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  • ASTROPHYSICS  (432)
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  • 2020-2024
  • 1975-1979  (433)
  • 1977  (433)
  • 1
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    The Soviet-American Conference on Cosmochemistry of the Moon and Planets, Part 2 (1977)
    In:  CASI
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    Publikationsdatum: 2019-08-28
    Beschreibung: The origin and evolution of the solar system is discussed based on ground and satellite observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-SP-370-PT-2 , LC-75-600013 , Soviet-American Conference on Cosmochemistry of the Moon and Planets; Jun 04, 1974 - Jun 08, 1974; Moscow; Russia
    Format: application/pdf
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  • 2
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    X-ray bursts - The maximum mass of a neutron star (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-08-28
    Beschreibung: A review of the great variety of observed properties of X-ray burst sources is presented, including the MXB 1730-355, called the rapid burster. Hypotheses regarding the sources of bursts are discussed, and two models for the rapid burster are described. The first postulates that they are caused by a collapsed object with a mass of approximately 10 solar masses surrounded by a disk of gas spiralling inward. The second posits a neutron star with a strong magnetic field. Theoretical questions regarding the mass of neutron stars are discussed, and prerequisites for such research are identified. Various research projects investigating these questions are described.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Mercury; 6; July-Aug
    Format: text
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  • 3
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    Contraction of the Orion Nebula cluster-molecular cloud A complex (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-08-28
    Beschreibung: Observational evidence is presented in support of the view that the width of the molecular lines in Orion is produced by a contraction of the cloud with a velocity directly proportional to the distance from the cloud center. The main support is provided by close agreement between the motions of the cloud and that of the stars embedded in it. A further implication of this agreement is that star formation occurred throughout the Orion cloud, rather than only in the dense center as predicted by the conventional picture of star formation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 217
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  • 4
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    Evolution of the moon: The 1974 model (1977)
    In:  CASI
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    Publikationsdatum: 2019-08-27
    Beschreibung: The interpretive evolution of the moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows: (1) The Beginning: 4.6 billion years ago, (2) The Melted Shell: 4.6 to 4.4 billion years ago, (3) The Cratered Highlands: 4.4 to 4.1 billion years ago, (4) The Large Basins: 4.1 to 3.9 billion years ago, (5) The Light-colored Plains: 3.9 to 3.8 billion years ago, (6) The Basaltic Maria: 3.8 to 3.0(?) billion years ago, and (7) The Quiet Crust: 3.0(?) billion years ago to the present. The contributions of the Apollo and Luna exploration toward the study of those stages of evolution are reviewed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 63-80
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  • 5
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    On the emission of neutrinos and gravitational waves in the formation of neutron stars (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-08-27
    Beschreibung: The various modes in which the energy generated by the formation of a neutron star or black hole due to collapse of a stellar core can appear are investigated, and physical constraints are placed on this energy distribution by noting that neutron stars appear to have been found in at least six X-ray binaries and one binary pulsar. The energy generated by a supernova during the collapse of a stellar core to a neutron star is considered along with the manner in which this energy is distributed in the different modes. It is shown that the gravitational binding energy of a neutron star is converted mostly into kinetic energy of rotation or is emitted as neutrinos, gravitational waves, or both. The energy release through mass ejection and cosmic rays is suggested to be no more than a few percent of the total energy involved. A possible scenario is outlined for the case where the initial rotation velocity of the collapsing core exceeds some critical limit. It is concluded that gravitational radiation will be the ultimate outlet for most of the binding energy in this case.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science; 51; 1, Se; Sept
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  • 6
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    Results of special mechanical analyses of Luna 16 material (1977)
    In:  CASI
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    Publikationsdatum: 2019-08-27
    Beschreibung: The studies carried out on the Luna 16 regolith have confirmed the data that were already published internationally. By means of activation analysis under irradiation in the reactor, activation analysis with a 14 MeV U-generator, and mass spectroscopy on samples of 10 or 20 mg, six main and 63 trace elements were quantitatively determined and compared with known data.
    Schlagwort(e): ASTROPHYSICS
    Materialart: The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, Pt. 2; p 697-702
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  • 7
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    Metal abundance in the Praesepe and Hyades clusters (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-08-27
    Beschreibung: Calcium K-line photometry is reported for 27 A-type stars in the Praesepe cluster, and the data obtained are compared with previous K-line observations of Hyades stars. It is found that calcium and other metals are generally overabundant in Praesepe relative to field stars and that there is a considerable scatter in metal-abundance indices. Comparison with the Hyades results indicates that the Praesepe stars are as metal-enriched as the Hyades stars. These results are taken as evidence favoring Eggen's (1960) proposal that the Hyades and Praesepe clusters should be regarded as a single group having, on the average, about a factor-of-two higher metal abundance than solar-neighborhood field stars as well as a high internal dispersion in metal-line strengths. The questions of where and how the Praesepe-Hyades stars acquired their high average metal abundances, K-line strengths, and associated dispersions are briefly considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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  • 8
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    Exploding stars, pulsars and black holes in space (1977)
    In:  CASI
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    Publikationsdatum: 2019-08-13
    Beschreibung: Brief factual reviews are provided for supernovae, pulsars and neutron stars, and black holes. Also discussed in general terms are red giants, white dwarfs, quasars and radio galaxies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-NEWS-RELEASE-77-243 , P77-10242
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  • 9
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    Arguments and evidence concerning non-cosmological redshifts - A partial summary (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Theories which imply an unconventional interpretation of the redshifts are examined, taking into account a new theory of cosmology reported by Segal, scenarios in which the redshifts do not arise from the expansion, and studies concerning a possible existence of systematic effects in the distribution of redshifts. Attention is given to rapidly varying QSOs and BL Lac objects, VLBI studies of a number of QSOs and related objects, and physical associations between objects with very different redshifts. It appears that observational evidence concerning these physical associations is the strongest evidence that objects with large noncosmological redshift components exist. On the other hand, there are a number of cases of QSOs close to galaxies at the same redshifts.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Conference on the evolution of the galaxies and its cosmological implications; Sep 08, 1976 - Sep 09, 1976; Paris; France
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  • 10
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    Temperature of solid particles in colloidal plasmas in space (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Lehnert (1970) has investigated the question of the relationship between the kinetic temperature and the internal temperature at which a solid coexists with a plasma in a thermal steady state. The reported investigation is a more refined version of Lehnert's preliminary analysis of this relationship. The electric potential of grains is considered along with the ambient radiation field and the grain temperatures in the thermal steady state. An illustrative calculation is conducted of the grain temperatures in the dense regions of the primordial circumsolar colloidal plasma envelope such as envisioned in the Alfven-Arrhenius model (1976) of the origin of the solar system. It is shown that under certain conditions the solid grains can coexist with the plasma phase up to fairly high plasma densities and temperatures.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Lunar Science Conference; Mar 14, 1977 - Mar 18, 1977; Houston, TX
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  • 11
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    Extreme ultraviolet observations of white dwarfs (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Observations shortward of the hydrogen Lyman limit provide sensitive determinations of stellar temperatures and interstellar absorption. Such data are of particular value in studies of hot white dwarfs, for which a large fraction of the emission occurs in the extreme-ultraviolet band (100-1000 A). Observations of HZ 43 and Feige 24 have been obtained with the Apollo-Soyuz extreme-ultraviolet telescope; both stars are copious EUV emitters, with four billionths and three billionths erg/sq cm sec in the 170-620-A band, respectively. The EUV data, combined with optical spectrophotometry, allow their temperatures to be estimated as 80,000 and 60,000 K, respectively. The corresponding interstellar neutral hydrogen column densities are about 4 by 10 to the 18th power per sq cm.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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  • 12
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    Hot gas in clusters of galaxies (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Radio and X-ray observations are discussed which seem to favor the presence of a hot intracluster gas in rich clusters of galaxies. On the assumption that the X-rays are produced by thermal bremsstrahlung, a temperature of the order of 100 million K and a density of a few thousandths per cu cm are computed for the intracluster gas. Theories on the origin and dynamics of this gas are reviewed, and the discovery of an iron line in the spectrum of the Perseus cluster is taken as strong evidence for thermal emission from a hot intracluster gas. Effects of and on the intracluster gas are considered, particularly the formation of radio-tail galaxies due to ram pressure on the galaxies in rich clusters, stripping of interstellar gas from the galaxies, and heating of the intracluster gas by the galaxies. It is concluded that the intracluster gas: (1) originated partially in primordial matter that collapsed into the clusters and partially in gas lost from the galaxies, (2) is in static or almost static equilibrium in the clusters, and (3) either is tightly bound or has an equation of state corresponding to a gamma value of less than 5/3.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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  • 13
