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  • General Chemistry  (11,581)
  • Cell & Developmental Biology  (4,285)
  • ASTROPHYSICS  (3,136)
  • 1980-1984  (10,276)
  • 1970-1974  (5,866)
  • 1950-1954  (2,860)
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Years
Year
  • 101
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    Galaxy formation (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Implications of the isotropy of the cosmic microwave background on large and small angular scales for galaxy formation are reviewed. In primeval adiabatic fluctuations, a universe dominated by cold, weakly interacting nonbaryonic matter, e.g., the massive photino is postulated. A possible signature of photino annihilation in our galactic halo involves production of cosmic ray antiprotons. If the density is near its closure value, it is necessary to invoke a biasing mechanism for suppressing galaxy formation throughout most of the universe in order to reconcile the dark matter density with the lower astronomical determinations of the mean cosmological density. A mechanism utilizing the onset of primordial massive star formation to strip gaseous protogalaxies is described. Only the densest, early collapsing systems form luminous galaxies.
    Keywords: ASTROPHYSICS
    Type: ESA Plasma Astrophys.; p 327-340
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  • 102
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    The QUASAT mission: An overview (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The QUASAT VLBI mission to provide images of the total intensity and polarized emission of compact radio sources in continuum and line with a combination of angular resolution and quality unattainable from Earth is summarized. The astrophysical goals encompass the study of active nuclei at scales appropriate to the outer reaches of accretion disks and the optical broad and narrow line regions; the study of galactic continuum sources in stars and in the galactic center; and spectroscopic studies of galactic and extragalactic molecular masers to determine their role in the life cycle of stars, and their use as direct distance indicators.
    Keywords: ASTROPHYSICS
    Type: ESA QUASAT: A VLBI Obs. in Space; p 13-18
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  • 103
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    The work on Comet Halley's orbit at ESOC (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The predominant error source in the final navigation for the Giotto Comet fly-by of Halley's nucleus is due to uncertainties in the comet's ephemeris. Efforts are being undertaken at ESOC to improve the prediction of the comet's state at the time of the encounter. Some of the aspects involved in the problem discussed include ways to improve old observations by re-measurement or re-reduction and encouragement to observers to take fine quality astrometric observations in the future, especially at critical times. Difficulties in the mathematical modelling of the non-gravitational forces and possible offsets of the comet's center-of-light from its center-of-mass are addressed. The available estimation techniques are also examined including one based upon selecting optimum observations.
    Keywords: ASTROPHYSICS
    Type: JPL Cometary Astrometry; p 188-202
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  • 104
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    The orbital motion of Comet Halley (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Since comet Halley is to be studied with spacecraft, new requirements arise for the accuracy to which the position of the methodology of constructing an exact theory is presented. The effect of all kinds of errors in building a mathematical model of motion and the effect of a shift of Halley's center-of-mass relative to the optical center are analyzed. The theory is based on the optical, angular observations of 1911 back to 1759 reduced to the mean equator and epoch of 1950.0 as well as the relative observations of 1682. The observations of 1982 were used to control the accuracy of the theory developed. Deviations of calculated values from measured values do not exceed 1.5 which confirms the good degree of accuracy of this theory. The comet's orbit is obtained using current optical data.
    Keywords: ASTROPHYSICS
    Type: JPL Cometary Astrometry; p 176-187
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  • 105
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    The orbits of Comets Halley and Giocobini-Zinner (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Ongoing activities to improve the orbits and ephemerides of comets Halley and Giacobini-Zinner are outlined. The nongravitational acceleration model of Marsden et al (1973) is used to represent the motion of these two comets over their observed intervals, and recent orbital updates are presented.
    Keywords: ASTROPHYSICS
    Type: Cometary Astrometry; p 167-175
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  • 106
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    Coma morphology and dust-emission pattern of periodic Comet Halley. II - Nucleus spin vector and modeling of major dust features in 1910 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The continuous ejection of dust from discrete emission sources on the rotating nucleus of the Comet Halley is modelled in order to explain the evolution of spiral jets which unwind from the nucleus condensation into envelopes or halos in the comet head. The model is applied to digitally processed images of three features of the comet taken from Mount Wilson plates during the 1910 fly-by. The model permits a determination of the motion and spin vector for each emission source, its cometocentric coordinates, and a function relating particle ejection velocity to the solar radiation pressure exerted on the ejecta. It is found that the obliquity of the comet orbit's plane to its equatorial plane is 45 deg, the axis of rotation period of 17.3 days. The derived function of particle ejection velocity to the solar radiation pressure implied no contribution from grains larger than 10 microns in radius. High dust loading of gas flows from the June 1910 emission sources is indicated. It is estimated that because of the favorable approach geometry of the Gioto spacecraft during its 1986 flyby, the likelihood of encountering dense jets of dust is small.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 89; 1408-142
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  • 107
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    A possible relationship between metal abundance and luminosity for disk galaxies (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Near-infrared colors have been measured for a sample of 31 late-type galaxies in the Pegasus I and Pisces clusters; system luminosities in the sample cover the range of M(H) between -19 and -23.5. The color index (J - K) correlates strongly with the absolute H magnitude; lower-luminosity systems have bluer colors. These observations are consistent with the assumption that the mean metal abundance of the old disk population decreases systematically with luminosity. The systematic variation (B - H) with absolute H magnitude reported recently by Tully et al. (1982) derives in part from this proposed systematic change of metallicity with luminosity. However, a relative increase in the number of newly formed stars and/or a systematic smaller age for lower-luminosity disks must still be posited in order to fully explain the observed (B - H), H relation.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 89; 1300-130
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  • 108
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    X-ray emission from clusters of galaxies (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Some X-ray spectral observations of approximately 30 clusters of galaxies from HEAO-1 are summarized. There exists strong correlation betwen X-ray luminosity, L(x), and temperature kT in the form L(x)alphaT to the 2.3 power. This result combined with the L(x) central galaxy density relation and the virial theorem indicates that the core dadius of the gas should be roughly independent of L(x) or Kt and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of KT and optical velocity dispersion seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. The evidence for cooling in the cores several clusters is discussed based on spectral observations with the Einstein solid state spectrometer.
    Keywords: ASTROPHYSICS
    Type: Physica Scripta (ISSN 0031-8949); T7; 157-162
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  • 109
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    X-ray observations of gamma-ray burst source locations (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: ASTROPHYSICS
    Type: Physica Scripta (ISSN 0031-8949); T7; 127
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  • 110
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    X-ray spectra and time variability of active galactic nuclei (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: X ray measurements taken with the HEAO-1 and -2 satellites are examined for clues to the source of emissions from active galactic nuclei (AGN). The data covered the energy range 2-100 keV and 0.5-4.5 keV and encompassed quasars, BL Lac objects, Seyfert I galaxies and broadline radio galaxies. The broadline spectra were best fit with a power law with a slope of about 0.68. The continua displayed roughly equivalent energy at all wavelengths except for radio bands. Spectral variability was detected in the BL Lac objects, which may emit optical, UV and soft X ray radiation from optically thin synchrotron emission with a hard X ray tail from inverse Compton scattering. No strong variability was evidenced with other AGN, suggesting that the emitting regions are below the Eddington luminosity and thus exhibit stable flow characteristics.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 3; 10-12
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  • 111
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    Turbulent compressible convection in a deep atmosphere. II - Two-dimensional results for main-sequence A5 and F0 type envelopes (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the present two-dimensional numerical study of turbulent compressible convection in the A5 and F0 main-sequence envelope types, ionization effects are included in the equation of state of the gas, and radiative transfer is modeled in a diffusive process with tabulated gas opacities. It is noted that the thermal effects of ionization significantly affect the dynamics of the flows and that an inversion of the mean density can be created and sustained in a dynamical situation. The substantial differences in the flows of A5 and F0 indicate development trends in the transition from the radiative to the convective mode of energy transport. As convection becomes more effective, the flow becomes more turbulent and the scaling effects of local scale heights become more significant.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 282; 550-556
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  • 112
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    Interplanetary flow systems associated with cosmic ray modulation in 1977-1980 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The hydromagnetic flow configurations associated with the cosmic ray modulation in 1977-1980 were determined using solar wind plasma and magnetic field data from Voyager 1 and 2 and Helios 1. The modulation was related to two types of large-scale systems of flows: one containing a number of transients such as shocks and postshock flows, the other consisting primarily of a series of quasi-stationary flows following interaction regions containing a stream interface and often bounded by a forward-reverse shock pair. Each of three major episodes of cosmic ray modulation was associated with the passage of a system of transient flows. Plateaus in the cosmic ray intensity-time profile were associated with the passage of systems of corotating streams.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 6579-658
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  • 113
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    First-flight escape from spheres with R(-2) density distribution (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Energy-independent first-flight transport kernels are evaluated for a spherical region with an R(-2) density distribution. The uncollided angular-flux distribution is obtained and integrated for a source distribution that is proportional to the density to give the uncollided emitted particle flux and current density. These are useful for the calculation of mass, energy, and momentum carried away by fast particles born in the medium. The data are relevant to estimate escape from weakly bound atmospheres such as comet comae, dilute circumstellar envelopes, and some unconfined laboratory plasmas.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 135; 1, Ju; 177-180
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  • 114
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    Wide-angle radio tail QSOs as members of clusters of galaxies. II - Direct optical observations and spectroscopy of QSO fields (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Deep, direct observations are obtained for the fields of 19 QSOs (redshift values 0.3-1.5) whose 'excess' galaxy counts in 1.17-sq arcmin fields centered on the QSOs confirm QSO redshift cosmological interpretations at the 99-percent confidence level. It is in addition indicated with 97-percent confidence that wide angle radio tail QSOs lie in richer concentrations of galaxies than undistorted QSOs. The results obtained also confirm that the 'excess' galaxies detected in the QSO fields have the same redshifts as the QSOs. These observations indicate that deep CCD observations of the fields of radio tail QSOs would provide a sample of distant clusters of galaxies at known redshifts (those of the QSOs).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 55; 533-550
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  • 115
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    Comparison of variations in the visible and ultraviolet spectra of a Centauri (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Short and long wavelength, high resolution IUE spectrographs of the He I spectrum variable star a Cen are the basis of the present equivalent width and central depth measurements of UV absorption lines. The period for cyclic intensity variations is determined by means of a four-parameter, least squares fit to a sinusoid. Other spectrographic and photometric intensity determinations of the He I 4026 A line are combined with the present data to yield a period of 8.81620 + or - 0.00006 days.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 55; 507-516
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  • 116
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    Role of 'core' and 'halo' solar electrons in ionization of the interstellar medium (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the present consideration of the probability of interstellar wind H and He atoms' survival of ionization by solar wind electrons, a dual temperature electron distribution is for the first time used to model the effects of 'core' (10 eV) and 'halo' (60 eV) solar electrons on survival probabilities. The interstellar wind has a higher probability of surviving halo rather than core electron ionization only at heliocentric distances smaller than 0.5 AU. For larger distances, halo and core survival probabilities are similar, and similarly insensitive to changes in (1) interstellar wind velocity at infinity, (2) the solar ratio of radiation to gravitational force, and (3) solar electron temperatures. At distances smaller than 0.5 AU, however, sensitivity significantly increases.
