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  • ASTROPHYSICS  (1,224)
  • 1990-1994  (1,224)
  • 1980-1984
  • 1990  (1,224)
  • 1
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    A model of the 8-25 micron point source infrared sky (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A model is developed that permits the representation of the Galactic disk and bulge, the molecular ring, extragalactic sky, and other Galactic structures in terms of the IR point-source sky. Full characterization is achieved for up to 87 types of Galactic sources in terms of scale heights and absolute magnitudes, and the model is guided by a parallel Monte Carlo simulation of the Galaxy at 12 microns. The model predicts differential and cumulative IR source counts for all bandpasses in the IRAS ranges and can therefore be employed to predict the character of the point-source sky related to IR space observations.
    Keywords: ASTROPHYSICS
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  • 2
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    The nature of interstellar/pre-cometary dust (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: During the past 15 years considerable progress in observational techniques has been achieved in the middle-infrared region (5000-500/cm, 2-20 microns), the region where most diagnostic molecular vibrations occur. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds and others obscured only by dust in the diffuse interstellar medium are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas and solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. By comparing these spectra with laboratory spectra one can determine the composition and abundance of the icy material frozen on the cold (- 10K) dust in the dark interior of molecular clouds and of the hydrocarbon component of dust in the diffuse interstellar medium. As these are the building blocks of comets, the work described here also gives insight into the nature of comets.
    Keywords: ASTROPHYSICS
    Type: ; : Optical Pattern Re
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  • 3
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    Turbulence in astrophysics (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Some of the astrophysical scenarios in which turbulence plays an important role are discussed in view of the comparative advantages of currently available models of turbulence phenomena; attention is given to a specific model that has undergone continuous refinement since 1985. The desideratum in this inquiry is a turbulence model which incorporates the best features of an a priori deterministic model, as well as a redundant set of results from full numerical simulations for a wide variety of turbulent flows; there should also be a simplification of the former, and an enlargement of the complexities of the latter.
    Keywords: ASTROPHYSICS
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  • 4
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    Cosmic impacts, cosmic catastrophes. II (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The role of extraterrestrial impacts in shaping the earth's history is discussed, arguing that cosmic impacts represent just one example of a general shift in thinking that has made the idea of catastrophes respectable in science. The origins of this view are presented and current catastrophic theory is discussed in the context of modern debate on the geological formation of the earth. Various conflicting theories are reviewed and prominent participants in the ongoing scientific controversy concerning catastrophism are introduced.
    Keywords: ASTROPHYSICS
    Type: Mercury (ISSN 0047-6773); 19; 21-25
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  • 5
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    Hydrocarbon emission features in the IR spectra of warm supergiants (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations in the 3-13 micron range are presented for two objects possessing the unidentified 21-micron feature, IRAS 22272 and IRAS 07134, which were obtained in the course of search for circumstellar aromatic hydrocarbon (PAH) emission bands. The 3.3 and 6.2 micron bands are attributed to circumstellar PAH molecules, and the 6-9 micron plateau and the 12- and 6.9-micron lines are attributed to larger, aromatic hydrocarbon clusters. These are the coolest stars known to exhibit the IR emission bands. The 21-micron feature is conjectured to also originate in a carbonaceous carrier.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 365; L23-L26
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  • 6
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    The absence of circumstellar dust debris around G giants (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The IRAS data base has been searched for evidence for circumstellar dust around luminosity class III G giants, stars whose progenitors are mostly main-sequence A stars. While 20 percent of all main-sequence A dwarfs have dust which absorbs at least 5 x 10 to the -6th of the light from the star, less than 3 percent of all G giants have such clouds. One possible explanation for the absence of detectable dust debris around the G giants is that the Poynting-Robertson effect leads to the decay of the dust around the main-sequence A stars, and that the supply of these grains is not renewed indefinitely. In this case, the derived upper limit to the grain radius of about 0.2 cm for the bulk of the grains emitting the far-infrared emission is consistent with data derived from ground-based submillimeter observations. Another possible explanation for the lack of grains around at least some G giants is that the dust around the original A dwarf is mainly composed of relatively volatile material like water ice which thermally evaporates in a relatively short time during the giant phase of higher luminosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 317-320
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  • 7
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    CO(J = 2 - 1) study of molecular clouds in the southwest arm of M31 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The first map of M31 in the CO(J = 2 - 1) transition, covering a 3 arcmin by 3 arcmin section of the SW arm-interarm region, is presented. The CO spectra in the arm region defined by H II regions are characterized by strong, narrow features which are interpreted here to be giant molecular clouds with masses of a few 100,000 solar masses. The interarm emission is interpreted as an ensemble of small clouds with masses of a few 10,000 solar masses. On the arm about 70 percent of the emission comes from large clouds, while off the arm essentially all of it comes from small clouds. The mass surface density on this section of M31 is about that of a comparable section of the Scutum arm of the Galaxy. The velocities of the giant clouds in the arm are shifted with respect to the rest of the molecular and atomic gas by about 15 km/s. This may be due to cloud response to passage through the spiral arm potential.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 195-207
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  • 8
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    Magnetically controlled circumstellar matter in the helium-strong stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper reports the observation and interpretation of the ultraviolet spectrum variations of nine helium-strong stars: HD 36485, 37017, 37479, 37776, 58260, 60344, 64740, 96446, and 133518. A unified model is developed to account for the observed correlation among three stellar properties: the line profile characteristics of the C IV and Si IV resonance doublets, the variations in the strength of these lines, and the inferred magnetic field geometry. It is proposed that circumstellar plasma is trapped in the stellar magnetosphere near the magnetic equator or is channeled to form jetlike outflows from the magnetic polar regions. These results, together with those of a previous study of the helium-weak sn stars, show that both helium-weak and helium-strong stars can possess magnetospherically trapped plasma, notwithstanding their different photospheric properties. New results for radii and temperatures of the helium-strong stars in Ori OB 1 and for HD 64740 from low-dispersion IUE spectra are also presented.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 665-676
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  • 9
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    First images of water vapor masers in the galaxy M33 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The first successful VLBI observations of 10 extragalactic H2O masers in the M33 galaxy are reported. A spectral-line VLBI synthesis map is constructed, the first of any extragalactic H2O maser sources. The map has the lowest noise of any K-band spectral line VLBI map yet produced. The maser emission extends over about 300 milliarcseconds and is divided into 14 distinct spatial components, the strongest of which has a correlated flux density of about 0.7 Jy. The relative positions of some of these components are determined accurately enough to provide first-epoch measurements for proper motion studies. The characteristics of the maser are similar to those of the most powerful maser in the Galaxy, W49N. A compact H II region is found close to the maser which is 1 pc in diameter and whose emission measure is about 6 x 10 to the 7th pc/cm exp 6. This region is the compact component of a more extended H II complex that extends over about 100 pc.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 364; 513-526
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  • 10
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    Gamma-ray burster counterparts - Archival data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper reports on the results of a search for optical transient images associated with gamma-ray bursters based on the collection of archival photographs at the Harvard College Observatory. This study searched through over 32,000 plates showing 16 gamma-ray burst error regions. The primary result is the identification of three optical transient images. The recurrence time scale for optical events with a gamma-ray to optical fluence ratio of less than 1000 is estimated to be 1.3 yr (with a 99-percent confidence interval of between 0.41 and 4.8 yr). A control study was simultaneously made where regions of the sky with no bursters were examined. The control region was 15.6 times larger than the burst search region, yet no optical transients were found. This paper describes in detail the methodology and the statistical results. Close attention is paid to a detailed analysis of the three optical transient images.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 364; 590-600
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  • 11
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    Meteoritic silicon carbide - Pristine material from carbon stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: All five gases in interstellar silicon carbide grains have grossly nonsolar isotopic and elemental abundances that vary with grain size but are strikingly similar to calculated values for the helium-burning shell of low-mass carbon stars. Apparently these grains formed in carbon-star envelopes, and were impregnated with noble gas ions from a stellar wind. Meteoritic SiC provides a detailed record of nuclear and chemical processes in carbon stars.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 348; 293-298
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  • 12
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    Quasinormal modes of Reissner-Nordstrom black holes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A matrix-eigenvalue algorithm is presented for accurately computing the quasi-normal frequencies and modes of charged static blackholes. The method is then refined through the introduction of a continued-fraction step. The approach should generalize to a variety of nonseparable wave equations, including the Kerr-Newman case of charged rotating blackholes.
