating is dominant for the stronger shocks. When perpendicular heating is dominant, downstream velocity distributions are for the most part Gaussian at low energies (core) and Lorentzian at high energies (halo). When parallel heating is dominant, however, these distributions are flat-topped at low energies, having power law extensions to higher energies. At the weaker shocks, the observations are consistent with electron heating resulting from conservation of the magnetic moment, whereas at the stronger shocks the heating is quite similar to that observed at the earth's bow shock.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 9949-995
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  • 18
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    Sharp shortward-shifted features in the spectra of O subdwarfs (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Preliminary inspection of archival high-dispersion ultraviolet spectra obtained by the International Ultraviolet Explorer reveal sharp shortward-shifted features in the spectra of O subdwarfs. In three examples presented here, BD + 75.325 deg, HD 128220 B, and BD + 28.4211 deg, stable, multiple, discrete shortward-shifted components of the N V, C IV, and Si IV resonance doublets are seen. The available data suggest that some of these features are persistent, being relatively stable in velocity and intensity over at least 9 months. It is tentatively suggested that the mechanism, or mechanisms, producing these discrete features operates universally in hot stars, from luminous O and B stars down through the O subdwarfs to include the hot white dwarfs. If true, this has important ramifications for current knowledge of mass loss in hot stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L87-L91
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  • 19
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    Images in the rocket ultraviolet - The starburst in the nucleus of M83 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Ultraviolet images of the SAB(s)c I-II galaxy M83 (NGC 5236) obtained with a rocketborne telescope in broad bandpasses centered at 1540 A and 2360 A show a bright resolved nuclear source which accounts for approximately 20 percent of the flux of the galaxy in both bandpasses. Low-resolution International Ultraviolet Explorer spectra of this source reveal an energy distribution similar to that of the starburst nucleus of NGC 7714. Strong blueshifted absorption lines can be interpreted as evidence for a nuclear wind powered by supernovae. Observations from UV, X-ray, optical, and far-infrared bandpasses are consistent with a starburst approximately one-sixth as strong as that in M82. A scaling of the M82 models of Rieke et al. (1980) predicts that the nucleus of M83 contains 10 to the 6th - 3 x 10 to the 7th solar masses in young stars and has a supernova rate of approximately 0.01 per yr.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L53-L56
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  • 20
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    X-ray observations of LMC X-3 with the monitor proportional counter aboard the HEAO 2 Einstein observatory - A comparison with Cygnus X-1 (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A comparison is presented of the black hole candidates LMC X-3 and Cygnus X-1 based on Einstein observations of LMC X-3 with the monitor proportional counter. A spectral analysis shows LMC X-3 to be more like the typical bright galactic X-ray source than Cygnus X-1. A search for periodic pulsations over a period range from 0.2 ms to over 1000 s set upper limits at the 90 percent confidence level of the order of 10 percent. An analysis of the aperiodic variability of LMC X-3 shows none of the shot noise behavior characteristic of Cygnus X-1. The absence of distinctive X-ray properties common to both sources suggests that the identification of black hole candidates on the basis of X-ray properties similar to Cygnus X-1 (or LMC X-3) is not reliable.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L65-L69
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  • 21
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    Stellar evolution in N-body simulations of disk galaxies. I (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Kalnajs (1972, 1976) Omega models of global mass and velocity distributions are employed in the present two-dimensional N-body simulation, which allows for a spectrum of particle masses, stellar explosions, explosion remnant interactions with an interstellar medium, and the creation of new stars from the gas. Two sequences of runs using the Omega values of 0.8 and 0.9 examine the separate and combined effects of particle mass distribution, the gravitational influence of an interstellar gas distribution on the N-body particles, and stellar evolution, allowing for stellar explosions and star formation from the gas. It is found that both Omega values' nonequilibrium results dramatically change when evolution is allowed to occur. These results call for more realistic coupled N-body and evolution simulations in order to improve the understanding of disk galaxy evolution.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 595-610
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  • 22
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    The (an)isotropy of the X-ray sky (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: An assessment is made of the extent to which the study of the isotropy of the X-ray sky has contributed to the present understanding of the structure of the universe at moderate redshifts. It is, of course, the anisotropic character of the sky flux that is valuable in this context. Although it is not currently possible to undertake measurements with the precision and small solid angles that are typically achieved in the microwave range, the comparatively crude limits from the X-ray fluctuations place limits on the largest scale structure of the universe. After indicating the nature of measurements made, with the HEAO 1 A-2 experiment, of the X-ray sky and its anisotropies, it is shown how these place limits on the origin of the X-ray sky and on any large scale structure of the universe.
    Schlagwort(e): ASTROPHYSICS
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  • 23
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    Comments concerning magnetic fields as a possible cause of rapid, irregular variability of early-type stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is noted that it is helpful to divide the atmosphere of an early-type star into two parts: a photosphere and a mantle. The photosphere can be modeled satisfactorily by normal model-atmosphere procedures. When modeling the mantle, one must take account of the deposition of nonradiative heat and momentum and one should recognize that the mantles of hot stars do not appear to be uniform or spherically symmetric. Five areas of discrepancy between classical theory and observation are noted and a possible way of modeling the mantles of early-type stars is outlined. The model consists of arcades of magnetic loops which form helmet-type structures in the equatorial band of the star, and of coronal-hole-type structures emmanating from weak unipolar regions which are chiefly distributed at polar latitudes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Hvar Observatory, Bulletin (ISSN 0351-2651); 7; 1, 19
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  • 24
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    Observational knowledge about the physical properties of O stars (1983)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Information about the effective temperatures, radii, and masses of O-type stars is presented. It is argued that rapid variations in the amount of light from O stars and the spectral distribution are a result chiefly of changes which occur in the envelope of the star. The stability of the photospheric layers of O stars against convection is reviewed and it is noted that late O stars and early B stars have a convection zone in the deeper parts of the photosphere. This convection zone is due to the second ionization of helium. Evidence is reviewed that most of the line-profile changes seen for O stars are generated by changes in the physical state of the mantle of the star, that is of the outer atmosphere where the deposition of non-radiative energy and momentum controls the physical state of the atmosphere. The physical state of the mantle may change in response to changes in the upper envelope of a star with a different time constant than the photosphere does.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Hvar Observatory, Bulletin (ISSN 0351-2651); 7; 1, 19; 1-15; Di
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  • 25
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    The effect of rotation on the hydrodynamics of stellar collapse (1980)
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): ASTROPHYSICS
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  • 26
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    Fragmentation in rotating isothermal protostellar clouds (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The paper reports results of an extensive set of three-dimensional hydrodynamic calculations performed to investigate the susceptibility of rotating clouds to gravitational fragmentation; only isothermal collapse sequences were considered. It is found that rotating isothermal gas clouds are unstable to fragmentation under a wide range of conditions. The degree of instability and the mode (ring vs. blob) of fragmentation is sensitive to alpha, but insensitive to beta. The initial amplitude of a perturbation does not appear to be crucial; fragmentation should occur eventually even for low-amplitude initial NAPs.
