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  • Astronomy
  • 2005-2009
  • 1995-1999  (182)
  • 1955-1959
  • 1950-1954
  • 1935-1939
  • 1996  (182)
  • 1
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    Far-infrared emission spectra of selected gas-phase PAHs: spectroscopic fingerprints (1996)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1996-10-25
    Description: The emission spectra of the gaseous polycyclic aromatic hydrocarbons (PAHs) naphthalene, chrysene, and pyrene were recorded in the far-infrared (far-IR) region. The vibrational bands that lie in the far IR are unique for each PAH molecule and allow discrimination among the three PAH molecules. The far-IR PAH spectra, therefore, may prove useful in the assignment of unidentified spectral features from astronomical objects.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhang, K -- Guo, B -- Colarusso, P -- Bernath, P F -- New York, N.Y. -- Science. 1996 Oct 25;274(5287):582-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Centre for Molecular Beams and Laser Chemistry, Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8849443" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; Astronomy ; Chrysenes/*chemistry ; Extraterrestrial Environment ; Naphthalenes/*chemistry ; Pyrenes/*chemistry ; Spectrum Analysis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 2
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    High Resolution UV Spectroscopy of H2 and N2 Applied to Observations of the Planets by Spacecraft (1996)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The next generation of high resolution UV imaging spacecraft are being prepared for studying the airglow and aurora of the Earth, the other terrestrial planets and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron impact collision cross sections of the major molecular planetary gases (H2, N2, CO2, O2, and CO). Spectra under optically thin conditions have been measured with a high resolution (lambda/delta(lambda) = 50000) UV spectrometer in tandem with electron impact collision chamber. High resolution spectra of the Lyman and Wemer band systems of H2 have been obtained and modeled. Synthetic spectral intensities based on the J-dependent transition probabilities that include ro-vibronic perturbations are in very good agreement with experimental intensities. The kinetic energy distribution of H(2p,3p) atoms resulting from electron impact dissociation of H2 has been measured. The distribution is based on the first measurement of the H Lyman-alpha (H L(alpha)) and H Lyman-beta (H L(beta)) emission line Doppler profiles. Electron impact dissociation of H2 is believed to be one of the major mechanisms leading to the observed wide profile of H L-alpha from Jupiter aurora by the Hubble Space Telescope (HST). Analysis of the deconvolved line profile of H L-alpha reveals the existence of a narrow line peak (40 mA FWHM) and a broad pedestal base (240 mA FWHM). The band strengths of the electron excited N2 (C(sup 3) Pi(sub(upsilon) - B(sup 3)Pi(sub g)) second positive system have been measured in the middle ultraviolet. We report a quantitative measurement of the predissociation fraction 0.15 +/- 01(sup .045, sub .01) at 300 K in the N2 c'(sub )4 (1)sigma(sup +, sub g) - x(1)sigma(sup +, sub g)(00) band, with an experimental determination of rotational line strengths to be used to understand N2 EUV emission from Titan, Triton and the Earth.
    Keywords: Astronomy
    Type: Journal of Electron Spectroscopy and Related Phenomena (ISSN 0368-2048); Volume 79; 429-432
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  • 3
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    Results from monitoring the broad-line radio galaxy 3C 390.3 (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The broad line radio galaxy 3C 390.3 was observed in a multiwavelength monitoring campaign by the Rosat high resolution imager (HRI), the International Ultraviolet Explorer and ground-based optical, infrared and and radio observations. The preliminary results from the campaign are reported, with emphasis on the X-ray observations. A large amplitude variability is observed. The light curve is dominated by a flare near JD 2449800, characterized by a doubling time scale of 9 days and a general increase in flux after the flare. The optical R and I band light curves show a general increase in flux. Spectra from the Advanced Satellite for Cosmology and Astrophysics (ASCA) obtained before and after the flare can be described by an absorbed power law.
    Keywords: Astronomy
    Type: ; 467-468
    Format: text
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  • 4
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    The first simultaneous X-ray/gamma-ray observations of Cyg X-1 by Ginga and OSSE (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The results of four simultaneous observations of Cygnus X-1 by Ginga and the orientated scintillation spectrometer experiment (OSSE) are presented. The X-ray/gamma ray spectra can be described by an intrinsic continuum and a component due to Compton reflection including an iron K alpha line. The intrinsic spectrum at X-ray energies is a power law with a photon spectral index of Gamma = 1.6. The intrinsic gamma ray spectrum can be phenomenologically described by either a power law without cutoff up to 150 keV and an exponential cutoff above this energy, or by an expoential cutoff power law and a second hard component.
