Astrophysics and Astronomy Commons^™

The Structure Of The Homunculus. Ii. Modeling The Physical Conditions In Η Carinae's Molecular Shell, Nathan Smith, Gary J. Ferland

Physics and Astronomy Faculty Publications

We present models that reproduce the observed double-shell structure of the Homunculus Nebula around η Carinae, including the stratification of infrared H₂ and [Fe II] emission seen in data obtained with the Phoenix spectrograph on Gemini South, as well as the corresponding stratified grain temperature seen in thermal-infrared data. Tuning the model to match the observed shell thickness allows us to determine the threshold density that permits survival of H₂. An average density of n_H~=(0.5-1)×10⁷ cm^-3 in the outer zone is required to allow H₂ to exist at all latitudes in the …

Discovery Of Atomic And Molecular Mid-Infrared Emission Lines In Off-Nuclear Regions Of Ngc 1275 And Ngc 4696 With The Spitzer Space Telescope, R. M. Johnstone, N. A. Hatch, Gary J. Ferland, A. C. Fabian, C. S. Crawford, R. J. Wilman

Physics and Astronomy Faculty Publications

We present Spitzer high-resolution spectra of off-nuclear regions in the central cluster galaxies NGC 1275 and NGC 4696 in the Perseus and Centaurus clusters, respectively. Both objects are surrounded by extensive optical emission-line filamentary nebulae, bright outer parts of which are the targets of our observations. The 10–37 μm spectra show strong pure-rotational lines from molecular hydrogen revealing a molecular component to the filaments which has an excitation temperature of ∼300−400 K. The flux in the 0−0 S(1) molecular hydrogen line correlates well with the strength of the optical lines, having about 3 per cent of the Hα+[N II] emission. …

Mid-Infrared Galaxy Classification Based On Silicate Obscuration And Pah Equivalent Width, H. W. W. Spoon, J. A. Marshall, J. R. Houck, Moshe Elitzur, L. Hao, L. Armus, B. R. Brandl, V. Charmandaris

Physics and Astronomy Faculty Publications

We present a new diagnostic diagram for mid-infrared spectra of infrared galaxies based on the equivalent width of the 6.2 μm PAH emission feature and the strength of the 9.7 μm silicate feature. Based on the positions in this diagram, we classify galaxies into nine classes ranging from continuum-dominated AGN hot dust spectra and PAH-dominated starburst spectra to absorption-dominated spectra of deeply obscured galactic nuclei. We find that galaxies are systematically distributed along two distinct branches: one of AGN and starburst-dominated spectra and one of deeply obscured nuclei and starburst-dominated spectra. The separation into two branches likely reflects …

Deep Mid-Infrared Silicate Absorption As A Diagnostic Of Obscuring Geometry Toward Galactic Nuclei, N. A. Levenson, M. M. Sirocky, L. Hao, H. W. W. Spoon, J. A. Marshall, Moshe Elitzur, J. R. Houck

Physics and Astronomy Faculty Publications

The silicate cross section peak near 10 μm produces emission and absorption features in the spectra of dusty galactic nuclei observed with the Spitzer Space Telescope. Especially in ultraluminous infrared galaxies, the observed absorption feature can be extremely deep, as IRAS 08572+3915 illustrates. A foreground screen of obscuration cannot reproduce this observed feature, even at a large optical depth. Instead, the deep absorption requires a nuclear source to be deeply embedded in a smooth distribution of material that is both geometrically and optically thick. In contrast, a clumpy medium can produce only shallow absorption or emission, which are …

Detection Of A Far-Infrared Bow Shock Nebula Around R Hya: The First Miriad Results, T. Ueta, A. K. Speck, R. E. Stencel, F. Herwig, R. D. Gehrz, R. Szczerba, H. Izumiura, A. A. Zijlstra, W. B. Latter, M. Matsuura, M. Meixner, M. Steffen, Moshe Elitzur

Physics and Astronomy Faculty Publications

We present the first results of the MIRIAD (MIPS InfraRed Imaging of AGB Dust shells) project using the Spitzer Space Telescope. The primary aim of the project is to probe the material distribution in the extended circumstellar envelopes (CSEs) of evolved stars and recover the fossil record of their mass-loss history. Hence, we must map the whole of the CSEs plus the surrounding sky for background subtraction while avoiding the central star that is brighter than the detector saturation limit. With our unique mapping strategy, we have achieved better than 1 MJy sr^-1 sensitivity in 3 hr of …

Energy Levels And Transition Probabilities For Boron-Like Fe Xxii, V. Jonauskas, P. Bogdanovich, F. P. Keenan, R. Kisielius, M. E. Foord, R. F. Heeter, S. J. Rose, Gary J. Ferland, P. H. Norrington