    Schlagwort(e): ASTROPHYSICS
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  • 27
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    Spectroscopic and polarimetric observations of NGC 1333 and the surrounding dark cloud complex (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Spectroscopy and polarimetry of several very red stars, noted on Near Infrared Photographic Sky Survey photographs in the region of NGC 1333, have yielded a 'map' suggesting the extent of polarization arising from a two-cloud structure in the region. Spectral types and color indices of the stars make it possible to infer that grain radii in the clouds exceed typical interstellar medium values and, further, that they increase with optical depth into the cloud. The present observations indicate that the cloud structure is far more extensive than previously realized.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 85; Dec. 198
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  • 28
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    Collapse and equilibrium of rotating, adiabatic clouds (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A numerical hydrodynamics computer code analysis of the collapse and establishment of equilibrium of adiabatic gas clouds restricted to axial symmetry found that the clouds are originally uniform in density and rotation. The method can compare the dynamic collapse and approach to equilibrium with the data on incompressible uniformly rotating equilibrium clouds and on equilibrium structures of differentially rotating polytropes. It is concluded that the stellar formation theory indicates that the low alpha fragments produced at the termination of the dynamic isothermal collapse phase of interstellar clouds may undergo significant dynamic collapse in an adiabatic regime leading to transitory ring formation and additional fragmentation on a smaller scale.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 242
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  • 29
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    Comparisons of interstellar CH/+/ and H2 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Copernicus observations of H2 toward stars in the Pleiades and 23 Orionis have been obtained because of their importance in understanding the formation of interstellar CH(+). No model of CH(+) equilibrium seems to agree very well with these observations; in particular, the suggestions that CH(+) is formed either from collisions between vibrationally excited H2 and C(+) or from radiative association of C(+) and H2 can apparently be excluded. These data do suggest that there is a correlation between the amounts of rotationally excited H2 and CH(+) which are present. Observations of the Pleiades also help interpretations of the reflection nebulae near these stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 242
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  • 30
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    Axial rotation, tangled magnetic fields, and theoretical models of very massive stars (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A simple method of computing theoretical models of very massive stars endowed with fast axial rotation and tangled magnetic fields is described and used in the present paper. Both of the two perturbing (nongravitational) forces induce changes in the luminosity and radius that are studied as functions of zero-age chemical composition, opacity, and evolutionary state of the interior. The central condensation of the star is found to have a significant influence on shifts of the upper main-sequence band in the H-R diagram if the perturbing force is concentrated in the stellar envelope (but not if the perturbing force is distributed so as to be approximately proportional to gravity everywhere); the layers of the envelope that contribute most heavily to the central condensation lie approximately at a radius fraction of r/R = 0.5. It is shown that fast uniform rotation and intense envelope magnetic fields lead to probably the largest possible shifts of the main-sequence band in the H-R diagram that rotation and magnetic fields can induce. These displacements are, however, too small to account for the total width of the observed main-sequence band at luminosities brighter than log (L/solar luminosity) = 4.5.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 242
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    The evolution of supernova remnants in different galactic environments and its effects on supernova statistics (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that only a small fraction of the many supernovae in the Galaxy produces observable supernova remnants; this fraction, which is found to depend weakly on the lower mass limit of the SN progenitors, and more strongly on the specific characteristics of the associated interstellar medium, decreases from about 15% near the galactic center to 10% at R(gal) of about 10 kpc and drops nearly to zero for R(gal) greater than 15 kpc. Whether an SNR is detectable is determined by the density of the ambient interstellar medium in which it is embedded; it is found that SNRs are detectable only above some critical density (about 0.1 per cu cm). The presence of large low-density superbubble cavities around stellar associations due to the combined effects of stellar winds and supernova shells strongly suggests that a large portion of the detectable SNRs must have runaway stars as their progenitors.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 242
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  • 32
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    The unique cosmic event of 1979 March 5 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The transient gamma-ray burst observed on March 5, 1979 by the nine spacecraft forming the interplanetary gamma-ray burst network is discussed. Measurements reveal the event to be unlike any previously observed gamma-ray burst or X-ray burster, with a maximum intensity greater than several thousandths erg/sq cm per sec, a rise time of less than 200 microsec, a narrow and featureless initial spike and a regular 8-sec oscillation with a compound pulse shape. The source of the transient has been localized to a region including the supernova remnant N 49 in the Large Magellanic Cloud, at a distance of 55 pc, and a ratio of X-ray point-source steady state to transient emission of less than 10 to the -9th was obtained. The identification of the burst source with the supernova remnant at that distance would require an enormous source output if it was radiated isotropically, and substantially less if beaming is present. Alternatively, the event could be explained by a nearby, invisible neutron star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Comments on Modern Physics; vol. 9
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  • 33
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    On the phase-locked polarization variations in Cygnus X-1 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The paper presents data on the accumulated V-band orbital phase curves of polarization in Cygnus X-1 which disagree with the analysis of Simmons, Aspin, and Brown (1980). No curves which conform to the canonical model were observed, and a noncanonical structure is indicated by F tests on third, fourth, and fifth harmonics, which have a probability of 0.85 as a group. The fifth harmonic has a probability of 0.99; in contrast, the fundamental harmonic has a probability of only 0.6, which is below the detection threshold. Therefore, major conclusions of Simmons et al based on a nonsymmetrical canonical model assuming that fundamental harmonics are present, but harmonics with n greater than 2 are absent, are unacceptable. Analysis of the author's data by Simmons et al is criticized on the grounds that he did not take into account the cumulative aspects of the data and did not recognize the need to average out the random noise generated by Cygnus X-1 over many orbital cycles.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 91; 1-2,; Nov. 198
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  • 34
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    The X-ray structure of two rich galaxy clusters and its implications for the detectability of microwave diminutions (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The X-ray observations of the galaxy clusters Abell 2319 and 576 show a reduced temperature of the microwave background due to the Suniaev-Zeldovich effect. The X-ray maps indicate smooth emission in these clusters concentrated toward the optical center; the surface brightness in the 1-3 keV band falls with the inverse square of radius outside a small core, and fits the Hubble's law of optical surface brightness of elliptical galaxies. The low temperature indicates that in A576 (1) the core radius of the gravitational potential is two to three times larger than inferred from galaxy counts, (2) the temperature rises with radius over most of the cluster and falls to zero at large radii, and (3) the gas does not obey the equation of state.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 241
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  • 35
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    Radial accretion of H-rich material onto a He white dwarf (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The nova outburst is modeled by spherically accreting H-rich material onto a 1 solar mass He white dwarf at a rate of 10 to the -8th solar mass/yr. The star accretes for 5848 years, when the nuclear reactions run away near the base of the accreted envelope. The nuclear-energy generation rate rises to 4.6(8) solar luminosities, and the envelope expands in response to it. However, nova-like mass ejection does not occur because the envelope is of insufficient mass, the base of the envelope is only mildly electron degenerate, and there is no enrichment of the CNO abundance. To overcome these limiting conditions, it is suggested that the H-rich material be accreted either more slowly than 10 to the -10th solar mass/yr or with angular momentum. Outbursts resulting in the former case should be similar to the nova models computed by Starrfield, Truran, and Sparks. Outbursts in the latter case should be strengthened, and novae might result because the H-rich material will be mixed into the surface layers of the white dwarf, as first suggested by Kippenhahn and Thomas (1978).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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  • 36