    Keywords: ASTROPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 32; 779-784
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  • 117
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    Symbiotic stars (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.
    Keywords: ASTROPHYSICS
    Type: Scientific American (ISSN 0036-8733); 251; 84-94
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  • 118
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    Interstellar scintillation and ultra-low-frequency gravitational wave observations (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: High precision pulsar timing measurements have been used to set upper limits on the flux of ultralong period (T greater than 3 years) stochastic gravitational waves. The data used to produce the current limits appear to be limited by timing noise that is intrinsic to the pulsars. Recently, however, there have been very low noise timing observations of the 1.5-millisecond pulsar. This suggests that significant sensitivity improvements in searches for ultralow frequency (ULF) gravitational waves may be possible. Here, the effects of the heretofore secondary noise source of phase scintillations caused by interstellar electron density fluctuations are calculated, and the prospects for improved ULF gravitational wave measurements using pulsar timing are discussed.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 307; 527
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  • 119
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    The scattering of energetic particles by waves in a finite beta plasma (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Solutions are presented for the dispersion relation of waves propagating parallel to the ambient magnetic field, in a plasma having an arbitrary ratio of thermal to magnetic pressure, beta. Previous results applicable only to wave frequencies much lower than the ion cyclotron frequency are extended to include all frequencies lower than the electron cyclotron frequency. The cyclotron turnovers are found to occur at significantly lower frequencies in finite beta plasmas. Cyclotron damping is significant for small wavelength waves. These results show that in energetic particle scattering by electromagnetic turbulence in a plasma with beta value greater than 40, scattering by waves with wave frequencies greater than the ion cyclotron frequency can be neglected. This condition is satisfied in many astrophysical plasmas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 334-338
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  • 120
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    Primordial gravitational waves and the blackbody radiation anisotropy (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: If relict gravitational waves deriving from a chaotic initial singularity contain a nonisotropic component, then this radiation can produce a frame dragging; effect which will induce a dipole anisotropy in the observed temperature distribution of the 3 K electromagnetic radiation background. The measured dipole and quadrupole distributions of the electromagnetic background can thus be used to bound the effective wave parameters of the nonisotropic part of the gravitational background. Using available data, the dimensionless amplitude of this nonisotropic part is found to be less than 0.0005 for wavelengths less than the Hubble radius. The effective energy density of this nonisotropic component of the gravitational radiation background is less than 2 x 10 to the -8th times the critical density.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 280; L39-L41
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  • 121
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    The laboratory simulation of unmagnetized supernova remnants Absence of a blast wave (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Supernova remnants are experimentally simulated by irradiating spherical targets with eight-beam carbon dioxide laser in a chamber containing finite amounts of neutral gas, the gas being ionized by radiation from the hot target. The expansion velocities of the target plasmas are approximately the same as the expansion velocities of supernova ejecta and the experiment is successfully scaled to the case of a supernova remnant in an unmagnetized, low-density, interstellar medium. No sweep-up of the ambient plasma is detected, indicating that no hydrodynamic shock wave is formed to couple the target ejecta to the ambient gas. The experiment implies that if supernova ejecta couple to the interstellar medium, magnetic-field effects may be crucial to the physical description.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 802-808
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  • 122
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    The mysterious 10 micron emission feature in the spectrum of Nova Aquilae 1982 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Broad-band 1.2-23 micron photometry and 1 percent resolution 7-14 micron spectrophotometry of Nova Aql 1982 are presented. This nova developed similarly to other dusty novae in that the appearance of thermal infrared emission from a circumstellar dust shell was coincident with a downward transition at visual wavelengths. A strong 10 micron emission feature appeared in the spectrum of Nova Aql 1982 during the dust shell development phase. This feature was not entirely similar to emission features previously observed in other stars with circumstellar shells. The contrast of the nova's 10 micron feature was larger than those observed in the SiC-rich shells of carbon stars. On the other hand, although the nova emission feature was reminiscent of the 10 micron silicate emission feature observed in oxygen-rich supergiants, it peaked at a slightly longer wavelength and there was no corresponding 20 micron emission feature. The contrast of the feature increased with time. It is concluded that an anomalous dust grain component, tentatively identified as SiC, nucleated and grew in the circumstellar shell of Nova Aql 1982.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 303-312
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  • 123
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    Image restoration of high resolution observations of the M87 jet (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Image-restoration techniques are applied to high-resolution (FWHM 0.5-1.0 arcsec) plates of the M87 jet obtained with the CFH telescope by Nieto and Lelievre (1982), and their description of the optical jet is confirmed. Most of the features detected are similar to those shown by the VLA map of Biretta et al. (1982), having a resolution of 0.12 arcsec. In particular, the restored images show evidence for an elongated nucleus and for a very sharp discontinuity in knot A which is not perpendicular to the jet axis. It also seems that the start of the oscillations and this discontinuity are not related. This similarity at a 0.2-arcsec scale suggests no relativistic motion (v less than 25,000 km/sec) throughout the jet.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 130; 1, Ja
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  • 124
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    Polarization of Comptonized photons (1984)
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    Publication Date: 2011-08-18
    Description: The polarization of Comptonized X-rays as a function of energy and emission angle is obtained. The geometry utilized is that of the semi-infinite plane with the source photons located on a plane at a finite optical depth below the surface. It is further shown what information is obtainable from polarization measurements at only two different energies. The observed values for the X-ray sources Cyg X-1 and Sco X-1 are used to illustrate the calculations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 279; 401-412
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  • 125
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    Temperature and elemental abundances in the Abell cluster A576 derived from X-ray observations (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Results of the Einstein Solid State Spectrometer (SSS) observations of the central region of Abell 576 combined with HEAO 1 spectra of the total cluster are reported. Line emission due to Fe, Si, and S from a hot plasma in the central region of the object are detected. Abundances roughly one-half of the solar value are derived for these elements. The total cluster spectrum is well fitted by a thermal bremsstrahlung model with a temperature of 4 +3.5 or -1.4 x 10 to the 7th K. This temperature is in conflict with the SSS temperature determination for the center of the cluster. This difference can be explained if cooling takes place in the central part of the cluster, or if the X-ray emission in the center is dominated by the emission of a single galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 279; 53-59
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  • 126
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    Dense cores in dark clouds - Young embedded stars at 2 micrometers (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Twenty-five visually opaque regions which contain strong sources of NH3 (1,1) line emission (dense cores) have been surveyed for evidence of associated stars at two microns. Five such stars have been found, of which three - in B5, L1489, and L1582 - are optically invisible and probably embedded in their associated cores. The stars in B5 and L1489 have 2-100 micron spectra and luminosity similar to those of HL Tau, a very young T Tauri star. These stars probably formed in the cores where they are now seen. These results tend to confirm earlier suggestions that low-mass stars form in dense cores.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 279; L27-L30
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  • 127
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    A sample of solar-type stars of known age (1984)
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    Publication Date: 2011-08-18
    Description: A sample of field F and G dwarfs of known ages is presented. All the dwarfs are secondaries of visual binaries in which the temperature and gravity of the hotter primary has been estimated from Stromgren photometry, and its age derived from reference to isochrones. This age is taken to apply to the secondary. Even in the case of F-type secondaries, which themselves have measured Stromgren indices, it is much better to estimate ages from the primaries as it is demonstrated that use of isochrones to determine age of stars not far evolved from the main sequence can lead to significant systematic overestimates of ages when the photometric measurements have typical random errors. A number of systems in which photometry is available for both components have primaries which appear much younger than the secondaries, suggesting a need for further investigation.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 89; 515-522
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  • 128
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    Comet Cernis - Icy grains at last? (1984)
