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  • Organic Chemistry  (1.384)
  • Life and Medical Sciences  (1.350)
  • ASTROPHYSICS  (1.088)
  • 1980-1984  (2.112)
  • 1975-1979  (1.710)
  • 1982  (2.112)
  • 1979  (1.710)
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  • 1980-1984  (2.112)
  • 1975-1979  (1.710)
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  • 1
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    Precise determination of the distances of galaxies (1979)
    In:  CASI
    Details
    Publikationsdatum: 2006-01-16
    Beschreibung: The use of the Space Telescope in the determination of the distances of galaxies is examined. The Space Telescope can check the local extragalactic distance scale to within 10-15 percent. The determination of relative distances of cosmic standard candles, viz. brightest M-supergiants and SNe I in E galaxies, is discussed. The M-supergiants map the velocity field out to v sub o approx. 3000 km s(-1) thus providing a firm basis for the determination of H sub o (global) from local distances, and the possibility to derive precise distances of all nearby field galaxies from their recession velocities. Photometry of the SNe I out to z = 0.5 leads to a direct determination of q sub o via the Hubble diagram, and the form of their light curves offers a fundamental test on the nature of redshifts. Other calculations are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Marshall Space Flight Center Sci. Res. with the Space Telescope; p 263-293
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  • 2
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    Requirements for predictions and real-time monitoring for the study of travelling interplanetary phenomena (1979)
    In:  CASI
    Details
    Publikationsdatum: 2006-01-16
    Beschreibung: Physical processes within quiescent as well as disturbed flows of solar wind plasma, energetic particles, and magnetic and electric fields from the Sun are considered. Specifically, travelling interplanetary phenomena to be studied during the years of the solar maximum of solar cycle 21 are covered. It is noted that predictions, while needed for long range, logistical planning, is secondary to the requirements of synoptic real time monitoring over a wide range of particle energies and spectral bandwidths.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Marshall Space Flight Center Solar-Terrest. Predictions Proc., Vol. 2; p 340-345
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  • 3
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    Kinetic theory in astrophysics and cosmology (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: Results associated with exact solution of the Einstein-Boltzmann and Einstein-Maxwell-Boltzmann equations are presented. The generalization of Ehler's killing vector approach for the distribution function to charged particles is considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 21 p
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  • 4
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    The problems of cosmology (1979)
    In:  CASI
    Details
    Publikationsdatum: 2006-01-16
    Beschreibung: Three examples that illustrate the expected role of the Space Telescope in cosmological investigations are described addressing the distribution of globular star clusters, universe expansion, and other classical cosmological problems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Marshall Space Flight Center Sci. Res. with the Space Telescope; p 295-312
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  • 5
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    The central regions of active galaxies and quasars (1979)
    In:  CASI
    Details
    Publikationsdatum: 2006-01-16
    Beschreibung: Theories describing the central regions of nonthermal extragalactic sources (radio galaxies, Seyfert nuclei, quasars, etc.) are examined in the light of the experimental possibilities afforded by the Space Telescope. In particular, the theory which proposes the accretion of stars or gas onto a black hole as the explanation of the central engine is discussed. Planned observations directed towards the problem of the mass, size, and structure of the central engine, and the phenomenological questions regarding the general environment of the central engine are outlined.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Marshall Space Flight Center Sci. Res. with the Space Telescope; p 197-214
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  • 6
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    Luminosity functions and evolution of globular clusters (1979)
    In:  CASI
    Details
    Publikationsdatum: 2006-01-16
    Beschreibung: The stellar dynamics of globular clusters are addressed in terms of luminosity functions, chemical topics, and dynamical topics
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Marshall Space Flight Center Sci. Res. with the Space Telescope; p 139-150
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  • 7
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    The Crab Nebula's progenitor (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The initial mass of the Crab Nebula's progenitor star is estimated by comparing the observed nebular chemical abundances with detailed evolutionary calculations for 2.4- and 2.6-solar-mass helium cores of stars with masses of 8 to 10 solar masses. The results indicate that the mass of the Crab's progenitor was between the upper limit of about 8 solar masses for carbon deflagration and the lower limit of about 9.5 solar masses set by the dredge-up of the helium layer before the development of the helium-burning convective region. A scenario is outlined for the evolution of the progenitor star. It is suggested that the Crab Nebula was probably the product of an electron-capture supernova.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 299; Oct. 28
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  • 8
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    Cosmic turbulence and the angular momenta of astronomical systems (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is suggested that gravitationally bound astronomical systems ranging from asteroids to galaxy superclusters may derive their rotation from a hierarchy of cosmic turbulence, thus explaining the empirical specific angular momentum-mass relationship (j approximately equal to M to the 3/4 power) exhibited by these systems. It is shown that many of the properties of these systems, e.g., the random orientation of their spin vectors, can be accounted for if astronomical objects form in a turbulent environment.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 261
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  • 9
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    Relativistic kinematics for motions faster than light (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-20197)
    Schlagwort(e): ASTROPHYSICS
    Materialart: vol. 35; Nov. 198
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  • 10
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    Water as a probe of star-forming regions (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Preliminary calculations employing statistical equilibrium techniques were carried out to determine brightness temperatures of water transitions occurring in the submillimeter band. The interesting candidates appear to be the 325 GHz, 380 GHz, and 448 GHz transitions, they are compared with the 183 GHz and 380 GHz transitions observed in the Orion Kleinmann-Low nebula and the combined results seem to be consistent with H2 densities of 100,000 -1 million cm-3 and a water column density of approximately 10 to 18th power. This implies a relative abundance of approximately 0.00001 which means that water may be about one twentieth of CO. In addition, it was found that for the conditions of the Orion plateau source, the 448 GHz line is expected to be a mild maser.