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    OSO-8 X-ray polarimeter and Bragg crystal spectrometer observations (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Results are discussed for observations of the Crab Nebula, Cyg X-1, and Cyg X-2 with the focusing mosaic graphite crystal X-ray polarimeter aboard OSO-8 as well as for observations of A0620-00 with the Bragg crystal spectrometer aboard the same satellite. The observed X-ray polarization of the Crab Nebula is shown to be in agreement with a previous measurement of the optical polarization and to confirm with very high confidence the earlier conclusion that the X-ray emission occurs by the synchrotron process. No evidence is found for polarization of X-rays from Cyg X-1, but a preliminary result of 4.8% + or 1.0% polarization at an energy of 2.6 keV and a position angle of 141.7 + or - 6.6 deg is reported for Cyg X-2. It is noted that this value is within the range expected for accretion disks. The spectrometry of A0620-00 yielded a continuous spectrum that can be accurately fitted with a thermal bremsstrahlung spectrum at a temperature of 15 million K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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  • 14
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    The origin of comets (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Empirical data related to questions regarding the origin of comets are examined, taking into account the primitive temperature and its evolution, the cometary C-12/C-13 isotope ratio, the chemistry of comets, and the solar-system related orbits of the comets. The theories of cometary origin considered are related to a condensation of comets from the solar nebula and a later ejection into Oort's cloud, a recent condensation of comets in situ, a capture of interstellar comets, and a reversal of the arrow of time in the traditional evolution of comets. The only hypothesis which seems to survive an evaluation of the theories on the basis of the existing data is that the comets were condensed some five billion years ago in the vicinity of the giant planets or beyond, at the outer edge of the solar nebula.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 15
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    Isotopic abundances in interstellar clouds (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Results of microwave measurements in dense interstellar clouds are discussed which pertain to determinations of relative isotopic abundances. Difficulties in deriving relative abundances from observations of the relative intensities of isotopic lines are examined, and measures available for coping with these complications are outlined. Results are presented concerning the relative abundances of C-13, O-17, O-18, N-15, Si-30, S-33, S-34, and D in a variety of interstellar clouds; the consistency of these results is evaluated. It is concluded that: (1) the relative abundances of C-13 and O-17 in interstellar clouds are generally higher than those in the solar system; (2) the abundances of N-15 and D are lower than the solar-system values; (3) the O-18 abundance is possibly higher than in the solar system; and (4) there are substantial variations in the isotopic abundances between different large interstellar clouds, with some of these variations not dependent on distance from the galactic center alone.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Topics in interstellar matter; Commission 34 Session, General Assembly; Aug 25, 1976; Grenoble; France
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  • 16
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    A comparison of the composition of new and evolved comets (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: The continuum to molecular emission intensity ratio in cometary spectra is examined as an indicator of initial composition of the comets. This ratio presumably measures the dust to gas ratio in comets, or the component of gas yielding visible emissions. The spectral relationships and compositions of new comets and more evolved ones are compared. No significant difference in the continuum to emission ratio was noted between new and more evolved comets, which is in contradiction to Oort's conclusion. This suggests that no systematic change occurs in the continuum to emission ratio as comets evolve from new to periodic. Perihelion passage does not seem to produce a general weakening of the continuum, although it occurs in individual cases.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 17
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    The pristine nature of comets (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Abundance considerations suggest that comets are likely to be the most pristine minor bodies in the solar system. In proportion to solar abundances, the present scanty data suggest that cometary oxygen is not depleted, whereas carbon is by a factor of 4 and hydrogen, by a factor of 2000. This implies that comets are less depleted in H, C, N, O than CI chondrites, namely 10:1 in hydrogen, 4:1 in carbon and 3:1 in oxygen. These results have been obtained by using dust-to-gas ratios in comets to measure the relative abundance of silicon and metals to volatile material, and the spectra of atomic lines, mainly from the vacuum ultraviolet, to determine the H/O and C/O ratios of the mixture of volatile molecules.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 18
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    Symposium on Recent Results in Infrared Astrophysics (1977)
    In:  CASI
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    Publikationsdatum: 2019-07-13
    Beschreibung: Abstracts of papers presented at a symposium titled Recent Results in Infrared Astrophysics are set forth. The abstracts emphasize photometric, spectroscopic, polarization, and theoretical results on a broad range of current topics in infrared astrophysics.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-TM-X-73190 , A-6856 , Jan 01, 1977; Moffett Field, CA; United States
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  • 19
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    Acceleration and modulation of electrons and ions by propagating interplanetary shocks (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: The theory and observation of shock spikes are reviewed. Models of the orbits of charged particles and their energization during interaction with discontinuities under various geometries are studied. In situ observations of shock spikes are discussed. These have shown that sharp spikes are found sometimes ahead of and sometimes behind the shock, with the highest energies being ahead. One generally observes larger, field-aligned ion anisotropies ahead of shocks rather than behind. Intensity modulation of protons, alpha particles, medium nuclei, and iron have been observed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: L. D. de Feiter Memorial Symposium; Jun 07, 1977 - Jun 10, 1977; Tel Aviv; Israel
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  • 20
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    The comet-solar wind interaction (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: The important roles of comets as natural probes of the solar wind, particularly at high heliographic latitudes and small heliocentric distances, unattained thus far by artificial space probes, is stressed. It is becoming clear the solar wind is not merely responsible for shaping and maintaining the cometary plasma tail, but is also indirectly responsible for the rapid ionization processes in the coma. Despite this, however, the detailed interaction of the solar wind with comets, which is underlined by the complex and time-varying morphology observed in the cometary head and the tail, constitutes a formidable problem, and is only very imperfectly understood at present. The current views are critically reviewed and an attempt is made to identify the dominant physical mechanisms that are involved.
    Schlagwort(e): ASTROPHYSICS
    Materialart: L. D. de Feiter Memorial Symposium; Jun 07, 1977 - Jun 10, 1977; Tel Aviv; Israel
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  • 21
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    Recent high energy gamma-ray results from SAS-2 (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Recent developments in gamma-ray astronomy due to the results from SAS-2 have focused on two areas. First, the emission from the plane of the Galaxy is the dominant feature in the gamma-ray sky. The galactic latitude and longitude distributions are consistent with the concept that the high-energy radiation originates from cosmic rays interacting with interstellar matter, and the measurements support a galactic origin for cosmic rays. Second, searches of the SAS-2 data for emission from localized sources have shown three strong discrete gamma-ray sources: the Crab nebula and PSR 0531 + 21, the Vela supernova remnant and PSR 0833-45, and a source near galactic coordinates 193 deg longitude, +3 deg latitude, which does not appear to be associated with other known celestial objects. Evidence has also been found for pulsed gamma-ray emission from two other radio pulsars, PSR 1818-04 and PSR 1747-46. A localized source near longitudes 76-80 deg may be associated with the X-ray source Cyg X-3.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 22
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    An upper limit for the flux of interstellar dust grains in the solar system (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Data from the LEAM (Lunar Ejecta and Meteorite experiment, a micrometeorite detector at the Apollo 17 landing site) have been examined for evidence of interstellar (IS) dust grains traversing the solar system. The analysis technique considers IS grains approaching the solar system from the local solar apex. A model calculates the grains' hyperbolic orbits into the solar system and predicts the impact directions on the moon. The observations are then compared with the predicted impact directions to measure the IS dust flux. No evidence has been found (at the 97.5% confidence level) for a flux greater than about 6 hundred-thousandths per sq m/sec for particles of at least 2 by 10 to the -14th power g.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 23
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    Accretion flows in binary X-ray systems (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Recent developments in the study of accretion flows in binary X-ray systems are reviewed, concentrating on issues concerning the gas flows rather than the radiation mechanisms. A model for Her X-1 is presented which illustrates the main structures expected to exist in the case where mass transfer is by Roche-lobe overflow and the X-ray source is a rotating magnetized neutron star. A model for Cyg X-1 is given which shows the accretion-flow structures to be expected if the compact object is a black hole, including an accretion wake and a very small accretion disk around the black hole. Physical parameters of the accretion flows in these two instances are examined along with some scale lengths that may be derived from these parameters by dimensional analysis. Detailed attention is given to neutron-star magnetospheres (for slow, intermediate, and fast rotators), accretion-disk structure, accretion from stellar winds, and the relationship between X-rays and the gas dynamics of accretion flows. It is suggested that accretion flows in binary X-ray systems be observed directly by means of high-resolution UV and X-ray spectroscopy.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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  • 24