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    Publication Date: 2011-08-18
    Description: An absorption feature at 2.9-3.0 microns has been detected for the first time in comet Cernis 19831 at 3.3 AU. The feature is interpreted as scattering by ice grains in the comet's coma. The thermal emission spectrum indicates that hot, micron-sized absorbing grains are also present in the coma.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 277; L75-L78
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  • 129
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    The near-infrared continuum emission of visual reflection nebulae (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the past, reflection nebulae have provided an astrophysical laboratory well suited for the study of the reflection properties of interstellar dust grains at visual and ultraviolet wavelengths. The present investigation is concerned with observations which were begun with the objective to extend to near-infrared wavelengths the study of grains in reflection. Observations of three classical visual reflection nebulae were conducted in the wavelength range from 1.25 to 2.2 microns, taking into account NGC 7023, 2023, and 2068. All three nebulae were found to have similar near-infrared colors, despite widely different colors of their illuminating stars. The brightness level shown by two of the nebulae at 2.2 microns was too high to be easily accounted for on the basis of reflected light. Attention is given to a wide variety of possible emission mechanisms.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 277; 623-633
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    Thermal metamorphism of Si2O3 - (A circumstellar dust analog) (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The thermal behavior of Si2O3, the metastable condensate from SiO vapor,has been studied experimentally. Si2O3 and its successor, amorphous quartz, have previously been shown to have infrared spectral features similar to some that appear in the spectra of grains in oxygen-rich circumstellar regions. Thermal annealing experiments show that only one Si2O3 decay process operates over the range between 750-1000 K. This process is a unimolecular disproportionation. The rate of this transformation can be expressed as k/hr = 10 to the 9th exp (-40 kcal/mole/RT). By using this rate constant, it is found that a significant fraction of freshly nucleated circumstellar grains can survive passage through a typical circumstellar shell virtually unaltered in structure. It is emphasized that this is only the first in a series of laboratory experiments intended to study the metamorphism of newly condensed circumstellar material ejected into the interstellar medium. Grains similar to these might have been incorporated into the primitive solar nebula, provided that they could also survive passage through the general interstellar medium.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; B657-B66
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    Infrared molecular emissions from comets (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The possibility of detecting IR molecular line emission from cometary parent molecules is explored. Due to the non-LTE conditions in the inner coma and the large amount of near IR solar flux, IR fluorescence will be a significant source of cometary emission and, in fact, will dominate the grain radiation in a sufficiently high resolution instrument. The detection of this line emission will be difficult due to absorption in the terrestrial atmosphere, but it appears possible to measure cometary H2O emission from airplane altitudes. As IR molecular line emission represents one of the few promising methods of detecting cometary parent molecules directly, further research on this problem should be vigorously pursued. Previously announced in STAR as N83-30344
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 782-797
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  • 132
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    Optical characteristics of young quasars as sources of the cosmic X-ray background (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The sources which dominate the thermal cosmic X-ray background cannot have X-ray spectra similar to the power laws measured for bright active galactic nuclei. The optical consequences of this disparity are pursued by considering a standard model for the photoexcitation and heating of the line-emitting gas surrounding a central source (e.g., such as a quasar). The optical line emission to be associated with compact young quasar sources having the same X-ray spectrum as the X-ray background is found to be substantially different from that characteristic of typical quasars. Implications on quasar source counts and the identification of such new objects are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 427-433
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  • 133
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    X-ray observations of broad absorption-line quasars (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The present 0.1-4 keV observer frame data was obtained for three broad absorption-line quasars with the imaging proportional counter on the Einstein Observatory. Data for one object, UM 232, are sufficiently good to tell that absorption at 1 keV is unimportant (quasar rest frame), which leads to an upper limit to the column density of absorbing gas of 10 to the 22nd/sq cm. Because this gas absorbs optical continuum and line emission, it must have a size of 10 to the 19th cm or greater, and therefore a density of less than 1000/cu cm. This absorbing gas is unlike the much denser clouds responsible for the broad emission lines. It is also calculated that the mass of absorbing gas is greater than 1 solar mass, and that it is at least 300 pc distant from the ionizing continuum source. Free-free absorption, which is calculated to be unimportant at frequencies above 2 GHz, is probably not the cause of the radio-quiet nature of this quasar in the 5 and 10.7 GHz survey of Strittmatter et al. (1980).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 423-426
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  • 134
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    Line emission from H II blister models (1984)
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    Publication Date: 2011-08-19
    Description: Numerical techniques to calculate the thermal and geometric properties of line emission from H II 'blister' regions are presented. It is assumed that the density distributions of the H II regions are a function of two dimensions, with rotational symmetry specifying the shape in three-dimensions. The thermal and ionization equilibrium equations of the problem are solved by spherical modeling, and a spherical sector approximation is used to simplify the three-dimensional treatment of diffuse ionizing radiation. The global properties of H II 'blister' regions near the edges of a molecular cloud are simulated by means of the geometry/density distribution, and the results are compared with observational data. It is shown that there is a monotonic increase of peak surface brightness from the i = 0 deg (pole-on) observational position to the i = 90 deg (edge-on) position. The enhancement of the line peak intensity from the edge-on to the pole-on positions is found to depend on the density, stratification, ionization, and electron temperature weighting. It is found that as i increases, the position of peak line brightness of the lower excitation species is displaced to the high-density side of the high excitation species.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 653-664
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  • 135
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    IRAS observations of NGC 1052 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The galaxy NGC 1052 has been observed with the IRAS satellite. The infrared emission at 100 microns is substantially larger than a smooth extrapolation of the radio data. Because of the large diaphragm size of IRAS, it is impossible to decide uniquely if the infrared radiation represents a self-absorbed nonthermal spectrum or thermal reradiation by heated dust.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 96; 973-976
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  • 136
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    The resonance lines of Hg II in IUE spectra of chemically peculiar stars (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Twenty IUE images of chemically peculiar (CP) stars are analyzed to demonstrate that the previously detected Hg II overabundances in CP stars is real. Attention was focused on the Hg II resonance lines at 1650 and 1942 A. A total of eight stars were scanned and spectrum synthesis computations were performed to characterize the model atmospheres for each object. The 1942 A line was found to be insensitive to effective temperature, microturbulence and isotopic mixture influences, and therefore well-suited to abundance analyses. A non-LTE process was ruled out as a source of the Hg anomaly. Finally, it is suggested that diffusion-type processes be attributed to Hg enhancements in main sequences B stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 725-735
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  • 137
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    HEAO 3 discovery of Al-26 in the interstellar medium (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new analysis technique was used with HEAO 3 satellite gamma ray data to quantify the galactic 1809 keV emission. A method of bins was applied in summing for specific scan directions, followed by fitting the source and background components. The 1809 keV line of Al-26 was significant because of the recent discovery that Al-26 was overabundant in meteoritic material and implanted during solar system formation. The HEAO 3 flux indicated a current decay of 3 solar masses of Al-26 per year in the interstellar medium, possibly occurring in red giants and massive main sequence stars. The ratio of the observed Al-26 to the Al-27 flux was similar to that measured in meteorites, which suggests that the ratio is normal for the galactic medium and that no supernova triggered the protosolar nebular collapse.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 578-585
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  • 138
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    The Vega particulate shell - Comets or asteroids? (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Infrared Astronomical Satellite (IRAS) science team has discovered a shell of particulate material around the star Vega. At the mean distance and temperature of the shell, the expected condensation products from a protostellar nebula would be dominated by frozen volatiles, in particular water ice. It is not possible to discriminate between dirty ice and silicate materials in the Vega shell on the basis of the IRAS data. The Vega shell is probably a ring of cometary bodies with an estimated minimum mass of 15 earth masses, analogous to one that has been hypothesized for the solar system. A possible hot inner shell around Vega may be an asteroid-like belt of material a few astronomical units from the star.