    Schlagwort(e): ASTROPHYSICS
    Materialart: ESA The Sci. Importance of Submillimetre Observations; p 129-130
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  • 11
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    Radiation from the accretion column of magnetized neutron stars (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Some developments in radiative transfer for magnetized neutron star conditions, and their application in models of the structure and properties of self-consistent polar cap emission regions are reviewed. Several of the assumptions and uncertainties involved are discussed, and present problems are indicated.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Max-Planck Inst. Phys. and Astrophys. Accreting Neutron Stars; p 253-274
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  • 12
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    Spectral evolution of active galactic nuclei - A unified description of the X-ray and gamma-ray backgrounds (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-22137)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 13
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    On OMC-1 temperatures determined from methyl cyanide observations (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: An analysis is performed on the J(k) = 12(k)-11(k) and 13(k)-12(k) transitions of methyl cyanide detected by other investigators in the direction of OMC-1. The original interpretation of those observations argues for the presence of two distinct temperature regions or possibly a temperature gradient within the cloud. The analysis presented here demonstrates that the observations of these particular molecular transitions are consistent with a single methyl cyanide emission region with a source kinetic temperature of 121.2 + or - 8.2 K and a molecular rotational temperature of 16.6 + or - 1.8 K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 14
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    A large scale height galactic component of the diffuse 2-60 keV background (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The diffuse 2-60 keV X-ray background has a galactic component clearly detectable by its strong variation with both galactic latitude and longitude. This galactic component is typically 10 percent of the extragalactic background toward the galactic center, half that strong toward the anticenter, and extrapolated to a few percent of the extragalactic background toward the galactic poles. It is acceptably modeled by a finite radius emission disk with a scale height of several kiloparsecs. The averaged galactic spectrum is best fitted by a thermal spectrum of kT about 9 keV, a spectrum much softer than the about 40 keV spectrum of the extragalactic component. The most likely source of this emission is low luminosity stars with large scale heights such as subdwarfs. Inverse Compton emission from GeV electrons on the microwave background contributes only a fraction of the galactic component unless the local cosmic ray electron spectrum and intensity are atypical.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 15
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    BL Herculis stars - Theoretical models for field variables (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Type II Cepheids with periods between 1 and 3 days, commonly designated as Bl Herculis stars, have been modeled here with the aim of interpreting the wide variety of light curves observed among the field variables. Previously modeled globular cluster members are used as standard calibration objects. The major finding is that only a small range of luminosities is capable of generating a large variety of light curve types at a given period. For a mass of approximately 0.60 solar mass, the models are able to reproduce the observed mean luminosities, dispersion of mean luminosities, periods, light amplitudes, light asymmetries, and phases of secondary features in the light curves of known BL Her stars. It is possible that the metal-rich variables (which are found only in the field) have luminosities lower than those of most metal-poor variables. The present revised mass for BL Her, a metal-rich object, is not significantly different from the mean mass of the metal-poor variables.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 259
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  • 16
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    A heuristic criterion for instability to fragmentation in rotating, interstellar clouds (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A heuristic criterion, based on linear perturbation analysis, is applied to the initial growth of density perturbations in isothermal or adiabatic gas clouds, with initially uniform density and uniform rotation. The heuristic criterion is shown to be consistent with the available results from numerical calculations of cloud collapse. The criterion predicts that perturbations varying as cos(m-phi) will be most likely to grow when m is small, unless the cloud is nearly pressureless.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 259
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  • 17
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    High energy X-ray observations of Cyg X-3 from OSO-8 - Further evidence of a 34.1 day period (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-18085)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Letters; 22; 4, 19; 1982
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  • 18
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    Neutron star collisions and the r-process (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that a natural consequence of the binary pulsar's evolution is a neutron star collision. Such a collision is expected to eject neutron-rich matter of an r-process character. Taking reasonable estimates for the number of such events over the history of the galaxy, it may be that they account for all of the r-process nuclei.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Letters; 22; 4, 19; 1982
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  • 19
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    The peculiar variable star R Aquarii and its jet (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observations of the variable star R Aquarii from 1928 to the present are examined to conclude that the star is a binary system with a jet. The orbital period of the objects is estimated at 22 yr, and a supercritical mass transfer that occurs once every 44 yr is suggested as a mechanism to explain deep minima observed on two occasions that many years apart. Calculations presented for the critical accretion rate of the two Miras indicated that one of the objects possesses a substantially stronger gravitational field than the other and features a large accretion disk. Oriental astronomical records from 930 AD are cited as evidence that a nova occurred in the vicinity of R Aquarii at that time. The system is noted to be the closest jet thus far observed, and the accretion disk may be visible with the Space Telescope.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 298; Aug. 5
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  • 20
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    The photospheric velocity field of Procyon (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Balloon-borne Ultraviolet Stellar Spectrometer observations of the profiles of two well observed spectral lines in the ultraviolet spectrum of Alpha CMI (Procyon; F5IV-V) are analyzed with a Fourier transform method in order to determine values of various parameters of the velocity field of the upper photosphere. A microturbulent line-of-sight velocity component of 0.9 + or - 0.4 km/s, a macroturbulent velocity component of 5.3 + or - 0.2 km/s, and a rotational velocity component of 10.0 + or - 1.2 km/s were determined. In these calculations a single-moded sinusoidal isotropic macroturbulent velocity function was assumed. The result appears to be sensitive to the assumed shape of the macroturbulence function.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science; 84; 2, Ju; June 198
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  • 21
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    On the structure of the outer layers of cool carbon stars (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Exposures on the spectra of four late C-type stars have been made with the IUE satellite in the wavelength range of the LWR camera (1900-3200 A). Two Mira variables near maximum light and two semiregular variables were observed. Although the exposure times used, which range up to 240 min in the low-resolution mode, were more than sufficient to record the continuum and emission lines of Mg II, Fe II, and Al II in normal M stars of similar magnitude and temperature, no light was recorded. It is concluded that the far-ultraviolet continuum is strongly depressed in these cool carbon stars. The absence of UV emission lines implies either that the chromospheric lines observed in M stars require an ultraviolet flux for their excitation, or that cool carbon stars have no chromosphere at all or that the opacity source is located above even the emission-line-forming region. This opacity source, which is probably some carbon condensate since it is weak or absent in M stars while absorbing strongly in C stars, is discussed both in terms of the chromospheric interpretation of the emission lines and in terms of their shock-wave interpretation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 111; 1, Ju; July 198
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  • 22
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    A precessing relativistic jet model for 3C 449 (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that the radio structure of 3C 449 can be matched with a model in which the jets are precessing and have relativistic (beta greater-than or equal to 0.4) velocities. The best-fit model implies a precession period of about 100,000 yr and a cone angle which increases with time. A similar model may be relevant for the radio structure of 3C 31. A brief discussion of the implications for 3C 449 is given.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 258
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  • 23
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    Collapse of accreting, rotating, isothermal, interstellar clouds (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The evolutions of the envelopes of collapsing, accreting, isothermal clouds have been numerically calculated for both spherically symmetric and rotating (axisymmetric) clouds. The results provide a cohesive picture of isothermal collapse, and their relationship to previous numerical calculations and similarity solutions is discussed. Even with a large initial rotation rate, the majority of the cloud envelope is accreted, in one case leaving behind a large-scale circulation current. The calculations are performed for both initially uniform density and centrally condensed clouds. Density and velocity profiles for a wide variety of observed systems are compared with those obtained in this study, providing a preliminary assessment of the stage of evolution and initial structure for the observed systems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 258