    Keywords: ASTROPHYSICS
    Type: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 41; 2986-299
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  • 13
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    Electron-positron pairs, Compton reflection, and the X-ray spectra of active galactic nuclei (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown here that reprocessing of radiation fron nonthermal pair cascades by cold material in the central parts of active galactic nuclei (AGN) gives rise to X-ray and gamma-ray spectra that satisfy current observational constraints. An average 1-30 keV X-ray spectral index alpha(x) of about 0.7 in the compact range 30-300 is obtained for a wide range of Lorentz factors of the injected electrons. The gamma-ray spectra are steep, with alpha(gamma) about two, and satisfy the observational constraints. Radiation from pair cascades exhibits steep power law decreases in soft X-rays similar to those observed in AGN. The overall picture is consistent with AGN having an accretion disk which intercepts and reprocesses a substantial fraction of the nonthermal continuum incident upon it from above and below.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 363; L1-L4
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  • 14
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    Analysis of the COS B data for evidence of linear polarization of Vela pulsar gamma rays (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The COS B spark chamber telescope observations of the Vela pulsar were analyzed for gamma-ray polarization. No significant quadrupole moment is found in the azimuthal distribution of the electron-positron pair production planes. However, analysis of the sensitivity indicates that even 100-percent polarization would not be detected. Therefore, the null result does not constrain the polarization of the Vela pulsar gamma-ray emission. This result contradicts the report of Caraveo et al. (1988) of possible evidence for polarization of the Vela pulsar gamma rays.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 363; 270-273
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  • 15
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    Gas release in comet nuclei (1990)
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    Publication Date: 2011-08-19
    Description: Processes taking place during the evolution of a comet nucleus are examined, taking into account the release of gas on crystallization and the gas flow through the porous nucleus. In particular, the stresses caused by the gas pressure, the contribution of gas flow to the heat transfer, and the rate of gas emission by the comet along its orbit were determined using a model of spherically symmetric comet nucleus made of porous amorphous ice, with 10 percent CO gas trapped in it. Several values of density and pore size are considered, and for each combination of parameters, the model is evolved for 20-30 revolutions in Comet P/Halley's orbit. It is shown that a model of 0.2 g/cu cm density reproduces well many of the light-curve and activity characteristics of Comet P/Halley.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 363; 274-282
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  • 16
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    Images in the rocket ultraviolet - Young clusters in H II regions of M83 (1990)
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    Publication Date: 2011-08-19
    Description: UV images of M83 at 1540 and 2360 A reveal 18 compact sources that are associated with H II regions. E(B - V) values were estimated individually from the observed UV and optical colors and the Galactic UV extinction curve, using theoretical flux distributions. The dereddened colors are consistent with ages up to 3 x 10 to the 6th yr. A maximum possible age of 6.5 x 10 to the 6th yr is obtained assuming foreground reddening only. The distribution of observed colors is consistent with the Galactic reddening curve but not with enhanced far-UV extinction, as in the LMC 30 Dor curve. The H-alpha fluxes suggest either that dust within the H II regions absorbs up to 70 percent of the Lyman continuum radiation or that a similar fraction of the H-alpha flux is below the surface brightness detection limit. Cluster mass estimates depend on the range of stellar masses present but are probably in the range 10,000-100,000 solar masses.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 363; 154-158
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  • 17
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    Dynamical instabilities in axisymmetric stellar systems. I - Oblate E6 models (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The stability of a set of models based on isothermal oblate E6 elliptical galaxies is studied using N-body techniques. The only stable models are those that are near the isotropic model and have nearly equal number of stars in retrograde and prograde orbits. Fast rotators are unstable to modes that appear to be analogous to the classical streaming instability seen in many disk systems. Systems with a large velocity dispersion in the direction of the cylindrical radius are unstable to modes that appear to be similar to the radial orbit instability observed in some spherical systems. However, evidence is presented that these two instabilities may be related, and an instability criterion that applies to both is constructed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 363; 66-78
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  • 18
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    Comparisons of SiO maser and long-period variable positions in the R Aquarii and Omicron Ceti binary systems (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It has been determined that the absolute position of the centroid of SiO maser-emitting spots toward both R Aqr and Omicron Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer, while the LPV positions were determined with the 8-in transit circle of the US Naval Observatory. These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system; statistical reasons for the discrepancy are suggested. High-resolution spectra of both sources are presented and possible models are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 663-666
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  • 19
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    Giotto IMS measurements of the production rate of hydrogen cyanide in the coma of Comet Halley (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ion composition measurements in the ionosphere of Comet Halley by the ion mass spectrometer (IMS) experiment on the Giotto spacecraft are used to estimate the relative abundance of HCN. From a comparison of the normalized number density of ions with mass-to-charge (M/q) ratio of 28 AMU/e with steady-state photochemical models, it can be determined that the production rate of HCN directly from the central nucleus is Q(HCN) is less than about 0.0002 Q(H2O) at the time of Giotto encounter. The related photochemical- model calculations also indicate that Q(NH3)/Q(H2O) at the time of Giotto encounter. The related photo-chemical model calculations also indicate that Q(HN3)/Q(H2O) equals about 0.005, in agreement with recent determination from ground-based observations. The estimated value of Q(HCN) is lower than the relative abundance of Q(HCN)/Q(H2O) of about 0.001, as derived from radio observations of the 88.6 GHz emission of the J = 1 - 0 transition of HCN. The difference may be the result of time variations of the coma composition and dynamics, as well as other model-dependent effects.
    Keywords: ASTROPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 8; 319-325
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  • 20
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    Exosat observations of Cygnus X-2 continuum and line spectrum (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analysis of five Exosat observations of Cyg X-2, taken around a full binary orbit is presented. The data were obtained using all instrumentation (1000 lines/mm Transmission Grating Spectrometer, Channel Multiplier Array + filters, Medium-Energy experiment, and Gas Scintillation Proportional Counter) simultaneously, and span the full energy range 0.5-20 keV. No clear evidence was found for a correlation of any of the source characteristics with orbital phase. During two of the observations, significant iron K emission at 6.7 keV was detected, the relative strength of which seems to correlate with total X-ray intensity during two sharp intensity dips. The previous detection of discrete emission features in the 12-19 A band with the Einstein grating is confirmed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 596-606
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  • 21
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    Thermal structure of neutral winds from young stellar objects (1990)
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    Publication Date: 2011-08-19
    Description: The physical processes that control the thermal structure of lightly ionized winds from cool protostars are discussed. Attention is concentrated on the hydrogen gas, and the heating, cooling, and chemical processes that affect the neutral and ionic species of atomic and molecular hydrogen are examined. Warm silicate dust may condense out of the cooling wind and may heat the gas through collisions. Singly ionized sodium atoms, which do not recombine for the mass-loss rates considered, set a lower limit to the ionization fraction in the wind. Magnetic fields, which are presumed to accelerate the wind, couple directly to the ionic component of the gas and transfer momentum and energy to the neutral component through collisions. This process of ambipolar diffusion is found to be the dominant source of heat input to the gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 546-569
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  • 22
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    The circumstellar dust envelopes of red giant stars. I - M giant stars with the 10-micron silicate emission band (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Spherical dust envelope models of red giant stars are constructed by solving the radiative transfer equations of the generalized two-stream Eddington approximation. The IRAS observations of M giant stars which show the 10-micron silicate emission band in IRAS LRS spectra are explained by the models with the dirty silicate grains with K proportional to lambda exp -1.5 for lambda greather than 28 microns. Under the assumption of steady mass flow in the envelope, this model analysis gives the following conclusions: (1) the strength of the silicate emission peak at 10 microns is a good indicator of the mass loss rate of the star, (2) no stars with the 10-microns silicate emission feature are observed in the range of mass loss rate smaller than 7 x 10 to the -8th solar mass/yr, and (3) the characteristic time of the mass loss process of M stars does not exceed a few 10,000 years.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 227; 2, Ja
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  • 23
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    WRA 751, a candidate for a new luminous blue variable (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presened on spectroscopic observations (carried out with the ESO 1.52-m telescope at La Silla, Chile) and measurements made by the Infrared Astronomical Satellite on the star WRA 751. It is estimated that the T(eff) of this star is 30,000 K and its E(B-V) is 1.8 mag. Comparison with evolutionary tracks of Maeder and Meynet (1980) indicates that WRA 751 is located in the region of luminous blue variables at a lower limit of the initial mass of about 50 solar masses. Its other physical characteristics, such as the light variability, strong Fe II lines, and the extinction-free spectral energy distribution, suggest that WRA 751 is a candidate for a new luminous blue variable.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 227; 1, Ja
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  • 24
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    The mixing length parameter alpha (1990)
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    Publication Date: 2011-08-19
    Description: The standard mixing length theory, MLT, treats turbulent eddies as if they were isotropic, while the largest eddies that carry most of the flux are highly anisotropic. Recently, an anisotropic MLT was constructed, and the relevant equations derived. It is shown that these new equations can actually be cast in a form that is formally identical to that of the standard isotropic MLT, provided the mixing length parameter, derived from stellar structure calculations, is interpreted as an intermediate, auxiliary function alpha(x), where x, the degree of anisotropy is given as a function of the thermodynamic variables of the problem. The relation between alpha(x) and the physically relevant alpha(l = Hp) is also given. Once the value alpha is deduced, it is found to be a function of the local thermodynamic quantities, as expected.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 227; 1, Ja