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    Meteor streams in the making (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: The well-known associations of meteor streams with periodic comets and the probable cometary origin of the zodiacal dust cloud point to the importance, in the cometary debris, of particles with masses exceeding roughly 10 to the -6th gram. It is shown that these large particles dominate in the sunward-oriented anomalous tails of comets. Their study is essential for meaningful estimates of the mass of meteor streams and of the injection rate of the cometary debris that contributes to the zodiacal cloud. Favorable conditions for the detection of anomalous tails can be recognized in advance, as demonstrated by the successful predictions for comets Kohoutek (1973 XII) and Bradfield (1975p). To answer the question as to whether short-period comets can support the zodiacal cloud, a study of anomalous tails at future returns of these comets is considered indispensable.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 25
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    Radiation pressure and Poynting-Robertson drag for small spherical particles (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Robertson's expression for the velocity-dependent effect of solar radiation on the motion of small particles is difficult because of its dependence on relativistic considerations, and it is also deficient in that it assumes perfectly absorbing particles. The present paper gives a heuristic derivation of the Poynting-Robertson effect. Robertson's expression for perfectly absorbing particles is obtained but on a much simpler physical basis, and an expression is also obtained for a particle that in general scatters, transmits, and absorbs light. Some numerical results on the solar radiation forces felt by small particles of cosmochemically important compositions are given.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 26
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    The constitution of cometary nuclei (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: The nongravitational term in the expression for the total force acting on a comet is calculated, and an upper limit is obtained for the product of the radial nongravitational term times the radius times the square root of the albedo. This condition is satisfied for ten periodic comets with q no greater than 1.5 AU, and the activity of these comets is consistent with control by H2O ice. Some of the comets must be spotty to account for their low albedo values. The effect of cosmic rays on comets, leading to frosting of their surface, is discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 27
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    A measurement of the interstellar C-12/C-13 isotopic abundance ratio toward Zeta Oph from observations of the 3957-A line of CH/+/ (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly, Special Session no CNO isotopes in astrophysics; Aug 30, 1976; Grenoble; France
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  • 28
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    Isotope ratios and chemical fractionation of CO in Lynds 134 (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: A radio observation of (C-12)(O-17) in the dust cloud Lynds 134 is reported, and the question of the (C-13)(O-16)/(C-12)(O-18) ratio across this cloud is considered. A value of approximately 0.28 is obtained for the (C-12)(O-17) column-density ratio, and it is shown that the (C-13)(O-16)/(C-12)(O-18) ratio is very different at two positions in the cloud separated by about 3.75 arcmin. (C-13)(O-16)/(C-12)(O-18) column-density ratios are calculated on the assumption of LTE and found to have a mean value of 4.8 at six positions in the most obscured part of the cloud; the same ratio is determined to be much larger and variable outside the cloud core. It is suggested that chemical fractionation of CO is occurring in this cloud, that (C-13)(O-16) is considerably enriched in its outer regions, and that the cloud's C-12/C-13 ratio is approximately 104.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly, Special Session no CNO isotopes in astrophysics; Aug 30, 1976; Grenoble; France
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  • 29
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    CNO nucleosynthesis and the nova outburst (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Predictions for CNO nucleosynthesis by the classical nova outburst are presented. Properties of the nova phenomenon pertinent to the production of CNO isotopes are discussed, the effect of beta(+) unstable nuclei on outburst evolution is examined, and the need for enhanced CNO nuclei in the envelope is described. Possible mechanisms for producing such enhancement are considered, and recent observations of enhanced CNO nuclei in nova ejecta are reviewed. Results of model evolutionary calculations are outlined which show that a thermonuclear runaway in the hydrogen envelope of a carbon-oxygen white dwarf can reproduce the gross features of the classical nova outburst, that the behavior of the outburst depends at least on the hydrogen-envelope mass and the degree of CNO enhancement, and that all degrees of isotopic enhancement result in an outburst that may be compared with observed events. Two enhancement mechanisms are identified, both of which involve mixing in the envelope.
    Schlagwort(e): ASTROPHYSICS
    Materialart: General Assembly, Special Session no CNO isotopes in astrophysics; Aug 30, 1976; Grenoble; France
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  • 30
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    Spectrum and isotropy of the submillimeter background radiation (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Infrared evidence referable to the spectrum and isotropy of the background radiation of the universe is considered, along with theoretical implications. Difficulties in the submillimeter region are indicated. Two types of anisotropy are treated: small-scale granularity (attributable to discrete sources such as galaxies or to condensation in the primordial plasma) and large-scale anisotropies; the anisotropies are discussed as possible indicators of the early history of the universe, and in relation to future possible generalized Michelson-Morley experiments (to detect effects on local physics of the existence of a universal rest frame). A complete blackbody spectrum is seen as the clear signature of the primordial fireball, and slight deviations from a perfect thermal spectrum (or perfect isotropy) are to be sought and scrutinized.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Infrared and submillimeter astronomy; Jun 08, 1976 - Jun 10, 1976; Philadelphia, PA
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  • 31
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    A review of the thermonuclear runaway model of a nova outburst (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Kraft's (1963) model for a nova outburst caused by a thermonuclear runaway in the hydrogen-rich matter accreted onto the white dwarf in a binary system is reviewed. Hydrostatic and hydrodynamic studies of this phenomenon are summarized, analyses of shock ejection based on hydrodynamic computer codes are discussed, and one specific hydrodynamic code is outlined. Results obtained with this code are presented and evaluated for an initial model containing a white dwarf with a hydrogen-rich envelope of 0.0001 to 0.001 solar mass in hydrostatic and thermal equilibrium. It is shown that an implicit hydrodynamic computer code is required in order to study the thermonuclear-runaway phenomenon. The early evolution of three models with different intrinsic luminosities is illustrated, and enhancement of CNO nuclei at the bottom of the hydrogen-rich envelope is investigated. It is suggested that the concentration of C-13, N-15, and O-17 should be greatly enhanced in nova ejecta.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Conference on Novae and related stars; Sep 07, 1976 - Sep 09, 1976; Paris; France
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  • 32
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    Surface brightness, standard candles and q/0/ (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: The most direct way to determine the deceleration parameter, q(0), of the universe is through the study of the redshift-magnitude relation of extragalactic sources. Progress has been slow because the necessary sources for this study must be standard candles, which have identical absolute total luminosity (balometric or monochromatic). The present paper shows, first of all, that, although necessary, this is not a sufficient condition for nonpoint-like (or resolved) sources. A modification of the redshift-magnitude relation is then described for a certain class of nonstandard candles using measurements of isophotal surface brightness. It is noted that such measurements can be used to standardize the central surface brightness of galaxies, but the standardization of the scale parameter remains beyond observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Conference on Redshifts and the expansion of the universe; Sep 06, 1976 - Sep 07, 1976; Paris; France
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  • 33
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    Dust evolution from comets (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: The studies of the evolution of cometary debris are reviewed. The subject is divided into three major sections: (1) the developments in the immediate vicinity of the cometary nucleus, which is the source of the dust; (2) the formation of the dust tail; and (3) the blending of the debris with the dust component of interplanetary matter. The importance of the physical theory of comets is emphasized for the understanding of the early phase of the evolution of cometary dust. A physico-dynamical model designed to analyze the particle-emission mechanism from the distribution of light in the dust tails is described and the results are presented. Increased attention is paid to large particles because of their importance for the evolution of the zodiacal cloud. Finally, implications are discussed for the future in situ investigations of comets.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 34
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    Molecular clouds (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Star Formation; Sep 06, 1976 - Sep 10, 1976; Geneva; Switzerland
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  • 35
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    Low-temperature condensates in comets (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: Recent observational data on the volatile fraction of comets are confronted with a model based on the fractional condensation, in the 80-100 K range, of a higher-temperature equilibrium obtained from a solar mixture, more or less depleted in oxygen and in hydrogen. It is possible to almost duplicate the observational data, only by assuming that the solar ratio of C/O is at least as large as 0.66 and that the hydrogen was drastically depleted by an unknown process in the primitive solar nebula. Although none of these two assumptions is at variance with present knowledge, the latter is sufficiently exotic to propose a simpler explanation, namely that comets could be made of interstellar grains relatively unprocessed by heat.