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  • 24
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    Laboratory measurements of amorphous silicate smokes and the infrared spectra of oxygen-rich stars (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The infrared spectra of smokes condensed from SiO-H2 and Mg-SiO-H2 vapors and of smoke samples annealed for various times at 1000 K and 1250 K are presented. The spectra of these materials show features in the 8-25 micron interval in addition to the well-known bands near 10 and 20 microns. It is suggested that these features may correspond to weak structures that can be seen in the infrared spectra of oxygen-rich stars. Observations are needed to determine the reality and characteristics of such weak features.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 257
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  • 25
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    The distribution of free electrons in the inner Galaxy from pulsar dispersion measures (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-18096)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 257
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  • 26
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    Star formation - The influence of velocity fields and turbulence (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that the Jeans mass for gravitational collapse can be very much reduced by the influence velocity fields, even when allowance is made for non-isothermal gas behavior. We examine the role of turbulence in establishing the initial stellar mass function and show that the flattening and/or turnover at the low mass end may be a signature of interstellar turbulence. We consider also the implications of primordial turbulence for the formation of stars in the early universe.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 256
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  • 27
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    A model of a comet coma with interstellar molecules in the nucleus (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The coma of a comet is modeled assuming the icy nucleus contains interstellar molecules. This composition overcomes discrepancies between observation and earlier model predictions for CN, C2, C3, and NH2 abundances. It is found that the abundances of CN, C2, and C3-bearing compounds in the nucleus must be constrained to trace amounts in order to account for the observed column densities. NH3 also cannot be abundant by more than about 1%. The model gives good agreement with observed relative ranges of neutral species in the coma as well as with their observed relative intensity dependence on heliocentric distance. The size of the nucleus and the heliocentric ranges considered are relevant to comet Halley.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 108; 2, Ap; Apr. 198
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  • 28
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    Radial evolution of power spectra of interplanetary Alfvenic turbulence (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-18097)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research; 87; May 1
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  • 29
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    Infrared emission line studies of the structure and excitation of H II regions (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Maps of five H II regions in one or more of the infrared fine-structure lines of Ne II (12.8 microns), Ar III (9.0 microns), and S IV (10.5 microns) have been obtained with angular resolutions ranging from 4 to 7 arcsec. The observations are used to discuss the morphology and excitation of these nebulae. Considerable diversity is found in the structures of the nebulae, probably resulting from differences in their ages and the circumstances of their formation. In all cases, more ionizing luminosity than would be provided by a single dominant ionizing star appears to be required, although uncertainties in the model nebulae make this conclusion uncertain.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 255
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  • 30
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    Evidence for extended X-ray emission from globular clusters (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Deep exposures with the Einstein Observatory show evidence for diffuse X-ray emission from three globular clusters. One possible interpretation of these observations is that the interaction between a cluster wind and a hot gaseous galactic halo is being observed. The one cluster for which the proper motion has been measured is consistent with this interpretation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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  • 31
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    A different type of maser star (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A systematic survey of short-period, semiregular variable stars has been made resulting in the detection of six new water masers. Of the 14 short-period maser stars now known, nine are classified as SRb variables. All are very late spectral type SRb's, typically M7, while the overwhelming majority of normal SRb stars is M4 to M6. Their 2.2-11 micron color indices are among the lowest of any known maser stars. They are presumably less dusty as well. Four of the SRb stars and two of the remainder do not obey the correlation between period and velocity spread of the emission features that is found for the Mira and long-period, semiregular variables. Finally, high galactic latitudes dominate; 13 of the 14 are in excess of 13 deg, and nine of these are greater than 25 deg. These facts suggest that the short-period semiregular variables - particularly in SRb stars - may be a very different type of maser star than the Mira and long-period semiregular variables.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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    The discovery of 50 minute periodic absorption events from 4U 1915-05 (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: An analysis of X-ray observations shows that the steady flux from 4U 1915-05 undergoes periodic absorption dips with a period of 50 minutes. This period most probably represents the underlying orbital period of the system, and variations in the depth and duration of these events suggest that they are caused by a bulge on the edge of the accretion disk at the point where the gas stream impacts the disk. The mass-losing star in this system is probably a low-mass white dwarf, and the spectrum of the dips indicates that the metallicity of the absorbing material is at least a factor of 17 below solar values. The discovery of the 50-minute binary period supports earlier suggestions that X-ray burst sources are in binary systems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 253
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  • 33
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    Search for interstellar superheavy hydrogen (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Models for fundamental physical interactions allow for the existence of stable or nearly stable elementary particles much heavier than the proton. Stellar spectra were searched for a positively charged superheavy particle, X(+), which, with a bound electron, should appear as apparently superheavy neutral hydrogen in the interstellar medium. An upper limit for the abundance of X relative to normal hydrogen in the line of sight toward the bright star gamma Cassiopeiae is 2 x 10 to the -8th.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Science; 216; Apr. 2
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  • 34
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    Resonant electrodynamic heating of stellar coronal loops - An LRC circuit analog (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The problem of electrodynamic coupling of stellar coronal loops where beta is less than 1 to underlying velocity fields where beta is greater than approximately 1 is treated. A rigorous analysis reveals that the physics can be represented by a simple yet equivalent LRC circuit analog. This derived analog suggests the existence of global structure oscillations which resonantly excite internal field line oscillations at a spatial resonance within the coronal loop. Even though the width of this spatial resonance, as well as the induced currents and coronal velocity field, within the resonance region explicitly depends on viscosity and resistivity, the resonant form of the generalized electrodynamic heating functions is virtually independent of irreversibilities. This is a classic feature of high-quality resonators that are driven externally by a broad-band source of spectral power.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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  • 35
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    Observations of interstellar zinc (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: IUE observations toward 10 stars have shown that zinc is not depleted in the interstellar medium by more than a factor of two, suggesting that its abundance may serve as a tracer of the true metallicity in the gas. A result pertinent to the history of nucleosynthesis in the solar neighborhood is that the local interstellar medium has abundances that appear to be homogeneous to within a factor of two, when integrated over paths of about 500 pc.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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  • 36
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    Electromagnetic cascades in pulsars (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The development of pair-photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters, and follows the curvature radiation emitted by the primary, the conversion of this radiation to e(+)e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma-ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma-ray spectrum above 25 MeV, and that the final gamma-ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 252
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  • 37
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    The X-ray spectrum of 3C 273 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 232
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  • 38
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    Interstellar C2 molecules toward Zeta Persei (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A search for absorption by interstellar C2 molecules, conducted at the (2-0) Phillips band near 8760 A, is reported for three stars. No interstellar absorption is seen in the spectra of 20 Tau and Epsilon Aur, at upper limits of approximately 5 mA and 1 mA, respectively. Toward Zeta Per, however, the R(0), Q(2), and Q(4) lines are detected, and a useful upper limit on the Q(6) line is obtained. The resulting column density, 1.4 x 10 to the 13th to 2.0 x 10 to the 13th per sq cm, and the excitation temperature, T = (78 plus or minus 25) K, show acceptable agreement with an existing theoretical model of the absorbing cloud.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 232