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  • 25
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    Far-infrared spectroscopy of the DR 21 star formation region (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Far-IR line and continuum observations of the DR 21 star formation region are presented. It is shown that the extended emission in the 63 micron forbidden O I, 35 micron forbidden Si II, and 158 micron forbidden C II lines is most likely produced in dense, warm photodissociation regions on the surfaces of atomic and molecular clumps of size smaller than 0.6 pc. The gas temperatures in these photoelectrically heated, predominantly atomic layers are 250-500 K and are maintained by FUV fluxes 10,000 or more times the average interstellar radiation field. Gas densities in the surface layers are in the range 10,000-50,000/cu cm. The gas phase abundance of Si(+) is inferred to be about 5 x 10 to the -6th relative to hydrogen, or about 0.15 of its solar abundance. The mass of atomic gas is at least 200 solar masses.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 132-144
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  • 26
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    An extremely carbon-poor planetary nebula in the Small Magellanic Cloud (1990)
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    Publication Date: 2011-08-19
    Description: An optical and ultraviolet study is presented of object 28 of Sanduleak et al. (1978) in the SMC. This object is an extreme type of I PN which apparently has undergone all three stages of nuclear dredge-up together with an appreciable amount of convective envelope burning. Optical and UV data are well-represented by a model in which the central star has a temperature of 180,000 K and a radius of 0.09 solar radius. A nebular mass of 0.71 solar mass and a central star mass of 0.65-0.71 solar mass are inferred. The object apparently evolved from a massive progenitor with main-sequence mass greater than five solar masses, which underwent both second and third nuclear dredge-up and very efficient hot bottom burning.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 101-106
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  • 27
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    The volume- and surface-binding energies of ice systems containing CO, CO2, and H2O (1990)
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    Publication Date: 2011-08-19
    Description: Laboratory-measured, temperature-dependent sticking efficiencies are presently used to derive the surface-binding energies of CO and CO2 on H2O-rich ices, with a view to determining the condensation and vaporization properties of these systems as well as to the measured energies' implications for both cometary behavior and the evolution of interstellar ices. The molecular volume and the surface binding energies are not found to be necessarily related on the basis of simple nearest-neighbor scaling in surface and bulk sites; this may be due to the physical constraints associated with matrix structure-associated physical constraints, which sometimes dominate the volume-binding energies.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 87; 188-192
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  • 28
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    The anomalous 3.43 and 3.53 micron emission features toward HD 97048 and Elias 1 - C-C vibrational modes of polycyclic aromatic hydrocarbons? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The 5-8 micron spectra obtained toward the two protostellar sources, HD 97048 and Elias 1 exhibit strong anomalous emission features at 3.43 and 3.53 microns. Combining these results with earlier data established that the emission in the general IR features is extended on at least a 20-arcsec scale. In view of the high energy density in the emission zone, as well as the apparent correspondence of the anomalous 3.43 and 3.53 micron features with weak emission shoulders associated with the general family of IR emission bands, an explanation for these observations in terms of C-C overtones and combination tones of large or dehydrogenated polycyclic aromatic hydrocarbons is judged to be provisionally suitable.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 360; 577-589
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  • 29
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    The structure and evolution of radiatively cooling jets (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The two-dimensional simulations presently used to characterize the structure and evolution of radiatively cooling supersonic jets reveal that cooling jet morphologies resemble those of adiabatic outflows, but with the fundamental difference that a dense, cold shell will condense out of the shocked gas at the head of the jet when the cooling distance behind either of the two principal shocks is smaller than the jet radius. For very high cooling rates, the material that accumulates at the head of the jet forms an extended plug of cold gas resembling the 'nose cone' observed in numerical simulations of strongly magnetized adiabatic jets. An investigation is made of the dependence of jet properties on the density ratio between the beam and the ambient medium, as well as on the strength of radiative cooling.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 360; 370-386
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  • 30
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    Studies in astronomical time series analysis. IV - Modeling chaotic and random processes with linear filters (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: While chaos arises only in nonlinear systems, standard linear time series models are nevertheless useful for analyzing data from chaotic processes. This paper introduces such a model, the chaotic moving average. This time-domain model is based on the theorem that any chaotic process can be represented as the convolution of a linear filter with an uncorrelated process called the chaotic innovation. A technique, minimum phase-volume deconvolution, is introduced to estimate the filter and innovation. The algorithm measures the quality of a model using the volume covered by the phase-portrait of the innovation process. Experiments on synthetic data demonstrate that the algorithm accurately recovers the parameters of simple chaotic processes. Though tailored for chaos, the algorithm can detect both chaos and randomness, distinguish them from each other, and separate them if both are present. It can also recover nonminimum-delay pulse shapes in non-Gaussian processes, both random and chaotic.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 359; 469-482
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  • 31
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    Kinetic instability associated with spherical shell distribution of cometary pickup ions (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The stability of ion shell distribution is an interesting and important issue in view of the fact that it is stable under perturbations propagating parallel to the ambient magnetic field, despite large amount of free energy it contains. It was found, however, that if the shell distribution of ions has a sufficient amount of drift speed with respect to the solar wind hydromagnetic waves, it can become unstable. The obliquely propagating hydromagnetic instability associated with the ion shell distribution was recently discovered. This letter presents the unified stability analysis of the ion shell distribution, under what condition the drift-induced instability of the type first discussed by Gary and Sinha (1989), and the oblique hydromagnetic instability discussed by Wu and Yoon (1990) are excited, and how the two types of instabilities are related.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1033-103
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  • 32
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    Imaging and two-dimensional spectra of the IR-bright galaxy NGC 2146 - A recent low-energy merger? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New data are presented on the IR-luminous galaxy NGC 2146 from several sources: direct imaging in B, R, and H-alpha; IR imaging in the J, H, and K bands; long-slit spectroscopy at optical and IR wavelengths; and scanning etalon observations in H-alpha. The results allow measurement of the interstellar extinction in the dust lane, and estimation of the true luminosity of the galaxy and nuclear regions. The spectra indicate that there is no active nucleus, and measure the changing ratio of forbidden to permitted lines across the galaxy. IR images and colors indicate the existence of a significant population of hot young stars in the central regions of the system. The H-alpha velocity maps show the full radial-velocity pattern, and suggest that the system consists of a disturbed disk and a merging or interacting arm which connects to the inner dust and radio structures. Outer H-alpha and H I structures appear to be the earlier remnants of this spiraling merger.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 100; 60-69
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  • 33
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    The fuelling of active galactic nuclei (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Accretion mechanisms for powering the central engines of active galactic nuclei (AGN) and possible sources of fuel are reviewed. It is a argued that the interstellar matter in the main body of the host galaxy is channeled toward the center, and the problem of angular momentum transport is addressed. Thin accretion disks are not a viable means of delivering fuel to luminous AGN on scales much larger than a parsec because of the long inflow time and effects of self-gravity. There are also serious obstacles to maintaining and regulating geometrically thick, hot accretion flows. The role of nonaxisymmetric perturbations of the gravitational potential on galactic scales and their triggers is emphasized. A unified model is outlined for fueling AGN, in which the inflow on large scales is driven by gravitational torques, and on small scales forms a mildly self-gravitating disk of clouds with inflow driven by magnetic torques or cloud-cloud collisions.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 345; 679-686
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  • 34
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    A 5.75-millisecond pulsar in the globular cluster 47 Tucanae (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A pulsar with a period of 5.75 ms and a dispersion measure of 25/cu cm pc has been found in the direction of 47 Tucanae. Despite its probable origin as a member of a binary system, timing measurements show that the pulsar is now single. The observed dispersion measure is consistent with the pulsar lying outside the Galactic electron layer and within 47 Tucanae, but it is very different from the value of 67/cu cm pc for the pulsars that were reported recently as being in this globular cluster. It is suggested that the latter pulsars probably do not in fact lie within 47 Tucanae.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 345; 598-600
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  • 35
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    Flat-spectrum radio sources - Cosmic conspiracy or relativistic neutrons? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The intensity spectrum of the core of radio-loud AGN varies smoothly from 10 exp 8.5 to 10 to the 16th Hz, and is flat between 10 to the 9th and 10 to the 10th Hz, implying that a single emission mechanism is responsible. It is proposed here that energy is transported from the central source by relativistic neutrons which travel freely over a large volume and decay into relativistic protons. The protons produce secondary electrons which generate the observed radiation. The photon spectra thus produced are largely model-independent and flat.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 345; 319-322
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  • 36
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    Evolution and detectability of comet clouds during post-main-sequence stellar evolution (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The destruction of volatile-rich comet disks and Oort-type clouds around luminous post-main-sequence stars is modeled. The models are in agreement with several aspects of existing observations of water and complex molecules in the envelopes of giant and supergiant stars. If confirmed, these results would establish the common existence of Oort-type clouds around other stars and would constitute indirect evidence for sites of past planetary formation.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 345; 305-308
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  • 37