    Schlagwort(e): ASTROPHYSICS
    Materialart: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 36
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    Observations of O VI (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: A useful spectroscopic tracer for a hot phase of interstellar gas is the O VI ion, which reaches its maximum concentration in collisional ionization between 100,000 and 1 million K. Presently, over 70 stars have been observed for O VI absorption by the Copernicus satellite. Nearly all of the stars show broad weak lines, but no evidence favoring a circumstellar origin for the gas can be found. An overall average for the electron density of the hot gas in the galactic plane is of the order of 0.001 per cu cm. The relative volume in space occupied by the hot-gas regions (and hence their internal density) is uncertain, but a filling factor in the range from 0.02 to 0.2 seems most plausible. Fluctuations in radial velocities and column densities suggest there are roughly 6 regions per kpc, each with an O VI column density of approximately 10 trillion per sq cm. The observed rms dispersion of radial velocities for these regions is 26 km/s.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Topics in interstellar matter; Commission 34 Session, General Assembly; Aug 25, 1976; Grenoble; France
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  • 37
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    Radial distribution of Beta meteoroids from the Pioneers 8 and 9 cosmic dust experiments (1977)
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    Publikationsdatum: 2019-07-13
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 38
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    Interpretation of cosmological information on radio sources (1977)
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    Publikationsdatum: 2019-07-13
    Beschreibung: The question of whether any cosmological information can be obtained from radio astronomy is considered. Specific attention is given to the discovery and cosmological interpretation of the microwave background radiation, attempts to derive a Hubble relation for the optical objects identified with radio sources, searches for relations between the angular diameters of radio sources and the redshifts of their optically identified counterparts as well as between angular diameter and radio flux, construction of log N - log S curves, and luminosity volume tests. A brief outline is given of the situation that might prevail if a significant population of radio sources is not at great distances and is associated with QSOs that have been ejected from relatively nearby galaxies. It is concluded that: (1) some types of cosmological investigations have been premature; (2) much of the discussion in this area still depends on the distances of QSOs; and (3) there is no conclusive proof that the population of radio sources is changing with epoch.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Symposium on Radio astronomy and cosmology; Aug 16, 1976 - Aug 20, 1976; Cambridge
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  • 39
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    A theoretical investigation of isotopic anomalies of xenon in terrestrial and extra-terrestrial samples (1977)
    In:  CASI
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    Publikationsdatum: 2019-07-13
    Beschreibung: The abundance and isotopic composition of noble gases in meteorites is discussed in relation to the composition of the early solar system. Carbonaceous chondrites contain a unique Xenon-X, which is rich in heavy and light isotopes. Variations in the occurrence of type-X and type-Y (the normal component) noble gases are of such magnitude that neither the injection of material from a nearby supernova nor presence of presolar grains can account for the anomalies in meteorites. Therefore, it is suggested that the entire solar system may have condensed from the debris of a single local supernova.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-CR-155255
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  • 40
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    Computer simulation of plasma and N-body problems (1977)
    In:  CASI
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    Publikationsdatum: 2019-07-13
    Beschreibung: Any spiral structure in computer-generated galaxies is generally short lived and the final state is a rotating bar. The bar thus obtained rotates more slowly than the stars. It has been argued that core/halo components have a stabilizing effect on galaxies and result in longer lived spiral structure. However, numerical experiments with large fixed stellar components representing the core/halo component show that multiarmed spiral structure develops and persists for many rotations but only in an evolving manner. That is, the spiral structure is either wound up into a tight pattern or it is wound up and then reappears again. A recent study of the effect of fixed core/halo components does show that the bar instability is indeed inhibited by a sufficiently large fixed component. The present study determines the effect of a self-consistent (rather than fixed) core/halo component in order to show whether there are any instabilities (such as two-stream) or other important interactions present that may be suppressed with a fixed core. Also studied were the effects of finite thickness of the disk and of three-dimensional essentially spherical core/halo components.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-CR-155517 , PGSTR-PH77-66
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  • 41
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    The Viking Relativity Experiment (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Measurements of the round-trip time of flight of radio signals transmitted from the earth to the Viking spacecraft are being analyzed to test the predictions of Einstein's theory of general relativity. According to this theory the signals will be delayed by up to approximately 250 microsec owing to the direct effect of solar gravity on the propagation. A very preliminary qualitative analysis of the Viking data obtained near the 1976 superior conjunction of Mars indicates agreement with the predictions to within the estimated uncertainty of 0.5%.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research; 82; 28; 4329-4334
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  • 42
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    The interstellar medium in the direction of the Crab Nebula - Reconciling soft X-ray and radio observations (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The total soft X-ray photoabsorption cross section of the interstellar medium (ISM) in the direction of the Crab Nebula is computed on the basis of a two-phase model of the ISM. This cross section is used to reanalyze Copernicus data on the X-ray spectrum of the Crab between 0.7 and 1.5 keV. The total hydrogen column density along the line of sight to that nebula is found to be approximately 2.6 by 10 to the 21st power H atoms/sq cm. This result is evaluated in light of the two-phase model of the ISM, and the predictions based on the X-ray data are compared with results of radio and UV observations. A discrepancy between the radio and X-ray measurements of the hydrogen column density is resolved by noting that 21-cm absorption measurements sample only the neutral hydrogen in clouds while X-ray measurements are sensitive to all forms of hydrogen in both cloud and intercloud regions. It is suggested that roughly 50% of the hydrogen in the direction of the Crab Nebula is in clouds and that 85% of this hydrogen is neutral and atomic.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 61; 3; Nov. 197
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  • 43
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    Absorption of X-rays in the interstellar medium (1977)
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    Publikationsdatum: 2019-06-28
    Beschreibung: The X-ray photoabsorption cross sections (per hydrogen atom) of interstellar clouds and the intercloud medium are calculated separately, taking into account abundance evolution, self-blanketing by grains, molecule formation, and ionization structure. A reference cross section describing a neutral monatomic gas of elements in solar abundances is computed for purposes of comparison, the cross section of the intercloud medium is calculated by assuming that 15% of the hydrogen is ionized, and the cross section of the clouds is computed for the cases where all hydrogen is in either molecular or atomic form. A comparison of the reference cross section with the others shows that a cross section is increased relative to the reference if abundances are enhanced or if molecular hydrogen exists and is decreased if atoms exist in grains or if hydrogen is ionized. It is noted that the total cross section will be a linear combination of the cross sections of the clouds and the intercloud medium and can reflect the characteristics of a particular line of sight.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 61; 3; Nov. 197
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  • 44
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    The masses of neutron stars - Observational constraints (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: The present state of empirical knowledge concerning neutron-star masses is reviewed on the basis of information obtained for the nine known X-ray pulsars in binary systems. Pulse profiles and other pulse parameters of these X-ray pulsars are examined, and allowable mass ranges are estimated for four X-ray pulsars in binary systems as well as for the binary pulsar PSR 1913+16. The approximate mass ranges obtained include 1.2 to 2.4 solar masses for 3U 0900-40, 0.7 to 4.3 solar masses for Cen X-3, 0.8 to 1.8 solar masses for SMC X-1, 0.0 to 2.3 solar masses for Her X-1, and either 1.4 to 1.8 solar masses or 0.0 to 1.8 solar masses for PSR 1913+16 if the companion is a normal white dwarf or some other type of star, respectively. Theoretical implications of these results are briefly considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: New York Academy of Sciences; vol. 302
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  • 45
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    Accretion magnetosphere stability. II - Polar cap 'drip' (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: The entry of plasma past the shielding magnetic field of a collapsed object is examined. It is concluded that a plausible entry mode is simply a 'dripping' motion of the polar caps of the magnetopause, owing to radiation of the hot compressed plasma there. The plasma 'drips' would hit the object's surface either near the magnetic poles or in a ring-shaped 'auroral' zone around the poles. Insofar as this entry mode is concerned, no special role is played by finite plasma resistivity since the plasma can reach the stellar object even if the conductivity is infinite.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 216
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  • 46
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    The correlation function for density perturbations in an expanding universe. I - Linear theory (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: The evolution of the two-point correlation function for adiabatic density perturbations in the early universe is studied. Analytical solutions are obtained for the evolution of linearized spherically symmetric adiabatic density perturbations and the two-point correlation function for these perturbations in the radiation-dominated portion of the early universe. The results are then extended to the regime after decoupling. It is found that: (1) adiabatic spherically symmetric perturbations comparable in scale with the maximum Jeans length would survive the radiation-dominated regime; (2) irregular fluctuations are smoothed out up to the scale of the maximum Jeans length in the radiation era, but regular fluctuations might survive on smaller scales; (3) in general, the only surviving structures for irregularly shaped adiabatic density perturbations of arbitrary but finite scale in the radiation regime are the size of or larger than the maximum Jeans length in that regime; (4) infinite plane waves with a wavelength smaller than the maximum Jeans length but larger than the critical dissipative damping scale could survive the radiation regime; and (5) black holes would also survive the radiation regime and might accrete sufficient mass after decoupling to nucleate the formation of galaxies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 216
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  • 47
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    An angular size for the compact radio source at the galactic center (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: Simultaneous very-long-baseline (100 million wavelengths) and intermediate-baseline (4 million wavelengths) interferometer observations at a wavelength of 3.7 cm in 1976.2 show that the galactic-center compact radio source has a linear size of approximately 140 AU. The observations also set an upper limit of about 0.1 Jy to the emission from any core of size less than roughly 10 AU at that epoch. The total flux density of the compact source was slightly higher than the value reported previously.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
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  • 48
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    An abundance analysis of Tau Herculis, B5 IV (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: An abundance analysis of the sharp-lined star Tau Herculis (B5 IV) has been performed using a fully line-blanketed model atmosphere. The derived abundances are similar to those of the sun and the normal main-sequence B stars Iota Her (B3 V) and Nu Cap (B9 V).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 181
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  • 49
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    Some O I oscillator strengths and the interstellar abundance of oxygen (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: Calculated and experimental oscillator strengths for the O I intersystem line at 1356 A and for other O I lines of interest in interstellar absorption-line studies are discussed. Attention is given to experimental f-values for the lines at 1302, 1305, and 1306 A, previous work on the f-values for the lines at 1356 and 1359 A, wave-function expansion, and calculations for permitted as well as intercombination lines. Copernicus observations of several interstellar absorption lines due to O I, C II, P II, and Ni II toward Zeta Oph are reported, equivalent widths are determined, and a curve-of-growth analysis is performed for the O I absorption lines. Oscillator strengths are recommended for the far-UV resonance lines of O I, and it is concluded that the oxygen in the interstellar H I regions toward Zeta Oph is depleted by 45% to 69%.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 181