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  • 39
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    Galaxies and gamma-ray astronomy (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The nature of the high-energy spectra of several types of active galaxies and their contribution to the measured diffuse gamma-ray emission between 1 and 150 MeV are considered, using X-ray spectra of active galaxies and SAS 2 data regarding the intensity upper limits to the gamma-ray emission above 35 MeV. It is found that a substantial increase in slope of the photon energy spectrum must occur in the low energy gamma-ray region for Seyfert galaxies, BL Lac objects, and emission line galaxies; the power-law spectra observed in the X-ray range must steepen substantially between 50 keV and 50 MeV. In addition, a cosmological integration shows that Seyfert galaxies, BL Lac objects, and quasars may account for most of the 1-150 MeV diffuse background, even without significant evolution.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 232
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  • 40
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    Magnetic Cepheids (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The role of a magnetic field in the pulsational behavior of classical Cepheids has been studied by computing linearized models of pulsating stellar envelopes pervaded by a well-tangled magnetic field. It is found that the 'pulsational' masses of Cepheids that are implied by the theoretical values of the quantities Q(0), P(1)/P(0), and (possibly) P(2)/P(0) can be brought into line with the large 'evolutionary' masses, if the pressure due to the postulated magnetic field is assumed to be comparable to the thermodynamic pressure everywhere in the pulsating layers. The field strengths that are required - several hundred gauss at the surface and several ten thousand gauss at the base - are quite reasonable from the point of view of the observed magnetic fields in Cepheids. The influence of the magnetic field on the location of the blue edge of the instability strip in the H-R diagram is estimated to be very slight.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 234
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  • 41
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    Model atmospheres, predicted spectra, and colors (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Theoretical models of stellar atmospheres and the process of forming a spectrum are reviewed with particular reference to the spectra of B stars. In the case of classical models the stellar atmosphere is though to consist of plane parallel layers of gas in which radiative and hydrostatic equilibrium exists. No radiative energy is lost or gained in the model atmosphere, but the detailed shape of the spectrum is changed as a result of the interactions with the ionized gas. Predicted line spectra using statistical equilibrium local thermodynamic equilibrium (LTE), and non-LTE physics are compared and the determination of abundances is discussed. The limitations of classical modeling are examined. Models developed to demonstrate what motions in the upper atmosphere will do to the spectrum and to explore the effects of using geometries different from plane parallel layer are reviewed. In particular the problem of radiative transfer is addressed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: B stars With and Without Emission Lines, Parts 1 and 2; p 165-197
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  • 42
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    Isolated grain condensation behavior: Computation methods and first results (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A set of efficient programs for calculation of condensation behavior in a system with either solar or carbon-rich elemental composition was developed to treat the course of condensation at very low pressures. These programs were applied to the problem of condensation at very low pressures. The minerals produced in the stellar and nova-related processes under study, including carriers of important volatile elements such as carbon and nitrogen, are candidates for accretion into meteorite parent bodies and planets, and may still be discernible in the enstatite chondrites.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Planetary Atmospheres Program; p 36-47
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  • 43
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    Theory of electron-positron showers in double radio sources (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A black hole of mass of about 300 million solar masses is assumed to be present in the nucleus of an active galaxy or quasar. With an axial magnetic field near 1000 gauss, a potential drop 10 to the 19th volts is generated by the unipolar induction of a rotating accretion disk surrounding the black hole. The possibility that the acceleration of electrons or positrons in the unipolar fields initiates an electromagnetic cascade shower at distances at least 10 to the 16th cm from the black hole is investigated. The scattering medium for the shower is considered to be the spectrum of low energy photons originating from the inner region of the disk. It is found that at completion of the cascade, power-law energy spectra of relativistic electrons and positrons and of gamma-rays emerge under appropriate conditions. If the cascade-initiating particles are collimated, the electrons and positrons emerge in a collimated beam. Such beams may power extragalactic double radio sources.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 262
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  • 44
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    The WC6 star HD76536 compact companion (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The variability of HD76536 was observed by IUE. Photometric variability is confirmed by measurements with the IUE fine error sensor. Profile changes in the ultraviolet emission lines and stellar wind absorptions were studied. Data favor a binary model with a low luminosity (perhaps compact) secondary.
    Schlagwort(e): ASTROPHYSICS
    Materialart: ESA 3rd European IUE Conf.; p 269-271
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  • 45
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    On redistribution and the equations for radiative transfer (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The derivation of the equations of statistical equilibrium are outlined, starting from the quantum density-matrix equations, drawing particular attention to the approximations and assumptions used in the development of tractable expressions. Then, using the quantum-fluctuation-regression theorem, emission and absorption coefficients are obtained for multilevel atomic systems which are nondegenerate except for m-substates. These coefficients are valid to first order in the incident intensity. Possible extensions to higher intensity broadband incoherent fields are suggested.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 46
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    Neutral hydrogen in elliptical galaxies with nuclear radio sources and optical emission lines (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-22136)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 259
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  • 47
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    Sensitive ammonia observations in the southern hemisphere (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The 64-m spacecraft communication antenna of the NASA-JPL Deep Space Network has been equipped for spectral line observations at K band (18-25 GHz). To demonstrate the potential of this system, preliminary observations of the (1, 1) transition of ammonia are reported for a selection of eight southern molecular clouds. Estimates of gas density and ammonia column density are reported for six sources.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 87; Aug. 198
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  • 48
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    A search for fragmentation debris near Ursa Major Stream stars (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Accretion models of planet formation and the early cratering history of the solar system suggest that planet formation is accompanied by a cloud of debris resulting from accumulation and fragmentation. A rough estimate of the infrared luminosities of debris clouds is presented for comparison with measured 10-micron luminosities of young stars. New measurements of 13 F, G, and K main-sequence stars of the Ursa Major Stream, which is thought to be about 270-million years old, place constraints on the amount of debris which could be present near these stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus; 50; Apr. 198
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  • 49
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    Large-scale magnetic fields in spiral galaxies (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The optical polarization vectors which measurements have shown to be parallel to the pronounced dark lanes of such galaxies as NGC 5128 and 4590 are interpreted as the consequence of a large scale, systematic field parallel to the dark lane that leads to the alignment of the grains. It is suggested that such polarization may also be produced by scattering off grains concentrated in the dark lane. It is recommended that there be further observational tests of the hypothesis that the observed polarization indicates the magnetic field in the galaxy.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 258
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  • 50
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    Cygnus X-3 observed at photon energies above 500 GeV (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: High-energy gamma rays from Cyg X-3 have been observed with the twin 11-m mirrors of NASA JPL's solar energy facility, using the atmospheric Cerenkov technique, resulting in data from about 100,000 air shower events with an approximate threshold energy of 500 GeV for the August 29 to September 6, 1981 period. A positive signal whose amplitude is 10.9 + or - 2.5% of the background cosmic ray rate appears near phase 0.6 of the 4.8-hour cycle, where phase 0.0 corresponds to minimum X-ray emission. This, together with previous Cerenkov detections, indicates that the high energy emission from Cyg X-3 is evolving on a time scale of a few years and suggests that the present form of the system has a recent origin.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 296; Apr. 8
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  • 51