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    Spontaneous formation of knots in relativistic flows - A model for variability in compact synchrotron sources (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A model is proposed in which regions of enhanced synchrotron emission are formed via radiative thermal instabilities in relativistic flows. A perturbed volume in which the magnetic field is enhanced by a few tens of a percent relative to the steady value collapses due to the increased cooling rate and consequent loss in pressure. The collapse further increases the magnetic field, leading to even shorter radiative lifetimes. The instability progresses in this way until either the external electron pressure is balanced by the perturbed magnetic pressure or the overall expansion of the flow becomes important. A fluid-dynamical treatment of the instability is performed, and the results are shown to apply to flux variations and formation of knots in the relativistic flows which are thought to occur in quasars and active galactic nuclei. The knots possess the same kinematic properties as the collimated flow and can thus be responsible for the apparent superluminal motions observed in compact radio sources.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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  • 37
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    Binary model of Circinus X-1. I - Eccentricity from combined X-ray and radio observations (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A binary star model is used to account for the 16.59-d flaring behavior of the X-ray emission from Circinus X-1. The orbital eccentricity of 0.8 + or - 0.1 is derived from the X-ray light curve by assuming that the sharp X-ray cut-off every 16.59-d is a result of bound-free absorption in the primary star's stellar wind. The shape of the light curve has changed over the last eight years, and this is interpreted as due to orbital precession of the binary system. Simultaneous radio and X-ray observations of the flare from Circinus X-1 on February 1-5, 1978 are reported. These are accounted for within the framework of the model. The radio observations at 5 GHz are used independently to derive a high value of the orbital eccentricity (e = 0.7).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 86; 3, Ju; July 198
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  • 38
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    IUE observations of the atmospheric eclipsing binary system Zeta Aurigae (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: IUE observations of the eclipsing binary system Zeta Aurigae made prior to and during the eclipse of the relatively small B8 V star by the cool supergiant star (spectral type K2 II) are reported. Spectral lines produced by the absorption of B star radiation in the atmosphere of the K star during eclipse can be used as a probe of the extended K star atmosphere, due to the negligible cool star continuum in the 1200-3200 A region. Spectra taken prior to eclipse are found to be similar to those of the single B8 V star 64 Ori, with the exception of very strong multi-component absorption lines of Si II, Si IV, C IV and the Mg resonance doublet with strong P Cygni profiles, indicating a double shell. Absorption lines including those corresponding to Al II, Al III, Cr II, Mn II, Fe II, Ni II and Ca II are observed to increase in strength and number as the eclipse progresses, with high-ionization-potential lines formed far from the K star, possibly in a shock wave, and low-ionization potential lines, formed in cool plasma, probably a cool wind, nearer to the K star. Finally, an emission-line spectra with lines corresponding to those previously observed in absorption is noted at the time the B-star continuum had disappeared.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 286; Aug. 7
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  • 39
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    The high-energy X-ray spectrum of Scorpius X-1 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 40
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    Quasi-stellar objects in the intergalactic medium - Source for the cosmic X-ray background (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Current estimates of QSO luminosity, number density, evolution, and spectral index are used to study whether the diffuse cosmic ray background is (1) entirely due to thermal bremmstrahlung of the intergalactic medium (IGM), (2) completely supplied by QSO X-rays, or (3) a combination of both. The upper limits on an IGM fractional density with respect to closure are Omega = 0.26, 0.24, and 0.21 for pure collisional, photo/collisional, and pure photoionization, respectively. These calculations give emission spectra, Compton distortion of the microwave background, and optical depths to distant QSOs for comparison with relevant data.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 41
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    A model of comet comae. II - Effects of solar photodissociative ionization (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Improvements to a computer model of coma photochemistry are described. These include an expansion of the chemical reactions network and new rate constants that have been measured only recently. Photolytic reactions of additional molecules are incorporated, and photolytic branching ratios are treated in far greater detail than previously. A total of 25 photodissociative ionization (PDI) reactions are now considered (as compared to only 3 PDI reactions previously). Solar PDI of the mother molecule CO2 is shown to compete effectively with photoionization of CO in the production of observed CO(+). The CO(+) density peak predicted by the improved model, for CO2 or CO mother molecules, is deep in the inner coma, in better agreement with observation than the old CO2 model. However, neither CO2 nor CO mother molecule calculations reproduce the CO(+)/H2O(+) ratio observed in comet Kohoutek. PDI products of CO2, CO, CH4, and NH3 mother molecules fuel a complex chemistry scheme, producing inner coma abundances of CN, C2, and C3 much greater than previously calculated.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 42
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    Laser spectroscopy of the CN radical and astrophysical applications (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The formation of CN radicals by flash photolysis of a number of parent molecules was monitored by laser induced fluorescence in the B2Sigma(plus)-X2Sigma(plus) transition of CN. The rotational and vibrational energy of the newly formed radicals in the X state was measured directly. Formation of CN(A2Pi) in the lower vibrational levels was determined by an indirect method based on resonant energy transfer to higher vibrational levels of the ground state. These laboratory studies have shown that high initial internal excitation of CN with rotational levels of maximum N equals 50-70 is the rule. In general, the formation of simple molecules in excited states is commonly the case. There appear to be astrophysical systems where radiation from these excited levels may be detectable. Such observations would serve as a probe of molecular formation.
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  • 43
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    The spectrum of IRC + 10216 from 2.0 to 8.5 microns (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Low-resolution spectra of IRC + 10216 have been obtained from 2 to 8.5 microns from NASA's Kuiper Airborne Observatory at an altitude of 12.5 km (41,000 feet). Observations were made during 1976 January and 1977 February. In both sets of data, the spectral flux reaches its maximum between 6.0 and 6.6 microns and the previously reported 3.1-micron feature is observed; no obvious new absorption features have been found. The new data together with other spectral data and measurements of the spatial extent of IRC + 10216 impose conditions that must be met by models of the continuum. Several simple models for 2-8.5 micron radiation are examined. The new continuum data impose a constraint on the size of the grains in the cooler, optically thin part of the object. Earlier photometry has been combined with the present data to yield an improved value of the average period: 644 + or - 17 days. It appears that the variability is irregular and that the minima have been deeper in recent years than they were in 1965-1969.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 44
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    Self-gravitating gas flow in barred spiral galaxies (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: A series of two-dimensional numerical experiments is performed in order to test the response of an isothermal, self-gravitating gas disk to a uniformly rotating, barlike gravitational potential. The barlike potential is an equilibrium stellar model from the n-body calculations of Miller and Smith (1979). In the bar-dominated, central regions of the disk, a gas bar whose phase depends primarily on the location of principal resonances in the disk is formed. This response can be understood in terms of orbit-crowding effects. In the gas-dominated outer regions of the disk, two-armed trailing spiral waves are formed. The local pitch angle of these waves increases with increasing fractional gas mass. These self-gravitating gas waves are not self-sustaining. They are driven from the ends of equilibrium stellar bars, and their phase does not depend on the location of resonances in the disk. The relevance of these self-gravitating waves to observations and models of barred spiral galaxies is discussed. It is concluded that these waves and their associated ringlike structures may be consistent with the morphological distribution of gas features in barred spiral galaxies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 45
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    Optical surface brightnesses of dusty galaxies (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: It is suggested that Freeman's (1970) result that the disk portions of spiral galaxies have a preferred central surface brightness might be the consequence of observing optically thick ensembles of a standard mix of stars and dust. Regardless of whether this hypothesis is correct, the observation that elliptical galaxies usually have central surface brightnesses considerably greater than the disk portions of spirals can be understood if there is much less dust within the elliptical systems. In particular, ellipticals probably have dust-to-total-mass ratios at least a factor of 100 smaller than in the disk portions of spirals, although there is no evidence that the dust-to-interstellar-gas ratios are different. When stars were forming within ellipticals, these galaxies were probably dustier than they are now, and their visible light output could have been substantially affected. It will probably be necessary to establish the dust content of galaxies as a function of redshift to use these objects as cosmological probes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 46
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    New spectroscopic constants for methane derived by using microwave transitions from the interstellar medium (1980)
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