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  • 50
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    New infrared objects associated with OH masers (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: Results of a search for IR radiation at 10 microns from a sample of OH maser sources are reported. An IR source is discovered near each of six OH masers which emit mainly at 1612 MHz in two distinct velocity ranges. It is shown that all the sources have varied with time, that two sources have exhibited significant variations in color temperature, and that the energy distributions of the six objects over the spectral range from 2 to 20 microns fall into two categories. Absorption in the 2.3-micron band of CO is detected in two sources, and four are found to display substantial silicate absorption features. The energy distributions of the sources indicate that pumping by 35-micron photons is feasible, but 2.8-micron pumping is very unlikely; the distributions are best explained as emission from very thick dust shells at temperatures of about 500 K. The data are taken as supporting the hypothesis that every double-peaked OH maser emitting principally at 1612 MHz is associated with an IR object. The nature of the objects inside the dust shells and their evolutionary state are briefly discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 217
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    Long-term changes in ultraviolet P Cygni profiles observed with Copernicus (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: The incidence and nature of variability occurring on time scales of years in the ultraviolet P Cygni profiles of 15 O and B stars are investigated using spectrophotometric data obtained with the Copernicus satellite. It is found that some change in at least a few details of the P Cygni profiles is evident in almost every case, that the changes in a few stars appear to represent substantial variations in the column densities of the particular ions observed, and that the changes in other stars are minor in nature and do not result from significant alterations in the quantity of material in the stellar winds. Most of the narrow absorption features are shown to be invariant in velocity, although their strengths have apparently changed in certain cases. The nature of the changes observed in each of the program stars is briefly described, the time scale for variability in the stellar winds is considered, and two stars (Zeta Pup and Delta Ori A) are identified for which some alteration in the total amount of material in the stellar wind has taken place. It is suggested that the narrow absorption features probably represent temperature gradients or plateaus in the stellar-wind velocity fields or may be caused by flat regions in the height dependence of the wind velocity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 217
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    The chemical evolution of molecular clouds (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: The nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
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    Constraints on the gravitational constant at large distances (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: D. R. Long (1976) and others have speculated that the gravitational force between point masses in the Newtonian regime might not be exactly proportional to 1/r squared. Distance-dependent deviations from the 1/r squared law can be represented by a distance-dependent gravitational 'constant', G(r). Long has summarized the experimental evidence which constrains G(r) to be very nearly constant for 5 cm less than r less than 1 m. This paper presents observational evidence for constancy in the range 1000 km less than r less than 10 to the eighth km, and points out that the value of G(r) identical to Gc in this range has not been experimentally determined. Constraints on G(r) in the intermediate distance range 10 m less than r less than 1 km are so poor that one cannot rule out the possibility that Gc differs greatly from the laboratory value Go. Models of the earth and sun are used to argue that Gc differs from Go by not more than approximately 40%. Methods of improving the determination of Gc are suggested.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review D - Particles and Fields; vol. 16
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  • 54
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    X-ray bursts and neutron-star thermonuclear flashes (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: A description is presented of a model concerning the production of X-ray bursts by thermonuclear flashes in the freshly accreted matter near the surface of an accreting neutron star. An investigation is conducted regarding the physical processes relevant to such thermonuclear flashes. It is concluded that thermonuclear flashes may account for some, but not all, of the observed X-ray burst sources. Attention is given to a neutron star undergoing accretion of mass from a binary stellar companion, aspects of energetics, nuclear reactions, and heat transport mechanisms.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 270; Nov. 24
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  • 55
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    The energetics of molecular clouds. I - Methods of analysis and application to the S255 molecular cloud (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Observations of the S255 molecular cloud in the radio lines of CO, (C-13)O, and H2O as well as in the IR region from 12 to 20 microns are presented. These results show that an extended molecular cloud is associated with the optically visible H II regions S255 - S257, both the kinetic temperature and molecular density are enhanced in an area centered on a compact near-IR source, this source is also coincident with an OH and an H2O maser (within the errors), and the IR source exhibits the silicon absorption feature. First-order techniques which allow physical properties of molecular clouds to be estimated and the energetics of the gas and dust in the clouds to be analyzed are developed and applied to S255. It is concluded that: (1) the gas cooling rate is much less than the dust cooling rate; (2) the primary energy flow is in the IR through dust emission over a range of temperatures; (3) the near-IR source is apparently responsible for the local peak in gas kinetic temperature; and (4) the exciting stars of nearby H II regions appear to be the primary heat sources for the overall molecular cloud.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 217
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  • 56
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    The correlation function for density perturbations in an expanding universe. II - Nonlinear theory (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: A formalism is developed to find the two-point and higher-order correlation functions for a given distribution of sizes and shapes of perturbations which are randomly placed in three-dimensional space. The perturbations are described by two parameters such as central density and size, and the two-point correlation function is explicitly related to the luminosity function of groups and clusters of galaxies
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 217
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  • 57
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    Multiple scattering in reflection nebulae. IV - The multiplicity of scattering (1977)
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    Publikationsdatum: 2019-06-27
    Beschreibung: The characteristics of higher order scattering in plane-parallel reflection nebulae of finite optical thickness have been examined. Measured both by the mean number of scatterings and the effective multiplicity, the importance of multiple scattering in such systems varies strongly with position as well as direction, and the effects cannot be taken into account by simple corrections only. It is found that the amount of higher order scattering is relatively insensitive to the shape of the phase function over a wide range of asymmetries, while the dependence of multiplicity on particle albedo, optical thickness of the nebula, and other geometrical factors is as expected. Pronounced asymmetries in the surface brightness distribution of strongly tilted plane-parallel nebulae are explained by different radial variations of the effective multiplicity along opposite radii on the projected nebular face.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series; 35; Sept
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  • 58
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    Multiple scattering in reflection nebulae. I - A Monte Carlo approach. II - Uniform plane-parallel nebulae with foreground stars. III - Nebulae with embedded illuminating stars (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: A method for calculating the surface brightness distribution on a plane-parallel reflection nebula of uniform density illuminated by a star located either in front of, behind, or arbitrarily inside the scattering medium is proposed. The Monte Carlo technique is used to find solutions to the radiative transfer problem. The scattering properties of the nebular particles are parameterized by the albedo for single scattering and a three-parameter analytic phase function. Calculations are then presented for the surface brightness distribution across the face of such nebulae with (1) a foreground star and (2) immersed stars. The calculations include the full effects of multiple scattering, are independent of a particular assumed grain material or size distribution, and are applicable to any wavelength region for which observations can be obtained.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series; 35; Sept
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  • 59
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    Radiative transfer in dusty nebulae (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: The effects of dust scattering on observable optical and infrared parameters, and the accuracy of approximate solutions were examined. The equation of radiative transfer in a static and homogeneous, but not necessarily uniform, distribution gas and dust around a central empty core with a point source of energy at its center was solved. The dust properties were characterized by a phenomenological extinction cross section, albedo and parameters describing the anisotropy of dust scattering. For ultraviolet photons, ionization equilibrium equations for the gas were solved, and for infrared photons a self-consistent dust temperature was calculated. Ray tracing was used to solve for the angular dependence of the intensity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-CR-155580 , SU-SUIPR-722
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  • 60
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    A survey of interstellar HI from L alpha absorption measurements 2 (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars. The distance to 10 stars exceeds 2 kpc and 34 stars lie beyond 1 kpc. Stars with color excess E(B-V) up to 0.5 mag are observed. The value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag). For stars with accurate E(B-V), the deviations from this mean are generally less than a factor of 1.5. A notable exception is the dark cloud star, rho Oph. A reduction in visual reddening efficiency for the grains that are larger than normal in the rho Oph dark cloud probably explains this result. The conversion of atomic hydrogen into molecular form in dense clouds was observed in the gas to E(B-V) correlation plots. The best estimate for the mean total gas density for clouds and the intercloud medium, as a whole, in the solar neighborhood and in the plane of the galaxy is 1.15 atoms per cu. cm; those for the atomic gas and molecular gas alone are 0.86 atoms per cu cm and 0.143 molecules per cu cm respectively. For the intercloud medium, where molecular hydrogen is a negligible fraction of the total gas, atomic gas density was found to equal 0.16 atoms per cu cm with a Gaussian scale height perpendicular to the plane of about 350 pc, as derived from high latitude stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-TM-78044 , X-681-77-255
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  • 61
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    The evolution of the moon and the terrestrial planets (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: The thermal evolutions of the Moon, Mars, Venus, and Mercury were calculated theoretically starting from cosmochemical condensation models. An assortment of geological, geochemical, and geophysical data were used to constrain both the present day temperature and the thermal histories of the planets' interiors. Such data imply that the planets were heated during or shortly after formation and that all the terrestrial planets started their differentiations early in their history.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 295-327
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  • 62
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    Results from the Apollo passive seismic experiment (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: Recent results from the Apollo Seismic Network suggest that primitive differentiation occurred in the outer shell of the moon to a depth of approximately 300 km and the central region of the moon is presently molten to a radius of between 200 and 300 km. If early melting to a depth of 300 to 400 km was a consequence of accretional energy, very short accretion times are required. It was shown that the best model for the zone of original differentiation is a crust 40 to 80 km thick, ranging in composition from anorthositic gabbro to gabbro, and overlying an ultramafic cumulate about 250 km thick. The best candidate for the molten core appears to be iron or iron sulphide. A new class of seismic signals recently were identified that may correspond to shallow moonquakes. These are rare, but much more energetic than the more numerous, deep moonquakes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: CONTRIB-44 , NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 389-401
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  • 63
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    In-situ measurements of lunar heat flow (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: During the Apollo program two successful heat flow measurements were made in situ on the lunar surface. At the Apollo 15 site a value of .0000031 W/sq cm was measured, and at the Apollo 17 site a value of .0000022 W/sq cm was determined. Both measurements have uncertainty limits of + or - 20 percent and have been corrected for perturbing topographic effects. The apparent difference between the observations may correlate with observed variations in the surface abundance of thorium. Comparison with earlier determinations of heat flow, using the microwave emission spectrum from the moon, gives support to the high gradients and heat flows observed in situ.
