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  • 1
    Publikationsdatum: 2019-06-27
    Beschreibung: Strengths and Stark widths of the prominent visible PbI and PbII lines are measured in emission by means of a gas-driven shock tube. Absolute ionic line strengths for 7s-7p and 7p-7d arrays conform well to quantum-mechanical sum rules and agree with theoretical predictions, but 6d-5f results differ markedly from central-field approximations. Neutral-line strengths agree satisfactorily with available comparison data. Semiempirical theory predicts the widths of PbII lines with characteristic reliability of better than 25%.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Physical Review A - General Physics; vol. 20
    Format: text
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  • 2
    Publikationsdatum: 2019-07-27
    Beschreibung: The high-quality Fermi LAT observations of gamma-ray pulsars have opened a new window to understanding the generation mechanisms of high-energy emission from these systems, The high statistics allow for careful modeling of the light curve features as well as for phase resolved spectral modeling. We modeled the LAT light curves of the Vela and CTA I pulsars with simulated high-energy light curves generated from geometrical representations of the outer gap and slot gap emission models. within the vacuum retarded dipole and force-free fields. A Markov Chain Monte Carlo maximum likelihood method was used to explore the phase space of the magnetic inclination angle, viewing angle. maximum emission radius, and gap width. We also used the measured spectral cutoff energies to estimate the accelerating parallel electric field dependence on radius. under the assumptions that the high-energy emission is dominated by curvature radiation and the geometry (radius of emission and minimum radius of curvature of the magnetic field lines) is determined by the best fitting light curves for each model. We find that light curves from the vacuum field more closely match the observed light curves and multiwavelength constraints, and that the calculated parallel electric field can place additional constraints on the emission geometry
    Schlagwort(e): Astronomy
    Materialart: GSFC.JA.6040.2012 , 2011 Fermi Symposium; 9 - 12, May 2011; Rome; Italy
    Format: application/pdf
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  • 3
    Publikationsdatum: 2019-06-27
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Journal of Quantitative Spectroscopy and Radiative Transfer; 23; Apr. 198
    Format: text
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  • 4
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    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: Results of determinations of neutral-cobalt transition probabilities measured relative to Co I 4150.43 A and Co II 4145.15 A, using a gas-driven shock tube as the spectroscopic light source. Results are presented for 139 Co I lines in the range from 3940 to 6640 A and 11 Co II lines in the range from 3840 to 4730 A, which are estimated to have reliabilities ranging from 8 to 50%.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Optical Society of America; vol. 64
    Format: text
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  • 5
    Publikationsdatum: 2019-07-19
    Beschreibung: One of the main results of the Fermi Gamma-Ray Space Telescope is the discovery of gamma-ray selected pulsars. The high magnetic field pulsar, PSR J0007+7303 in CTA1, was the first ever to be discovered through its gamma-ray pulsations. Based on analysis of 2 years of LAT survey data, we report on the discovery of I-ray emission in the off-pulse phase interval at the approx. 6sigma level. The flux from this emission in the energy range E 〉 or =::: 100 MeV is F(sub 100) = (1.73+/-0.40) x 10(exp -8) photons/sq cm/s and is best fitted by a power law with a photon index of Gamma = 2.54+/-0.14. The pulsed gamma-ray flux in the same energy range is F(sub 100) = (3.95+/-0.07) x 10(exp -7) photons/sq cm/s and is best fitted by an exponentially-cutoff power-law spectrum with a photon index of Gamma = 1.41+/-0.23 and a cutoff energy E(sub c) = 4.04+/-0.20 GeV. We find no flux variability neither at the 2009 May glitch nor in the long term behavior. We model the gamma-ray light curve with two high-altitude emission models, the outer gap and slot gap, and find that the model that best fits the data depends strongly on the assumed origin of the off-pulse emission. Both models favor a large angle between the magnetic axis and observer line of sight, consistent with the nondetection of radio emission being a geometrical effect. Finally we discuss how the LAT results bear on the understanding of the cooling of this neutron star.
    Schlagwort(e): Astronomy
    Materialart: GSFC.ABS.5880.2012
    Format: application/pdf
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  • 6
    Publikationsdatum: 2019-06-27
    Beschreibung: Strengths and Stark-effect widths of the Sn I and Sn II lines prominent between 3200 and 7900 A are measured with a spectroscopic shock tube. Absolute strengths of 17 ionic lines are obtained with estimated (22-50)% accuracy and conform to appropriate quantum-mechanical sum rules. Relative transition probabilities for nine prominent neutral tin lines, normalized to radiative-lifetime data, are compared with other experiments and theoretical predictions. Parameters for Stark-effect broadening are measured over a range of plasma electron densities. Broadening data (with accuracies of 15-35%) for one neutral and ten ionic lines of tin are compared to theoretical predictions.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Physical Review A - General Physics; vol. 20
    Format: text
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  • 7
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    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: Stark shift of the B II line at 3451 A due to plasma microfields was measured in a luminous shock tube. Line profiles, photographically recorded in second order, were compared with closeby wavelength fiduciaries from low-pressure rare-gas lamps. Electron densities for each exposure were found by fitting H-beta profiles to theoretical line shapes. Results, estimated reliable to 25-30%, are compared with theoretical predictions.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Physical Review A - General Physics; vol. 15
    Format: text
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  • 8
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    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: Absolute transition probabilities of the three most prominent visible Br II lines are measured in emission. Results compare well with Coulomb approximations and with line strengths extrapolated from trends in homologous atoms.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Physical Review A - General Physics; vol. 14
    Format: text
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  • 9
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    In:  Other Sources
    Publikationsdatum: 2019-07-19
    Beschreibung: Observations of gravitational waves from massive black hole mergers will open a new window into the era of structure formation in the early universe. Past efforts have concentrated on calculating merger rates using different physical assumptions, resulting in merger rate estimates that span a wide range (0.1 - 1 0A4 mergers/year). We develop a semi-analytical, phenomenological model of massive black hole mergers that includes plausible combinations of several physical parameters, which we then turn around to determine how well observations with the Laser Interferometer Space Antenna (LISA) will be able to enhance our understanding of the universe during the critical z approx. 5 - 30 epoch. Our approach involves generating synthetic LISA observable data (total BH masses, BH mass ratios, redshifts, merger rates), which are then analyzed using a Markov Chain Monte Carlo method, thus finding constraints for the physical parameters of the mergers. We find that our method works well at estimating merger parameters and that the number of merger events is a key discriminant among models, therefore making our method robust against observational uncertainties. Our approach can also be extended to more physically-driven models and more general problems in cosmology.
    Schlagwort(e): Astronomy
    Materialart: 24th Texas Symposium on Relativistic Astrophysics; Dec 08, 2008 - Dec 12, 2008; Vancouver, BC; Canada
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  • 10
    Publikationsdatum: 2019-07-13
    Beschreibung: In order to test the hypothesis of ionized PAHs as possible carriers of the UIR bands, we realized a computational exploration on selected PAHs of small dimension in order to identify which changes ionization would induce on their IR spectra. In this study we performed ab initio calculations of the spectra of neutral and positively ionized naphthalene, anthracene, and pyrene. The results are significantly important. The frequencies in the cations are slightly shifted with respect to the neutral species, but no general conclusion can be reached from the three molecules considered. By contrast, the relative intensities of most vibrations are strongly affected by ionization, leading to a much better agreement between the calculated CH/CC vibration intensity ratios and those deduced from observations.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 408; 2; p. 530-538.
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