    Keywords: Astronomy
    Type: Conference proceedings of the International Conference on X-Ray Astronomy and Astrophysics; 139-140; MPE-263
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  • 5
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    The Role of Vortices in the Formation of the Solar System (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: To show that robust vortices can exist in the solar nebula, a pseudospectral model has been developed to examine the evolution of the vortex in a Keplerian shear. Calculations show that a vortex can exist for 10(exp 4)yr at Jupiter's radius.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 183-186; NASA-CP-3343
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  • 6
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    Dust Coagulation in Protoplanetary Accretion Disks (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. In particular, we consider the coagulation of grains due to collisional aggregation. The coagulation of the particles is calculated by solving numerically the non-linear Smoluchowski equation. The different physical processes leading to relative velocities between the grains are investigated. The relative velocities may be induced by Brownian motion, turbulence and drift motion. Starting from different regimes which can be identified during the grain growth we also discuss the evolution of dust opacities. These opacities are important for both the derivation of the circumstellar dust mass from submillimeter/millimeter continuum observations and the dynamical behavior of the disks. We present results of our numerical studies of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) alpha-model. For several periods and disk radii, mass distributions of coagulated grains have been calculated. From these mass spectra, we determined the corresponding Rosseland mean dust opacities. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is considered. Significant changes in the thermal structure of the protoplanetary nebula are observed. A 'gap' in the accretion disk forms at the very frontier of the coagulation, i.e., behind the sublimation boundary in the region between 1 and 5 AU.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 167-170; NASA-CP-3343
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  • 7
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    Imaging Polarized Dust Emission in Star Formation Regions with the OVRO MM Array (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: We present OVRO interferometric observations of linearly polarized emission from magnetically aligned dust grains which allow the magnetic field geometry in nearby star formation regions to be probed on scales ranging from 100 to 3000 AU. Current results include observations of the young stellar objects NGC1333/IRAS 4A, IRAS 16293-2422 and Orion IRc2-KL.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 45-48; NASA-CP-3343
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  • 8
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    PAH Emission in the Orion Bar (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The emission from polycyclic aromatic hydrocarbons (PAH's) in the Orion Bar region is investigated using a combination of narrow-band imaging and long-slit spectroscopy. The goal was to study how the strength of the PAH bands vary with spatial position in this edge-on photo-dissociation region. The specific focus here is how these variations constrain the carrier of the 3.4 micron band.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 121-124; NASA-CP-3343
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  • 9
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    Time Dependent Models of Grain Formation Around Carbon Stars (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Carbon-rich Asymptotic Giant Branch stars are sites of dust formation and undergo mass loss at rates ranging from 10(exp -7) to 10(exp -4) solar mass/yr. The state-of-the-art in modeling these processes is time-dependent models which simultaneously solve the grain formation and gas dynamics problem. We present results from such a model, which also includes an exact solution of the radiative transfer within the system.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 73-76; NASA-CP-3343
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  • 10
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    The 11 micron Silicon Carbide Feature in Carbon Star Shells (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Silicon carbide (SiC) is known to form in circumstellar shells around carbon stars. SiC can come in two basic types - hexagonal alpha-SiC or cubic beta-SiC. Laboratory studies have shown that both types of SiC exhibit an emission feature in the 11-11.5 micron region, the size and shape of the feature varying with type, size and shape of the SiC grains. Such a feature can be seen in the spectra of carbon stars. Silicon carbide grains have also been found in meteorites. The aim of the current work is to identity the type(s) of SiC found in circumstellar shells and how they might relate to meteoritic SiC samples. We have used the CGS3 spectrometer at the 3.8 m UKIRT to obtain 7.5-13.5 micron spectra of 31 definite or proposed carbon stars. After flux-calibration, each spectrum was fitted using a chi(exp 2)-minimisation routine equipped with the published laboratory optical constants of six different samples of small SiC particles, together with the ability to fit the underlying continuum using a range of grain emissivity laws. It was found that the majority of observed SiC emission features could only be fitted by alpha-SiC grains. The lack of beta-SiC is surprising, as this is the form most commonly found in meteorites. Included in the sample were four sources, all of which have been proposed to be carbon stars, that appear to show the SiC feature in absorption.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 61-64; NASA-CP-3343
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