    Schlagwort(e): ASTROPHYSICS
    Materialart: CONTRIB-2141 , NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 283-293
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  • 64
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    Lunar igneous rocks and the nature of the lunar interior (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: Lunar igneous rocks, properly interpreted, can give useful information about mineral assemblages and mineral chemistry as a function of depth in the lunar interior. Though intensely brecciated, terra rocks reveal, in their chemistry, evidence for a magmatic history. Partial melting of feldspathic lunar crustal material occurred in the interval 4.6 to 3.9 Gy. Melting of ilmenite-bearing cumulates at depths near 100 km produced parent magmas for Apollo 11 and 17 titaniferous mare basalts in the interval 3.8 to 3.6 Gy. Melting of ilmenite-free olivine pyroxenites (also cumulates?) at depths greater than 200 km produced low-titanium mare basalts in the interval 3.4 to 3.1 Gy. No younger igneous rocks have yet been recognized among the lunar samples and present-day melting seems to be limited to depths greater than 1000 km.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 127-135
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    Comparison of lunar rocks and meteorites: Implications to histories of the moon and parent meteorite bodies (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: There are many similarities between lunar samples and stone meteorites. Lunar samples, especially from the highlands, indicate that they have been affected by complex and repeated impact processes. Similar complex and repeated impact processes have also been operative on the achondritic and chondritic meteorites. Similarities between lunar and meteoritic rocks are discussed as follows: (1) Monomict and polymict breccias occur in lunar rocks, as well as in achondritic and chondritic meteorites, having resulted from complex and repeated impact processes; (2) Chondrules are present in lunar meteorites, as well as in a few achondritic and most chondritic meteorites. They apparently crystallized spontaneously from molten highly supercooled droplets which may have formed from impact melts or, perhaps, volcanic processes (as well as from the solar nebula, in the case of meteoritic chondrites); (3) Lithic fragments vary from little modified (relative to the apparent original texture) to partly or completely melted and recrystallized lithic fragments. Their detailed study allows conclusions to be drawn about their parent rock types and their origin, thereby gaining insight into preimpact histories of lunar and meteoritic breccias. There is evidence that cumulate rocks were involved in the early history of both moon and parent meteorite bodies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 183-199
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    Lunar highland rock types: Their implications for impact-induced fractionation (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: Lunar rocks may be classified into three major groups: (1) coarse-grained igneous rocks, (2) fine-grained igneous rocks, and (3) breccias. Group 1 is interpreted as primitive lunar crustal rocks that display various degrees of crushing and/or annealing. Group 2 is interpreted as volcanic rocks. Group 3 is interpreted as resulting from impacts on the lunar surface and is subdivided on the basis of matrix textures into fragmental breccias, crystalline breccias that have been annealed, and crystalline breccias with igneous matrices. A synthesis of the data concerning lunar highlands polymict breccias compels the prediction that the breccias should have homogeneous matrices from rock to rock within regions of the highlands of limited size where impact mixing has been efficient and extensive. But the returned breccias, even from one landing site, display a wide range in composition. This incompatibility between prediction and observation is a paradox that may be resolved by a process that acts after impact mixing to cause a differentiation of the breccia compositions. Partial melting of the local average crustal composition (as modeled by the average soil composition for each site) and separation of melt and residue in ejecta and/or fall-back blankets are compatible with the reviewed data and may resolve the paradox.
    Schlagwort(e): ASTROPHYSICS
    Materialart: CONTRIB-230 , The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 91-126
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    Petrogenesis of lunar rocks: Rb-Sr constraints and lack of H2O (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: Rb and Sr isotopic data and other chemical data indicate major lunar differentiation at about 4.6 AE (AE = 10 to the 9th power years) and very limited subsequent differentiation. The constraints of limited differentiation after 4.6 AE and the apparent lack of H2O on the moon, when applied to the derivation and petrogenesis of lunar samples, suggest the following: (1) soil samples, breccias, metaclastic rocks, and feldspathic basalts represent mixtures of repeatedly modified clastic material, which was utimately derived from materials formed during the 4.6 AE differentiation; and (2) mare basalts crystallized from melts which formed by partial melting, and which developed without equilibrium between the melt and crystalline residuum.
    Schlagwort(e): ASTROPHYSICS
    Materialart: CONTRIB-2474 , NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 81-90
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  • 68
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    Geochemical zoning and early differentiation in the moon (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: The volatile elements (e.g., Rb, Pb, Tl, Bi, Cs) seem to have been depleted at the time of lunar accretion. Accordingly, it may be assumed that the moon initially accreted from refractory material. The good correlation between volatile/involatile element ratios (e.g., Cs/U, K/La, K/Zr) in both highland and maria samples means that element distribution in lunar crustal rocks is not governed by volatility differences. This and other evidence encourages the view that the moon was accreted homogeneously. A consequence of homogeneous accretion theories is that very efficient large-scale element fractionation is required to account both for the high near-surface concentrations of refractory elements (e.g., Th, U, REE, Zr, Ba, etc.) and for the Ca-Al-rich crust.