    Keywords: ASTROPHYSICS
    Type: Science (ISSN 0036-8075); 224; 987-989
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  • 139
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    A circumstellar disk around Beta Pictoris (1984)
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    Publication Date: 2011-08-19
    Description: A circumstellar disk has been observed optically around the fourth-magnitude star Beta Pictoris. First detected in the infrared by the Infrared Astronomy Satellite last year, the disk is seen to extend to more than 400 astronomical units from the star, or more than twice the distance measured in the infrared by the Infrared Astronomy Satellite. The disk is presented to earth almost edge-on and is composed of solid particles in nearly coplanar orbits. The observed change in surface brightness with distance from the star implies that the mass density of the disk falls off with approximately the third power of the radius. Because the circumstellar material is in the form of a highly flattened disk rather than a spherical shell, it is presumed to be associated with planet formation. It seems likely that the system is relatively young and that planet formation either is occurring now around Beta Pictoris or has recently been completed.
    Keywords: ASTROPHYSICS
    Type: Science (ISSN 0036-8075); 226; 1421-142
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  • 140
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    An improved thermal model for cometary nuclei (1984)
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    Publication Date: 2011-08-19
    Description: A thermal model for cometary nuclei is presented and used in comparisons of predictions with data on Halley's comet. The model considers the surface boundary conditions and heat diffusion equations, the sublimation rate of ice, the energy balance, and the dust production rate. Projections were made for the Halley nucleus over 18 latitudes from -85 to +85 deg, from 185 d before to 110 d after perihelion, and in 20 layers of its surface in 1.3 cm increments. Sublimation is predicted to increase by a factor of 2.2 every orbit, thereby allowing 320 returns for a nucleus with a coma, 710 returns with a bare ice nucleus. The gas production during the Giotto intercept at 0.9 AU will be 4.4 x 10 to the 29th molecules/sec, close to an estimate made during the 1910 return.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; C358-C36
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  • 141
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    The galaxy as a self-regulated star-forming system - The case of the OB associations (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is proposed that the energy and momentum injected from OB associations can act as the regulators of high-mass star formation throughout the disk of a spiral galaxy. The mechanism, interacting blast waves driven by supernovae and stellar winds, leads to a generalized Schmidt law for the star formation rate and could explain in a natural way the galactic gradients of metals and star formation rate. The formation of massive stars is determined by the average ambient density in the disk while low-mass star formation is regulated by the density in molecular clouds. That is, there are two modes of star formation, but the physical mechanism is the same in both cases.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 285; 813-817
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  • 142
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    Pair production rates in mildly relativistic magnetized plasmas (1984)
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    Publication Date: 2011-08-19
    Description: Electron-positron pairs may be produced by either one or two photons in the presence of a strong magnetic field. In magnetized plasmas with temperatures kT approximately sq mc, both of these processes may be important and could be competitive. The rates of one-photon and two-photon pair production by photons with Maxwellian, thermal bremsstrahlung, thermal synchrotron and power law spectra are calculated as a function of temperature or power law index and field strength. This allows a comparison of the two rates and a determination of the conditions under which each process may be a significant source of pairs in astrophysical plasmas. It is found that for photon densities n(gamma) or = 10 to the 25th power/cu cm and magnetic field strengths B or = 10 to the 12th power G, one-photon pair production dominates at kT approximately sq mc for a Maxwellian, at kT approximately 2 sq mc for a thermal bremsstrahlung spectrum, at all temperatures for a thermal synchrotron spectrum, and for power law spectra with indices s approximately 4.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 285; 747-757
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  • 143
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    Photon-photon absorption and the uniqueness of the spectra of active galactic nuclei (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of the feedback of e(+)-e(-) pair reinjection in a plasma due to photon-photon absorption of its own radiation was examined. Under the assumption of continuous electron injection with a power law spectrum E to the minus gamma power and Compton losses only, it is shown that for gamma 2 the steady state electron distribution function has a unique form independent of the primary injection spectrum. This electron distribution function can, by synchrotron emission, reproduce the general characteristics of the observed radio to optical active galactic nuclei spectra. Inverse Compton scattering of the synchrotron photons by the same electron distribution can account for their X-ray spectra, and also implies gamma ray emission from these objects. This result is invoked to account for the similarity of these spectra, and it is consistent with observations of the diffuse gamma ray background.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 112-115
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  • 144
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    Infrared observations of interacting/merging galaxies (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present sample of 20 galaxy systems, selected on the basis of morphological evidence for the tidal interaction or merger of two galaxies and observed at 1-10 microns, is noted to include 11 systems, detected at 10 microns, which have on average a significantly higher IR luminosity than noninteracting galaxies. The enhanced IR radiation is due to star formation bursts. On the basis of IR Astronomical Satellite results for a sample of galaxies, as much as 30 percent of all the far-IR emission observed arises in bursts of star formation that are triggered by interactions, and massive stars account for most of the luminosity in these bursts. It is suggested, in view of a massive star formation rate in the interacting and merging galaxies that is about 3 times higher than in noninteracting systems, that much of this star formation occurred in either nuclear regions or merger remnants.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 95-107
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  • 145
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    Mass loss from red giants - A simple evolutionary model for NGC 7027 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: NGC 7027 is a young planetary nebula with the remnants of a red giant circumstellar envelope surrounding the central, ionized region. By comparing the outer molecular envelope with the inner ionized material, it is argued that the mass loss rate has decreased by at least a factor of 3, and more probably by about a factor of 10, during the past 1000 years. From this result, it is argued that the luminosity of the central star has also decreased substantially during the same time, consistent with models for the rapid evolution of stars just after they evolve off the asymptotic giant branch. In this picture, the distance to NGC 7027 is less than 1300 pc. NGC 7027 was the last (and best) example of a star where apparently the momentum in the outflowing mass /M(dot)v/ is considerably greater than the momentum in the radiation field (L/c). With the above description of this object, the evidence is now strong that quite often the mass lost from late-type giants is ultimately driven to infinity by radiation pressure on grains. If M(dot)v is as large as L/c for asymptotic branch stars, then it is expected that the total amount of mass lost during this stage of evolution is of the same magnitude as the initial mass of the star, and therefore this mass loss can profoundly affect the star's ultimate fate.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 630-632
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  • 146
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    Gravitational spurs and resonances - Effects of small mass disturbers in spiral galaxy disks (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In the present simulations of a disturber in a complete stellar disk without the restrictive assumption, the disturber parameters of the NGC 206 cloud in M 31 were assumed as a realistic example. The resulting spur around the disturber was comparable in shape, size, and strength to Julian and Toomre's (1966) results. In addition, a complicated evolving pattern of strong density peaks appeared well inside and outside the disturber's orbit. Simulation with a ten-times-more-massive disturber showed a more clearly defined version of the same initial pattern, two spiral arms of density peaks rotating with the disturber in the stronger arm. The orbital radii of the density peaks correspond to those of epicyclic resonances with the orbiting disturber potential.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 62-67
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  • 147
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    A search for 183 GHz emission from water in late-type stars (1984)
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    Publication Date: 2011-08-19
    Description: A search was made for 183 GHz line emission from water vapor in the direction of twelve Mira and two semiregular variables. Upper limits to the emission are in the range of 2000 to 5000 Jy. It is estimated that thermal emission from the inner regions of late type stellar envelopes will be on the order of ten Jy. Maser emission, according to one model, would be an order of magnitude stronger. From the limited set sampled, the possibility of very strong maser emission at 183 GHz cannot yet be ruled out.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 310-313
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  • 148
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    Brackett-alpha line profiles of young stellar objects (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Profiles of the Br-alpha line of H I at a velocity resolution of 45 km/s are presented for the compact imbedded infrared objects BN, S106/IRS 3, GLS 490, GL 961, GL 989, Mon. R2/IRS 2, and for the visible objects LkH-alpha 101, T Tau, and R Mon. A proportionality obtained between Br-alpha luminosity and bolometric luminosity is shown to extend over three orders of magnitude, supporting the idea that the physical conditions and gas motions in the circumstellar envelopes of stellar objects are closely related over a wide range of luminosities. The Br-alpha line strengths are compared to radio continuum flux densities in the context of stellar wind models. Momentum deposition rates deduced from Br-alpha or radio continuum fluxes are consistent with those available in the radiation fields, which appear capable of driving the ionized gas outflows in the vicinity of the core sources. The results of a comparison of the H-alpha and Br-alpha profiles for T Tau are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 289-301
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  • 149
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    Instabilities in line-driven stellar winds. I - Dependence on perturbation wavelength (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analytical study is presented of the stability of absorption line-driven flows, such as found in stellar winds, in the presence of small-amplitude disturbances. A generalized calculation of the perturbed direct extinction force is performed and the evolution of the perturbation into the nonlinear regime and the dynamical results of perturbation in the scattered radiation field are examined. An expression is derived for the wavenumber variation of the perturbed line force from the milieu of nonoverlapping lines which have a power-law distribution in opacity. A linear dispersion analysis is carried out to model the growth and propagation of radiative-acoustic waves in absorption line-driven flows, which are found unstable to perturbations that may be smaller than the Sobolev length. No damping mechanism was found that would eliminate the absorption line-driven flows.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 284; 337-350
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  • 150
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    Shock acceleration in active galactic nuclei and quasars (1984)
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    Publication Date: 2011-08-19
    Description: A model of spherical accretion on a massive black hole as the energy source for active galactic nuclei and quasars is considered. According to the model, the kinetic energy of the infalling material is randomized by a collisionless shock around the black hole. Relativistic protons are produced with high efficiency via first order Fermi shock acceleration and, because their kinetic energy is much larger than the gravitational potential energy, do not fall into the black hole. The model can produce relativistic particles with flat spectra needed to account for the radiation from these sources, including their broad band spectral characteristics. Since all electrons are secondaries resulting from proton-proton collisions throughout the volume of the source, this model avoids the Compton catastrophe problem.