Physics and Astronomy Faculty Publications

The Multiconfiguration Dirac-Fock method is used to calculate the energies of the 407 lowest levels in FeXXII. These results are cross-checked using a suite of codes which employ the configuration interaction method on the basis set of transformed radial orbitals with variable parameters, and takes into account relativistic corrections in the Breit-Pauli approximation. 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, as well as the five largest values from each level be it of E1, M1, E2, M2, or E3 …

Determining The H+ Region / Pdr Equation Of State In Star-Forming Regions, N. P. Abel, Gary J. Ferland

Physics and Astronomy Faculty Publications

The emission-line regions of starburst galaxies and active nuclei reveal a wealth of spectroscopic information. A unified picture of the relationship among ionized, atomic, and molecular gas makes it possible to better understand these observations. We performed a series of calculations designed to determine the equation of state-the relationship among density, temperature, and pressure-through emission-line diagnostic ratios that form in the H⁺ region and the photodissociation region (PDR). We consider a wide range of physical conditions in the H⁺ region. We connect the H⁺ region to the PDR by considering two constant pressure cases: one with no …

Physical Conditions In Orion's Veil. Ii. A Multicomponent Study Of The Line Of Sight Toward The Trapezium, N. P. Abel, Gary J. Ferland, C. R. O'Dell, G. Shaw, Thomas H. Troland

Physics and Astronomy Faculty Publications

Orion's Veil is an absorbing screen that lies along the line of sight to the Orion H II region. It consists of two or more layers of gas that must lie within a few parsecs of the Trapezium cluster. Our previous work considered the Veil as a whole and found that the magnetic field dominates the energetics of the gas in at least one component. Here we use high-resolution STIS UV spectra that resolve the two velocity components in absorption and determine the conditions in each. We derive a volume hydrogen density, 21 cm spin temperature, turbulent velocity, and kinetic …

Spatially Resolved Mid-Infrared Spectroscopy Of Ngc 1068: The Nature And Distribution Of The Nuclear Material, R. E. Mason, T. R. Geballe, C. Packham, N. A. Levenson, Moshe Elitzur, R. S. Fisher, E. Perlman

Physics and Astronomy Faculty Publications

We present spatially resolved, near-diffraction-limited 10 μm spectra of the nucleus of the Seyfert 2 galaxy NGC 1068, obtained with Michelle, the mid-IR imager and spectrometer on the 8.1 m Gemini North Telescope. The spectra cover the nucleus and the central 6.0” × 0.4” of the ionization cones at a spatial resolution of approximately 0.4” (≈30 pc). The spectra extracted in 0.4” steps along the slit reveal striking variations in continuum slope, silicate feature profile and depth, and fine-structure line fluxes on subarcsecond scales, illustrating in unprecedented detail the complexity of the circumnuclear regions of NGC 1068 at mid-IR …

Physical Conditions In The Interstellar Medium Toward Hd 185418, Gargi Shaw, Gary J. Ferland, R. Srianand, N. P. Abel

Physics and Astronomy Faculty Publications

We have developed a complete model of the hydrogen molecule as part of the spectral simulation code Cloudy. Our goal is to apply this to spectra of high-redshift star-forming regions where H₂ absorption is seen, but where few other details are known, to understand its implication for star formation. The microphysics of H₂ is intricate, and it is important to validate these numerical simulations in better understood environments. This paper studies a well-defined line of sight through the Galactic interstellar medium (ISM) as a test of the microphysics and methods we use. We present a self-consistent calculation of …

Near-Infrared And The Inner Regions Of Protoplanetary Disks, Dejan Vinković, Željko Ivezić, Tomislav Jurkić, Moshe Elitzur

Physics and Astronomy Faculty Publications

We examine the “puffed-up inner disk” model proposed by Dullemond, Dominik, & Natta for explaining the near-IR excess radiation from Herbig Ae/Be stars. Detailed model computations show that the observed near-IR excess requires more hot dust than is contained in the puffed-up disk rim. The rim can produce the observed near-IR excess only if its dust has perfectly gray opacity, but such dust is in conflict with the observed 10 μm spectral feature. We find that a compact (~10 AU), tenuous (τ_V ≲ 0.4), dusty halo around the disk inner regions contains enough dust to readily explain …

A Systematic Study On The Thermodynamic And Transport Properties Of Layered Ruthenates, Xiunu Lin

University of Kentucky Doctoral Dissertations

In the 4d transition metal oxides, the extension of the 4d orbitals leads to comparable and thus competitive kinetic and coulomb energies. As a result, small perturbations can induce significant changes in their physical properties, giving rise to a class of exotic phenomena that are rarely found in other materials. The ruthenates materials with readily tunable parameters open an avenue to study the strong electronic correlation in the rarely explored territory: the 4d transition metal oxides.

The bilayered system, Ca₃Ru₂O₇, belongs to the Ruddlesden-Popper series in which the physical properties are intimately linked to …

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.

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 …

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 …

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 …

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 …

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.

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.