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  • 47
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    Comment on the paper 'A cosmological limit on the possible variation of G' (1980)
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 191
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  • 48
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    HEAO A-2 observations of the X-ray spectra of the Centaurus and A1060 clusters of galaxies (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: X-ray spectral observations of two nearby low-luminosity clusters of galaxies are presented. For the Centaurus cluster an emission feature at 7.9 keV is detected at about one-third of the strength of the 6.7 keV line. This higher energy line represents K-beta emission from highly ionized iron. In addition, it is demonstrated that for neither the Centaurus nor the A1060 cluster can an isothermal model with an Fe emission line adequately fit the data. Instead, the simplest models which provide acceptable fits include a second, harder component which may be either a second exponential or a power law. The implications of the two-component nature of the continuum on the Fe abundance and the X-ray surface-brightness distribution are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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  • 49
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    Observation and search for gamma rays 1-20 MeV from the Crab, NGC 4151, Cyg X-1, Cyg X-3, CG 135+1 and 3C 273 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Observations and limiting values for the flux of 1-20 MeV gamma rays from the Crab, the Seyfert galaxy NGC 4151, the black hole candidate Cyg X-1, Cyg X-3 and the two nearest quasars CG 135+1 and 3C 273 are reported. Measurements of the energy and scatter angle of gamma rays at zenith angles between 10 and 30 deg were obtained by a balloon-borne double-scatter gamma-ray telescope. The flux from the Crab from 1.2 to 10 MeV is found to be 0.0039 + or - 0.0020 photons/sq cm per sec, and the energy distribution of the flux from 1.2 to 20 MeV is determined. Two-standard-deviation upper limits to the gamma-ray flux in the intervals 1.2-3, 3-5, 5-10 and 10-20 MeV of 0.0003, 0.0002, 0.00006 and 0.00004 photons/sq cm/sec are found for NGC 4151, Cyg X-1 and Cyg X-3, while those of 0.0005, 0.0003, 0.0001 and 0.00004 photons/sq cm per sec are determined for both quasars. These upper limits are interpreted as restricting confirmed gamma-ray sources to the Crab and NP 0532, and as evidence against Seyfert galaxies as the source of cosmic diffuse radiation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 284; Apr. 17
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  • 50
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    Simultaneous X-ray and optical observations of rapid variability in Scorpius X-1 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Copernicus and SAS-3 observations of Sco X-1 during very active states show strong and rapid X-ray flickering with time scales as short as 20 sec. Simultaneous optical photometry reveals similar and remarkably well correlated flickering of lower amplitude. The level of correlation decreases when the X-ray source becomes fainter, but optical and X-ray fluxes, averaged over 1 min, are usually well correlated for B magnitudes less than 12.9. Cross-correlation analysis of the data during periods of high activity shows no really significant time delay between X-ray and optical features, although the cross-correlation function peaks systematically for positive lag values (optical following X-rays). The amplitude of the X-ray flickering exhibits a strong energy-dependence consistent with the well-known intensity versus spectral-hardness relation derived from previous observations. The highly correlated optical activity is interpreted as due to reprocessing of X-ray photons in the binary system.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 191
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  • 51
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    Mass loss from UW Canis Majoris (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The present analysis is an application of the theory described by Lucy (1971) for the calculation of P Cygni resonance line profiles formed by isotropic and coherent scattering in spherically symmetric expanding circumstellar envelopes. Copernicus satellite measurements of resonance features in the FUV spectrum of the O 7 supergiant UW Canis Majoris (= HD 57060) are compared with theoretical P Cygni profiles. Grids of line profiles are computed using four free parameters which contain information about the velocity law, ionization equilibrium, temperature, and envelope density. Thus, with the assumption of a spherically symmetric steady flow, and of solar element abundances, the stellar mass loss rate and the electron temperature of the expanding shell can be derived. The mass flow is treated in a fully transonic way, i.e., the Sobolev approximation is applied.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 83; 3, Ma; Mar. 198
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    IUE observations of the hot components in two symbiotic stars (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Recent IUE observations reveal striking differences in the UV spectra of two symbiotic stars, R Aqr and RW Hya. RW Hya is found to be an unexpectedly intense source of UV radiation. The measurements reported demonstrate the presence of a hot component in each star, supporting the view that each is a binary system with a luminous red primary and a hot, subluminous companion. In one case, the hot companion manifests itself by exciting a compact nebulosity; in the other case the continuous spectrum of the hot star is directly detected, while the continuum of nebulosity excited by the hot star is detected at longer wavelengths.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 284; Mar. 13
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    Collapsing cloud models for Bok globules (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The dynamic collapse of rotating gas clouds is calculated for a wide range of initial conditions. Properties of cloud models are compared with observed radio and optical properties of Bok globules, to test the hypothesis that globules undergo collapse and to determine parameters which are not easily observed. Five of the six globules studied are consistent with collapse models. It is inferred that these objects have masses of about 100 solar masses and ages smaller than their free-fall times. Inferred initial densities are much larger than minimum densities for gravitational collapse, suggesting that collapse is initiated by strong external compression or that globules are fragments of larger condensed clouds. Values inferred for the (C-13)O/H2 ratio are smaller than previous estimates and depend strongly on cloud density.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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    Cosmological tests of the Hoyle-Narlikar conformal gravity (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: For the first time the Hoyle-Narlikar theory with creation of matter and a variable gravitational constant G, is subjected to the following cosmological tests: (1) the magnitude versus z relation, (2) the N(m) versus m relation for quasars, (3) the metric angular diameters versus z relation, (4) the isophotal angles versus z relation, (5) the log N-log S radio source count, and finally (6) the 3 K radiation. It is shown that the theory passes all these tests just as well as the standard cosmology, with the additional advantage that the geometry of the universe is uniquely determined, with a curvature parameter equal to zero. It is also interesting to note that the variability of G affects the log N-log S curve in a way similar to the density evolution introduced in standard cosmologies. The agreement with the data is therefore achieved without recourse to an ad hoc density evolution.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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  • 55
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    Radial distribution of forbidden Fe X and forbidden Fe XIV emission in the Cygnus Loop. II (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 235
    Format: text
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  • 56
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    On C4H versus vibrationally excited CO in IRC + 10216 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The identification of the 114,221-MHz line in the spectrum of the evolved carbon star IRC +10216 with a blend of the rotational transition of C4H and the first rotational transition of vibrationally excited CO is investigated. A spectrum of the source was obtained using an 11-m telescope in the range covering the N = 12 to 11 and 11 to 10 spin-doublet rotational transitions of C4H. Two peaks of equal intensity and width are found in each band, suggesting a spin rotation constant of 1.06 for the 12 to 11 doublet and 1.09 for the 11 to 10 doublet, and excluding the possibility that vibrationally excited CO made any contribution to the 12 to 11 doublet. An additional survey of the regions from 103.8 to 107.5 and 113.3 to 117.0 GHz has revealed no new lines stronger than 0.1 K in the spectrum of IRC +10216.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 235
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    Case for an open universe (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The determination of the geometrical structure of the universe through the magnitude-vs-redshift relation in standard cosmology has not been very successful, mainly because of the intrinsic insensitivity of the m-vs-z relation to a deceleration parameter, which determines the spatial curvature and therefore the geometry. By relaxing the assumption usually made, i.e., the identity of gravitational and atomic clocks, sufficient sensitivity is achieved. Existing observational evidence then leads one to conclude that the universe is open.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review Letters; 44; Mar. 17
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  • 58
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    Black holes, quasars, and the universe /2nd edition/ (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Topics of astronomy are discussed in terms of black holes, galaxies, quasars, and models of the universe. Black holes are approached through consideration of stellar evolution, white dwarfs, supernovae, neutron stars, pulsars, the event horizon, Cygnus X-1, white holes, and worm holes. Attention is also given to radio waves from high speed electrons, the radiation emitted by quasars, active galaxies, galactic energy sources, and interpretations of the redshift. Finally, the life cycle of the universe is deliberated, along with the cosmic time scale, evidence for the Big Bang, and the future of the universe.