    Schlagwort(e): ASTROPHYSICS
    Materialart: CONTRIB-229 , NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 55-61
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    The spectrum of HM Sagittae: A planetary nebula excited by a Wolf-Rayet star (1977)
    In:  CASI
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    Publikationsdatum: 2019-06-27
    Beschreibung: A total of image tube spectrograms of HM Sagittae were obtained. More than 70 emission lines, including several broad emission features, were identified. An analysis of the spectra indicates that HM Sagittae is a planetary nebula excited by a Wolf-Rayet star. The most conspicuous Wolf-Rayet feature is that attributed to a blend of C III at 4650 A and He II at 4686 A.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-TM-X-71415 , X-685-77-253
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    Laboratory studies of bimolecular reactions of positive ions in interstellar clouds, in comets, and in planetary atmospheres of reducing composition (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series; 33; Apr. 197
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    X-ray bursts from magnetized accretion disks (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: A model for the X-ray bursts of MXB 1730-335 and 3U 1820-30 (identified with the globular cluster NGC 6624) is presented in which a burst is due to the flarelike release of magnetic energy generated and stored as a toroidal field in an accretion disk. To fit the observed parameters, this model requires compact objects of the order of 10 solar masses, presumably black holes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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  • 72
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    Transfer of polarized radiation in self-absorbed synchrotron sources. I - Results for a homogeneous source (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources. Relativistic electrons (independent of the presence of any cold plasma) can quite easily produce in such sources significant Faraday rotation and/or conversion of linear to circular polarization. Structural inhomogeneities do not obviate the importance of these phenomena in compact nonthermal sources. Contrary to the calculation of Pacholczyk and Swihart (1975), the circular polarization for a homogeneous source changes sign just below the self-absorption turnover as the source becomes opaque, even when polarization conversion dominates; however, for a physically realistic source, structural inhomogeneity may alter this behavior. The observational evidence bearing upon these effects is reviewed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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    Unidentified lines in molecular clouds and a search for C-14 in IRC +10216 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Two spectral features have been detected toward the Kleinmann-Low infrared nebula in Orion that agree in frequency with the 7(25)-7(16) and 7(35)-7(26) rotational transitions of the ring-structured molecule ethylene oxide (CH2)2O. A feature agreeing in frequency with the 8(24)-8(45) transition probably also was detected; however, seven other transitions in (CH2)2O were not. Additional unidentified lines were detected in Ori A and Sgr B2. Searches for H(C-14)N and (C-14)O in the luminous carbon star IRC +10216 were unsuccessful. However, an unidentified line was found in IRC +10216 that was not detected in the KL nebula.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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    Development of a spectral break in the nonthermal emission of AO 0235+164 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Results are reported for braod-band photometry of the BL Lac object AO 0235+164 carried out over the spectral range from 0.36 to 3.5 microns in December 1975 and in October and November 1976. It is found that the continuum of this object steepened at visible wavelengths between December 1975 and October 1976, but maintained a relatively constant slope in the near-IR despite a factor-of-ten decrease in flux from the maximum level. Visible-wavelength data are cited which appear to suggest that the steepening of the visible spectrum occurred in less than 300 days, while the near-IR level may have been nearly constant. It is shown that the observed change in the spectral shape of the visible-wavelength continuum cannot be explained in terms of a 'composite' model consisting of an unchanging galaxy and a varying nonthermal source with constant spectral index. Two other general classes of models are considered: intrinsic variability and extrinsic modulation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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    Gravitational radiation from binary systems in alternative metric theories of gravity - Dipole radiation and the binary pulsar (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The generation of gravitational radiation in several currently viable metric theories of gravitation (Brans-Dicke, Rosen, Ni, and Lightman-Lee) is analyzed, and it is shown that these theories predict the emission of dipole gravitational radiation from systems containing gravitationally bound objects. In the binary system PSR 1913 + 16, this radiation results in a secular change in the orbital period of the system with a nominal magnitude of 3 parts in 100,000 per year. The size of the effect is proportional to the reduced mass of the system, to the square of the difference in (self-gravitational energy)/(mass) between the two components of the system, and to a parameter, xi, whose value varies from theory to theory. In general relativity xi equals 0, in Rosen's (1973) theory xi equals -20/3, and in Ni's (1973) theory xi equals -400/3. The current upper limit on such a secular period change is one part in 1 million per year. It is shown that further observations of the binary system that tighten this limit and that establish the masses of the components and the identity of the companion may provide a crucial test of otherwise viable alternatives to general relativity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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    On the fragmentation of cosmic gas clouds. III - The initial stellar mass function (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Radiation from the first opaque protostellar fragments to form in a nonhomologously collapsing molecular cloud can provide a significant heat source in regions where the matter remains relatively diffuse over the initial free-fall time scale. This energy input provides a negative feedback that gradually inhibits fragmentation as larger protostellar fragments form that are also more effective radiators. A highly simplified model is described that yields an expression for the initial mass function in stellar clusters. Dynamical dissipation, driven by the more massive protostars, tends to decouple the gas and grain temperatures and steepen the mass function. Fragmentation of less massive stars appears to proceed more efficiently when the heavy-element abundance is decreased, indicating the possibility of an inverse correlation between gradients in Z and M/L. Other possible observational tests of fragmentation are also suggested.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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  • 77
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    The effect of vacuum birefringence on the polarization of X-ray binaries and pulsars (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: In a strong magnetic field the vacuum becomes birefringent. This effect is especially important for pulsars at X-ray wavelengths. Any polarized X-ray emission from the surface of a magnetic neutron star becomes depolarized as it propagates through the magnetic field. The soft X-ray emission from AM Her, believed to be a magnetic white dwarf, may show about one radian of phase retardation. In this case, circular polarization of the X-ray flux would be a characteristic signature of vacuum birefringence.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 215
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  • 78
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    Radiative regulation of gas flow within clusters of galaxies - A model for cluster X-ray sources (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 215
    Format: text
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  • 79
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    The decompression of cold neutron star matter (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The ejection of cold neutron-star matter is examined, and an attempt is made to determine whether the final composition of this matter may be similar to that normally associated with the hot high-neutron-flux r-process. A semiempirical liquid-drop model is used for the nucleus, and the equilibrium composition of the matter is determined by assuming it to be in its absolute ground state at a given density. Physical mechanisms operating during the expansion are analyzed, and the composition of the ejected matter is found as a function of its density during expansion. The results indicate that it is virtually impossible for deuterium to form, that neutrons can be captured only after beta decay increases the atomic numbers of nuclei, and that no free neutrons can escape. It is concluded that neutron-star ejecta can produce heavy neutron-rich nuclei and may produce somewhat heavier nuclei than a standard r-process.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
    Format: text
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  • 80
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    A high-resolution infrared spectrum of IRC +10216 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The IR-emitting core and shell of IRC +10216 are investigated using a high-resolution spectrum covering the wavelength interval between 3 and 5 microns. Line identifications made or confirmed include those due to (C-12)(O-16), (C-13)(O-16), (C-12)(O-17), and (C-12)(O-18). A mean heliocentric velocity of about -32 km/s is obtained from the 42 least blended (C-12)O and (C-13)O lines, and the following isotopic abundance ratios are derived by comparing equivalent widths of the observed lines: C-12/C-13, C-12/C-14, O-16/O-17, and O-17/O-18. The structure of the expanding gas shell is examined, an explanation is offered for the lack of P Cygni profiles in the spectrum, and an unsuccessful search for other molecules is briefly discussed. It is concluded that a low C-12/C-13 ratio is not necessarily a signature of a carbon star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
    Format: text
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  • 81
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    The nebulosity near the quasar 3C 249.1 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Spectroscopic observations made 2 arcsec away from 3C 249.1 with a cooled SIT camera spectrograph and with a multichannel spectrometer yield convincing evidence for the presence of fairly narrow emission lines of forbidden O II, forbidden O III, forbidden Ne III, and perhaps H-beta. The redshift of these emission lines, z = 0.3125, is, within the accuracy of the observations, the same as that of the broad emission lines in the quasar itself; this appears to rule out a gravitational-redshift interpretation for the quasar redshift. The main difficulty in making models for the extended emission-line region is that of understanding the strong forbidden O II lines. For this purpose, shell, cloud, and disk models are discussed, as is time-dependent ultraviolet illumination of the nebula. Simple models, in which the nebular is exposed to the unaltered extrapolated quasar continuum flux, fail to produce the observed line ratios.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
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  • 82
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    Stimulated Raman scattering and the extreme high-velocity H2O maser features in W49 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Stimulated Raman scattering of the intense 22.2-GHz water-vapor maser radiation within W49 is examined as a possible explanation of the extremely broad spectrum of W49 extending to + or - 200 km/sec apparent Doppler velocity. Under the most favorable conditions, Raman scattering from ammonia molecules is calculated to be observable. It is unlikely that the Raman process contributes appreciably in the case of W49, as it fails to predict the observed spatial and spectral distribution of the radiation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 89
    Format: text
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  • 83
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    One-millimeter observations of the Crab Nebula (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 89
    Format: text
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  • 84
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    Copernicus spectra and infrared photometry of 42 Orionis (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The Orion sword star 42 Ori is embedded in a nebula north of and separated from the Orion nebula. The B1 V star is probably normal. Other members of the multiple remain poorly defined, and the nebula may exhibit some peculiarities that may depend on them. Copernicus ultraviolet spectra of the star are described here, especially in the form of tables of wavelength identifications. The properties of the interstellar material in the line of sight are also discussed. Infrared photometry is presented which suggests that the ratio of total to selective extinction ranges from 3 to 3.5 for the interstellar matter in the direction of 42 Ori. The IR photometry provides no evidence for companion stellar or circumstellar components.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 89
    Format: text
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  • 85