    Keywords: ASTROPHYSICS
    Type: Max-Planck Inst. fuer Physik und Astrophysik X-Ray and UV Emission from Active Galactic Nuclei; p 185-187
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  • 151
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    Measurement of the formaldehyde ortho to para ratio in three molecular clouds (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of ortho and para H2CO in two types of clouds, a warm cloud (Orion A) and two cold clouds (L183 and TMC1), are presented. The ortho to para ratio in Orion deduced from the H2(C-13)O data is about three, while that for TMC1 is about one and that for L183 is 1-2. The former value is in agreement with the value calculated from chemical models of ortho and para H2CO production. The values for the cold clouds are consistent with thermal equilibrium at a temperature slightly smaller than 10 K.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 137; 2, Au; 211-222
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  • 152
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    Multiple circumstellar shells and radiation pressure on grains in the outflows from late-type giants (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is pointed out that mass loss from red giants and supergiants is sometimes as high as 0.0001 solar mass per year. This mass loss represents a major source of new interstellar matter. The present investigation is concerned with the phenomena involved in stellar mass loss, taking into account a comparison of currently available observations with plausible models. The case of the extended circumstellar envelope around IRC +10216 is considered. In observations about mass loss from circumstellar shells, it is sometimes found that the P Cygni profiles are split into two or more sharp, distinct components. The question is considered whether such narrow separate components can be understood in terms of the radiation pressure model. A grain growth model is discussed along with outflow velocity, radiation pressure, and mass loss rates. The models are compared with observations from Alpha Orionis, Mira, and IRC +10216. It is concluded that a hybrid model for the mass loss from some late-type stars seems appropriate. Under certain conditions, outflow speeds of 10 to 20 km/s can be understood.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 282; 200-205
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  • 153
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    The nature of the filaments northeast of the supernova remnant IC 443 (1984)
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    Publication Date: 2011-08-18
    Description: New optical spectrophotometry of the faint filaments northeast of the bright supernova remnant IC 443 show emission-line ratios very similar to those seen in the bright filaments of IC 443 and other supernova remnants. This suggests that these northeastern filaments also represent shock-heated interstellar gas and are not simply the southern boundary of the neighboring H II region S249 as previously suspected. If these filaments are associated with IC 443, they then reveal a much more extended remnant structure than previously assumed and permit a relatively accurate determination of IC 443's distance via its interaction with S249.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 658-664
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  • 154
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    Nearby molecular clouds. I - Ophiuchus-Sagittarius, b greater than 10 deg (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of a 370-sq-deg area at b = 10-24 deg in the Oph-Sag region at the 115-GHz 1-0 transition of CO, obtained with a 256-channel spectrometer on the 1.2-m mm-wave telescope at Columbia University during winter 1980-1981 are reported. Observing parameters include full beamwidth at half power 8 arcmin, resolution 1 or 0.5 deg, velocity resolution 0.65 km/s, and frequency-shifting-mode shift 5 MHz; the data-processing scheme is described in detail. The results are presented in a map and a diagram and discussed with regard to other observations. An extended complex of molecular clouds near the sun and probably connected with the Aquila Rift, the Rho Oph Cloud, and the Gould Belt is detected. A correlation is found between the CO line intensity and the H I deficiency observed in the region, suggesting H2 formation with H2 column densities up to 1 x 10 to the 21st/sq cm.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 634-638
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    The chemistry of phosphorus in dense interstellar clouds (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Laboratory experiments show that the ion-molecule chemistry of phosphorus is significantly different from that of nitrogen in dense interstellar clouds. The PH3 molecule is not readily formed by gas-phase, ion-molecule reactions in these regions. Laboratory results used in a simple kinetic model indicate that the most abundant molecule containing phosphorus in dense clouds is PO.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 139-143
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  • 156
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    Rapid expansion of polytropes (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An extremely massive unevolved star may be idealized as an n = 3 polytropic sphere supported by radiation pressure. Such a polytrope is subject to explosive, supersonic expansion, whose later stages can be described by similarity solution of the dynamical equations. This picture is confirmed by numerical hydrodynamic simulation, which shows that an n = 3 polytrope, initially at rest near equilibrium, undergoes an explosive expansion which approaches the similarity solution at large times.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 819-824
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  • 157
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    The unusually soft X-ray spectrum of LMC X-3 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Spectral studies of LMC X-3 using the HEAO 1 A-2 experiment and the Einstein Solid State Spectrometer show that the X-ray spectrum is extremely soft relative to the vast majority of galactic accretion-driven X-ray sources, but similar to that of black hole candidates in their 'high state'. Rapid approximately 1 s flickering comparable to that seen from Cyg X-1 in its low state was not detected. In the 1977-1979 interval LMC X-3 was for most (if not all) of its time in a 'high state'. The fact that several other steady and transient X-ray sources also have similarly soft X-ray spectra and should be regarded as potential black hole candidates is noted. The spectra of these sources are not well described by any one simple model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 354-359
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  • 158
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    Ultraviolet spectroscopy of the planetary nebula in the Fornax galaxy (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The planetary nebula in the Fornax dwarf spheroidal galaxy is carbon rich, according to calculations based on measurements of the 1909 A emission line doublet of semiforbidden C III obtained with the International Ultraviolet Explorer. The ratio N(C)/N(O) is approximately equal to 3.7, comparable to the largest reliably determined carbon/oxygen ratios in high excitation planetaries of the Milky Way. The present result is based on four low-dispersion spectra with a combined exposure time of 27.2 hours; the Fornax planetary nebula is probably the most distant known planetary that can be observed with IUE. The IUE data were analyzed together with visible-wavelength emission-line fluxes reported by Danziger et al. (1978) to compute abundances for various elements. In terms of chemical composition, the Fornax nebula resembles planetary nebulae in the Magellanic Clouds more closely than it does typical or carbon-rich planetaries in the Galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 615-617
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  • 159
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    Notes on the system TV Geminorum (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Low-resolution SWP spectra and high-resolution LWR spectra of the SRc variable star TV Gem have been studied. The available ultraviolet spectrophotometry and UBV photometry of the system can be interpreted in terms of the blended light from a B3.5 IV star and an M1 Iab star. The separation of the two stars is less than about 3 arc sec. Since the magnitude difference is a minimum in the B filter, being about 1.6 mag there, direct observation of TV Gem in a passband at 4400 A under conditions of good seeing might reveal the blue companion. No evidence was found for absorption lines of Mg II formed in the part of the wind of the M star which is projected against the disk of the B star.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 96; 305-309
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  • 160
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    The line continuum luminosity ratio in active galactic nuclei - or, on the 'Baldwin effect' (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The luminosity dependence of the equivalent width of CIV in active galaxies, the 'Baldwin' effect, is shown to be a consequence of a luminosity dependent ionization parameter. This law also agrees with the lack of a 'Baldwin' effect in Ly alpha or other hydrogen lines. A fit to the available data gives a weak indication that the mean covering factor decreases with increasing luminosity, consistent with the inference from X-ray observations. The effects of continuum shape and density on various line ratios of interest are discussed. Previously announced in STAR as N83-35975
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 558-563
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  • 161
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    High-sensitivity IRAS observations of the Chamaeleon I dark cloud (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Very sensitive IRAS observations of a region of 0.8 sq deg in the Chamaeleon I cloud have revealed 70 compact sources. Hot sources are field stars; warm sources are associated with pre-main-sequence (PMS) stars in the cloud center; others may be in an even earlier phase of gravitational collapse. Cool sources, detected only at the long wavelengths, surround the main cloud and appear to be associated with small globules. Only a small fraction (less than 20 percent) of the total luminosity of the known PMS objects is emitted in the IRAS bands. This has important implications for the classification of the newly discovered embedded objects.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 278; L53-L55
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  • 162