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    Apparent orbit of the spectroscopic binary Beta Arietis with the time Mark III Stellar Interferometer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The spectroscopic binary Beta Ari has been directly resolved with the Mark III Stellar Interferometer. Observations in 1988 were analyzed to determine the visual orbit of the system with the following results: eccentricity = 0.903 +/- 0.012, semimajor axis = 0.0361 +/- 0.0003 arcsec, inclination = 44.7 +/- 1.3 deg, longitude of periastron = 209.1 deg +/- 1.2 deg, position angle of ascending node = 79.1 deg +/- 0.8 deg. The measured magnitude difference between two components, Delta m = 2.63 +/- 0.22 at 800 nm, yields individual visual magnitudes of m(v1) = 2.70 +/- 0.02 and m(v2) = 5.80 +/- 0.20. Combined with data from spectroscopic observations, masses M1 = (2.34 +/- 0.10) solar masses, M2 = (1.34 +/- 0.07) solar masses, and geometrical parallax pi = 0.053 arcsec +/- 0.002 arcsec are derived. These results demonstrate that both components of Beta Ari agree well with the empirical mass-luminosity relation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 641-645
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  • 38
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    A model of the pre-Sedov expansion phase of supernova remnant-ambient plasma coupling and X-ray emission from SN 1987A (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper examines the mechanism responsible for coupling supernova (SN) remnant to the ambient medium during the pre-Sedov or the so-called free expansion phase, immediately following the progenitor explosion. A theory is developed for the interaction of an SN piston with the ambient medium during the pre-Sedov phase. The possibility of X-ray production by the high-speed portion of the piston during this phase is investigated. The relevant observations of high-energy emissions from the SN 1987A, including the X-ray spectrum, luminosity, and temporal development, are considered. It is shown that the commonly assumed snowplow model for SNR evolution is valid, because of the action of a variety of collisionless two-stream instabilities that permit the coupling of the ambient plasma with SNR.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 549-571
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  • 39
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    A test of the association of infrared activity with bars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The hypothesis that high FIR luminosities in noninteracting galaxies are dependent on material fed into their nuclei or into circumnuclear rings along bars can be tested by NIR imaging. A sample of 22 galaxies was selected from the Revised Shapley-Ames Catalog, that have FIR luminosities greater than 10 to the 10th lunar luminosities and hot colors between 60 and 100 microns, indicative of possible nuclear starbursts, but are not interacting or classified as Seyfert galaxies. Fifteen galaxies of the sample of 16 that are not clearly barred from optical data and are isolated were imaged at 1.6 micron and 2.2 microns. In an evaluation of the IR images, at least eight of these galaxies do not appear to have bars. Strong bars therefore do not appear to be an absolute requirement for high IR luminosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 416-429
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  • 40
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    Stellar dynamics of powerful radio galaxies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New data on the stellar dynamics of 20 powerful radio galaxies (PRGs) were collected with the KPNO 4 m using the RC spectrograph and a TI CCD and were combined with similar data in the literature to generate a total sample of 47 PRGs. A detailed investigation of the various PRG subgroups (normal/peculiar optical morphology, and presence/absence of optical emission lines) revealed important distinctions among these groups as well as distinctions between some PRGs and normal elliptical galaxies. It is found that PRGs with peculiar optical morphologies are dynamically peculiar as well: their stellar velocity dispersions are lower than those of both elliptical galaxies and PRGs with normal optical morphologies, and they show evidence for more rotational support. Results suggest that some of the PRGs are the product of a merger of two galaxies, at least one of which was a disk system.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 399-415
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  • 41
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    Comment on 'Local generation of electrostatic bursts at Comet Giacobini-Zinner: Modulation by steepened magnetosonic waves' by A. L. Brinca et al (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 8287-828
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  • 42
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    New bound on neutrino dipole moments from globular-cluster stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Neutrino dipole moments mu(nu) would increase the core mass of red giants at the helium flash by delta(Mc) = 0.015 solar mass x mu(nu)/10 to the -12th muB (where muB is the Bohr magneton) because of enhanced neutrino losses. Existing measurements of the bolometric magnitudes of the brightest red giants in 26 globular clusters, number counts of horizontal-branch stars and red giants in 15 globular clusters, and statistical parallax determinations of field RR Lyr luminosities yield delta(Mc) = 0.009 + or - 0.012 solar mass, so that conservatively mu(nu) is less than 3 x 10 to the -12th muB.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 64; 2856-285
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  • 43
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    Studies of H I and D I in the local interstellar medium (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-dispersion IUE spectra are presented of the hydrogen Ly-alpha chromospheric emission line of two nearby late-type stars, Capella and Lambda And. Both interstellar H I and D I Ly-alpha absorption can be seen against the chromospheric line, and the density, velocity dispersion, and bulk velocity of the gas in those lines of sight are derived. Limits are placed on the D/H ratio. The results are consistent with the current picture of the local interstellar medium.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 223-228
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  • 44
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    Efficient star formation in the spiral arms of M51 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The molecular, neutral, and ionized hydrogen distributions in the Sbc galaxy M51 (NGC 5194) are compared. To estimate H2 surface densities observations of the CO (J = 1 - 0) transition were made in 60 positions out to a radius of 155 arcsec. Extinction-corrected H-alpha intensities were used to compute the detailed massive star formation rates (MSFRs) in the disk. Estimates of the gas surface density, the MSFR, and the ratio of these quantities, MSFR/sigma(p), were then examined. The spiral arms were found to exhibit an excess gas density, measuring between 1.4 and 1.6 times the interarm values at 45 arcsec resolution. The total (arm and interarm) gas content and massive star formation rates in concentric annuli in the disk of M51 were computed. The two quantities fall off together with radius, yielding a relatively constant MSFR/sigma(p) with radius. This behavior is not explained by current models of star formation in galactic disks.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 135-148
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  • 45
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    The ephemeris of X 1822 - 371 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: From the analysis of eclipses observed with the HEAO-1, Einstein, Exosat and Ginga satellites, it is shown that the orbital period of X1822 - 371 is increasing on a time-scale of 2.9 million yr. The period change, one of only three determined amongst the LMXBs, is in the opposite sense to the expected evolutionary trend, but in the same sense as the period change of Cyg X-3. The observation of an eclipse simultaneously in the X-ray and optical bands shows that the optical eclipse is asymmetric and has a minimum 3 min later than that of the X-ray eclipse, reflecting a pronounced asymmetry in the optically emitting disk structure.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 244; 39P-43P
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  • 46
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    Signatures of aging silicate dust (1990)
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    Publication Date: 2011-08-19
    Description: A self-consistent explanation for the width, strength, and position of spectral features which may be diagnostic of the structure and composition of circumstellar and interstellar silicate grains is presented based on a long series of laboratory experiments using simple oxide analogs. The ratio of the integrated absorption strength of the grains near 10 mu to that near 20 mu is shown to decrease monotonically with increased processing. This ratio may be diagnostic of the relative age of the silicate. The oxidation state of iron in the grains is directly related to both the near-IR grain opacity and enhanced absorption in the UV. The oxidation state of both iron and silicon is directly related to the rate of nucleation, growth, and processing in a circumstellar outflow, as well as to the processing history of the grain after it reaches the interstellar medium. Other diagnostic indicators of the average silicon oxidation state, degree of structural polymerization, and dispersion in the average degree of structural polymerization are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 163; 1, Ja
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  • 47
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    Orbital periods of recurrent novae (1990)
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    Publication Date: 2011-08-19
    Description: The class of recurrent novae (RN) with thermonuclear runaways contains only three systems (T Pyx, U Sco, and V394 CrA), for which no orbital periods are known. This paper presents a series of photometric observations where the orbital periods for all three systems are discovered. T Pyx is found to have sinusoidal modulation with an amplitude of 0.08 mag and a period of 2.3783 h (with a possible alias of 2.6403 h). U Sco is found to be an eclipsing system with an eclipse amplitude of roughly 1.5 mag and an orbital period of 1.2344 days. V394 CrA is found to have sinusoidal modulation with an amplitude of 0.5 mag and a period of 0.7577 days. Thus two out of three RN with thermonuclear runaways (or five out of six for all RN) have evolved companions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 355; L39-L42
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    The effect of catastrophic collisional fragmentation and diffuse medium accretion on a computational interstellar dust system (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of catastrophic collisional fragmentation and diffuse medium accretion on a the interstellar dust system are computed using a Monte Carlo computer model. The Monte Carlo code has as its basis an analytic solution of the bulk chemical evolution of a two-phase interstellar medium, described by Liffman and Clayton (1989). The model is subjected to numerous different interstellar processes as it transfers from one interstellar phase to another. Collisional fragmentation was found to be the dominant physical process that shapes the size spectrum of interstellar dust. It was found that, in the diffuse cloud phase, 90 percent of the refractory material is locked up in the dust grains, primarily due to accretion in the molecular medium. This result is consistent with the observed depletions of silicon. Depletions were found to be affected only slightly by diffuse cloud accretion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 355; 518-535
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  • 49
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    Optical environments of radio quasars (1990)
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    Publication Date: 2011-08-19
    Description: CCD images of 36 radio-loud quasars in the redshift range 0.1-0.75 are discussed. The objects were chosen to represent the full range of radio structure found with VLA A-configuration observations. Measured quantities are compared and correlated from both radio and optical observations. At least 70 percent of the quasars show evidence for current or recent interaction. Consideration is given to host galaxy sizes and luminosities, states of tidal interaction and numbers of companions, radio morphology, and luminosity.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1715-172
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  • 50