    Schlagwort(e): ASTROPHYSICS
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  • 59
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    Turbulence and the stability of molecular clouds (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Molecular clouds may be stabilized against gravitational collapse by the turbulent velocity field within them. It is suggested that the energy derived from differential galactic rotation can maintain the turbulent flow in the interstellar medium. The characteristic decay time for interstellar turbulence is found to be about 10-billion years. The rate and efficiency of star formation in giant molecular clouds reflect the stochastic nature of turbulence.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 242
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  • 60
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    A wave model for dwarf novae (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The rapid coherent oscillation during a dwarf nova outburst is attributed to an accretion-driven wave going around the white dwarf component of the binary system. The increase and decrease in the period of this oscillation is due to the change in the velocity of the wave as it is first being driven and then damped. Qualitatively, a large number of observations can be explained with such a model. The beginnings of a mathematical representation of this model are developed.
    Schlagwort(e): ASTROPHYSICS
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  • 61
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    Collapse, equilibrium, and fragmentation of rotating, adiabatic clouds (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Numerical calculations of the collapse of adiabatic clouds from uniform density and rotation initial conditions show that when restricted to axisymmetry, the clouds form either near-equilibrium spheroids or rings. Rings form in the collapse of low thermal energy clouds and have a ratio of rotational kinetic energy to the absolute value of gravitational potential energy greater than approximately 0.43. When the axisymmetric constraint is removed and an initial m = 2 density variation is introduced, clouds either collapse to form near-equilibrium ellipsoids or else fragment into binary systems through a bar phase. Ellipsoids form in the collapse of high thermal energy clouds and have a rotational kinetic energy/absolute value of gravitational potential energy ratio less than approximately 0.27. The results are consistent with the critical values of the rotational kinetic energy/absolute value of gravitational potential energy ratio for instabilities in Maclaurin spheroids, and suggest that protostellar clouds may undergo a dynamic fragmentation in the nonisothermal collapse regime.
    Schlagwort(e): ASTROPHYSICS
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  • 62
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    X-ray line emission from the supernova remnant G292.0 + 1.8 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The Solid State Spectrometer on the Einstein Observatory has detected line emission from Mg, Si and S in the thermal X-ray spectrum of the supernova remnant G292.0 + 1.8. An over-abundance of sulfur and a probable under-abundance of iron relative to their solar values is indicated by the data. The X-ray and optical data for this object support an interpretation of emission originating in ejecta from the comparatively recent explosion of a massive (about 20-solar-mass) progenitor star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 193
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  • 63
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    A survey of chromospheric Ca II H and K emission in field stars of the solar neighborhood (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Fluxes in 1 A bands at the centers of the H and K lines are being measured in main-sequence F-G-K-M stars in the northern half of the Woolley et al. (1970) 'Catalog of stars within twenty-five parsecs of the sun', in a survey not yet completed. Results for 486 stars are presented in the form of flux-color diagrams and discussed in light of evidence that chromospheric activity declines with age in main-sequence stars. Support is noted for the reality of the Sirius moving group. The relative numbers of more-active (Hyades-like) and less-active (solar-like) F-G stars are tolerably in agreement with a nearly constant rate of formation, but there exists an apparent deficiency in the number of F-G stars exhibiting intermediate activity. The possibility that the gap is an accidental characteristic of the sample will be investigated by extending the survey to southern declinations and greater distances.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 92
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  • 64
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    The X-ray pulsars 4U 1145-61 and 1E 1145.1-6141 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Observations of the neighboring X-ray pulsars 4U 1145-61 and 1E 1145.1-6141 obtained by OSO 8, HEAO 1 and the Einstein Observatory between 1975 and 1979 are reported. A temporal analysis of Einstein Solid State Spectrometer and Monitor Proportional Counter data, OSO 8 A and C detector data and HEAO 1 A-2(3) experiment data confirms the presence of two periodicites at 291 and 297 sec in the region, with the shorter period located within 3 arcmin of 4U 1145-61. Observations indicate the spectrum of 4U 1145-61 to obey a power law with an index of 1.5 out to at least 60 keV, with little variation with pulse phase, and a 500-eV EW iron line at 6.7 keV. The spectrum of the other source is found to be more absorbed. Similarities between the pulsars are noted, and it is suggested that they may be the result of pulsar formation in a homogeneous cloud of progenitors.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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  • 65
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    Observations of Cygnus X-3 with the Einstein /HEAO 2/ X-ray Observatory The period derivative and the asymmetric X-ray light curve (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Cygnus X-3 was observed by the Monitor Proportional Counter on the Einstein (HEAO 2) X-ray Observatory for 2.4 days in 1978 December. The analysis of the data from these observations is used in conjunction with a self-consistent re-examination of previous results from the Uhuru, ANS, COS B, and SAS 3 satellites to investigate earlier reports that the 4.8 hour period of Cygnus X-3 is increasing. It is found that there is indeed a period derivative, P = (1.78 plus or minus 0.40) x 10 to the -9th s/s, which confirms the principal conclusion of previous authors. The possibility that the X-ray source is in an elliptical orbit and that some, or all, of the observed period derivative may be due to apsidal motion is discussed. The elliptic orbit hypothesis explains the observed asymmetry in the average X-ray light curve and leads to the conclusion that the most likely companion to the X-ray source is a helium star, possibly with a light hydrogen envelope
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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  • 66
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    An observational H-R diagram for early-type stars (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: An observational H-R diagram for the O and B stars is discussed and compared with the predicted positions of massive model stars for the case of no mass loss and the case of mass loss. It is shown that the flux effective temperatures of O and B supergiants and of early O stars are less than the effective temperatures which might be inferred from the relative intensities of lines from two stages of ionization of an element.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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    X-ray observations of the Seyfert 1 galaxies AKN 120 and MCG 8-11-11 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A new X-ray source, H0523-00, with the optically variable Seyfert 1 galaxy AKN 120 is identified. The source has a 2-10 keV X-ray flux of 2 x 10 to the -11th ergs/sq cm s which corresponds to a 2-10 keV X-ray luminosity of 10 to the 44th ergs/s. X-ray observations over a 1.5 year time span combined with contemporaneous optical photometry show a decrease in the optical with no corresponding decrease in the X-ray. In contrast, similar observations of MCG 8-11-11 show a contemporaneous decrease in optical and X-ray fluxes. It is noted that the infrared and X-ray spectral slopes for these two objects are similar, with the optical being steeper by roughly one unit.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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  • 68
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    The detection of a companion star to the Cepheid variable Eta Aquilae (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Ultraviolet spectra have been obtained with IUE of the classical Cepheid Eta Aquilae at several phases in the 7.18 day period. Significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1600 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the nonvariable emission is consistent with the flux expected from a main-sequence companion star with an effective temperature of about 9500 K (A0 V). The observed ultraviolet flux and spectral type are used to compute a distance of 300 pc to the system, in agreement with the distance predicted using the period luminosity relation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 69