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    Parity nonconservation and the origin of cosmic magnetic fields (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Three mechanisms of cosmic magnetic field generation are discussed: (1) asymmetric decay of particles emitted by rotating black holes; (2) asymmetric proton emission by black holes due to weak radiative corrections, and (3) equilibrium parity-violating currents. It is shown that all three mechanisms can produce a seed field sufficiently strong to account for the present galactic fields.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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    Cometary NH - Ultraviolet and submillimeter emission (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A description is presented of the results of computer calculations on the molecule NH, which is an important constituent of cometary comae, and a probable, but an as yet undetected, interstellar species. Attention is given to spectroscopic properties, the treatment of solar spectral data, and radiative transfer calculations. The results of calculations for the Einstein A-coefficients are given in an appendix, where the entries for the X-X and A-A transitions depend on the assumed permanent electric-dipole moment squared. Rotational-spin-Lambda-doublet energy levels used for statistical equilibrium population densities are listed in a table.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 253
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  • 53
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    Interplanetary gas. XXVIII - A study of the three-dimensional properties of interplanetary sector boundaries using disconnection events in cometary plasma tails (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Studies of the solar wind on the basis of cometary plasma tail observations are considered. Niedner and Brandt (1978, 1979) have concluded that the plasma tail frequently disconnects from the cometary head, and that these disconnection events (DEs) are produced by magnetic reconnection at sector boundary passages. They proposed that the disconnections are a natural combination of Alfven's model and the solar-wind sector structure first discovered by Wilcox and Ness (1965). The DEs can be utilized as probes of interplanetary sector structure. Correlations between DEs and sector boundaries observed at earth are considered, and sector boundary properties deduced from DEs are discussed. Attention is given to a review of the warped sheet model, the latitude extent of sector structure, the sector boundary tilt, and specific sources of error in the tilt angles derived from DEs.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series; 48; Jan. 198
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  • 54
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    On syntheses of the X-ray background with power-law sources (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The conditions under which the combined emission from power-law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low-luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit steeper spectra at higher energies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 253
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  • 55
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    Hot wind from Gamma/2/ Velorum observed in the ultraviolet carbon lines (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The close binary system Gamma(2) Vel, consisting of a WC8 and an O9 I star, has been observed in the ultraviolet at various phases. Preliminary analysis of selected data shows that the temperature of the stellar wind from this binary increases outward. This suggests that an additional source of energy other than radiation pressure may exist for the wind. The mass flow occurs in all directions from the binary. However, there is evidence of an increase in the mass flow through the third Lagrangian point, although from the extant data it is not possible to decide whether or not a similar increase in the mass outflow occurs through the second Lagrangian point. There is also evidence of mass surge, which probably is independent of orbital phase.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 252
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  • 56
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    Neutral hydrogen emission and absorption in three active Irr II galaxies (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Peak optical H I absorption depths of 10% are found in a neutral hydrogen emission-absorption study of the active-nucleus Irr II galaxies NGC 520, 5363, and 5506. It is suggested that the absorption is due to a few standard clouds within several hundred parsecs of the nucleus, in the narrow-line emission region. The width of the absorption features is interpreted as being due to random motions of the gas within the absorbing clouds, in contrast to the large widths of the emission features that are due to the overall rotation of the galaxy.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 252
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  • 57
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    The remarkable 400 micron source NGC 6334/I/North/ (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observations at 400 microns of the NGC 6334 complex have confirmed the discovery of an unusual 1000-solar mass object, NGC 6334/I(North), which was not detected by broad-band 100-micron survey observations. The results suggest that this cool source (T = 19 + or - 5 K) is an active star formation region in a very early stage of evolution. The observed infrared luminosity of the source, 7000 solar luminosities, requires the presence of one or more embedded B stars or the formation of a dense protostellar core. Derived dust and gas densities agree well with results from molecular line observations of the complex. Nearby 100 micron peaks I and V were also observed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 259
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  • 58
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    The path and surviving tail of a comet that fell into the sun (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A satisfactory orbital solution for Comet Howard-Koomen-Michels 1979 XI is found on the assumption that the comet's line of apsides coincided with that of the Kreutz sungrazing comet group. The derived perihelion distance then shows that this is the first known case of a comet falling into the sun. A dust tail that survived the comet is studied as a particle flow phenomenon controlled by no force other than solar gravity and solar radiation pressure. The tail's outline is interpreted in terms of an onset of dust production, a peak repulsive force on the particles, and a circumsolar dustfree zone due to particle sublimation. It is shown that the surviving debris consisted mostly of absorbing, submicron size particles in hyperbolic trajectories convex to the sun and curving toward the earth. The tail width may be a product of the interaction of charged dust in the tail with a complicated structure of the coronal magnetic field.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 87; July 198
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    Extragalactic gamma radiation - Use of galaxy counts as a galactic tracer (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-20109)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 109; 2, Ma; May 1982
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    The light curve of periodic comet Halley 1910 II (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Photometric parameters for periodic comet Halley 1910 II have been derived from 144 total visual magnitude estimates. The pre-perihelion data are best represented by an absolute magnitude of 5.47 and a power-law exponent of 4.44; post-perihelion results show that the absolute magnitude brightened to 4.94, and the exponent decreased to 3.07. Only small fluctuations in brightness about the power-law solutions are noted. Based on these results, a forecast of the visual brightness of periodic comet Halley's 1985-1987 apparition is presented.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 87; June 198
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    Large-scale variations of the interplanetary magnetic field - Voyager 1 and 2 observations between 1-5 AU (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-13594)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research; 87; June 1
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    Accretion disk coronae (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-20106)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 257
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    Solar-stellar astrophysics (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Nonthermal physical processes in the solar atmosphere are discussed. The solar atmospheric regions are defined, and solar convection and its phenomena are explained. The relationship of the solar dynamo, magnetic field, and flares is explored. The solar atmospheric velocity fields are discussed, and the unresolved problem of the nature of atmospheric heating is detailed. The solar wind heating and acceleration are discussed and the need for global solar atmospheric models is emphasized. The application of these solar nonthermal processes to the stars in general is then taken up, employing the same categories as were applied to the solar atmosphere.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Comments on Modern Physics; vol. 9
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  • 64
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    Energy distribution in the strongly interacting binary system SX Cassiopeiae (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: IUE spectra and optical scans covering the 110-680 nm interval were obtained in a search for a source which would resolve the anomalous presence of strong Balmer emission lines in the SX Cas eclipsing binary system, which is inconsistent with the usual spectral classification of the components as A6 III + G6 III. The IUE spectra unexpectedly show such strong emission lines as those of C IV, N V and Si IV, which require higher temperatures that the already anomalously high Balmer lines, and a continuum several magnitudes higher than the extrapolated continuum of an A6 star. A model in which the UV continuum originates in the transition zone between the A6 star and an accretion disk fails to reproduce the observed energy distribution. A revision of component spectral types to B7 + K3 III removes the UV excess.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 256
