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1997

University of Kentucky

Articles 1 - 9 of 9

Full-Text Articles in Physics

Do The Broad Emission Line Clouds See The Same Continuum That We See?, Kirk Korista, Gary J. Ferland, Jack Baldwin Oct 1997

Do The Broad Emission Line Clouds See The Same Continuum That We See?, Kirk Korista, Gary J. Ferland, Jack Baldwin

Physics and Astronomy Faculty Publications

Recent observations of quasars, Mrk 335 and the HST quasar composite spectrum, have indicated that many quasars have remarkably soft ionizing continua (f ∝ ~ ν-2, 13.6-100 eV). We point out that the number of photons with hν > 54.4 eV is insufficient to create the observed strengths of the He II emission lines. While the numbers of photons which energize C IV λ1549 and O VI λ1034 are sufficient, even the most efficiently emitting clouds for these two lines must each cover at least 20%-40% of the source. If the typical quasar ionizing continuum is indeed this …

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Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland Sep 1997

Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

The narrow emission line spectra of active galactic nuclei are not accurately described by simple photoionization models of single clouds. Recent Hubble Space Telescope images of Seyfert 2 galaxies show that these objects are rich with ionization cones, knots, filaments, and strands of ionized gas. Here we extend to the narrow-line region the ``locally optimally emitting cloud'' (LOC) model, in which the observed spectra are predominantly determined by powerful selection effects. We present a large grid of photoionization models covering a wide range of physical conditions and show the optimal conditions for producing many of the strongest emission lines. We …

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Charge Transfer Between Neutral Atoms And Highly Ionized Species: Implications For Iso Observations, Gary J. Ferland, K. T. Korista, D. A. Verner, A. Dalgarno Jun 1997

Charge Transfer Between Neutral Atoms And Highly Ionized Species: Implications For Iso Observations, Gary J. Ferland, K. T. Korista, D. A. Verner, A. Dalgarno

Physics and Astronomy Faculty Publications

We estimate rate coefficients for charge transfer between neutral hydrogen and helium and moderately to highly ionized heavy elements. Although charge transfer does not have much influence on hot collisionally ionized plasmas, its effects on photoionized plasmas can be profound. We present several photoionization models that illustrate the significant effect of charge transfer on the far-infrared lines detected by ISO.

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Physical Conditions Of The Coronal Line Region In Seyfert Galaxies, Jason W. Ferguson, Kirk Korista, Gary J. Ferland Jun 1997

Physical Conditions Of The Coronal Line Region In Seyfert Galaxies, Jason W. Ferguson, Kirk Korista, Gary J. Ferland

Physics and Astronomy Faculty Publications

The launch of the Infrared Space Observatory and new atomic data have opened a window for the study of high-ionization gas in active galactic nuclei (AGNs). We present the results of a large number of photoionization simulations of the "coronal line" region in AGNs, employing new atomic data from the Opacity and Iron Projects. Our grid of line emission spans 8 orders of magnitude in gas density and 14 orders of magnitude in ionizing flux in an effort to identify the optimal conditions in which these lines form. We show that coronal lines form at distances from just outside the …

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Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland Apr 1997

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.

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Grains In Ionized Nebulae. Ii. Heavy-Element Depletion, J. B. Kingdon, Gary J. Ferland Mar 1997

Grains In Ionized Nebulae. Ii. Heavy-Element Depletion, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

The presence of grains in gaseous nebulae can have significant effects on the thermal balance and radiative line transfer in these objects. The depletion of condensable elements onto grains provides evidence that dust exists in the ionized regions of nebulae. In this paper, we consider the elements Sc, Ti, V, and Cr, all of which are strongly depleted in the general interstellar medium. We construct simple three-level atoms for several ions of these elements, and incorporate them into our photoionization code CLOUDY. For both a model planetary nebula and a model H II region, we find that several lines of …

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An Atlas Of Computed Equivalent Widths Of Quasar Broad Emission Lines, Kirk Korista, Jack Baldwin, Gary J. Ferland, Dima Verner Feb 1997

An Atlas Of Computed Equivalent Widths Of Quasar Broad Emission Lines, Kirk Korista, Jack Baldwin, Gary J. Ferland, Dima Verner

Physics and Astronomy Faculty Publications

We present graphically the results of several thousand photoionization calculations of broad emission-line clouds in quasars, spanning 7 orders of magnitude in hydrogen ionizing flux and particle density. The equivalent widths of 42 quasar emission lines are presented as contours in the particle density-ionizing flux plane for a typical incident continuum shape, solar chemical abundances, and cloud column density of N(H) = 1023 cm-2. Results are similarly given for a small subset of emission lines for two other column densities (1022 and 1024 cm-2), five other incident continuum shapes, and a gas …

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On Protostellar Disks In Herbig Ae/Be Stars, Anatoly Miroshnichenko, Željko Ivezić, Moshe Elitzur Jan 1997

On Protostellar Disks In Herbig Ae/Be Stars, Anatoly Miroshnichenko, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

The spectral shape of IR emission from Herbig Ae/Be stars has been invoked as evidence for accretion disks around high-mass protostars. Instead, we present here models based on spherical envelopes with an r-1.5 dust density profile that successfully explain the observed spectral shapes. The spectral energy distributions of eight primary candidates for protostellar disks are fitted in detail for all wavelengths available, from visual to far-IR. The only envelope property adjusted in individual sources is the overall visual optical depth, and it ranges from 0.3 to 3. In each case, our models properly reproduce the data for IR excess, …

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[Fe Iv] In The Orion Nebula, R. H. Rubin, R. J. Dufour, Gary J. Ferland, P. G. Martin, C. R. O'Dell, J. A. Baldwin, J. J. Hester, D. K. Walter, Z. Wen Jan 1997

[Fe Iv] In The Orion Nebula, R. H. Rubin, R. J. Dufour, Gary J. Ferland, P. G. Martin, C. R. O'Dell, J. A. Baldwin, J. J. Hester, D. K. Walter, Z. Wen

Physics and Astronomy Faculty Publications

Using the Goddard High-Resolution Spectrograph on the Hubble Space Telescope, we measured the flux of [Fe IV] (3d5 4P5/2 --> 3d5 6S5/2) λvac = 2836.56 Å in the Orion Nebula, the first detection of an [Fe IV] line in an H II region. A useful upper limit is set on the sum of fluxes of [Fe IV] (3d5 4D5/2, 3/2 --> 3d5 6S5/2) λvac = 2568.4, 2568.2 Å. By comparing these observations with predicted fluxes from simply ``retrofitting'' our two previous photoionization models, …

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