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    Observations of 40-70 micron bands of ice in IRAS 09371 + 1212 and other stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IRAS 09371 + 1212 is still an absolutely unique object. This M giant star, with circumstellar CO and a spectacular bipolar nebula, displays unique IRAS FIR colors which had been attributed to strong emission in the 40-70-micron bands of ice, as subsequently supported by the observation of a strong 3.1-micron absorption band. The results of the KAO observations have confirmed its unusual nature: the far-infrared bands of ice are by far the strongest known. Its dust temperature, 50 K or less, is by far the lowest known for a late-type circumstellar envelope.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 355; L27-L30
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    The physical and infrared spectral properties of CO2 in astrophysical ice analogs (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results of measurements of the infrared spectroscopic and condensation-vaporization properties of CO2 in pure and mixed ices are presented. Detailed examination of five infrared CO2 bands, 2.20, 2.78, 4.27, 15.2, and 4.39 microns, shows that the peak position, FWHM, and profile of the bands provide important information about the composition, formation, and subsequent thermal history of the ices. Absorption coefficients and their temperature dependence for all five CO2 bands are determined. The temperature dependence variation is found to be less than 15 percent from 10 to 150 K, i.e., the temperature at which H2O ice sublimes. The number of parameters associated with the physical behavior of CO2 in CO2- and H2O-rich ices, including surface binding energies, and condensation and sublimation temperatures, are determined under experimental conditions. The implications of the data obtained for cometary models are considered.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 355; 357-372
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  • 52
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    Heating and melting of small icy satellites by the decay of Al-26 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effect of radiogenic heating due to Al-26 on the thermal evolution of small icy satellites is studied. The object is to find the extent of internal melting as a function of the satellite radius and of the initial Al-26 abundance. The implicit assumption, based on observations of young stars, is that planet and satellite accretion occurred on a time scale of about 10 to the 6th yr (comparable with the lifetime of Al-26. The icy satellites are modeled as spheres of initially amorphous ice, with chondritic abundances of K-40, Th-232, U-235, and U-238, corresponding to an ice/dust mass ratio of 1. Evolutionary calculations are carried out, spanning 4.5 x 10 to the 9th yr, for different combinations of the two free parameters. Heat transfer by subsolidus convection is neglected for these small satellites. The main conclusion is that the initial Al-26 abundance capable of melting icy bodies of satellite size to a significant extent is more than 10 times lower than that prevailing in the interstellar medium (or that inferred from the Ca-Al rich inclusions of the Allende meteorite, about 7 x 10 to the -7th by mass).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 355; 281-286
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    Shocked forbidden O I 63 micron line emission from the supernova remnant IC 443 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations of the fine-structure emission from the forbidden O I 63 micron line in the SNR IC 443 are presented. It is shown that the emission correlates well with the distribution of line emission from shock-excited molecular hydrogen, which leads to the conclusion that the line is shock-excited. X-ray heating as well as UV-heating from a photodissociation region is ruled out as a possible excitation mechanism for the emission. It is shown that the forbidden O I 63 micron line is an important contributor to the total emission in the IRAS 60 micron band, estimated as approximately 40-75 percent of the total band flux. An attempt to shock model the line emission from IC 443 is made; however, to match the observational evidence, it has to be assumed that the shock is J-type, and that the oxygen chemistry is suppressed so that oxygen remains in atomic form and does not get converted into H2O. However, no theoretical rationale for these assumptions can be provided.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 355; 197-209
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  • 54
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    Forbidden-line emission and infrared excesses in T Tauri stars - Evidence for accretion-driven mass loss? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is suggested that disk accretion provides the requisite external source to power the winds of T Tauri stars. As a test of this hypothesis, a potential accretion diagnostic for a representative sample of stars is compared to diagnostics of the wind strength. The luminosity of H-alpha, formed in the inner wind, and the luminosity of the forbidden emission lines, formed in the outer wind, are used as wind diagnostics, while the excess infrared luminosity is used as a potential accretion diagnostic. It is found that forbidden-line O I 6300 A and H-alpha line luminosities are correlated with each other over two orders of magnitude; this is interpreted as the indication of a wide range of mass-loss rates among the given sample of T Tauri stars. The luminosity of each of these lines is also found to be correlated with excess infrared luminosity. However, neither the forbidden nor the H-alpha luminosity is well correlated with the photospheric luminosity, leading to a conclusion that it is the disk, not the star, which primarily determines the strength of wind indicators in T Tauri stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 354; 687-700
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    Massive soliton stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 354; 302-309
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    Ultraviolet observations of the enigmatic bipolar nebula M1-92 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IUE observations of the bipolar nebula M1-92 indicate that this object is an evolved object and possibly a preplanetary nebula. Data acquired in the SWP camera clearly show a flat UV continuum indicative of a relatively unobscured O subdwarf. Data acquired in the long wavelength region of the SWP and in the LWP camera reveal an object which mimics the characteristics of an F2 supergiant. These results, combined with other data at visual and infrared wavelengths, strongly favor that the central object of M1-92 is an evolved binary system. The He I 5876 and 6678 A absorption seen in optical spectra is extremely problematic. This, plus the presence of Fe II, Mg II, and Mg I absorption arising from resonance transitions and transitions from low-lying metastable levels, leads to the suggestion that the object resembling an F2 star is actually an early-type subdwarf cloaked in a thick circumstellar nebula. This interpretation and the similarities of the IR flux distribution to Vy 2-2, a preplanetary prototype, is consistent with M1-92 being in the process of forming a planetary nebula. The bipolar flow, the optical Fe II and ultraviolet Mg II emission of M1-92 are also characteristics of T Tauri stars. Although constraints definitely rule out that M1-92 is a pre-main-sequence object, these similarities imply that in many cases it may be difficult to distinguish between T Tauri stars and protoplanetary nebulae.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 354; 262-266
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    A Comptonization model for the submillimeter background (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new measurement of the submillimeter portion of the cosmic microwave background by Matsumoto et al. (1988) indicates that there may be a large excess of energy over that of a blackbody spectrum of temperature 2.74 K. Several models are presented with cosmological heat sources which produce Compton y-distortions large enough to fit the submillimeter background. The models adopt generic forms for these heat sources in terms of the expansion rate and the energy density of other forms of matter in the universe. A specific realization of the models in terms of a decaying vacuum is presented. Unique thermal histories are predicted in which the universe does not globally recombine. A rise in the spectrum at long wavelengths due to free-free emission of the hot intergalactic medium is predicted, and the accompanying mu-distortions are estimated.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 353; 399-405
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    Simultaneous multifrequency observations of the Seyfert 1 galaxy NGC 4051 - Constant optical-infrared emission observed during large-amplitude X-ray variability (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Simultaneous infrared, optical, ultraviolet, and X-ray observations of the low-luminosity Seyfert 1 galaxy, NGC 4051 are reported. A new method of reduction was developed to correct the optical flux for atmospheric variations due to seeing and extinction. The X-ray flux varied by factors of up to 2 on time-scales of tens of minutes, while the optical flux remained steady to within 1 percent. The results rule out all models, including Compton scattering and synchrotron models, in which a single electron population is responsible for the formation of both the infrared-to-optical and the X-ray spectra. The optical emission region must be an order of magnitude larger than, or completely separate from, the X-ray source.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 243; 713-720
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    Very low luminosity stars with very large amplitude flares (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: CCD frames of CZ Cnc, KY Cep, the gamma-ray burster optical transient, and NSV 12006 are analyzed. Also studied are 549 archival photographic plates of the CZ Cnc field. These observations are compared with the data of Lovas (1976). Flare events on CZ Cnc are examined. Based on the data it is noted that CZ Cnc is a main-sequence star, has a magnitude of 16.1, a distance of 100 pc, occasional large-amplitude flares, and frequent flares with amplitudes greater than 4 mag.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 353; L25-L28
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    The X-ray flux dipole of active galactic nuclei and the peculiar motion of the Local Group (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: X-ray emission from 30 resolved AGN's are used to study the dipole moment of their flux distribution on the sky. The data are derived from the Piccinotti et al. (1982) survey. X-ray fluxes are analyzed in terms of the alignment with the direction of the Local Group (LG) of galaxies. It is observed that the direction of the dipole moment of the flux is (313 deg, 38 deg); the dipole direction deviates from the LG velocity by 39 deg. It is detected that the amplitude of the dipole is about 50 percent of the corresponding monopole. Based on a comparison of the data with previous observations it is suggested that the X-ray emission from AGNs traces the underlying mass distribution at least as strongly as optical and IR emission from galaxies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 353; L3-L6
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    Luminosity-velocity diagrams for Virgo Cluster spirals. I - Inner rotation curves (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Optical rotation curves are presented for the innermost portions of nine spiral galaxies in the Virgo Cluster. The emission-line (H-alpha and forbidden N II) velocity data are to be used in combination with new CCD photometry to construct luminosity-velocity diagrams, in a continuing investigation of an apparent initial linear branch and its potential as a distance indicator. Compared to recent H I data, the present optical rotation curves generally show systematically steeper inner gradients. This effect is ascribed to the poorer resolution of the H I data and/or to holes in the gas distribution.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 353; 90-102
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    Local gravitomagnetism (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In a simple two-body system, the gravitomagnetic components of the metric in the local quasi-inertial frame of one of the bodies is calculated. The local geometry in this frame which is freely falling along the geodesic but is directionally fixed with respect to distant stars is primarily defined by the gravitomagnetic components of the local metric. This metric serves to track down the various contributions from the local and distant source and thus provides further insight to the nature of gravitomagnetism. As a result it is shown that in the quasi-inertial frame geodetic precession is a gravitomagnetic phenomenon. Furthermore a connection between local gravitomagnetic effects and Einstein's principle of equivalence is established.