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 …

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 …

The Origin Of Fe Ii Emission In Active Galactic Nuclei, J. A. Baldwin, Gary J. Ferland, K. T. Korista, F. Hamann, A. Lacluyzé

Physics and Astronomy Faculty Publications

We used a very large set of models of broad emission line region (BELR) clouds in active galactic nuclei to investigate the formation of the observed Fe II emission lines. We show that photoionized BELR clouds cannot produce both the observed shape and observed equivalent width of the 2200-2800 Å Fe II UV bump unless there is considerable velocity structure corresponding to a microturbulent velocity parameter v_turb≥100 km s^-1 for the locally optimally emitting cloud models used here. This could be either microturbulence in gas that is confined by some phenomenon such as MHD waves or a …

Dirac-Fock Energy Levels And Transition Probabilities For Oxygen-Like Fe Xix, V. Jonauskas, 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

Multiconfigurational Dirac-Fock calculations are reported for 656 energy levels and the 214 840 electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transition probabilities in oxygen-like FeXIX. The spectroscopic notations as well as the total transition probabilities from each energy level are provided. Good agreement is found with data compiled by NIST.

Physical Conditions In Orion's Veil, N. P. Abel, C. L. Brogan, Gary J. Ferland, C. R. O'Dell, G. Shaw, Thomas H. Troland

Physics and Astronomy Faculty Publications

Orion's veil consists of several layers of largely neutral gas lying between us and the main ionizing stars of the Orion Nebula. It is visible in 21 cm H I absorption and in optical and UV absorption lines of H I and other species. Toward θ¹ Ori C, the veil has two remarkable properties, a high magnetic field (~100 μG) and a surprising lack of H₂, given its total column density. Here we compute photoionization models of the veil to establish its gas density and its distance from θ¹ Ori C. We use a greatly improved …

12C/13C Ratio In Planetary Nebulae From The Iue Archives, R. H. Rubin, Gary J. Ferland, E. E. Chollet, R. Horstmeyer

Physics and Astronomy Faculty Publications

We investigated the abundance ratio of ¹²C/¹³C in planetary nebulae by examining emission lines arising from C III 2s2p³P^o_2,1,0 → 2s²¹S₀. Spectra were retrieved from the International Ultraviolet Explorer archives, and multiple spectra of the same object were co-added to achieve improved signal-to-noise ratio. The ¹³C hyperfine structure line at 1909.6 Å was detected in NGC 2440. The ¹²C/¹³C ratio was found to be ~4.4+/-1.2. In all other objects, we provide an upper limit for the flux of the 1910 Å line. For 23 …

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 …

Relativistic Allowed And Forbidden Transition Probabilities For Fluorine-Like Fe Xviii, V. Jonauskas, F. P. Keenan, M. E. Foord, R. F. Heeter, S. J. Rose, P. A. M. Van Hoof, Gary J. Ferland, K. M. Aggarwal, R. Kisielius, P. H. Norrington

Physics and Astronomy Faculty Publications

Energy levels and the corresponding transition probabilities for allowed and forbidden transitions among the levels of the ground configuration and first 23 excited configurations of fluorine-like Fe XVIII have been calculated using the multiconfigurational Dirac-Fock GRASP code. A total of 379 lowest bound levels of Fe XVIII is presented, and the energy levels are identified in spectroscopic notations. Transition probabilities, oscillator strengths and line strengths for electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transitions among these 379 levels are also presented. The calculated energy levels and transition probabilities are compared with experimental data.

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 …

The Flaring H2o Megamaser And Compact Radio Source In Markarian 348, A. B. Peck, C. Henkel, J. S. Ulvestad, A. Brunthaler, H. Falcke, Moshe Elitzur, K. M. Menten, J. F. Gallimore

Physics and Astronomy Faculty Publications

We report on single-dish monitoring and extremely high angular resolution observations of the flaring H₂O megamaser in the Seyfert 2 galaxy Mrk 348. The H₂O line is redshifted by ~130 km s^-1 with respect to the systemic velocity, is very broad, with an FWHM of 130 km s^-1, and has no detectable high-velocity components within 1500 km s^-1 on either side of the strong line. Monitoring observations made with the Effelsberg 100 m telescope show that the maser varies significantly on timescales as short as 1 day and that the integrated line …

Chemical Abundances In Broad Emission Line Regions: The "Nitrogen-Loud'' Quasi-Stellar Object Q0353-383, J. A. Baldwin, F. Hamann, K. T. Korista, Gary J. Ferland, M. Dietrich, C. Warner

Physics and Astronomy Faculty Publications

The intensity of the strong N V λ1240 line relative to C IV λ1549 or to He II λ1640 has been proposed as an indicator of the metallicity of quasi-stellar object (QSO) broad emission line regions, allowing abundance measurements in a large number of QSOs out to the highest redshifts. Previously, it had been shown that the (normally) much weaker lines N III] λ1750 and N IV] λ1486 could be used in the same way. The redshift 1.96 QSO 0353-383 has long been known to have N III] and N IV] lines that are far stronger relative to Lyα or …