1,173 research outputs found
Atomic X-Ray Spectra of Accretion Disk Atmospheres in the Kerr Metric
We calculate the atmospheric structure of an accretion disk around a Kerr
black hole and obtain its X-ray spectrum, which exhibits prominent atomic
transitions under certain circumstances. The gravitational and Doppler
(red)shifts of the C V, C VI, O VII, O VIII, and Fe I-XXVI emission lines are
observable in active galaxies. We quantify the line emissivities as a function
of radius, to identify the effects of atmospheric structure, and to determine
the usefulness of these lines for probing the disk energetics. The line
emissivities do not always scale linearly with the incident radiative energy,
as in the case of Fe XXV and Fe XXVI. Our model incorporates photoionization
and thermal balance for the plasma, the hydrostatic approximation perpendicular
to the plane of the disk, and general relativistic tidal forces. We include
radiative recombination rates, fluorescence yields, Compton scattering, and
photoelectric opacities for the most abundant elements.Comment: 4 pages, 1 figure, to appear in the Proc. of the 10th Marcel
Grossmann Meeting on General Relativity, World Scientific, Rio de Janeiro,
July 20-26, 200
The Fe XXII I(11.92 A)/I(11.77 A) Density Diagnostic Applied to the Chandra High Energy Transmission Grating Spectrum of EX Hydrae
Using the Livermore X-ray Spectral Synthesizer, which calculates spectral
models of highly charged ions based primarily on HULLAC atomic data, we
investigate the temperature, density, and photoexcitation dependence of the
I(11.92 A)/I(11.77 A) line ratio of Fe XXII. We find that this line ratio has a
critical density n_c \approx 5x10^13 cm^-3, is approximately 0.3 at low
densities and 1.5 at high densities, and is very insensitive to temperature and
photoexcitation, so is a useful density diagnostic for sources like magnetic
cataclysmic variables in which the plasma densities are high and the efficacy
of the He-like ion density diagnostic is compromised by the presence of a
bright ultraviolet continuum. Applying this diagnostic to the Chandra High
Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find
that the electron density of its T_e \approx 12 MK plasma is n_e =
1.0^{+2.0}_{-0.5} x 10^14 cm^-3, orders of magnitude greater than that
typically observed in the Sun or other late-type stars.Comment: 11 pages including 3 encapsulated postscript figures; LaTeX format,
uses aastex.cls; accepted on 2003 April 3 for publication in The
Astrophysical Journa
QCD spectroscopy with three light quarks
We report about a simulation using three dynamical Wilson quarks and on the
progress in going to small quark masses.Comment: Lattice2001(spectrum), 3 pages, 4 figure
Diverter AI based decision aid, phases 1 and 2
It was determined that a system to incorporate artificial intelligence (AI) into airborne flight management computers is feasible. The AI functions that would be most useful to the pilot are to perform situational assessment, evaluate outside influences on the contemplated rerouting, perform flight planning/replanning, and perform maneuver planning. A study of the software architecture and software tools capable of demonstrating Diverter was also made. A skeletal planner known as the Knowledge Acquisition Development Tool (KADET), which is a combination script-based and rule-based system, was used to implement the system. A prototype system was developed which demonstrates advanced in-flight planning/replanning capabilities
Reprocessing of Soft X-ray Emission Lines in Black Hole Accretion Disks
By means of a Monte Carlo code that accounts for Compton scattering and
photoabsorption followed by recombination, we have investigated the radiation
transfer of Ly alpha, He alpha, and recombination continua photons of H- and
He-like C, N, O, and Ne produced in the photoionized atmosphere of a
relativistic black hole accretion disk. We find that photoelectric opacity
causes significant attenuation of photons with energies above the O VIII
K-edge; that the conversion efficiencies of these photons into lower-energy
lines and recombination continua are high; and that accounting for this
reprocessing significantly (by factors of 21% to 105%) increases the flux of
the Ly alpha and He alpha emission lines of H- and He-like C and O escaping the
disk atmosphere.Comment: 4 pages including 4 encapsulated postscript figures; LaTeX format,
uses aastex.cls and emulateapj5.sty; accepted on 2004 January 13 for
publication in The Astrophysical Journa
Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
New X-ray observatories (Chandra and XMM-Newton) are providing a wealth of
high-resolution X-ray spectra in which hydrogen- and helium-like ions are
usually strong features. We present results from a new collisional-radiative
plasma code, the Astrophysical Plasma Emission Code (APEC), which uses atomic
data in the companion Astrophysical Plasma Emission Database (APED) to
calculate spectral models for hot plasmas. APED contains the requisite atomic
data such as collisional and radiative rates, recombination cross sections,
dielectronic recombination rates, and satellite line wavelengths. We compare
the APEC results to other plasma codes for hydrogen- and helium-like
diagnostics, and test the sensitivity of our results to the number of levels
included in the models. We find that dielectronic recombination with
hydrogen-like ions into high (n=6-10) principal quantum numbers affects some
helium-like line ratios from low-lying (n=2) transitions.Comment: 5 pages, 6 figures, accepted by ApJ Letter
Adiabatic and Non-Adiabatic Contributions to the Free Energy from the Electron-Phonon Interaction for Na, K, Al, and Pb
We calculate the adiabatic contributions to the free energy due to the
electron--phonon interaction at intermediate temperatures, for the elemental metals Na, K, Al, and Pb. Using our
previously published results for the nonadiabatic contributions we show that
the adiabatic contribution, which is proportional to at low
temperatures and goes as at high temperatures, dominates the
nonadiabatic contribution for temperatures above a cross--over temperature,
, which is between 0.5 and 0.8 , where is the melting
temperature of the metal. The nonadiabatic contribution falls as for
temperatures roughly above the average phonon frequency.Comment: Updated versio
Hadron Spectrum in QCD with Valence Wilson Fermions and Dynamical Staggered Fermions at $6/g^2=5.6
We present an analysis of hadronic spectroscopy for Wilson valence quarks
with dynamical staggered fermions at lattice coupling at
sea quark mass and 0.025, and of Wilson valence quarks in quenched
approximation at and 5.95, both on lattices. We
make comparisons with our previous results with dynamical staggered fermions at
the same parameter values but on lattices doubled in the temporal
direction.Comment: 32 page
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