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    The atmosphere of Sirius B. II - Extreme-ultraviolet observations (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The letter reports an observation of Sirius in the extreme-ultraviolet (100-1000 A) band, using a grazing-incidence telescope flown aboard the Apollo-Soyuz mission. No positive flux is detected; under the arbitrary assumption of flat incident spectrum, an upper limit to the flux in the 170-620 A band is 5 billion erg/sq cm per sec. A detailed model-atmosphere analysis, when combined with the EUV limits, places severe constraints on models which attribute the previously reported soft X-ray (44-60 A) flux to thermal radiation from deep layers of the atmosphere of the white dwarf Sirius B. EUV radiation should be detectable from Sirius B just below the sensitivity threshold of the current data, or a thermal origin for the X-ray flux is untenable. If the X-ray flux is thermal, the present results provide extremely sensitive constraints on the temperature and helium abundance of Sirius B: the white dwarf has an effective temperature of 32,000 K to 32,500 K and a helium abundance (relative to hydrogen) of 0.0001 to 0.0002.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
    Format: text
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  • 86
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    Far-ultraviolet studies. II - Galactic-latitude dependence of the 1530 A interstellar radiation field (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: A 0.62-sq cm Geiger counter, sensitive between 1425 and 1640 A, was used to map the far-ultraviolet brightness of about half the sky, providing an experimental measurement of the far-ultraviolet interstellar radiation field. At 1530 A, the energy density is approximately 7.4 by 10 to the -17th power erg/cu cm per A. Comparison with integrations of star catalogs calibrated to the ultraviolet shows, as expected, that the bulk of the radiation comes directly from B- and A-type stars. The galactic-latitude dependence of the radiation is analyzed in an unsuccessful attempt to set limits on the absorbing and scattering properties of the interstellar grains in the far-ultraviolet. Excess radiation observed at the galactic pole is probably residual airglow from above the rocket altitude.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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  • 87
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    The structure of eight globular clusters (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Star counts on short-exposure plates are presented for eight globular clusters. The data are given to several limiting magnitudes for each cluster. Projected radial distributions are determined from the star counts; no significant segregation is observed among the distributions to various limiting magnitudes. The structural parameters of the clusters (core radii and concentration factors) are determined from best-fitting King curves to the observed distributions. The central densities, total masses, central escape velocities, and relaxation times are also calculated. NGC 6093 (M80) and NGC 7099 (M30) have dense compact stellar cores, similar to the established globular X-ray sources. Upper limits are given for the masses of possible central black holes in the eight clusters.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
    Format: text
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  • 88
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    On the binary nature of AM Herculis (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Emission lines of hydrogen and helium observed in the spectrum of AM Her show a 3.1-hour radial-velocity variation. The period and amplitude of the variation indicate a close low-mass system different from previously known X-ray binaries. The period of the radial-velocity variation is significantly different from the period of optical-polarization variation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
    Format: text
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  • 89
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    Accretion of rotating fluids by barytropes - Numerical results for white-dwarf models (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Numerical sequences of rotating axisymmetric nonmagnetic equilibrium models are constructed which represent the evolution of a barytropic star as it accretes material from a rotating medium. Two accretion geometries are considered - one approximating accretion from a rotating cloud and the other, accretion from a Keplerian disk. It is assumed that some process, such as Ekman spin-up or nonequilibrium oscillations, maintains nearly constant angular velocity along cylinders about the rotation axis. Transport of angular momentum in the cylindrically radial direction by viscosity is included. Fluid instabilities and other physical processes leading to enhancement of this transport are discussed. Particular application is made to zero-temperature white-dwarf models, using the degenerate electron equation of state. An initially nonrotating 0.566-solar-mass white dwarf is followed during the accretion of more than one solar mass of material. Applications to degenerate stellar cores, to mass-transfer binary systems containing white dwarfs, such as novae and dwarf novae, to Type I supernovae, and to galactic X-ray sources are considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
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  • 90
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    Spatial distribution of Compton-produced X-ray flux from rich and regular clusters of galaxies (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The spatial distribution of radio and X-ray fluxes from rich and regular clusters of galaxies is discussed. A diffusion model is investigated in which high-energy electrons are ejected from a point source at the center of the cluster. While diffusing out, the electrons lose energy by Compton scattering with the universal blackbody photons, thus producing the X-ray emission. Traversing intracluster magnetic fields, the electrons emit synchrotron radio emission. For the Coma cluster of galaxies good agreement is found between the observed and predicted X-ray counting-rate distribution for the Compton model. From the observed radio data a value of about 3 by 10 to the -8th power gauss is deduced for the average magnetic-field strength in the central region of Coma.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
    Format: text
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  • 91
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    The relativistic equations of stellar structure and evolution (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The general-relativistic equations of stellar structure and evolution are reformulated in a notation which makes easy contact with Newtonian theory. Also, a general-relativistic version of the mixing-length formalism for convection is presented.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
    Format: text
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  • 92
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    The line blanketing and structure of the atmosphere of Arcturus (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Model atmospheres for the K2 III star Arcturus (alpha Boo), calculated with various representations of the atomic and molecular opacity, are compared with the observed flux distribution and a published semiempirical temperature structure. A model computed with the opacity-sampling method and with an effective temperature of 4250 K and a surface gravity of 50 cm/sec per sec matches well, while models with other representations of the opacity produce distinctly worse fits. The effective temperature is well determined at 4250 + or - 100 K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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  • 93
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    Ionization fronts as phase transitions (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Model weak D-type ionization fronts have been constructed which include the effects of magnetic pressure and H I coolants. Ly-alpha cooling is found to suppress the high-temperature peak of 15,000 to 20,000 K found in earlier models. Ionization fronts are found to be closely related to phase transitions.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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  • 94
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    X-ray clusters of galaxies - Correlations with optical morphology and galaxy density (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The entire sample of 37 X-ray clusters of galaxies detected by the Ariel 5 satellite at high latitudes is analyzed optically. Morphological types (for all clusters) and central galaxy densities (for all clusters with measured redshifts) are determined, and the positions, redshifts, and richness groups of the set of Southern Hemisphere X-ray clusters are estimated. The X-ray luminosity is found to be correlated with both cluster morphology and central galaxy density. The observed correlations are consistent with a thermal-bremsstrahlung model in which the hot intracluster gas density is proportional to the galaxy density, and the temperature is proportional to the galaxy velocity dispersion.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 217
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  • 95
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    Orbit determination accuracies using satellite-to-satellite tracking (1977)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: The uncertainty in relay satellite sate is a significant error source which cannot be ignored in the reduction of satellite-to-satellite tracking data. Based on simulations and real data reductions, it is numerically impractical to use simultaneous unconstrained solutions to determine both relay and user satellite epoch states. A Bayesian or least squares estimation technique with an a priori procedure is presented which permits the adjustment of relay satellite epoch state in the reduction of satellite-to-satellite tracking data without the numerical difficulties introduced by an ill-conditioned normal matrix.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA-TM-X-71408 , X-931-77-189
    Format: application/pdf
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  • 96
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    Photometry of slow X-ray pulsars. II - The 13.9 minute period of X Persei (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Results are presented for time-resolved narrow-band photometry and spectrophotometry of X Per performed in an unsuccessful effort to confirm previously reported observations of 13.9-min pulsations in the intensity of the He II line at 4686 A. No features that are synchronous with a 13.9-min period are found in the optical data, and simultaneous X-ray observations of 3U 0352+30 are reported which show that a strong 13.9-min X-ray modulation was present during the optical photometry. Some implications of the X-ray periodicities observed for X Per are considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
    Format: text
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  • 97
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    The compact radio sources in 4C 39.25 and 3C 345 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Long-baseline interferometry of the quasars 4C 39.25 and 3C 345 at 10.65 and 14.77 GHz shows that the centimeter radio source in each object is double, with component separations of 0.0020 arcsec (4C 39.25) and 0.0013 arcsec (3C 345 at 1974.5). For each source, the separation is the same at both frequencies, as well as similar to the structure observed at 7.85 GHz (and 5.0 GHz for 4C 39.25). The spectra of the individual components are derived and shown to vary with time approximately as expected for expanding self-absorbed synchrotron sources. The magnetic fields in the components are estimated to be as high as 0.1 gauss, but the structure of the sources appears to be unrelated to the magnetic-field orientation derived from low-resolution polarization measurements. The component separation in 4C 39.25 has not changed for several years, whereas 3C 345 shows rapid expansion.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
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  • 98
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    On Compton and thermal models for X-ray emission from clusters of galaxies (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
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  • 99
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    Long-term behavior of MXB 1730-335 (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: The rapid burster MXB 1730-335 was detected on at least two occasions in 1971 and 1972 by Uhuru, and coverage is available from late 1970 to early 1973. Combined with ANS coverage in 1975 and 1976, as well as published SAS-3 and Ariel-5 observations (1976-1977), a unique record of long-term burst activity is now available for this source. There appear to be burst-active states of approximately one to two months' duration that occur with a duty cycle of about 15%. The burst activity appears to be recurrent with a time scale of roughly 0.5 to 1 year. Implications for burster models are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
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  • 100
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    X-ray clusters of galaxies - Correlation of X-ray luminosity with galactic content (1977)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: All 14 X-ray clusters of galaxies detected by the Ariel 5 satellite at high galactic latitudes with redshifts of less than 0.05 are analyzed optically for galaxy content. A strong correlation is found between cluster X-ray luminosity and galaxy type: the fraction of spiral galaxies in a cluster decreases rapidly with increasing X-ray luminosity. The observed correlation is consistent with a combined model of thermal bremsstrahlung emission from a hot intracluster gas and stripping of the spiral galaxies caused by the ram pressure of the same intracluster gas.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
    Format: text
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