105 research outputs found

    Determination of the temperature of a dense plasma from a spectral line shift

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    The method of maximum spectral line shift proposed by Bardocz, et al, (1966) was successfully applied in the diagnostics of dense plasmas produced by high power pulse discharges. It is pointed out that the effect of the shock wave pressure on the spectral line shift has to be taken into account in order to obtain accurate results with this method for high power discharges. A pressure dependent function was introduced in the expression given by those authors to provide the necessary correction

    Nonautonomous Hamiltonians

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    We present a theory of resonances for a class of non-autonomous Hamiltonians to treat the structural instability of spatially localized and time-periodic solutions associated with an unperturbed autonomous Hamiltonian. The mechanism of instability is radiative decay, due to resonant coupling of the discrete modes to the continuum modes by the time-dependent perturbation. This results in a slow transfer of energy from the discrete modes to the continuum. The rate of decay of solutions is slow and hence the decaying bound states can be viewed as metastable. The ideas are closely related to the authors' work on (i) a time dependent approach to the instability of eigenvalues embedded in the continuous spectra, and (ii) resonances, radiation damping and instability in Hamiltonian nonlinear wave equations. The theory is applied to a general class of Schr\"odinger equations. The phenomenon of ionization may be viewed as a resonance problem of the type we consider and we apply our theory to find the rate of ionization, spectral line shift and local decay estimates for such Hamiltonians.Comment: To appear in Journal of Statistical Physic

    Theory and simulation of spectral line broadening by exoplanetary atmospheric haze

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    Atmospheric haze is the leading candidate for the flattening of expolanetary spectra, as it's also an important source of opacity in the atmospheres of solar system planets, satellites, and comets. Exoplanetary transmission spectra, which carry information about how the planetary atmospheres become opaque to stellar light in transit, show broad featureless absorption in the region of wavelengths corresponding to spectral lines of sodium, potassium and water. We develop a detailed atomistic model, describing interactions of atomic or molecular radiators with dust and atmospheric haze particulates. This model incorporates a realistic structure of haze particulates from small nano-size seed particles up to sub-micron irregularly shaped aggregates, accounting for both pairwise collisions between the radiator and haze perturbers, and quasi-static mean field shift of levels in haze environments. This formalism can explain large flattening of absorption and emission spectra in haze atmospheres and shows how the radiator - haze particle interaction affects the absorption spectral shape in the wings of spectral lines and near their centers. The theory can account for nearly all realistic structure, size and chemical composition of haze particulates and predict their influence on absorption and emission spectra in hazy environments. We illustrate the utility of the method by computing shift and broadening of the emission spectra of the sodium D line in an argon haze. The simplicity, elegance and generality of the proposed model should make it amenable to a broad community of users in astrophysics and chemistry.Comment: 16 pages, 4 figures, submitted to MNRA

    Coherence-imaging approach to time-resolved charge-exchange recombination spectroscopy in high-temperature plasma

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    A coherence-based, or interferometric approach to spectral analysis of charge-exchange recombination (CXR) emission radiation from high-temperature plasma probed or heated using energetic neutral beams, offers a number of advantages over wavelength-domain instruments. The spectral-line shift and broadening are obtained from measurements of the spectralcoherence at a given fixed time delay. The coherence is monitored by first approximately isolating the spectral line of interest using an interference filter and subsequently imaging the spectral scene using a field-widened electro-optic path-delay-modulated polarization interferometer.Interferometers have the advantage of high-light throughput (no slit aperture). Moreover, because the spectral information is encoded at harmonics of the electro-optic modulation frequency, a single detector suffices to capture the spectral information, thereby opening the possibility for time-resolved two-dimensional spectralimaging. When unwanted spectral features are passed by the interference filter, the interpretation of the coherence phase and amplitude images can become ambiguous. By modulating the particle beam source, however, we show that coherence imaging using a single-delay modulatable interferometer can distinguish and characterize the Doppler-broadened CXR emission component against a significant background of continuum and intrinsic radiation, or pollution from nearby spectral features

    Dephasing of Local Vibrations in a Planar Lattice of Adsorbed Molecules

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    We investigate anharmonically coupled high- and low-frequency excitations in a planar lattice of adsorbed molecules interacting with phonons of a crystal. Dephasing of high-frequency local vibrations by low-frequency resonance modes is described in terms of temperature Green's function. The equations obtained are solved, first, with a small ratio of the anharmonic coupling coefficient for high- and low-frequency modes to the resonance width, and second, in the low-temperature limit. High-frequency spectral line positions and widths depend on dispersion laws and resonance mode lifetimes. It is shown that lateral interactions of low-frequency modes of adsorbed molecules can lead to a significant narrowing of high-frequency spectral lines, which is consistent with experimental data.Comment: REVTeX, 11 pages, no figure

    Detection of Gravitational Redshift on the Solar Disk by Using Iodine-Cell Technique

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    With an aim to examine whether the predicted solar gravitational redshift can be observationally confirmed under the influence of the convective Doppler shift due to granular motions, we attempted measuring the absolute spectral line-shifts on a large number of points over the solar disk based on an extensive set of 5188-5212A region spectra taken through an iodine-cell with the Solar Domeless Telescope at Hida Observatory. The resulting heliocentric line shifts at the meridian line (where no rotational shift exists), which were derived by finding the best-fit parameterized model spectrum with the observed spectrum and corrected for the earth's motion, turned out to be weakly position-dependent as ~ +400 m/s near the disk center and increasing toward the limb up to ~ +600 m/s (both with a standard deviation of sigma ~ 100 m/s). Interestingly, this trend tends to disappear when the convectiveshift due to granular motions (~-300 m/s at the disk center and increasing toward the limb; simulated based on the two-component model along with the empirical center-to-limb variation) is subtracted, finally resulting in the averaged shift of 698 m/s (sigma = 113 m/s). Considering the ambiguities involved in the absolute wavelength calibration or in the correction due to convective Doppler shifts (at least several tens m/s, or more likely up to <~100 m/s), we may regard that this value is well consistent with the expected gravitational redshift of 633 m/s.Comment: 28 pages, 12 figures, electronic materials as ancillary data (table3, table 4, ReadMe); accepted for publication in Solar Physic
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