    Keywords: ASTROPHYSICS
    Type: General Relativity and Gravitation (ISSN 0001-7701); 22; 10, 1
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    On the nature and implications of starburst-driven galactic superwinds (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Optical spectroscopic data are presented on the ionized nebulae associated with 14 galaxies that are strong far-IR emitters. It is found that the data provide both qualitative and quantitative support for the 'superwind' model in which the kinetic energy provided by SNe and winds from massive stars in a central starburst drives a large-scale outflow that can shock heat and accelerate ambient interstellar and circumgalactic gas. Clear kinematic signatures of an outflow along the galaxy's minor axis are found for the three nearest far-IR galaxies (FIRGs). The FIRG nebulae are highly overpressured relative to the Galactic ISM, with the pressure dropping systematically with distance from the nucleus. Superwinds are energetically adequate to power both the observed optical and X-ray nebulae, and the relative emission-line intensities and their radial variations are consistent with ionization by wind-driven shocks, but not with photoionization by normal O stars or an AGN. The possible astrophysical implications of superwinds are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 74; 833-868
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    Astrophysics and cosmology closing in on neutrino masses (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Massive neutrinos are expected in most grand unified theories that attempt to unify the strong and electroweak interactions. So far, heroic laboratory experiments have yielded only upper bounds on the masses of the elusive neutrinos. These bounds, however, are not very restrictive and cannot even exclude the possibility that the dark matter in the universe consists of neutrinos. The astrophysical and cosmological bounds on the masses of the muon and tau neutrinos, m(nu sub mu) and m(nu sub tau), which already are much more restrictive than the laboratory bounds, and the laboratory bound on the mass of the electron neutrino, m(nu sub e) can be improved significantly by future astrophysical and cosmological observations that perhaps will pin down the neutrino masses. Indeed, the recent results from the solar neutrino experiments combined with the seesaw mechanism for generating neutrino masses suggest that m(nu sub e) of about 10 to the -8th electron volts, m(nu sub mu) of about 0.001 electron volts, and m(nu sub tau) of about 10 electron volts, which can be tested in the near future by solar neutrino and accelerator experiments.
    Keywords: ASTROPHYSICS
    Type: Science (ISSN 0036-8075); 250; 1529-153
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    Line emission from clumpy photodissociation regions (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A theoretical parameter study of dense photodissociation regions is presented. It is found that when the gas density is sufficiently high relative to the FUV flux, self-shielding of the molecules can move the C(+)/CO and H/H2 atomic-molecular transitions close to the surfaces of the molecular cloud, where they can feel the full effect of heating by the FUV radiation field. For n of 100,000/cu cm, collisional deexcitation of the FUV-pumped H2 can move the lower levels toward the LTE, producing line ratio resembling those of shocked regions for these low-v levels, while the high-v level line ratios retain a 'fluorescent' value. Appreciable emission in high-J transitions of CO originates in this warm molecular gas. Comparison with observations suggests that a small volume filling factor of high density clumps embedded within a moderate density interclump medium are a common phenomenon in photodissociation regions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 620-639
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    Core mass at the helium flash from observations and a new bound on neutrino electromagnetic properties (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Existing measurements of the bolometric magnitudes of the brightest red giants in 26 globular clusters are used to determine the brightness difference between the tip of the red giant branch (on average found to be 0.1 mag brighter than the brightest red giant) and RR Lyrae stars. The metallicity variation of the result agrees perfectly with theoretical predictions. In conjunction with previous determinations of the number ratio of horizontal-branch versus red giant stars, with statistical parallax determinations of RR Lyrae absolute luminosities, and with theoretical predictions based on the Sweigart and Gross evolutionary sequences, this result yields an allowed range for a hypothetical core mass variation relative to the standard results of (0.009 + or - 0.012) solar mass. If neutrinos had anomalous electromagnetic dipole moments, the increased energy loss near the helium flash would lead to an increased core mass. Constraints on neutrino electromagnetic properties are determined from the color-magnitude diagrams of the globular clusters.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 559-568
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    Variations in the abundance of transiently heated particles within nearby molecular clouds (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IRAS images of molecular clouds in the Chamaeleon, Taurus, and Ursa Major complexes show that the mid-IR emission from transiently heated particles is distributed very differently from the 100 micron emission from large dust grains. The ratio between 12 and 100 micron emission varies by more than one order of magnitude in each complex from about 5 times to about one-quarter of the average value in the solar neighborhood. Within a complex, color variations are seen on all scales. No significant variations of the I(v)(100 micron)/A(v) ratio are observed between clouds of widely different mid- to far-IR color. It is shown that neither the large amplitude of the color variations nor their morphology can be explained by changes of the excitation by the UV radiation field and it is concluded that the color variations trace variations in the abundance of transiently heated particles. A scenario is proposed which relates the abundance variations to the cycling of interstellar matter between the gas-phase and grain surfaces.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 364; 136-145
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    X-ray study of superclusters (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Batuski-Burns list of candidate superclusters was searched for X-ray emission in the HEAO 1 A-2 data base. No significant flux in excess of integrated member cluster emission was detected in directions associated with estimated supercluster centroids; a 3 sigma upper limit to the mean individual excess flux is 5 x 10 to the -12th ergs/sq cm/s. Implications of this bound are discussed in terms of fainter member clusters, hot diffuse gas, and active and normal galaxies. Prospects of supercluster observations related to future X-ray missions are also outlined.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 364; 1-6
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    Comparison of picked-up protons and water group ions upstream of Comet Halley's bow shock (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The similarities and differences between the picked-up cometary protons and water-group (WG) ions upstream of the bow shock of Comet Halley are examined using measurements obtained by the ion mass spectrometer and plasma analyzer experiments on board Giotto. It was found that the dependencies of the pitch angle and the energy diffusion rates of the cometary protons and WG ions on the ion densities and on the angle alpha between the interplanetary field and the solar wind velocity vector were very different. This finding could not be explained in terms of presently available theories and models.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 18745-18
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    Evolution of radio quasars from redshift 0.6-3.7 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents the results of VLA radio imaging of 58 radio-loud quasars with redshift 2.0 or higher, which fill the redshift-luminosity plane as evenly as possible. This work completes a survey of about 250 quasars covering redshifts from 0.6-3.7, which attempts to sample luminosity and look-back time in a uniform way. Within the constraints of possible selection effects it is found that the relative population of extended and unresolved sources changes with redshift in a way that suggests that radio quasars may live longer and spend more time as large triple sources in the present epoch than in the earlier universe. There appear to be few low-luminosity radio quasars at high redshift. Ejection of material appears to occur on one side at a time, with usually at least one reversal of direction in the source lifetime. The velocity of ejection appears to be mildly relativistic at high redshift, but of lower velocity in the present epoch. There is also evidence suggestive of changes in the IGM with cosmic time; however, the data presented do not show the minimum in density at z about 2 that has been suggested for cluster environments.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 100; 1441-145
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    Hypervelocity dust particle impacts observed by the Giotto magnetometer and plasma experiments (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes 13 very short events in the magnetic field of the inner magnetic pile-up region of Comet Halley observed by the Giotto magnetometer experiment together with simultaneous plasma data obtained by the Johnstone plasma analyzer and the ion mass spectrometer experiments. The events are due to dust impacts in the milligram range on the spacecraft at the relative velocity between the cometary dust and the spacecraft of 68 km/sec. They are generally consistent with dust impact events derived from spacecraft attitude perturbations by the Giotto camera. Their characteristic shape generally involves a sudden decrease in magnetic-field magnitude, a subsequent overshoot beyond initial field values, and an asymptotic approach to the initial field (somewhat reminiscent of the magnetic-field signature after the AMPTE releases in the solar wind). These observations give a new way of analyzing ultra-fast dust particles incident on a spacecraft.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1809-181
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    MCG 06-45-001 - Not a local group galaxy (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations of (C-12)O and (C-13)O J = 1 to 0 for MCG 06-45-001 are examined. It is argued that two features of CO emission with velocities of 1 and 10 km/s indicate that the object is similar to the Galactic molecular clouds in the immediate vicinity, and not to a spiral galaxy as suggested previously. It is considered that CO emission cannot arise from a spiral galaxy at a distance of 2-5 Mpc and that the object is unlikely to be a nearby dwarf. The feature at 10 km/s is considered to arise from a molecular cloud associated with an H II region, which produces the observed IRAS flux.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 362; L9-L12
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    A simple analytic model for the evolution of captured galactic disks (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The general analytic solution developed by Steinman-Cameron and Durisen and published in 1988 for the evolution of dissipative nonplanar disks is applied to captured galactic disks in model galaxies with nonspherical, scale-free, logarithmic gravitational potentials. Such potentials produce flat rotation curves, similar to those seen in real galaxies. In this case, the analytic solution yields a self-similar structure for the warps and twists that develop while the disks is settling. Being scale-free in a simple, analytic form, this solution is completely defined by only a few dimensionless fitting parameters. As a result, it can be utilized as a mathematical tool to fit settling disks in real galaxies. The minimum time it takes for a disk to settle into a steady state orientation is also a scale-free quantity when expressed in units of the precession period or the orbit period. For realistic parameters, settling times are on the order of one-half to two periods. The use of the time-dependent structure of settling disks as a probe of the three-dimensional mass distribution of the host galaxies, including dark halos, is discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 357; 62-70
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    The nature of unidentified 12 micron IRAS sources at high Galactic latitudes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A sample of 47 previously uncatalogued objects located above a Galactic latitude of 50 deg, and detected at 12 microns by the IRAS, is studied using near-infrared photometry. Ground-based observations show that the objects consist primarily of late-type M giant stars with long-wavelength excesses probably due to emission from dust associated with mass loss. The sample contains one oxygen-rich giant star undergoing rapid mass loss; an extremely cool (1230 K) carbon star 12560-1656 that may be as far as 10 kpc away; and a luminious quasar 13349-2438. The absence of nearby, low-luminosity infrared sources in this sample limits the space density of field brown dwarf stars. The fact that almost all the IRAS 12 micron sources have stellar counterparts visible on both the red and blue Palomar Observatory Sky Survey prints provides a tool for discriminating ordinary red stars.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1569-158
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    Periodic Comet Machholz and its idiosyncrasies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The dynamics and physical characteristics of Comet P/Machholz are analyzed. The discovery of the comet (Machholz, 1986) is discussed, including the observational conditions and the theory that the comet is inactive over extensive periods of time. Consideration is given to observations of the two tails of Comet P/Machholz (Emerson, 1986), the brightness variations and light curve of the comet, and nuclear photometry of the comet (Green, 1987). It is suggested that the increase in activity beginning one day after perihelion was triggered by a discrete source within 15 deg of the rotation pole that became sunlit after perihelion. Also, the possibility that Comet P/Machholz is associated with a meteor stream is examined.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1268-127