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    Apparent superluminal motion in the quasar NRAO 140 (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Very long baseline interferometer (VLBI) measurements of the compact radio structure in the quasar NRAO 140 (z = 1.258) have been obtained at three epochs at a wavelength of 2.8 cm. These observations indicate that the two most compact radio components are separating at an angular rate of 0.10-0.14 milli-arcsec per year. For cosmological distances H sub 0 = 50 and q sub 0 = 0, this corresponds to a velocity of separation (in the quasar's rest frame) of 10 + or - 2 times the speed of light, c; for H sub 0 = 100 and q sub 0 = 1, the value is (3.1 + or - 0.6) c. Other interpretations of the temporal changes in correlated flux density and closure phase are discussed and are considered unlikely. The derived velocities are consistent with an earlier prediction that the separation velocity should be greater than about 4 c. Extrapolation back to the epoch of zero separation indicates that the expansion originated between late 1963 and late 1968 (under the assumption of constant velocity). This range includes the beginning of an isolated outburst in flux density at 2.8 cm. These results cannot be used to make any statements concerning the validity of cosmological interpretations of QSO redshifts.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 255
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  • 66
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    Rotational temperatures of cyanodiacetylene in Sagittarius B2, TMC-1, and IRC +10216 (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
    Format: text
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  • 67
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    The local interstellar medium (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Analysis of the velocities of optical interstellar lines shows that the sun is immersed in a coherently moving local interstellar medium whose velocity vector agrees with that of the interstellar wind observed through backscatter of solar H Ly-alpha and He lambda 584 photons. The local interstellar medium consists of both cool clouds and warm intercloud medium gas, has a mass of perhaps approximately 30 solar masses, does not have severe depletion of trace elements from the gas phase, and appears to be material which has been shocked and accelerated by stellar winds and supernovae associated with the Sco-Oph OB association.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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  • 68
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    4C 18.68 - A QSO with precessing radio jets (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: High-resolution VLA radio maps at 20 cm and 6 cm wavelengths of the quasar 4C 18.68 reveal an extended halo of about 20 arcsec containing complex curved structures extending east and west from the central source. The central source has a flat spectrum, while the spectrum generally steepens with distance from the center of the structure. The details of the structure and polarization of the emission suggest relativistic ejection in opposing directions by a precessing or rotating double jet with a period of about 50,000 years, consistent with the presence of two interacting massive bodies in the central source.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 253
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    On the folding phenomenon of comet tail rays (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that the folding phenomenon of the comet tail rays is compatible with the Ferraro isorotation law if the comet tail magnetic field has no azimuthal component, that is, B sub phi (the polar angle) equals zero. Considering electric drift due to convectional electric fields, a formula is obtained for the angular rate of a ray closure which reduces to that of Ness and Donn (1966) if the velocity profile across the tail is linear. The magnetic field B of approximately 20-40 gammas in the coma and less than about 10 gammas in the distant tail is estimated under typical solar wind conditions at 1 AU.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 198
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  • 70
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    The derivation of Halley parameters from observations (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Nominal value model parameters for the nucleus (size, mass, rotation, albedo, hydrogen production) the dust and gas for P/Halley at 0.9 AU postperihelion are derived from the light curve and spectra of Halley and by modeling the effect of the nongravitational forces, e.g., the outgassing rocket type effect of the nucleus. In those cases where Halley observations are not sufficient, the average value derived from a larger set of other comets is used, or data from comet Bennett, Halley's best analog, are taken. A flow diagram shows how the parameter values are derived and to what extent these derived values are interdependent. Previously announced in STAR as N82-23097
    Schlagwort(e): ASTROPHYSICS
    Materialart: (ISSN 0273-1177)
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    Einstein Observatory results on active galactic nuclei (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The results of Einstein Observatory surveys of active galactic nuclei (AGN) are reviewed. The ubiquity of X-ray emission from AGNs was confirmed. The relations between X-ray and optical luminosities, between X-ray and radio properties, and between X-ray and optical-UV line emission found by the surveys are summarized and briefly discussed. The possible causes of observed X-ray emission from jets in Cen-A, 3C273, and M87 are considered. The active nucleus discovered in the optically 'dull' galaxy NGC 4156 is covered, and a model for NGC 4151 based on detailed spectral studies is briefly discussed. This model establishes the global symmetry of the AGN clouds, their approximate sizes, and their ionization state. Difficulties encountered in attempting to explain the cosmic X-ray background in terms of AGN contributions are addressed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: (ISSN 0273-1177)
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  • 72
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    IUE observations of cataclysmic variables (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The four years of IUE operation have revealed that the ultraviolet region of the spectrum contributes a dominant share of the emerging energy from cataclysmic variables and provides important clues to the physical nature of these systems. The implications of the continuum flux distributions and line spectra for the determination of the accretion rates and mass loss rats are considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: (ISSN 0273-1177)
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  • 73
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    HEAO 1 observations of the X-ray pulsar 4U 1626-67 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Results are reported for an observation of the 7-s pulsar 4U 1626-67 with the A-2 experiment on HEAO 1. The phase-averaged X-ray spectrum between 0.7 and 60 keV is complex, as are the constituent spectra, which change radically as a function of pulse phase. Included in this spectral change is the sudden appearance and subsequent decay of a continuum or emission feature with a mean energy of 19 keV, which contains about one-half the power in this spectral range. Pulse-timing results include a new determination of the pulse period and a factor of 8 reduction in the upper limit for the light travel time for orbital periods between 1 and 7 hours. These findings are discussed and compared with the general nature of pulsar spectra.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 231
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  • 74
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    Statistical equilibrium in cometary C2. II - Swan/Phillips band ratios (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Statistical equilibrium calculations have been made for both the triplet and ground state singlets for C2 in comets, using the exchange rate as a free parameter. The predictions of the results are consistent with optical observations and may be tested definitively by accurate observations of the Phillips and Swan band ratios. Comparison with the one reported observation indicates compatibility with a low exchange rate and resonance fluorescence statistical equilibrium.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 231
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  • 75
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    Pioneer 10 studies of interplanetary shocks at large heliocentric distances (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Pioneer 10 Ames plasma analyzer data collected in the 6.1 to 12.6 AU range of heliocentric distances (November 1974 to April 1977) have been examined for interplanetary shock waves. Eighteen shock signatures have been identified, with four of these being of the reverse type and the remainder the forward type. Sonic Mach numbers in the range from 3 to 10 are estimated for these events.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Geophysical Research Letters; 6; June 197
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    Discovery of two distorted interstellar bubbles (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: During an extensive program of direct imagery of emission nebulae, arcuate structures have been found around two stars. A well-defined shocklike structure is found about the T Orionis variable LL Ori, located to the side of the Orion Nebula. A less extensive shocklike structure is also found about the runaway star Zeta Oph. These structures can be best described in terms of distorted interstellar bubbles. A direct consequence of this interpretation is an independent estimate of the rates of mass loss for these stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 23
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    An upper limit for the total energy of relativistic particles contained in the early stages of supernova explosions (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A model is proposed for the emission of X-rays from supernova explosions wherein the thermal distribution of photons from a supernova photosphere is inverse Compton scattered by relativistic electrons within or near the surface of the star. Using this model, upper limits for the number of relativistic electrons and their total energy are established on the basis of upper limits to the observed X-ray luminosity of a supernova during maximum light. These upper limits, in conjunction with radio frequency upper limits obtained by Brown and Marscher, strongly suggest that supernovae do not produce significant numbers of relativistic particles until at least 70 years after the initial outburst. This, in turn, implies that young supernovae cannot account for the radio and X-ray variability of active galactic nuclei and quasars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 230
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    Gamma rays from accretion onto rotating black holes (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Ionized matter falling onto an isolated rotating black hole will be heated sufficiently that proton-proton collisions will produce mesons, including neutral pions, which decay into gamma rays. For massive (1000-solar mass) black holes, the resulting gamma-ray luminosity may exceed 10 to the 36th erg/s with a spectrum peaked near 20 MeV.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 74; 1, Ap; Apr. 197