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    On the time variability of Circinus X-1 - A comparison with Cygnus X-1 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The time variability and spectral characteristics obtained from Uhuru observations of Cir X-1 (4U 1515-56) are compared with observations of Cyg X-1 (4U 1956+35). It is found that Cir X-1 has a more variable spectrum (with perhaps a state over the 4 days spanned by the data), is less 'noisy', and has correlated fluctuations (as evidenced by the nonzero cross-correlation function between two energy bands) of shorter duration than those present in the shot noise of Cyg X-1.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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  • 70
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    X-rays from RS Canum Venaticorum systems - A HEAO 1 survey and the development of a coronal model (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The paper presents HEAO 1 low-energy X-ray observations of 59 known or suspected RS CVn systems cited in the lists of Hall (1976), Eggen (1978), and the circulars of the Working Group on RS CVn systems of IAU Commission 42. The data are used to argue against the validity of the minimum flux coronal models. A coronal loop model is used to derive expressions for the loop parameters in terms of observable quantities, and find acceptable solutions for RS CVn systems. It is concluded that the difference between solar activity and that observed in RS CVn systems may be merely a matter of scale.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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    Comments on stellar boundary cooling and the reality of supermetallicity (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The paper discusses the 'super-metal-rich' (SMR) stars and reexamines Peterson's analysis of the SMR prototype mu Leo (1978) with regard to a postulated error in continuum error. Model atmospheres are used to compute theoretical equivalent widths and to explore the sensitivity of these widths to metallicity, temperature, surface gravity, and microturbulence. It is shown that Peterson's results are sensitive to continuum placement, and that her data does not indicate that the temperature gradient is steeper in mu Leo than in normal giants. It is concluded that the SMR stars are very metal rich and are also somewhat boundary cooled, possibly due to high metallicity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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  • 72
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    Gamma rays from Penrose powered black holes in Centaurus A, 3C 273, and NGC 4151 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Gamma-ray observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC spectrum is attributed to Penrose Compton scattering, and the absence of an MeV break in the spectra of Cen A and 3C 273 implies Penrose pair production. Central black hole masses of tens of millions of solar masses for NGC 4151 and Cen A, and tens of billions of solar masses for 3C 273, are obtained. Attention is also given to accretion rate, the efficiency of accretion, QSOs and Seyferts.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 236
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    The plane of symmetry of interplanetary dust in the inner solar system (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Observations of the zodiacal light from the space probes Helios 1 and 2 between 1.0 and 0.3 AU show - superimposed on the general radial dependence - a systematic variation of brightness and brightness distribution with position in the orbit which is caused by the inclination of the symmetry plane of interplanetary dust with respect to the ecliptic. By suitable choice of the observing geometry, the inclination and the ascending node of the symmetry plane can be determined directly from the data without recourse to model calculations. The resulting values of i equals 3.0 plus or minus 0.3 deg, Omega equals 87 plus or minus 4 deg are not compatible with a concentration of interplanetary dust to the invariable plane of the solar system. The data support the simple view that the distribution of interplanetary dust in the inner solar system is characterized throughout by one plane of symmetry and suggest that this plane extends to at least 1 AU.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 82; 3, Fe; Feb. 198
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    A laboratory study of magnesium-tetrabenz-porphyrin - Lack of agreement with diffuse interstellar bands (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The visible and infrared spectra and thermal behavior of the bis-pyridal-magnesium-tetrabenz-porphyrin molecule proposed as the carrier of the diffuse interstellar bands were measured. Of the six band coincidences reported by Johnson (1977), only one, 4430 A, occurs in these experiments. This coincidence requires a special environment, not likely to occur in interstellar space but the infrared spectrum does not support Johnson's vibrational scheme. These spectroscopic and thermal measurements contradict the hypothesis that this molecule causes the diffuse bands.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science; 68; 1, Ma; Mar. 198
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    Production of carbon, sulfur, and CS in Comet West (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Results from ultraviolet spectrographic observations of Comet West (1975n) in the 1620-3960 A wavelength range are presented. Objective grating imagery of the comet reveals for the first time emission from sulfur atoms and CS molecules as well as previously observed lines or bands in carbon atoms and CO(+), CO2(+) and OH molecules. Some evidence exists for emission in the C2 Mulliken bands and in the CO Cameron bands. On the basis of the observations, production rates of C (ground state), C(1D), S, and CS are inferred to be 3.8 x 10 to the 29th per sec, 4.4 x 10 to the 29th per sec, 1.7 x 10 to the 28th per sec, and greater than approximately 3.1 x 10 to the 27th per sec, respectively.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 242
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    The diffuse gamma-ray background in the Hoyle-Narlikar cosmology (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The paper analyzes the contributions of QSOs, BL-Lac objects and Seyfert galaxies to the diffuse gamma-ray background within the framework of the Hoyle-Narlikar theory. It is shown that the inconsistency reported in standard theory, namely that the evolutionary function needed to explain the gamma-ray data is very different from the one derived from the optical part of the spectrum, is no longer present. It is also shown that the contribution of a variable gravitational 'constant' to the expression for the diffuse background is the same as that of a density evolution function.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 92; 1-2,; Dec. 198
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    Neutrino, gamma-ray, electron, and positron production in an ultrarelativistic plasma (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Neutrino, gamma-ray, electron and positron production resulting from inelastic proton-proton collisions in a highly relativistic plasma such as may exist in extragalactic radio or gamma-ray burst sources is examined. The source functions of primary (pions, kaons, and neutrons) and secondary (photons, electrons, positrons and neutrinos) products of relativistic nuclear collisions are computed for the cases of power law and Maxwellian relativistic proton distributions. It is shown that in plasma which is optically thin to interactions between the plasma and secondary gamma-rays, electrons and positrons, only a small fraction of the initial energy is emitted in the observable form of neutrinos and gamma rays. In an optically thick plasma on the other hand, most of the energy of the relativistic protons is found to be equally divided between gamma rays and neutrinos, although only the neutrinos may escape freely to be observed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 241
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  • 78
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    Dust-to-gas ratio in the outer regions of spiral galaxies (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Some spiral galaxies are surrounded by extended clouds of neutral hydrogen; if dust is associated with this gas, the dust should appear as a faint extended reflection nebula illuminated by the light from the entire galaxy. It is suggested that observations of the surface brightness of the outer regions of M83 and M101 could be worthwhile, since these two galaxies are bright and have extended surrounding gas clouds. Such studies would be of interest with regard to the possible presence of faint extended halos of stars around galaxies, the extent of the metallicity gradients in galaxies, and the value of the dust-to-gas ratio in quasar absorption-line systems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 241