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    The high-energy X-ray spectrum of Centaurus XR-3 observed from OSO 8 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of the X-ray binary Cen XR-3 in the 20-120 keV energy range by means of OSO 8's high energy X-ray spectrometer, during July 16-19, 1975, and July 5-14 and 28-29, 1978, indicate that the source was in a high luminosity state during 1975 and a low luminosity one in 1978. While mean orbital light curves appear similar in shape in both years, orbit-to-orbit intensity variations are noted. Spectral, luminosity, and the 4.84 sec modulation are characterized. Cen XR-3 may be a system in which mass transfer by Roche lobe overflow, and by accretion from a stellar wind, are both effective in the production of observable X-ray radiation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 266-269
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  • 163
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    IUE and ground-based observations of the Hubble-Sandage variables in M31 and M33 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Ultraviolet spectra were obtained from the International Ultraviolet Explorer for the brightest Hubble-Sandage (H-S) variables in M31 and M33. The ultraviolet fluxes were then used in combination with ground-based visual and infrared photometry to determine the energy distributions, luminosities, and temperatures of these stars. When corrected for interstellar extinction, the integrated energy distributions yield the total luminosities and blackbody temperatures of the H-S variables. The resulting bolometric magnitudes and temperatures confirm that these peculiar stars are indeed very luminous, hot stars. They occupy the same regions of the bolometric magnitude vs temperature diagram as Eta Car and P Cyg in the Galaxy and S Dor in the LMC.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 124-136
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  • 164
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    The gamma-ray spectrum of Centaurus A - A high-resolution observation between 70 keV and 8 MeV (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The NASA/Goddard Space Flight Center Low Energy Energy Gamma ray Spectrometer (LEGS) observed the nearby active nucleus galaxy Centaurus A (NGC 5128) during a balloon flight on 1981 November 19. There is no evidence of a break in the spectrum or of any line features. The 1.6 MeV limit is a factor of 8 lower than the 1974 line flux, indicating that, if the 1974 feature was real, and, if it was narrow, then the line intensity decreased significantly between 1974 and 1981. The lack of observed annihilation radiation from Cen A, combined with the temporal variations that are seen in the X-ray and gamma-ray intensities, constrain the size of the emission region to be between 10 to the 13th power and 5 x 10 to the 17th power cm. Previously announced in STAR as N83-35990
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 112-118
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  • 165
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    Protostellar formation in rotating interstellar clouds. IV Nonisothermal collapse (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Radiative transfer in the Eddington approximation is included in a multidimensional, self-gravitational, hydrodynamical computer code. Details of the numerical solution and thermodynamic relations are given. Comparison calculations with previous spherically symmetrical models of protostellar collapse are used to validate the basic approach and the artifices which allow the explicit hydrodynamics code to follow the accretion of gas onto a quasi-equilibrium core. A series of axisymmetric models is used to investigate the importance of rotation in collapsing clouds, as the initial amount of angular momentum is lowered, with an emphasis on the possible formation of rings. Rings readily form even in the nonisothermal regime except for very low initial angular momenta; even these clouds may experience ring formation prior to reaching stellar densities. The models imply that other effects (such as gravitational torques or turbulent viscosity) may be necesary to avoid binary formation and thus result in a presolar nebula consistent with the assumptions of either Safronov or Cameron.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 277; 768-782
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  • 166
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    Photon escape probabilities in a semi-infinite plane-parallel medium (1984)
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    Publication Date: 2011-08-18
    Description: It is shown in this work how to obtain the probabilities of photons escaping from a cold electron plasma environment after having undergone an arbitrary number of scatterings. This is done by retaining the exact differential cross section for Thomson scattering as opposed to using its polarization and angle averaged form. The results are given in the form of recursion relations. The geometry used is the semi-infinite plane-parallel geometry witlh a photon source located on a plane at an arbitrary optical depth below the surface. Analytical expressions are given for the probabilities which are accurate over a wide range of initial optical depth. These results can be used to model compact X-ray galactic sources which are surrounded by an electron-rich plasma.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 691-705
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  • 167
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    Long-period classical Cepheids - Theory versus observation (1984)
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    Publication Date: 2011-08-18
    Description: New full amplitude models of classical Cepheids having periods longer than 13 days have been calculated, allowing the complete systematics of the observed light and velocity curves of classical Cepheids to be discussed in detail. Assuming that a normal evolutionary mass-luminosity relation is obeyed, the models reproduce such empirical phenomena as the full Hertzsprung progression of light and velocity curves and the gradual shift in phase of the Hertzsprung bump, together with the persistence in phase of the postmaximum shoulder on the light curve. Also reproduced are the retardation of maximum expansion velocity after maximum light, the correlation of light and velocity amplitudes, and the period-amplitude scatter diagram for both the light and the velocity amplitude. The average period predicted for a Cepheid light curve type is noted to be about 40 percent longer than that actually observed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 593-601
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  • 168
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    Radio emission from the outer parts of stellar atmospheres (mantles) at centimeter wavelengths and the winds of early-type stars (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is noted that when magnetic lines of force are present in the mantle of an early-type star, gyroresonance radiation at radio wavelengths may occur at detectable levels in addition to bremsstrahlung. An expression is derived for the effective value of the ratio of the emissivity in gyroresonance radiation to that in bremsstrahlung, and some numerical values are estimated using values of the parameters which may be typical for conditions in the mantles of early-type stars. The volume emissivity in gyroresonance radiation may exceed that for bremsstrahlung by a large factor. The implications of this result for the interpretation of the radio fluxes from early-type stars are discussed. It is shown that the radio-frequency radiation emerging from a hot star probably consists of gyroresonance radiation from an array of magnetic loops as well as bremsstrahlung from a low-density wind. It is argued that it is probable that the estimates of rate of mass loss made ignoring the possibility of gyroresonance radiation may be too large by a factor of at least 10.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 583-592
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  • 169
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    Variability of the ultraviolet spectrum of BL Lacertae objects (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Attention is given to repeated observations of the two nearby BL Lac objects, Mrk 421 and PKS 0521-36, comparing the temporal behavior of their continuum in the 1300-3000 A range with that observed in intrinsically bright BL Lac objects and in Seyfert galaxies. Also discussed are the emission lines in the UV and optical spectrum of PKS 0521-36. It is suggested that the difference in variability pattern between BL Lac objects and Seyfert galaxies may be due to differences in the properties of the nonthermal continuum related to differences in accretion regimes, although it is more probably due to the presence of different continuum components in Seyfert galaxies. In BL Lac objects, the UV spectrum is likely to be synchrotron radiation from an optically thin source.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 466-471
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  • 170
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    4.6 micron absorption features due to solid phase CO and cyano group molecules toward compact infrared sources (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 533-543
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    Texas Symposium on Relativistic Astrophysics, 11th, Austin, TX, December 12-17, 1982, Proceedings (1984)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: Various papers on relativistic astrophysics are presented. The general subjects addressed include: particle physics and astrophysics, general relativity, large-scale structure, big bang cosmology, new-generation telescopes, pulsars, supernovae, high-energy astrophysics, and active galaxies.
    Keywords: ASTROPHYSICS
    Type: (ISSN 0077-8923)
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  • 172
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    The composition of interstellar grain mantles (1984)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: The molecular composition of interstellar grain mantles employing gas phase as well as grain surface reactions is studied. The calculated mixtures consist mainly of the molecules H2O, H2CO, N2, CO, O2, CO2, H2O2, NH3, and their deuterated counterparts in varying ratios. The exact compositions depend strongly on the physical conditions in the gas phase. The calculated mixtures are compared to the observations by using laboratory spectra of grain mantle analogs. The two are in reasonable agreement except for the strength of the 6.8-micrometers band. A possible solution for this discrepancy is discussed. Finally, future observations are suggested which may shed further light on the composition of interstellar grain mantles.