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    Sporadic mass ejection in red supergiants (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A general mechanism first proposed by Burke (1969) is applied to red supergiants for determining the spin-down rate and angular-momentum loss of rotating stars. This model relies principally on sporadic mass ejection, which is assumed to be the result of turbulent elements accelerating material in cool supergiant atmospheres. Mass is preferentially expelled in the forward direction of rotation, resulting in a rapid loss of angular momentum on time scales of 10,000 to 1 million years in the supergiant evolutionary phase. Such rotational breaking will occur if the turbulent elements have characteristic sizes a few percent of the stellar radius and rms velocities one-third the escape speed of the star. This model predicts the formation of a cool silicate disk or torus around the star because of the preferred expulsion of material near equatorial regions of the supergiant.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 228
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    Absorption models for low-frequency variability in compact radio sources (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The consequences of the most plausible version of the absorption model for low-frequency variability in compact extragalactic radio sources are considered. The general restrictions placed on such a model are determined, and observational tests are suggested that can be used either to support the model or to discriminate among its various versions. It is shown that low-frequency variability in compact radio sources can be successfully explained by a class of models in which the flux is modulated by changes in free-free optical depth within an intervening ionized medium. Two versions of such a model are distinguished, one involving large changes in optical depth and the other, small changes. It is noted that while absorption effects are capable of causing rapid flux and structural variations at centimetric wavelengths, the models predict detailed behavior that is in direct conflict with observational data.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 228
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  • 81
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    Comptonization of X-rays by low-temperature electrons (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A method is described for calculating the spectrum that results from the Compton scattering of a monochromatic source of X-rays by low-temperature electrons, both for initial-value relaxation problems and for steady-state spatial diffusion problems. The method gives an exact solution of the inital-value problem for evolution of the spectrum in an infinite homogeneous medium if Klein-Nishina corrections to the Thomson cross section are neglected. This, together with approximate solutions for problems in which Klein-Nishina corrections are significant and/or spatial diffusion occurs, shows spectral structure near the original photon wavelength that may be used to infer physical conditions in cosmic X-ray sources. Explicit results, shown for examples of time relaxation in an infinite medium and spatial diffusion through a uniform sphere, are compared with results obtained by Monte Carlo calculations and by solving the appropriate Fokker-Planck equation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 228
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    Photoneutrino reactions in a superstrong magnetoactive plasma (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The neutrino luminosity due to the photoneutrino process in the presence of a superstrong magnetoactive electron plasma appropriate for neutron stars is computed. The results indicate that for relatively low temperatures, between 100 million and 500 million K, the energy loss rate is significantly reduced both in the low-density regime below about 10 million g/cu cm (by the magnetic field) and in the high-density regime above that value (by plasmon excitations). These effects are temperature dependent, and they are less pronounced when the temperature is in the range from 500 million to 1 billion K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 227
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    Detection of HC/O-18//plus/ in Sagittarius B2 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Line emission at 85.1 GHz attributed to the J equals 1-0 rotational transition of the formyl ion HC(O-18)(plus) has been detected in Sgr B2 (OH). The double isotopic ratio (O-16/O-18)/(C-12/C-13) in the formyl ion in Sgr B2 is estimated to be in the range 5-10, hence within a factor 2 of the terrestrial value of 5.5. This determination implies that the C-13/C-12 ratio near the galactic center does not differ greatly from that in local molecular clouds.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 227
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    Galactic distribution models of gamma-ray burst sources (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The log N-log S relationships for several galactic distribution models of gamma-ray burst sources are derived. The resulting curves are substantially different from the galactic curves usually assumed (slope = -1). There is a relatively weak dependence on the radial distribution assumed but a strong dependence on scale height. Available observational data from several experiments appear to rule out both thin disk distributions and extended halo distributions which have a strong radial density dependence. The prospects are good for obtaining self-consistent distribution data from future large-area detectors.
    Schlagwort(e): ASTROPHYSICS
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    Scale covariance and G-varying cosmology. II - Thermodynamics, radiation, and the 3 K background (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Within the framework of a scale-covariant theory of gravitation, a semiclassical description of particles and photons is given. Thermodynamic relations consistent with the modified conservation equations are derived. Application to a system of radiation shows that the observed 3-K background radiation can be interpreted, within the present framework, as a remnant of equilibrium radiation in the past. As the theory postulates a nonstandard coupling between gravitation and electrodynamics, the assumption that Einstein's theory of gravitation is unchanged forces modifications at the atomic level. The use of Minkowskian spacetime in atomic physics is found to be adequate only over small, but not large, time scales compared with the age of the universe. As a result, a relation between energy and the frequency of a free photon is demonstrated. Possible observational consequences of this relation are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series; 41; Oct. 197
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    Large-scale structure of X-ray clusters of galaxies (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Observations from the A-2 experiment on HEAO-1 are used to search for very large-scale structure (exceeding a degree) in 40 X-ray sources in clusters of galaxies. Significant evidence for extension is found only in the relatively nearby Perseus and Virgo clusters. For the remainder of the sources the results place stringent limits on the flux in any very large component.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 189
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    The violent interstellar medium (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Observational evidence for high-velocity and high-temperature interstellar gas is reviewed. The physical processes that characterize this gas are described, including the ionization and emissivity of coronal gas, the behavior and appearance of high-velocity shocks, and interfaces between coronal gas and cooler interstellar gas. Hydrodynamical models for the action of supernova explosions and stellar winds on the interstellar medium are examined, and recent attempts to synthesize all the processes considered into a global model for the interstellar medium are discussed.
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    HEAO 1 observations of 4U1232+07 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: An analysis of the NRL HEAO 1 observations of the Virgo cluster and 3C 273 has revealed X-ray emission from a region between these two objects. The most satisfactory explanation is the presence of two weak X-ray sources, for which error boxes have been obtained. One source is likely to be the peculiar galaxy IC 3576, suggested by Margon et al. (1972) as the source 2U 1231+07=4U 1232+07. The error box resulting from combining the present observations with the 4U data strengthen the X-ray identification with this extremely interesting galaxy. There are numerous possibilities for the other X-ray source, including the interacting pair of galaxies NGC 4410a and NGC 4410b (NGC 4410a/b).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 281; Oct. 11
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    VV 5-32-63/64 - The 'supermassive double galaxy' in Abell 1775 revisited (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Spectroscopy is presented for galaxies in A 1775, the cluster containing VV 5-32-63/64, an apparent double galaxy which has long been considered a gravitationally bound system with supermassive components (10 to the 13th solar masses). However, this model has run afoul of recent radio observations, which detected an extremely long straight radio tail emanating from the eastern galaxy in the pair. The present observations indicate that if both galaxies are members of the same cluster, the cluster radial-velocity dispersion (1522 km/sec) is large enough to account for the velocity difference between the two VV galaxies (1650 km/sec). It is therefore suggested that the VV galaxies are not gravitationally bound and need not be supermassive. The large velocity dispersion measured for A 1775 also strains suggested velocity dispersion vs X-ray luminosity relations for clusters of galaxies, as A 1775 has not yet been detected at X-ray wavelengths.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 91
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    Infrared spectroscopy of stars (1979)
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    Publikationsdatum: 2011-08-17
    Beschreibung: This paper reviews applications of IR techniques in stellar classification, studies of stellar photospheres, elemental and isotopic abundances, and the nature of remnant and ejected matter in near-circumstellar regions. Qualitative IR spectral classification of cool and hot stars is discussed, along with IR spectra of peculiar composite star systems and of obscured stars, and IR characteristics of stellar populations. The use of IR spectroscopy in theoretical modeling of stellar atmospheres is examined, IR indicators of stellar atmospheric composition are described, and contributions of IR spectroscopy to the study of stellar recycling of interstellar matter are summarized. The future of IR astronomy is also considered.
