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Full-Text Articles in Physical Sciences and Mathematics
Suppression Of Dielectronic Recombination Due To Finite Density Effects. Ii. Analytical Refinement And Application To Density-Dependent Ionization Balances And Agn Broad-Line Emission, D. Nikolić, T. W. Gorczyca, K. T. Korista, Marios Chatzikos, Gary J. Ferland, Francisco Guzmán, P. A. M. Van Hoof, R. J. R. Williams, N. R. Badnell
Suppression Of Dielectronic Recombination Due To Finite Density Effects. Ii. Analytical Refinement And Application To Density-Dependent Ionization Balances And Agn Broad-Line Emission, D. Nikolić, T. W. Gorczyca, K. T. Korista, Marios Chatzikos, Gary J. Ferland, Francisco Guzmán, P. A. M. Van Hoof, R. J. R. Williams, N. R. Badnell
Physics and Astronomy Faculty Publications
We present improved fits to our treatment of suppression of dielectronic recombination at intermediate densities. At low densities, most recombined excited states eventually decay to the ground state, and therefore the total dielectronic recombination rate to all levels is preserved. At intermediate densities, on the other hand, collisions can lead to ionization of higher-lying excited states, thereby suppressing the dielectronic recombination rate. The improved suppression factors presented here, although highly approximate, allow summed recombination rate coefficients to be used to intermediate densities. There have been several technical improvements to our previously presented fits. For H- through B-like ions the activation …
Confocal Laser Induced Fluorescence With Comparable Spatial Localization To The Conventional Method, Derek S. Thompson, Miguel F. Henriquez, Earl E. Scime, Timothy N. Good
Confocal Laser Induced Fluorescence With Comparable Spatial Localization To The Conventional Method, Derek S. Thompson, Miguel F. Henriquez, Earl E. Scime, Timothy N. Good
Physics and Astronomy Faculty Publications
We present measurements of ion velocity distributions obtained by laser induced fluorescence (LIF) using a single viewport in an argon plasma. A patent pending design, which we refer to as the confocal fluorescence telescope, combines large objective lenses with a large central obscuration and a spatial filter to achieve high spatial localization along the laser injection direction. Models of the injection and collection optics of the two assemblies are used to provide a theoretical estimate of the spatial localization of the confocal arrangement, which is taken to be the full width at half maximum of the spatial optical response. The …
Accurate Determination Of The Free–Free Gaunt Factor – Ii. Relativistic Gaunt Factors, P. A. M. Van Hoof, Gary J. Ferland, R. J. R. Williams, K. Volk, Marios Chatzikos, M. Lykins, R. L. Porter
Accurate Determination Of The Free–Free Gaunt Factor – Ii. Relativistic Gaunt Factors, P. A. M. Van Hoof, Gary J. Ferland, R. J. R. Williams, K. Volk, Marios Chatzikos, M. Lykins, R. L. Porter
Physics and Astronomy Faculty Publications
When modelling an ionized plasma, all spectral synthesis codes need the thermally averaged free–free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum. Until now no data set exists that would meet these needs completely. We have therefore produced a table of relativistic Gaunt factors over a much wider range of parameter space than has ever been produced before. We present tables of the thermally averaged Gaunt factor covering the range 10log γ2 = −6 to 10 and 10log u = −16 to 13 for …
Accurate Determination Of The Free–Free Gaunt Factor – I. Non-Relativistic Gaunt Factors, P. A. M. Van Hoof, R. J. R. Williams, K. Vollk, Marios Chatzikos, Gary J. Ferland, M. Lykins, R. L. Porter, Ye Wang
Accurate Determination Of The Free–Free Gaunt Factor – I. Non-Relativistic Gaunt Factors, P. A. M. Van Hoof, R. J. R. Williams, K. Vollk, Marios Chatzikos, Gary J. Ferland, M. Lykins, R. L. Porter, Ye Wang
Physics and Astronomy Faculty Publications
Modern spectral synthesis codes need the thermally averaged free–free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum emitted by an ionized plasma. Until now no set of data exists that would meet this need in a fully satisfactory way. We have therefore undertaken to produce a table of very accurate non-relativistic Gaunt factors over a much wider range of parameters than has ever been produced before. We first produced a table of non-averaged Gaunt factors, covering the parameter space 10log ϵi = −20 to +10 …
Radiative Cooling Ii: Effects Of Density And Metallicity, Ye Wang, Gary J. Ferland, Matt Lykins, R. L. Porter, Peter A. M. Van Hoof, R. J. R. Williams
Radiative Cooling Ii: Effects Of Density And Metallicity, Ye Wang, Gary J. Ferland, Matt Lykins, R. L. Porter, Peter A. M. Van Hoof, R. J. R. Williams
Physics and Astronomy Faculty Publications
This work follows Lykins et al. discussion of classic plasma cooling function at low density and solar metallicity. Here, we focus on how the cooling function changes over a wide range of density (nH <1012 cm−3) and metallicity (Z < 30 Z⊙). We find that high densities enhance the ionization of elements such as hydrogen and helium until they reach local thermodynamic equilibrium. By charge transfer, the metallicity changes the ionization of hydrogen when it is partially ionized. We describe the total cooling function as a sum of four parts: those due to H&He, the heavy …