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    X-ray observations of Algol (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The Solid State Spectrometer on Einstein has been used to study Algol. Two observations six months apart were made, both including a primary optical eclipse. No corresponding X-ray eclipses were seen. During the second observation the source was flaring and was on the average a factor of three brighter. The spectrum on both occasions was consistent with a two-component thermal equilibrium model with temperatures of approximately 7.5 and 40 million degrees. Attempts to insert a third component indicate the temperature distribution to be bimodal. Models for the X-ray emission are discussed and it is suggested that it most likely originates from an active corona surrounding the K star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 239
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    Far-infrared spectra of W51-IRS 2 and W49 NW (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Measurements of the far-infrared spectra of the powerful H II regions W51-IRS 2 and W49 NW from 65 to 345 per cm with about 9 per cm resolution were obtained by using an airborne Michelson interferometer. The most remarkable feature of the far-infrared spectra of the two regions is the smoothness of the continuum; no evidence is found in the spectra for features of H2O ice at 45 and 62 microns. The spectrum of W51 is well fitted by a 70 K blackbody with a diameter of 14 arc sec, but the spectrum of W49 NW is narrower than a blackbody. The implications of the apparently high peak optical depths of these sources are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 81
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    Stellar winds, supernovae, and the origin of the H I supershells (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: It is shown that the H I shells and supershells, recently reported by Heiles, are a natural by-product of the interaction of the stellar winds and supernovae, originating from stars in typical OB associations, with the surrounding interstellar medium. The validity of this model is supported by its ability to reproduce observed characteristics of the shells such as the shell sizes and shapes as a function of their distances from the galactic center. This process may also be responsible for injecting synthesized elements into the galactic halo.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
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  • 82
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    The evolution of the dust shell of Nova Serpentis 1978 (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Photometric measurements of Nova Serpentis 1978 from V to 19.5 microns covering the first 240 days of the nova's development are reported. A free-free expansion phase was followed by the condensation of a dust shell that became optically thick at both visible and infrared wavelengths. Carbon grains grew to radii of approximately 0.3 microns during the condensation period. The grains appeared to sputter or evaporate for a period of approximately 100 days following infrared maximum. It is found that the condensed carbon comprised 2% of the ejected mass, which implies that carbon abundance was enhanced in the nova shell. The angular expansion rate of the shell yields a distance of approximately 5 kpc and a luminosity of approximately 3000 solar luminosities for Nova Serpentis 1978.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 237
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  • 83
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    Cosmological considerations on the diffuse gamma-ray isotropic background (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Bignami et al (1979) have recently studied the problem of the origin of the diffuse gamma-ray isotropic radiation. They have concluded that within standard cosmology with Lambda = 0 and p = 0, BL Lacertae objects and Seyfert galaxies can account for most of the diffuse radiation if they have not evolved in time. For QSOs, an evolutionary factor is allowed by the data. From the study of radio data, however, it is known that strong evolutionary effects are expected. The discrepancy cannot be explained by changing the geometry of the universe. Contrary to the case of standard cosmology, it is found that in order to fit the diffuse gamma-ray background, the evolutionary function required is almost identical to the one previously determined from the study of the log N-log S relation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 235
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  • 84
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    Numerical models for cometary dust environments (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The development of a numerical model for the dust environment near a comet is described. The major components of the model are a simple treatment of the acceleration of the dust by the gas outflow from an isothermal icy nucleus, a detailed treatment of the dust particle trajectories controlled by solar gravity and radiation pressure, including the formation of the dust envelope and tail, and a simple treatment of the radiation from the dust in the visible and thermal infrared. The results of recent comet observations are used to estimate parameter values for the model, including dust-to-gas ratios by light and by mass, the distribution of dust and gas emission on the nuclear surface, the distributions of dust particle size, density, mass, and radiative properties, and other quantities. Gas and dust production rates as functions of time are derived from observed light curves using the simple photometric theory. Sample results are presented for the dust concentration, flux and fluence along the trajectory of a spacecraft which flies by Comet P/Halley in 1986.
    Schlagwort(e): ASTROPHYSICS
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  • 85
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    An outer ion coma model in two dimension (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A simple cometary outer ion coma model is constructed by adopting published results from numerical MHD computations. The ion composition and density distributions so derived are used to highlight some of the basic features of cometary plasma flows and the need for cometary ion observations with absolute brightness calibration.
    Schlagwort(e): ASTROPHYSICS
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  • 86
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    Search for hydrogen atoms and the noble gas abundances in the head of Comet Schwassmann - Wachmann 1 (1974 II) from Voyager 2 UVS spectra (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): ASTROPHYSICS
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  • 87
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    The nature of cometary dust from remote sensing (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observational data on the thermal emission from cometary dust grains and theoretical models constructed to explain them are reviewed. Consideration is given to grain temperature, the size distribution of the grains, thermal-emission models, the silicate component, dust-grain albedo, and icy grains; model predictions and observations are compared in graphs. It is pointed out that no unambiguous detection of icy grains has been achieved, probably because these grains are vaporized within a few hundred km of the nucleus when the comet is within 2.5 AU of the sun.
    Schlagwort(e): ASTROPHYSICS
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  • 88
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    Electromagnetically-tracked free-mass gravitational wave antennas (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The response to a gravitational wave of two free masses whose relative motion is monitored with an electromagnetic tracking signal is derived. The results indicate a two-feature signature in one-way data and a three-feature signature in two-way data. The effect is applied to gravitational wave experiments using laser interferometers, spacecraft Doppler tracking, planetary ranging, and pulsar timing analysis. Actual results are presented from spacecraft Doppler experiments and from pulsar timing data analysis, with new upper limits being set on a possible cosmic gravitational wave background via the pulsar data.
    Schlagwort(e): ASTROPHYSICS
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  • 89
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    Infrared properties of extragalactic H II complexes (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Infrared observations of relatively isolated giant H II complexes in the LMC and the spiral arms of M33 and M101 are discussed, and complexes which extend over several kiloparsecs near the galactic centers are examined. The 30 Doradus nebula is emphasized, showing the variation of the 50-100 micron color temperature with position in that object. Ten-micron scans through the nucleus of NGC 1097 are compared to a visual photograph, showing the enhanced infrared emission which occurs at the nucleus and at the ring of H II regions about 1 kpc from the nucleus.