    Keywords: ASTROPHYSICS
    Type: Royal Observatory Proc. of the Workshop on Lab. and Observational Infrared Spectra of Interstellar Dust; p 41-48
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  • 173
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    Dust in space and comets; Proceedings of the Topical Meeting, Graz, Austria, June 25-July 7, 1984 (1984)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: Consideration is given to: the mass loading of planetary magnetospheres by rocky satellites; the effects of electrostatic forces on the vertical structure of planetary rings; and dust motion in Jupiter's tilted magnetic field. Other topics include: IRAS observations of cometary dust; dust environment models for Comet P/Halley; plasma processes and solar wind interaction; and cometary interplanetary field enhancements in the solar wind. Consideration is also given to: the impact of dust grains on fast fly-by spacecraft; EUV observations of Comet Halley; and the thermal model and thermo-mechanical stresses in cometary nuclei.
    Keywords: ASTROPHYSICS
    Type: (ISSN 0273-1177)
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  • 174
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    Meteoroid capture into earth orbit by atmospheric drag (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A probabilistic analysis, based on orbital mechanics, is performed to evaluate the chances of meteoroids entering into earth orbit and the potential population of such objects. The problem is addressed in terms of meteoroids on earth collision courses, slowed by atmosphere entry/exit, entering elliptical orbits with apogees above the atmosphere. The overall capture probability is derived by integrating the capture fraction dependence on velocity and size over the probability frequency distribution of the collision courses. Account is taken of eventual orbit decay, lunar infall and ejection after encounters with the moon. The results indicate that the probability that a natural 10-100 m diam object has achieved earth orbit is negligibly small.
    Keywords: ASTROPHYSICS
    Type: AIAA PAPER 84-2055
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  • 175
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    Astrophysical materials science: Theory (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A method of structural expansions for use in determining the equation of state of metallic hydrogen (and indeed other metals) up to the 4th order in the perturbation theory was developed. The electrical and thermal transport properties of the planetary interior of Jupiter were calculated. The nature of the interaction between molecules at short range and the importance of multicenter terms in arriving at an adequate description of the thermodynamic functions of condensed molecular hydrogen were also investigated.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-177021 , NAS 1.26:177021
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    Circumstellar Dust Disks Around Young Stars (1984)
    In:  CASI
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    Publication Date: 2014-09-17
    Description: Kuiper Airborne Observatory observations of several resolved far-infrared structures that are likely to represent disks formed during the process of the collapse of a cloud to form a star are discussed. An infrared radiation nebula, star HH57, and SVS13 were studied. Forty seven and 95 micron maps of far infrared radiation are given.
    Keywords: ASTROPHYSICS
    Type: Airborne Astron. Symp.; p 199-203
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  • 177
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    Carbon Stars: There Is No Such Thing as a Dead Leg (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-17
    Description: The spectra of carbon stars is discussed. Spectral flux curves, molecular bands, molecular absorptions, stellar temperatures, and comparison of emission features in various carbon stars are among the topics considered.
    Keywords: ASTROPHYSICS
    Type: Airborne Astron. Symp.; p 204-223
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  • 178
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    Interstellar Grain Mantles (1984)
    In:  CASI
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    Publication Date: 2014-09-17
    Description: Techniques for determining the composition of small dust grains in interstellar matter are discussed. The best way to study the composition of interstellar grain mantles is by infrared spectroscopy. The absorption features in a complete infrared spectrum from 2 to 15 microns can be used as fingerprints to identify the absorbing molecule. Ground-based observations around 3 microns confirmed the presence of H2O ice in interstellar grain mantles, through the detection of the 3.08 micron OH stretching vibration. The detection of other molecules, in particular the carbon bearing molecules, is however hampered by atmospheric absorption in the 5-8 micron region and the presence of the strong ice and silicate bands, which dominate the 3 and 10 micron region respectively. Kuiper Airborne Observatory observations of the 5-8 micron region of the spectrum are therefore extremely important to determine the composition of interstellar grain mantles. The 5 to 8 micron spectra of molecular cloud sources was obtained using a 24 detector grating spectrometer. An important characteristic of this spectrometer is that the whole spectrum is obtained simultaneously. It is therefore relatively easy to correct for atmospheric transmission.
    Keywords: ASTROPHYSICS
    Type: Airborne Astron. Symp.; p 240-246
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  • 179
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    Magnetic Alignment Theory and the Interpretation of Polarization (1984)
    In:  CASI
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    Publication Date: 2014-09-16
    Description: The theory of magnetic spinning alignment is outlined. It is shown that a classical enhanced thermal Davis and Greenstein mechanism may be considered as a limiting case of Purcell's suprathermal spinning alignment theory when the number of active sites on a given grain becomes very important and/or for very short lived suprathermal sites. The results are applied to the interstellar medium and some problems in which it may be important are discussed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 315-318
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    A Wide Latitude CO Survey of Molecular Clouds in the Northern Milky Way (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: It is now well established that molecular clouds are an important part of the interstellar medium, containing much or most of the dense, cold component of the gas, and producing the massive stars and supernovae responsible for the diffuse, hot component. It would therefore appear essential in formulating a complete picture of the local interstellar medium to have some knowledge of the distribution and properties of nearly molecular clouds. The Goddard-Columbia 1.2 meter telescope was used to carry out a wide latitude, low angular resolution survey of CO along most of the first galactic quadrant and a small part of the second. A plane-of-the-sky map, which resulted from numerically integrating the survey over radial velocity, is presented. The Great Rift and the Aquila Rift molecular clouds of the Milky Way are discussed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 235-238
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    Distances of Local Clouds from Optical Line Observations (1984)
    In:  CASI
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    Publication Date: 2014-09-16
    Description: The interstellar D-line of Na 1 toward 49 stars were observed in order to determine the distance (125 plus or minus 25 pc) to a cold H 1 cloud. This sheet of gas may be part of the back side of the shell formed by the Loop I supernova.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 117-121
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    IUE Observations of the Gaseous Component of the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Discovery of interstellar Ge, Ga, and Kr is reported. Several intercombination lines of Fe 2 are detected. The depletion is most pronounced in Ca, Ti, and V. The highly ionized gas C 4 and Si 4 is not co-extensive with the Si 2 and C 2 gas nor with the O 6 gas. The molecular gas (CO) shows very small velocity dispersion (b approximately 1 km/sec). HD 149404 has the richest interstellar spectrum (except molecules) of all the stars in this study. HD 147889, the heavily obscured star in the Rho Oph cloud, has the strongest interstellar CO spectrum. Noisy nature of the spectra precludes detection of other molecules.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 89-90
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    A Type Stars as Probes of the Local Interstellar Medium (1984)
    In:  CASI
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    Publication Date: 2014-09-16
    Description: With the aim to sample the Local Interstellar Medium (LISM), it was proposed to use A stars as targets. The Mg II UV lines seem to be the best interstellar absorption candidates. Several hundreths of A stars can be reached within 100 pc. First preliminary results (20 lines of sight) are presented, based on previous Copernicus and actual IUE observations.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 75-80
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  • 184
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    Dark Matter near the Sun: Simulated Star Counts and the Oort Limit (1984)
    In:  CASI
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    Publication Date: 2014-09-16
    Description: An ensemble of orbits passing through the solar position was generated for a specific mass model of the galaxy. These orbits are randomly sampled to form simulated density distributions of tracer stars perpendicular to the galactic disk. The simulated distributions are analyzed to determine the sampling errors in a self consistent derivation of the total amount of matter near the Sun (the Oort limit).