Suppression Of Dielectronic Recombination Due To Finite Density Effects, D. Nikolić, T. W. Gorczyca, K. T. Korista, Gary J. Ferland, N. R. Badnell
Suppression Of Dielectronic Recombination Due To Finite Density Effects, D. Nikolić, T. W. Gorczyca, K. T. Korista, Gary J. Ferland, N. R. Badnell
Physics and Astronomy Faculty Publications
We have developed a general model for determining density-dependent effective dielectronic recombination (DR) rate coefficients in order to explore finite-density effects on the ionization balance of plasmas. Our model consists of multiplying by a suppression factor those highly-accurate total zero-density DR rate coefficients which have been produced from state-of-the-art theoretical calculations and which have been benchmarked by experiment. The suppression factor is based upon earlier detailed collision-radiative calculations which were made for a wide range of ions at various densities and temperatures, but used a simplified treatment of DR. A general suppression formula is then developed as a function of …
Radiative Cooling In Collisionally Ionized And Photoionized Plasmas, Matt Lykins, Gary J. Ferland, Ryan L. Porter, Peter A. M. Van Hoof, R. J. R. Williams, Orly Gnat
Radiative Cooling In Collisionally Ionized And Photoionized Plasmas, Matt Lykins, Gary J. Ferland, Ryan L. Porter, Peter A. M. Van Hoof, R. J. R. Williams, Orly Gnat
Physics and Astronomy Faculty Publications
We discuss recent improvements in the calculation of the radiative cooling in both collisionally ionized and photoionized plasmas. We are extending the spectral simulation code CLOUDY so that as much as possible of the underlying atomic data are taken from external data bases, some created by others and some developed by the CLOUDY team. This paper focuses on recent changes in the treatment of many stages of ionization of iron, and discusses its extensions to other elements. The H- and He-like ions are treated in the isoelectronic approach described previously. Fe II is a special case treated with a large …
Ion-By-Ion Cooling Efficiencies, Orly Gnat, Gary J. Ferland
Ion-By-Ion Cooling Efficiencies, Orly Gnat, Gary J. Ferland
Physics and Astronomy Faculty Publications
We present ion-by-ion cooling efficiencies for low-density gas. We use Cloudy (version 10.00) to estimate the cooling efficiencies for each ion of the first 30 elements (H-Zn) individually. We present results for gas temperatures between 104 and 108 K, assuming low densities and optically thin conditions. When nonequilibrium ionization plays a significant role the ionization states deviate from those that obtain in collisional ionization equilibrium (CIE), and the local cooling efficiency at any given temperature depends on specific nonequilibrium ion fractions. The results presented here allow for an efficient estimate of the total cooling efficiency for any ionic …
Revisiting He-Like X-Ray Emission-Line Plasma Diagnostics, R. L. Porter, Gary J. Ferland
Revisiting He-Like X-Ray Emission-Line Plasma Diagnostics, R. L. Porter, Gary J. Ferland
Physics and Astronomy Faculty Publications
A complete model of helium-like line and continuum emission has been incorporated into the plasma simulation code Cloudy. All elements between He and Zn are treated, any number of levels can be considered, and radiative and collisional processes are included. This includes photoionization from all levels, line transfer, including continuum pumping and destruction by background opacities, scattering, and collisional processes. The model is calculated self-consistently along with the ionization and thermal structure of the surrounding nebula. The result is a complete line and continuum spectrum of the plasma. Here we focus on the ions of the He I sequence and …
He I Emission In The Orion Nebula And Implications For Primordial Helium Abundance, R. L. Porter, Gary J. Ferland, K. B. Macadam
He I Emission In The Orion Nebula And Implications For Primordial Helium Abundance, R. L. Porter, Gary J. Ferland, K. B. Macadam
Physics and Astronomy Faculty Publications
We apply a recently developed theoretical model of helium emission to observations of both the Orion Nebula and a sample of extragalactic H II regions. In the Orion analysis, we eliminate some weak and blended lines and compare theory and observation for our reduced line list. With our best theoretical model we find an average difference between theoretical and observed intensities (Ipred/Iobs-1)=6.5%. We argue that both the red and blue ends of the spectrum may have been inadequately corrected for reddening. For the 22 highest quality lines, with 3499 Å≤λ≤6678 Å, our best model …
J-Resolved He I Emission Predictions In The Low-Density Limit, R. P. Bauman, R. L. Porter, Gary J. Ferland, K. B. Macadam
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 …
Theoretical He I Emissivities In The Case B Approximation, R. L. Porter, R. P. Bauman, Gary J. Ferland, K. B. Macadam
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.