    Schlagwort(e): ASTROPHYSICS
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  • 90
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    X-ray emission from pre-main-sequence stars, molecular clouds and star formation (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The pre-main sequence X-ray emitting stars observed in molecular clouds appear to provide the bulk of the ionization. Newly forming stars therefore control the coupling of the magnetic field to the cloud. Since this coupling itself is believed to be responsible for the rate of cloud collapse, it is suggested that there is a natural feedback mechanism, involving observed X-rays, which is capable of regulating molecular cloud evolution and the rate of star formation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 272; Sept. 15
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  • 91
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    A note on compressibility and energy cascade in turbulent molecular clouds (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observed velocity-size correlations are reexamined in the light of an improved theory of turbulent energy cascade that is developed. It is shown that observed velocity-size correlations cannot be compared with the Kolmogorov law, which is based on incompressible turbulent flow. The fact that the log v-log(l/rho) scaling law (v the turbulent velocity, l the associated region size, and rho the fluid density) predicted for compressible energy cascade is always steeper than that observed in molecular clouds indicates the injection rather than the dissipation of mechanical energy at smaller scales of motion. It is also shown that the concept of strict energy cascade may not be generally applicable in the interstellar medium. The agreement between theory and observation turns out to be best for small cool clouds and cloud cores, suggesting that, for these regions at least, the dominant process in establishing the observed v-l-rho correlation is a turbulent energy cascade.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 272; Sept. 15
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  • 92
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    A large molecular cloud toward the SNR W50 and SS 433 (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The CO 1 yields 0 transition at 115 GHz has been mapped over an area of more than 6 deg sq toward W50, the extended SNR surrounding the peculiar object SS 433. W50 is found to lie at the end of a filamentary molecular cloud 4 deg long and 1 deg wide that closely matches a conspicuous dust lane on the Palomar Sky Survey; the cloud's kinematic distance is within 0.7 of 2.2 kpc, in agreement with the distance 2-3.3 kpc estimated for the SNR, and its mass is about 120,000 solar masses. Though there is little evidence of star formation in the molecular filament, or evidence of an interaction between the filament and W50 (or SS 433), the positional coincidence of the two, their similar distance, and their displacement nearly two molecular scale heights from the plane all suggest a physical relationship or common origin. One possibility is that both the molecular filament and the stellar progenitor of W50 were ejected from a large active molecular complex lying in the plane at l = 40 deg.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 272; Sept. 15
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  • 93
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    Correlated particle and magnetic field observations of a large-scale magnetic loop structure behind an interplanetary shock (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: From a survey of observations on ISEE-3, an example of correlated particle and magnetic field observations of a large-scale magnetic loop structure is presented. Bidirectional proton fluxes were observed for a period of 40 hours in the energy range 35-1600 keV approximately 12 hours after the passage of the interplanetary shock of December 11, 1980, and directly after the passage of a discontinuity. For each of the eight logarithmically spaced energy channels, a three-dimensional anisotropy analysis reveals streaming along both directions of the magnetic field. The magnetic field rotated slowly but steadily through approximately 180 deg during this same 40-hour period; this is consistent with the existence of a large-scale loop with extent greater than 0.5 AU. The observations suggest that the particles are being injected into the loop sunward of the spacecraft; they appear as bidirectional fluxes in the outermost regions of the loop arising from a combination of focusing and near scatter-free transport.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 10; Sept
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  • 94
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    The effect of MHD instabilities on the flaring of cometary plasma tails (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The hypersonic pressure balance model of flaring in cometary plasma tails of Ershkovich et al. (1982) has been modified to include the effects of magnetohydrodynamic (MHD) instabilities occurring along the ionopause in the outer-tail regions. The effect of instability is to mix the solar-wind and comet-tail plasmas, increasing the tail magnetic field strength above that calculated from magnetic flux conservation. The earlier model assumed the ionopause to be a tangential discontinuity surface (flux conserving) at all distances, with the result that the magnetic field approached zero in the outer regions of strongly flaring tails. The present model is more realistic and is in better agreement with measurements of cometary plasma tail widths and flaring angles. This agreement leads to an important conclusion that the magnetic flux is not conserved in distant comet tails.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 272; Sept. 1
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  • 95
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    On searches for periodic pulsed emission - The Rayleigh test compared to epoch folding (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Rayleigh test has been recently invoked as a method of searching a time series for periodic pulsations. In this paper, this technique is discussed and compared to epoch folding, a technique which has had widespread use in X-ray astronomy. It is found that the Rayleigh test provides a more sensitive approach to the search for periodic pulsations when the pulses are sinusoidal or of broad duty cycle, such as those typical of the pulsing X-ray sources. Epoch folding, on the other hand, is more sensitive to the narrow pulses typical of radio pulsars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 272; Sept. 1
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  • 96
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    Electrodynamic coupling in magnetically confined X-ray plasmas of astrophysical origin (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Explicitly magnetic field-independent relationships that quantitatively connect the thermodynamic state of the confined beta-less-than-one X-ray plasma to the confining magnetic loop characteristics and the stressing velocity at beta greater than about one are presented. The derived relations fall into two categories: (1) diffuse heating resulting from efficient transport of energy throughout the magnetic loop volume, and (2) isolated heating within the electrodynamic dissipation shell. For each of these cases the Joule dissipation, shear viscous dissipation, and compressional dissipation are considered. Each of these models is characterized by three thermodynamic scalings that are parametrized by the magnetic loop properties and by the stressing velocity. Eliminating the magnetic field intermediary from these relations and normalizing the inverse aspect ratio and the magnetic expansion factor with respect to solar conditions results in a single, unique velocity scaling law for each model.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 15
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  • 97
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    The detection of H2 in cool carbon stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Spectra of several carbon stars in the two micron region are examined and compared with synthetic spectra from model atmospheres. Molecular hydrogen has been directly observed in carbon stars for the first time through the quadrupole 1-0 S(1) line at 4712.9/cm. It is definitely present in several Mira variables, and is definitely not present in several irregular variables and one Mira variable. A discrepancy between the predicted and observed line depths at different temperatures is shown. Resolution of the discrepancy by change of temperature alone would require an upward revision of the present effective temperature scale by at least 600 K. Several possible resolutions of the dilemma are briefly examined.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 270; July 15
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  • 98
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    Very long baseline interferometry at a wavelength of 3.4 mm (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The first detection of interference fringes by VLBI at a wavelength of 3.4 mm during observations of 3C84 are reported. The compact source in the nucleus of 3C84 was observed for a 9-hr period on the 485 km baseline between the Owens Valley Radio Observatory and the Hat Creek Observatory. The fringe data are given and the derivation of the correlated flux densities is described. The findings are discused in the context of previous obervations. The results demonstrate that there are no unforeseen technical difficulties associated with millimeter VLBI, and that the sensitivity of existing systems is sufficient to observe objects brighter than a few Jy. The observations are consistent with the millimeter wavelength radio structure of 3C84 being more compact than its centimeter wavelength structure.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 303; June 9
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  • 99
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    Comment on 'A comparative study of rotational properties of high-velocity and low-velocity early-type stars' (1983)
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 267
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  • 100
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    Theoretical study of silicon dicarbide (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Silicon dicarbide was first observed in 1926 in spectra of cool carbon stars. The carrier of these bands around 5000 A was tentatively identified as SiC2 by Kleman (1956) who produced similar spectra by inserting silicon into the graphite tube of a King furnace heated to over 2500 K. This identification was strengthened by subsequent mass spectral studies which showed SiC2 as a major molecular component of vaporized silicon carbide. The present investigation is concerned with calculations which were initiated in an attempt to understand more recent astronomical observations of unidentified lines in the millimeter-wave region of the spectrum. The calculations were designed to determine the ground state equilibrium structure and to obtain vibrational and rotational constants. Calculations for estimating the positions and structure of low-lying electronic states were also performed. Self-consistent field (SCF) calculations were performed assuming a closed-shell electronic structure analogous to that in C3. Calculations were conducted for symmetric CSiC, and asymmetric SiCC forms.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 266
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