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Series

University of Kentucky

2005

Articles 1 - 9 of 9

Full-Text Articles in Physics

Pumping Or Mixing System Using A Levitating Magnetic Element, Aexandre N. Terentiev Nov 2005

Pumping Or Mixing System Using A Levitating Magnetic Element, Aexandre N. Terentiev

Physics and Astronomy Faculty Patents

A system capable of pumping or mixing fluids using a rotating magnetic element or bearing levitated by a cold superconducting element is disclosed.

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The H Ii Region/Pdr Connection: Self-Consistent Calculations Of Physical Conditions In Star-Forming Regions, Nicholas Paul Abel, Gary J. Ferland, G. Shaw, Peter A. M. Van Hoof Nov 2005

The H Ii Region/Pdr Connection: Self-Consistent Calculations Of Physical Conditions In Star-Forming Regions, Nicholas Paul Abel, Gary J. Ferland, G. Shaw, Peter A. M. Van Hoof

Physics and Astronomy Faculty Publications

We have performed a series of calculations designed to reproduce infrared diagnostics used to determine physical conditions in star-forming regions. We self-consistently calculate the thermal and chemical structure of an H II region and photodissociation region (PDR) that are in pressure equilibrium. This differs from previous work, which used separate calculations for each gas phase. Our calculations span a wide range of stellar temperatures, gas densities, and ionization parameters. We describe improvements made to the spectral synthesis code Cloudy that made these calculations possible. These include the addition of a molecular network with ~1000 reactions involving 68 molecular species and …

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J-Resolved He I Emission Predictions In The Low-Density Limit, R. P. Bauman, R. L. Porter, Gary J. Ferland, K. B. Macadam Jul 2005

J-Resolved He I Emission Predictions In The Low-Density Limit, R. P. Bauman, R. L. Porter, Gary J. Ferland, K. B. Macadam

Physics and Astronomy Faculty Publications

Determinations of the primordial helium abundance are used in precision cosmological tests. These require highly accurate He I recombination rate coefficients. Here we reconsider the formation of He I recombination lines in the low-density limit. This is the simplest case, and it forms the basis for the more complex situation in which collisions are important. The formation of a recombination line is a two-step process, beginning with the capture of a continuum electron into a bound state and followed by radiative cascade to ground. The rate coefficient for capture from the continuum is obtained from photoionization cross sections and detailed …

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A Multi-Instrument Study Of The Helix Nebula Knots With The Hubble Space Telescope, C. R. O'Dell, W. J. Henney, Gary J. Ferland Jul 2005

A Multi-Instrument Study Of The Helix Nebula Knots With The Hubble Space Telescope, C. R. O'Dell, W. J. Henney, Gary J. Ferland

Physics and Astronomy Faculty Publications

We have conducted a combined observational and theoretical investigation of the ubiquitous knots in the Helix Nebula (NGC 7293). We have constructed a combined hydrodynamic + radiation model for the ionized portion of these knots and have accurately calculated a static model for their molecular regions. Imaging observations in optical emission lines were made with the Hubble Space Telescope's STIS, operating in a "slitless" mode, complemented by WFPC2 images in several of the same lines. The NICMOS camera was used to image the knots in H2. These observations, when combined with other studies of H2 and …

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Molecular Hydrogen In Star-Forming Regions: Implementation Of Its Microphysics In Cloudy, G. Shaw, Gary J. Ferland, N. P. Abel, P. C. Stancil, P. A. M. Van Hoof May 2005

Molecular Hydrogen In Star-Forming Regions: Implementation Of Its Microphysics In Cloudy, G. Shaw, Gary J. Ferland, N. P. Abel, P. C. Stancil, P. A. M. Van Hoof

Physics and Astronomy Faculty Publications

Much of the baryonic matter in the universe is in the form of H2, which includes most of the gas in Galactic and extragalactic interstellar clouds. Molecular hydrogen plays a significant role in establishing the thermal balance in many astrophysical environments and can be important as a spectral diagnostic of the gas. Modeling and interpretation of observations of such environments requires a quantitatively complete and accurate treatment of H2. Using this microphysical model of H2, we present illustrative calculations of prototypical astrophysical environments. This work forms the foundation for future investigations of these and …