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    Test of the gravitational redshift effect at Saturn (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The results of a test of the gravitational redshift effect at Saturn are reported. Measurements of the redshift were obtained with the Voyager 1 spacecraft during its encounter with Saturn in 1980. Because the spacecraft was equipped with an ultrastable crystal oscillator (USO), it is possible to test the redshift effect at an interesting level of accuracy. Assuming that radiation in the Saturn magnetosphere has had a negligible effect on the USO, the prediction of general relativity to an accuracy of 1 percent is verified. This limit could be of interest for constraining possible alternative theories of gravity.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 64; 1322-132
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    Dark matter and the age of globular clusters (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ability of weakly interacting particles called cosmions to suppress convection in the cores of horizontal-branch stars is investigated numerically. It is found that such convection-breaking in horizontal-branch stars by cosmions or by any other novel mode of energy transfer induces thermal relaxation oscillations with a period of about 500,000 yr, corresponding to the core Kelvin-Helmholtz time scale. These thermal pulses can be understood analytically in terms of a simple two-zone model. Observationally, the brightness and brightness dispersion of horizontal-branch stars increases, the periods of RR Lyrae stars change over a pulsation time scale, and the duration of central helium burning slightly decreases. None of these effects is in conflict with observations but, on the contrary, point to a speculative resolution of the age problem for globular clusters and to an alternative explanation of the period fluctuations of RR Lyrae stars.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 343; 347
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    Further evidence for differential rotation in V1057 Cygni (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Further tests of the accretion disk hypothesis for FU Orionis objects are presented. High spectral resolution, high signal to noise, 5820-6830 A and 7500-9370 A spectra of V1057 Cyg reveal a correlation between linewidth and line transition lower excitation potential expected from this hypothesis. The magnitude of the effect compares favorably with that predicted by synthetic disk spectra. Additional evidence for previously documented spectral type and linewidth versus wavelength correlations is also presented. This kinematic evidence strongly supports the accretion disk hypothesis.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 349; 328-334
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    Theoretical study of the spectroscopy of ZrO (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The absorption bands of ZrO have been observed in stars, particularly S stars. Here, theoretical transition probabilities are presented for the dipole-allowed transitions between the six lowest singlet and triplet states of ZrO. The results should be sufficiently reliable to provide opacity data for use in modeling stellar atmospheres. The theoretical radiative lifetime for the e 3Pi state is less than the experimental value as measured by the decay of resonant fluorescence. However, the theoretical electronic transition moments for the gamma system and the B 1Pi - X 1Sigma(+) system are much smaller than those deduced from emission studies. The calculated lifetime for the C 1Sigma(+) state is in excellent agreement with the laser-induced fluorescence studies. The as yet unobserved E 1Phi - A 1Delta band system is found to be relatively strong.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 349; 369-375
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    Studies of dust grain properties in infrared reflection nebulae (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model has been developed for reflection nebulae around luminous IR sources embedded in dense dust clouds. The shape of the IR spectrum is shown to be the result of a combination of the scattering properties of the dust, the spectrum of the illuminating source, and foreground extinction, while geometry plays a minor role. Comparison of the model results with IR observations of the reflection nebula surrounding OMC-2/IRS 1 shows that either a grain size distribution like that found in the diffuse ISM, or consisting of larger grains, can explain the observed shape of the spectrum. However, the absolute intensity level of the scattered light, as well as the observed polarization, requires large grains. By adding water-ice mantles to the silicate and graphite cores, the 3.08 micron ice-band feature observed in the spectra of several IR reflection nebulae has been modeled. It is shown that this ice band arises naturally in optically thick reflection nebulae containing ice-coated grains.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 349; 107-119
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  • 81
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    The infrared spectrum of Comet Bradfield (1987s) and the silicate emission feature (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Infrared (1-20 microns) observations of Comet Bradfield (1987s) from three observatories are reported. Silicate emission is prominent in all the data, from heliocentric distance r = 0.87 to 1.45 AU. A CVF spectrum at r = 1.45 AU shows a peak at 11.3 microns identified as crystalline olivine; the spectral shape is similar to that in Halley. Dust optical properties are similar to those of the grains in Halley's jets. Dust production rate near perihelion was about 10 to the 6th g/s and varied as N exp-2. It is suggested that some differences in grain properties among comets could result from difference in the thermal history of the nuclear surface and the relative fraction of the dust particles originating in the subsurface icy layer versus the devolatilized mantle.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 348; 312-321
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  • 82
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    The discovery of magnetically controlled circumstellar matter in the helium-weak stars HD 5737 and HD 79158 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The paper reports the discovery, using combined IUE spectroscopy and Zeeman polarimetric magnetic field measurements, of magnetically controlled circumstellar material in two helium-weak stars. HD 5737 = Alpha Sculptoris is, except for its extreme helium deficiency, similar to the He weak sn star HD 21699. A unique period for the magnetic and C IV and Si IV variations of 21.65 days is reported. The effective (longitudinal) field nulls coincide extremely well with C IV line strength maxima. The magnetic field and equatorial trapped plasma are highly oblique to the rotation axis (about 70 deg), and the line variations appear to be stable. Similar magnetospheric variations in HD 79158 = 36 Lyncis have been discovered, for which no period had been previously available. The period is 3.84 days, yet it too displays magnetic-equatorial plasma. The magnetospheric axis is highly oblique to the rotation axis, around 80 deg.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 348; 242-252
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  • 83
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    Luminous asymptotic giant branch stars in the Large Magellanic Cloud (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A search has been conducted for optically obscured asymptotic giant branch (AGB) stars in the LMC. The results obtained are noted to rule out the presence of sufficient high-luminosity 'cocoon' stars to explain the observed deficit of several hundred luminous AGB stars between the predictions of standard AGB evolution models and the observed luminosity function. Bolometric magnitudes as low as -5 are inferred for these sources; it is suggested that this phase can be triggered at low luminosities, truncating AGB evolution and leading to the observed scarcity of AGBs with M(bol) greater than -6.0 mag.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 348; 98-119
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  • 84
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    The origin of the far-infrared luminosity from spiral galaxies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relationship between the far-infrared and H-alpha luminosity has been investigated for a sample of 124 spiral galaxies. After correcting the H-alpha luminosities for an average 1 mag of extinction and extrapolating the IRAS 40-120 micron luminosity to 1000 microns, it is found that the mean ratio of H-alpha to far-infrared luminosity is comparable to that expected from H II regions powered by stars with masses larger than 6 solar masses. This result constitutes strong evidence in support of the view that high-mass O and B stars are responsible for both the H-alpha and far-infrared emission in spiral galaxies of high, billion solar luminosities or greater, far-infrared luminosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 350; L25-L28
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  • 85
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    Local gravity and large-scale structure (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The magnitude and direction of the observed dipole anisotropy of the galaxy distribution can in principle constrain the amount of large-scale power present in the spectrum of primordial density fluctuations. This paper confronts the data, provided by a recent redshift survey of galaxies detected by the IRAS satellite, with the predictions of two cosmological models with very different levels of large-scale power: the biased Cold Dark Matter dominated model (CDM) and a baryon-dominated model (BDM) with isocurvature initial conditions. Model predictions are investigated for the Local Group peculiar velocity, v(R), induced by mass inhomogeneities distributed out to a given radius, R, for R less than about 10,000 km/s. Several convergence measures for v(R) are developed, which can become powerful cosmological tests when deep enough samples become available. For the present data sets, the CDM and BDM predictions are indistinguishable at the 2 sigma level and both are consistent with observations. A promising discriminant between cosmological models is the misalignment angle between v(R) and the apex of the dipole anisotropy of the microwave background.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 349; 408-414
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  • 86
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    Three dimensional reconnection in astrophysical plasmas (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Theoretical issues related to three-dimensional reconnection and its application to the space and astrophysical environment are reviewed. Consideration is given to the meaning of reconnection in three dimensions, the way in which periodic and nonperiodic magnetic topologies alter the physics of reconnections, and the effects of chaotic magnetic fields on the reconnection process.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 10; 9, 19
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  • 87
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    WHT observations of cataclysmic variables in globular clusters. II - The CV candidates in M71 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented from photometric and spectroscopic observations of the six UV-bright objects in M71 which Richer and Fahlman (1988) proposed as candidate cataclysmic variables. It is found that the two brightest of these candidates are probably hot subdwarfs. It is suggested that the remaining candidates are more likely to be white dwarfs and subdwarfs than cataclysmic variables.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 242; 9P-13P
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  • 88
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    The Mg II h and k interstellar lines in the spectrum of the G-type giant HD 156854 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The results of the measurements and analysis of the IUE observations of the 2800 Mg II doublet in the spectrum of HD 156854, a G9 III star, are presented. The relative power of the magnesium chromosphere, R(Mg) = 0.00001, is in agreement with the known data for giants of the same class. The emission profiles of this doublet present absorption cores, which are of interstellar origin. Taking into account the interstellar depletion of Mg, the derived density of interstellar hydrogen is n(H) = 0.001/cu cm, which agrees with the conclusion (Paresce 1984) about the possibility of large hydrogen concentrations in some directions of the Galaxy far from the sun.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 102; 1387-139
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  • 89
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    The interaction of active comets with the solar wind (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The interaction of the solar wind with active comets is investigated based on observations of cometary plasma processes and studies of comets using telescopes and photographic plates. Data were also collected when a spacecraft flew through the tail of Comet Giacobini-Zinner in 1985 and five spacecraft encountered Comet Halley in 1986. The solar wind is considered to be supersonic (thermal Mach number 2-10) and to carry a magnetic field twisted into an Archimedean spiral by the rotation of the sun. Since the wind can change its properties during the time a spacecraft is inside the ionosphere or magnetosphere of the body being studied, it is difficult to separate spatial from temporal effects. Photoionization results in addition of plasma to the solar wind. Between the outer and inner edges of the cometosheath, the increasing rate of ion pickup causes the flow to slow down until it stagnates, while the plasma density and the magnetic field strength increase.