The Effects Of Low-Temperature Dielectronic Recombination On The Relative Populations Of The Fe M-Shell States, S. B. Kraemer, Gary J. Ferland, J. R. Gabel
The Effects Of Low-Temperature Dielectronic Recombination On The Relative Populations Of The Fe M-Shell States, S. B. Kraemer, Gary J. Ferland, J. R. Gabel
Physics and Astronomy Faculty Publications
We examine the effects of low-temperature, or Δn=0, dielectronic recombination (DR) on the ionization balance of the Fe M shell (Fe IX-Fe XVI). Since Δn=0 rates are not available for these ions, we have derived estimates based on the existing rates for the first four ionization states of the CNO sequence and newly calculated rates for L-shell ions of third-row elements and Fe. For a range of ionization parameter and column density applicable to the intrinsic absorbers detected in ASCA, Chandra, and XMM-Newton observations of Seyfert galaxies, we generated two grids of photoionization models, with and …
Grain Size Distributions And Photoelectric Heating In Ionized Media, P. A. M. Vanhoof, J. C. Weingartner, P. G. Martin, K. Volk, Gary J. Ferland
Grain Size Distributions And Photoelectric Heating In Ionized Media, P. A. M. Vanhoof, J. C. Weingartner, P. G. Martin, K. Volk, Gary J. Ferland
Physics and Astronomy Faculty Publications
Ever since the pioneering study of Spitzer, it has been widely recognized that grains play an important role in the heating and cooling of photoionized environments. This includes the diffuse interstellar medium and H II regions, planetary nebulae and photodissociation regions. A detailed code is necessary to model grains in a photoionized medium since the interactions of grains with their environment include a host of microphysical processes. In this paper we will use the spectral synthesis code CLOUDY for this purpose. A comprehensive upgrade of the grain model has been recently incorporated into CLOUDY. One of these upgrades is the …
He I 2.06 Micron Emission From Nebulae, Gary J. Ferland
He I 2.06 Micron Emission From Nebulae, Gary J. Ferland
Physics and Astronomy Faculty Publications
The spectrum emitted by any astronomical plasma is sensitive to a variety of details, some of which may not be obviously important. This paper describes the sensitivity of the He I 2.06 μm line to the gas opacity at ionizing energies. The intensity of the line relative to a hydrogen line depends on the He+/H+ ratio, but also on the ratio of continuous to He I Lyα line opacity, since this determines whether the Lyα line can scatter often enough to be converted to the 2.06 μm line. The intensity of the infrared line relative to Hβ …
Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland
Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland
Physics and Astronomy Faculty Publications
Many large-scale numerical simulations of astrophysical plasmas must also reproduce the hydrogen ionization and the resulting emission spectrum, in some cases quite accurately. We describe a compact model hydrogen atom that can be readily incorporated into such simulations. It reproduces the recombination efficiency and line spectrum predicted by much larger calculations for a very broad range of densities and temperatures. Uncertainties in hydrogen collision data are the largest source of differences between our compact atom and predictions of more extensive calculations and underscore the need for accurate atomic data.