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 326-331
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    Measuring EUV Line Emission from the Hot Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: In the local interstellar medium, the presence of hot gas was inferred from measurements of oxygen VI absorption in the ultraviolet, and from diffuse emission in the extreme ultraviolet (EUV) and soft X-ray regions. A spectrometer that is very sensitive to gas in this temperature range is described. The spectrometer uses an array of plane ruled gratings at grazing incidence in the extreme off plane mount. A set of Kirkpatrick-Baez mirrors focuses the conically diffracted light on to one of two microchannel plate detectors. The field of view of the instrument is 0.2 deg by 12 deg. The predicted sensitivity ranges from 50 to 200 ph/(sq cm sec str) with a resolving power of 15 to 50 over the 50 to 700 angstrom wavelength band.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 348-352
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    Future Studies of the Local Interstellar Medium with Space Telescope and Columbus (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The spectrographs aboard Space Telescope and Columbus which will provide important new information about the interstellar medium in the immediate vicinity of the sun are described. The space telescope's highest resolution is adequate to define the multicomponent nature of interstellar absorption lines and to measure thermal line widths exceeding 3 km/s. The Columbus spacecraft will contain spectrographs capable of resolutions of 3 x 10 to the 4th power between 912 and 1200 A and 500 between 100 and 900 A. In the short wavelength region, lines of He I and II, are observable. If the 3 x 10 to the 4th power resolution spectrograph provides extended wavelength coverage to 770 A, lines of Ne VIII which are expected from 8 x 10 to the 5th power K gas are accessible. The ST HRS and Columbus spectrographs enable the study of a wide range of problems relating to cold, warm, and hot gas in the local ISM.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 333-343
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  • 187
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    Large-scale Bubble Structure of the Intersteller Medium (ISM) and Properties of the Local Spiral Arm (LSA) (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Bubbles which are very common structure units in the Galaxy and galaxies were examined. Collection of radio, optical, infrared and X-ray observations of the Cyg superbubble (CSB) region of the sky show that the CSB is not a single bubble object. Between 50 to 75 percent of its X-ray emission is ascribed to discrete sources. The other 25 to 50% X-ray emission, probably originates from bubbles around 8 OB associations of the region. All bubbles located within the spiral structure of Galaxy, M31 and M33 have diameter 300 pc. The large distance of stellar association from the galactic plane (GP) combined with picture of the gas distribution within the LSA shows that a Reyleigh-Taylor instability in the LSA can develop and give use to the formation of compact stellar clusters, such as the Cyg OB2 association. Development stages of the Reyleigh-Taylor instability, some peculiarities of the dust distribution and departures of the local structure from the galactic grand design suggest the absence of a spiral shockwave in the LSA.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 305-310
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    The Parallax of Pulsar 0950+08 and the Local Free Electron Density (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: A parallax of 7.9 + or - 0.8 mas for PSR 0950+08, corresponding to a distance of 130 + or - 15 pc is reported. The measured pulse dispersion of this pulsar implies an average free electron density of 0.023 + or 0.002/cu cm along the line of sight. This parallax measurement is subject to systematic errors and questions of interpretation which are not yet fully explored.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 281-283
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  • 189
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    Polarization of radio molecular lines and mapping of magnetic field direction (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Two level calculations by others for the linear polarizations expected for molecular emission lines from interstellar clouds are extended by considering a number of coupled rotational states of a diatomic molecule. Higher transitions commonly have strengths comparable with that of the J=1-0 transition so that depolarization due to coupling between the various J states might be expected to reduce the predicted linear polarization. The significance of the null observational results obtained recently by Wannier, Scoville, and Barvainis is assessed. The inclusion of additional states tends to decrease the maximum polarizations, though the calculated polarization is increased under conditions for which superthermal excitation occurs.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 274-275
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  • 190
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    The Smallest Sizes of Diffuse Interstellar Clouds (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: By observing the difference in optical depths between absorption spectra toward the two components of double sources, the variations in opacity over lengths of less than 0.1 up to 10 pc inside diffuse interstellar clouds were measured. Significant variations were detected on scales larger than about 0.2 pc, but not less. This may represent the minimum size for diffuse cloud structure. By comparing the variations of Gaussian fitted line parameters, it was found that variations in the internal velocity field of diffuse clouds explain the data better than tiny independent cloudlets.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 258-262
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  • 191
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    Absorption Line Studies and the Distribution of Neutral Gas in the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Previous published absorption line studies performed at ultraviolet and visual wavelengths are combined with new ultraviolet data in order to map out the distribution of HI within 150 pc of the Sun. Newly presented data for distances less than 50 pc further support the local cloud model as presented by Bruhweiler (1982). The Sun is embedded, near the edge of a diffuse cloud with total column density 2 x 10 to the 19th power/sq cm. Most observed directions within 50 pc away from the cloud body reveal trace amounts of gas (N)HI) approximately 10 to the 18th power/sq cm presumably arising in the outer skin of the local cloud. At greater distances (50 approximately or d approximately or 150 pc) most directions show significant absorption with N(HI) 10(19)/sq cm. Two directions, one toward the northern galactic pole (NGP), the other toward beta CMa exhibit unusually low HI column densities out to distances of 150 to 200 pc. However, substantial amounts of gas N(HI) 10 to the 19th power/sq cm, are seen toward the NGP at greater distances. The implicatons of these results on astronomy at wavelengths shortward of 912A are discussed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 39-50
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  • 192
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    Broadening of the Interplanetary Helium Cone Structure Due to Elastic Collisions of LISM Helium Atoms with Solar Wind Ions (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Neutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the Sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 32-37
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  • 193
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    Helium and Hydrogen of the Local Interstellar Mdium Observed in the Vicinity of the Sun (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The Sun illuminates the hydrogen and helium atoms of the interstellar medium through which it travels. As a result, the Sun and the whole solar system are imbedded in a glow of the resonance lines of hydrogen (H Lyman alpha; 121.6nm) and helium (58.4nm). From the intensity distribution of the glow in the solar system, the density of H and He in the local interstellar medium (LISM) and the direction of the relative motion between the Sun and the LISM in the vicinity of the Sun are derived. The velocity module and the LISM temperature are more adequately found from a measurement of the Lyman alpha line shape, which is an image of the velocity distribution of H atoms. The result is summarized and together the methods of interpretation and difficulties are dicusssed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 3-23
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  • 194
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    Optical Emission Line Studies and the Warm, Ionized Component of the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Observations of diffuse, galactic H alpha, N2 lambda 6583, and S2 6716 emission lines provide evidence for a warm (10,000K), primarily ionized component of the interstellar medium distribution throughout the galactic disk. This component of the interstellar gas has an electron density approximately equals 0.1-0.2/cu cm and occupies about 10 to 30% of the interstellar volume. Interstellar H alpha emission near the galactic poles, the dispersion measure of a nearby pulsar, and observations of interstellar gas flowing into the solar system indicate that this ionized component is an important constituent of the interstellar medium in the solar neighborhood. The intensity of the H alpha background at high galactic latitudes implies that this component is maintained by an average hydrogen ionization rate in the vicinity of the Sun of (2-4) x 100,000 s(-1) per square cm of galactic disk. The emission measure is 1.3 to 2.3 cm (-6) pc toward the galactic poles. The sources of this ionization were not identified but may include escaping Lyman continuum radiation from planetary nebulae, hot white dwarfs, and early type stars.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 97-108
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  • 195
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    Deuterium Abundance in the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The present situation of deuterium abundance evaluation in interstellar space is discussed, and it is shown that it should be or = .00001 by studying in more detail lambda the Sco line of sight and by observing two NaI interstellar components toward that star, it can be shown that the D/H evaluation made toward lambda Sco is in fact related to the local interstellar medium (less than 10 pc from the Sun). Because this evaluation is also or = .00001 it is in striking contrast with the one made toward alpha Aur (D/H or = .000018 confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 84-88
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  • 196
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    Feii and Mgii in the Nearby Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Ultraviolet spectra with 15 km/s resolution of bright stars were searched for FeII and MgII interstellar lines. Equivalent widths of absorption for 8 stars are presented and average line-of-sight densities n(FeII) = 4 x 10(-8) and n(MgII) = 2 x 10(-7)/cubic cm are calculated. This represents approximately n(H) = 0.03/cuib cm.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 71-74
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  • 197
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    Observations of Interstellar HI Toward Nearby Late-type Stars (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: High-disperson Copernicus and IUE observations of chromospheric Ly alpha emission are used to study the distribution of HI in the local interstellar medium. Interstellar parameters are derived toward 3 stars within 5 pc of the Sun, and upper limits are given for the Ly alpha flux from 9 other stars within 10 pc.
    Keywords: ASTROPHYSICS
    Type: Local Interstellar Medium, No. 81; p 61-63
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  • 198
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    Particle Acceleration (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-13
    Description: A phenomenological account of particle acceleration is provided along with a detailed summary of the current status of theoretical studies of particle acceleration. Problems are presented which remain when specific mechanisms and observations are confronted. The following specific topics are addressed: solar particle acceleration, interplanetary particle acceleration, and extrasolar particle acceleration.
    Keywords: ASTROPHYSICS
    Type: Solar Terrest. Phys.; 52 p
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  • 199
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    A Model of the Soft X-ray Background as a Blast Wave Viewed from Inside (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The suggestion that the soft X-ray background arises in part from the Sun which is inside a large supernova blastwave was examined by models of spherical blastwaves. The models can produce quantitative fits to both surface brightnesses and energy band ratios when t = 10 to the 5th power E sub o = 5 x 10 to the 50th power ergs, and n sub approx. 0.004 cm to the -3 power. The models are generalized by varying the relative importance of factors such as thermal conduction, Coulomb heating of electrons, and external pressure; and to allow the explosions to occur in preexisting cavities with steep density gradients, or by examination of the effects of large obstructions or other anisotrophies in the ambient medium.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 297-300
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  • 200
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    The Z-dependence of the Spin Temperature of HI (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Results relating to the following aspects of hydrogen clouds are presented: (1) the vertical distribution of cold H T clouds; (2) possible systematic warming of H T clouds at high absolute values of z; (3) possible increase of the fraction of warm intercloud medium H T with high absolute values of z; and (4) the effect of optical depth on previous H T emission surveys.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 269-273
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