    Keywords: ASTROPHYSICS
    Type: Earth in Space (ISSN 1040-3124); 3; 10-14
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  • 90
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    X-ray illuminated stellar winds - Ionization effects in the radiative driving of stellar winds in massive X-ray binary systems (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents calculations of the effect of changing X-ray ionization conditions on the radiative force experienced by the stellar wind material in a massive X-ray binary system. The radiative line force from the radiation field of the primary is parameterized in terms of the Castor et al. (1975) force multiplier. The results show that the line force decreases sharply, but in a nonlinear way, with increasing X-ray ionization. The dynamic consequences of this effect are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 321-331
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  • 91
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    Ponderable soliton stars and cosmic background radiation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A theory is developed to describe the possible perturbations of the cosmic background radiation (CBR) by radiation from ponderable soliton stars in the early universe. Since the temperature of such stars is in the range of 10 to the 6th K, thermalization of their emitted radiation is possible. Two models are considered: one in which thermalization is ignored and one in which decoupling from thermalization is considered as a sudden process. The expected perturbation of the CBR is probably less than 1 percent and is largely around the short-wavelength end, in the form of point radio sources. This result is consistent with the most recent COBE measurements.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 107-114
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  • 92
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    Ponderable soliton stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 93-106
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  • 93
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    Detection of an expanding H I shell in the old supernova remnant CTB 80 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An expanding H I shell associated with the SNR CTB 80 has been detected. The expansion velocity and size indicate that the H I shell is an SNR shell. The center, shape, and mass of the shell match those of the IR shell detected by Fesen et al. (1988), supporting the idea that the pulsar has caught up with the SW portion of the shell and has produced its peculiar radio morphology. The shell's large 60 to 100 micron ratio implies that the larger grains may have been preferentially destroyed by the shock.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 364; 178-186
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  • 94
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    The C2 Ballik-Ramsay transitions in carbon stars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The bands of C2 are an important source of opacity in the near-infrared spectral region of carbon stars. In the 2 micron spectral region, the Delta v = -1 and -2 transitions of the Ballik-Ramsay b 3Sigma(g)(-) - a 3Pi(u) system are especially important. A general method for calculating highly accurate transition parameters of the Ballik-Ramsay band is presented. This method allows the easy calculation of the satellite lines and the forbidden lines resulting from the perturbation of the upper b 3Sigma(g)(-) state by the X 1Sigma(0)(+) state. Included in the calculation is the effect of the isotopic molecules (C-12)2, (C-12)(C-13), and (C-13)2. Three consistency tests of the calculated strengths are presented. A comparison of synthetic spectra is made with an observed spectrum of WZ Cas in the 3940/cm spectral region.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 74; 769-783
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  • 95
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    Discrete phase changes within nonlinear steepened magnetosonic waves - Comet Giacobini-Zinner (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Some features of steepened magnetosonic waves are discussed with reference to the Giacobini-Zinner data set. In particular, attention is given to the discovery of discrete intervals of both phase rotation and lack of phase rotation within a single wavelength and also to the presence of intervals of 'backward' rotations (right-hand polarized in the spacecraft frame) within the magnetosonic wave. Possible explanations of these features are reviewed, and it is suggested that these features are nonlinear manifestations of the wave steepening process.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1817-182
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  • 96
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    Distributed coma sources and the CH4/CO ratio in Comet Halley (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Early analyses of the Ion Mass Spectrometer (IMS) data from the Giotto flyby of Comet P/Halley indicated significant abundances of CH(+) sub n (n = 1 to 4). The source of these ions was assumed to be frozen CH4 in the nucleus. An abundance of about 2 percent CH4 was consistent with this interpretation, resulting in a ratio of CH4/CO that is greater than the predicted limits for interstellar clouds or the solar nebula. However, subsequent analyses of data from the Giotto Neutral Mass Spectrometer indicate distributed sources of CO and H2CO in the coma that are most likely associated with organic (CHON) particles, rich in CH-bearing compounds that decay and produce CH(+) sub n species. A model is presented that qualitatively accounts for the measured spatial distribution of CO and H2CO, and indicates that most of the CH(+) sub n deduced from the Giotto IMS data may originate from organic compounds in the coma dust and not from volatiles released directly from the nucleus. As a consequence, the absence of CH4 in the icy phase of the nucleus is consistent with the observations with an upper limit of about 0.5 percent to the ratio CH4/CO. This is an important criterion for theories of comet formation.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1813-181
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  • 97
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    The 60 micron to 20 centimeter infrared-to-radio ratio within spiral galaxies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A detailed comparison is presented of the distribution of 60 micron IR and 20 cm radio continuum emission within 25 galaxies, mostly disk spirals. Local maxima in the thermal IR and nonthermal radio emission are found to be spatially coincident on scales of less than about 0.4 kpc in the nearest sample galaxies. The IR-red disk in normal spirals appears to be characterized by a shorter scale length than that of the radio continuum disk, suggesting that the IR-to-radio ratio should decrease as a function of radius. A model that successfully accounts for the observations is introduced which is based on the assumptions of steady-state star formation activity within the disk on kpc scales and a tight coupling between the origins of the dust-heating radiation and the radio-emitting cosmic-ray electrons. The underlying source is described as an exponential disk. The results also suggest that a random walk process cannot by itself describe the temporal evolution of cosmic rays.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 362; 59-73
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  • 98
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    The formation and structure of fluffy cometary nuclei from random accumulation of grains (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is now generally accepted that solid bodies in the solar system are formed by accumulation of solid grains. The mechanism of formation of smaller bodies, less than some tens of kilometers in radius, is investigated. These include planetesimals and comets. Results indicate that essentially complete agglomeration occurs for relative velocities of less than about 1000 cm/sec and fairly efficient mass build-up occurs up to 5000/cm. These velocities are consistent with current models of the primordial solar nebula. The temperature produced in a collision will be under 20 K. For ice/dust grains, the resultant aggregates will be of low density with their volatiles preserved. Cometary nuclei with radii of a few km will be irregularly shaped and fragile with low mean density and significant interanl density variations. The characteristics of such a structure could account for the observed properties of comets.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 235; 1-2,
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  • 99
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    Hot and cold gas toward young stellar objects (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-resolution M band spectra are presented for the seven embedded IR sources W3 IRS 5, S140 IRS1, NGC 7538 IRS 1, NGC 7538 IRS 9, GL 2136, LkH-alpha 101, and MWC 349A, and the data are combined with previously published work for W33A and GL 2591. Cold CO is seen toward all nine sources, with temperatures from 11 K to 66 K. Column densities of cold CO are presented. Hot gas is seen toward eight of the nine objects with temperatures from 120 K to 1010 K. New lower limits to the hot gas density are obtained. The hot gas toward GL 2591, GL 2136, W3 IRS 5, and S140 IRS 1 is probably very near the central source and heated via gas-grain collisions. The optical depth in the silicate feature is strongly correlated with the (C-13)O column density, confirming that silicate optical depth is a useful measure of gas column density. The ratio of solid-to-gaseous CO is obtained for seven sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 363; 554-573
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  • 100
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    Gas and dust emission from comets and life spans of active areas on their rotating nuclei (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Outgassing and dust emission from discrete regions on the nuclei of comets are investigated with regard to the processes of activation, dormancy, reactivation, and extinction. With regard to P/Halley, P/Encke, P/Tempel 2, P/Machholz, P/Takamizawa, Bowell and some other new comets, the evolution of one active region of the nucleus surface appears to be independent of the evolution of another active region. The traditional concept of deactivation as a slow and monolithic process needs to be replaced with a more dynamic concept of intermittent periods of dormancy and reactivation of individual vents, varying in size. Life spans of discrete sources of activity are estimated to be at a few hundred revolutions about the sun for comets with perihelia at heliocentric distances of less than 2 AU, if the bulk density is very low.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 100; 1293-131
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