    Schlagwort(e): ASTROPHYSICS
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  • 91
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    Observed properties of interstellar dust (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Recent information on the observed properties of interstellar dust is reviewed, with an attempt made to clarify some of the observational uncertainties associated with obtaining dust parameters. Attention is given to interstellar extinction, the interstellar dust distribution, the dust-to-gas ratio, and light scattering by dust grains. Interstellar polarization is also examined, along with heavy-element depletion in the interstellar medium, thermal emission from interstellar dust grains, diffuse interstellar features, and the composition and origin of interstellar grains.
    Schlagwort(e): ASTROPHYSICS
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  • 92
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    Stellar magnetic fields - The role of a magnetic field in the peculiar M giant, HD 4174 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Principles of coronal heating via basic electrodynamic effects, viz., resonant absorption of Alfven surface waves (quiescent) and magnetic tearing instabilities (impulsive), are detailed to argue three principles which may have application to late-type evolved stars. First, if one observes that B-squared/8 pi is much greater than rho times v-squared in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. Second, low mass-loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere, which constrain hydrodynamic flows when the magnetic body forces exceed the driving forces. Third, given that such magnetic loops effect an enhancement of the local heating rate, a positive correlation is predicted between the existence of a corona and low mass-loss rates. Application of these principles is made in the case of the peculiar M giant star HD 4174, which is purported to have a kilogauss magnetic field. Several of its spectroscopic peculiarities are shown to be consistent with the above principles, and further observational checks are suggested. Possible application to dMe and RS CVn objects is sketched.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 91
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    Standort Signatur Erwartet Verfügbarkeit
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  • 93
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    Physical parameter profiles of selected X-ray flares (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Soft X-ray proportional-counter data for nine X-ray flares of class C1 to M1 occurring during the Skylab mission, have been analyzed to yield temperature, volume emission measure, electron density and thermal energy content. Profiles of these quantities are presented, using 1-min averages of 2.5-s resolution data. The event profiles are discussed and comparisons with previous studies made.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics Supplement Series; 38; Oct. 197
    Format: text
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  • 94
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    Pulse-phase spectroscopy of Hercules X-1 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The 6-18 keV and the 40-60 keV X-ray spectrum of Hercules X-1 were simultaneously observed with the A-2 experiment on HEAO-1. By combining these measurements with the results of an earlier observation of this X-ray pulsar, evidence was found for a component of emission above 40 keV which is above an extrapolation from lower energies, by a factor which depends on the phase of the pulse. These data were compared to previous hard X-ray observations and possible models were discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 188
    Format: text
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  • 95
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    Cosmic far-ultraviolet background radiation - Probe of a dense hot intergalactic medium (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Line and continuum radiation fluxes have been computed for a wide range of enriched intergalactic medium (IGM) models. Observations of the diffuse extragalactic light at optical and far-ultraviolet wavelengths are found to provide a potentially important probe of a dense hot intergalactic medium. If the diffuse X-ray background is produced by this gas, the models constrain the cosmological density parameter (Omega) to be less than 0.4. The associated Compton distortions of the cosmic blackbody background radiation and the optical depths to distant quasars at X-ray wavelengths are also evaluated.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 231
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
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    Double core evolution and X-ray binaries (1979)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The evolution of a 16-solar mass star and a 1-solar mass neutron star is followed through the common-envelope binary phase. It is found that the encounter of the neutron star with a yellow giant leads to coalescence of the two cores, while encounter with a red giant leads to hydrodynamic expansion and probable ejection of the common envelope. Within the context of the two rotation laws (1) uniform rotation (investigated in the present study), and (2) uniform specific angular momentum (considered in an earlier study), the results are independent of the choice for the angular-momentum distribution in the common envelope. Implications of the results for the binary pulsar phase are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Letters; 20; 2, 19; 1979
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  • 97
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    Reversal of the /O III/lambda 4363/H sub gamma lambda 4340 ratio in the planetary nebula IC 4997 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Five image-tube spectrograms of the planetary nebula IC 4997 obtained during August 1977 show that the intensity forbidden ratio O III 4363 A/H-gamma 4340 A was equal to unity, but a sixth one obtained in April 1978 showed the ratio to be 0.91. These results represent a significant increase in the intensity ratio, which had been declining from 1895 to 1962 (when it was considerably less than unity), and is interpreted as resulting from a gradual increase in temperature of the nebula's central star accompanied by a transient event which led to a temporarily high value for the ratio in mid-1977.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 231
    Format: text
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  • 98
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    X-ray observations of AM Herculis from OSO 8 (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: X-ray observations of the white dwarf binary system AM Herculis in the range 2 to 250 keV, taken by OSO 8, are presented and compared with balloon and Ariel 5 measurements. The composite spectrum of the 2 to 40 and 20 to 250 keV fluxes determined by the proportional counter and the high energy scintillation spectrometer, respectively, on board the satellite is shown averaged over the entire binary cycle. Variations in spectral shape and intensity between the OSO 8 results and balloon measurements taken 10 to 20 days apart are observed. Results indicate the presence of a spectral break at about 15 keV on some occasions, similar to that seen in Her X-1, however presumably caused by a different mechanism than in the neutron star. It is also considered unlikely that the gamma-ray tail observed by Ariel 5 existed during OSO 8 observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 279; June 7
    Format: text
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  • 99
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    NGC 1275 /3C 84/ - Similar structure in the optical and 3-mm radio variations (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Optical and 3.3-mm data for the Seyfert galaxy NGC 1275 (3C 84) are compared. Similarities exist between the variations at the two wavelengths with regard to amplitude, time scale, and interval between events. The question is raised whether these similarities may be the result of a common triggering mechanism.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 91
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  • 100
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    An analysis of the infrared continuum of comets. II - Comet Kohoutek (1979)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: An analysis of the infrared observations of comet Kohoutek has been carried out on the basis of silicate grain models. The 'observed' grain temperature has been obtained as a function of the heliocentric distance, and it is compared with the expected distribution. In the visible region, one requires for the refractive index, (m = n-ik), n of about 1.6 and k less than 0.05. The total number of grains varies essentially as the inverse square of radial distance; the size of the particles in the antitail of the comet Kohoutek is greater than 5 microns. The ratio of infrared flux from grains to the incident solar flux at wavelengths of a few microns is calculated.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 84; May 1979
    Format: text
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