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Energy Levels And Transition Probabilities For Nitrogen-Like Fe Xx, V. Jonauskas, P. Bogdanovich, F. P. Keenan, M. E. Foord, R. F. Heeter, S. J. Rose, Gary J. Ferland, R. Kisielius, Peter A. M. Van Hoof, P. H. Norrington Apr 2005

Energy Levels And Transition Probabilities For Nitrogen-Like Fe Xx, V. Jonauskas, P. Bogdanovich, F. P. Keenan, M. E. Foord, R. F. Heeter, S. J. Rose, Gary J. Ferland, R. Kisielius, Peter A. M. Van Hoof, P. H. Norrington

Physics and Astronomy Faculty Publications

Energies of the 700 lowest levels in Fexx have been obtained using the multiconfiguration Dirac-Fock method. Configuration interaction method on the basis set of transformed radial orbitals with variable parameters taking into account relativistic corrections in the Breit-Pauli approximation was used to crosscheck our presented results. Transition probabilities, oscillator and line strengths are presented for electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transitions among these levels. The total radiative transition probabilities from each level are also provided. Results are compared with data compiled by NIST and with other theoretical work.

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Theoretical He I Emissivities In The Case B Approximation, R. L. Porter, R. P. Bauman, Gary J. Ferland, K. B. Macadam Mar 2005

Theoretical He I Emissivities In The Case B Approximation, R. L. Porter, R. P. Bauman, Gary J. Ferland, K. B. Macadam

Physics and Astronomy Faculty Publications

We calculate the He I case B recombination cascade spectrum using improved radiative and collisional data. We present new emissivities over a range of electron temperatures and densities. The differences between our results and the current standard are large enough to have a significant effect not only on the interpretation of observed spectra of a wide variety of objects, but also on determinations of the primordial helium abundance.

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Self-Consistent Dynamic Models Of Steady Ionization Fronts. I. Weak-D And Weak-R Fronts, W. J. Henney, S. J. Arthur, R. J. R. Williams, Gary J. Ferland Mar 2005

Self-Consistent Dynamic Models Of Steady Ionization Fronts. I. Weak-D And Weak-R Fronts, W. J. Henney, S. J. Arthur, R. J. R. Williams, Gary J. Ferland

Physics and Astronomy Faculty Publications

We present a method for including steady state gas flows in the plasma physics code Cloudy, which was previously restricted to modeling static configurations. The numerical algorithms are described in detail, together with an example application to plane-parallel ionization-bounded H II regions. As well as providing the foundation for future applications to more complex flows, we find the following specific results regarding the effect of advection on ionization fronts in H II regions: (1) Significant direct effects of advection on the global emission properties occur only when the ionization parameter is lower than is typical for H II regions. For …

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The Vlt-Uves Survey For Molecular Hydrogen In High-Redshift Damped Lyman Α Systems: Physical Conditions In The Neutral Gas, Raghunathan Srianand, Patrick Petitjean, Cédric Ledoux, Gary J. Ferland, Gargi Shaw Jan 2005

The Vlt-Uves Survey For Molecular Hydrogen In High-Redshift Damped Lyman Α Systems: Physical Conditions In The Neutral Gas, Raghunathan Srianand, Patrick Petitjean, Cédric Ledoux, Gary J. Ferland, Gargi Shaw

Physics and Astronomy Faculty Publications

We study the physical conditions in damped Lyman α systems (DLAs), using a sample of 33 systems towards 26 quasi-stellar objects (QSOs) acquired for a recently completed survey of H2 by Ledoux, Petitjean & Srianand. We use the column densities of H2 in different rotational levels, together with those of C I, C I*, C I**, C II* and singly ionized atomic species to discuss the kinetic temperature, the density of hydrogen and the electronic density in the gas together with the ambient ultraviolet (UV) radiation field. Detailed comparisons are made between the observed properties in DLAs, the …

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