Astrophysics and Astronomy Commons^™

Silcom Quantum Walls: Fabrication And Opticla Analysis, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the,anddirection, and each slab surfaces is extended in the-plane and normal to thedirection. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of the phonons is highly dependent on …

Design Of A Device Independent Computer Graphic Software Package, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the <110>, <112> and <111> direction, and each slab surfaces is extended in the <110>-<112> plane and normal to the <111> direction. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of …

Atomic Data For Astrophysics. Ii. New Analytic Fits For Photoionization Cross Sections Of Atoms And Ions, D. A. Verner, Gary J. Ferland, K. T. Korista, D. G. Yakovlev

Physics and Astronomy Faculty Publications

We present a complete set of analytic fits to the nonrelativistic photoionization cross sections for the ground states of atoms and ions of elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization thresholds, the fits are based on the Opacity Project theoretical cross sections interpolated and smoothed over resonances. At higher energies, the fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections.

Simulations Of Electrostatic Modes Of Non-Neutral Plasmas With Small Aspect Ratio In A Penning Trap, Grant W. Mason, Ross L. Spencer, Jonathan A. Bennett

Faculty Publications

The dependence on induced charge, experimental geometry, and temperature of electrostatic modes in very low aspect ratio non-neutral plasmas in a Penning trap is considered. The modes are of interest as non-destructive diagnostics of the shape of the plasmas. These investigations include equilibrium calculations of plasma shapes and profiles at finite temperature and particle-in-cell simulations of axisymmetric modes. The results of the simulations are compared to the zero-temperature theory by Dubin [Phys. Rev. Lett. 66, 2076 (1991)] taken to first-order in the aspect ratio and to experimental measurements by Weimer et al. [Phys. Rev. A 49, 3842 (1994)]. In general, …

Very High Density Clumps And Outflowing Winds In Qso Broad-Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, R. F. Carswell, F. Hamann, M. M. Phillips, D. A. Verner, Belinda J. Wilkes, R. E. Williams

Physics and Astronomy Faculty Publications

Intercomparison of the spectra of seven high-luminosity quasi-stellar objects (QSOs) shows that there is a gradation of properties in their broad emission-line regions (BELRs) that can be understood as differing mixtures of different gas components. Six of these seven objects have unusually narrow BELR profiles, which greatly facilitates the disentangling of blends and measuring of weak lines. In the QSO 0207 - 398, the BELR is made up of at least three kinematically distinct components; its spectrum is in fact a composite of the spectra of the more homogeneous BELRs in the QSOs at either end of our sequence of …

The Chemical Enrichment Of Gas In Broad Absorption Line Qsos: Rapid Star Formation In The Early History Of Galaxies, Kirk Korista, Fred Hamann, Jason W. Ferguson, Gary J. Ferland

Physics and Astronomy Faculty Publications

Utilizing spectra from ground-based and Hubble Space Telescope observations, Korista et al. identified at least 12 broad absorption lines in the broad absorption line (BAL) QSO 0226-1024 (z_em = 2.256), many for the first time. In the present paper we use seven of their measured column densities to investigate the BAL gas ionization equilibrium and metallicity. We assume that the metal abundances follow the rapid star formation (RSF) models of Hamann & Ferland or are simply scaled from solar ratios to (1) limit the free parameters in constraining the overall metallicity and (2) test the applicability of such a …

High Metal Enrichments In Luminous Quasars, Gary J. Ferland, Jack A. Baldwin, Kirk T. Korista, Fred Hamann, R. F. Carswell, Mark Phillips, Belinda J. Wilkes, Robert E. Williams

Physics and Astronomy Faculty Publications

We discuss observations of the broad emission line in luminous intermediate redshift quasars, with emphasis on Q0207 -398. This object has relatively sharp lines, allowing us to deconvolve the profiles into distinct components. In this paper we examine the high ionization region, which we show must be matter-bounded, partially transparent to ionizing radiation. We measure a large N V λ1240/He II λ1640 ratio in Q0207-398, but detailed calculations predict this ratio to be ~1 for standard cloud properties. We show that no choice of incident continuum, ionizing photon flux, density, or even the appeal to nonradiative energy sources, can reproduce …

Atomic Data For Astrophysics. I. Radiative Recombination Rates For H-Like, He-Like, Li-Like, And Na-Like Ions Over A Broad Range Of Temperature, D. A. Verner, Gary J. Ferland

Physics and Astronomy Faculty Publications

We present new calculations and analytic fits to the rates of radiative recombination towards H-like, He-like, Li-like and Na-like ions of all elements from H through Zn (Z=30). The fits are valid over a wide range of temperature, from 3 K to 10⁹ K.

Polarization Of Astronomical Maser Radiation. Iii. Arbitrary Zeeman Splitting And Anisotropic Pumping, Moshe Elitzur

Physics and Astronomy Faculty Publications

General solutions of the maser polarization problem are presented for arbitrary absorption coefficients. The results are used to calculate polarization for masers permeated by magnetic fields with arbitrary values of χ_B, the ratio of Zeeman splitting to Doppler linewidth, and for anisotropic (m-dependent) pumping. In the case of magnetic fields, one solution describes the polarization for overlapping Zeeman components, χ_B < 1. The χ_B → 0 limit of this solution reproduces the linear polarization derived in previous studies, which were always conducted at this unphysical limit. Terms of higher order in χ_B have a negligible effect on …

A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

Presents a train model that shows the long-range spatial correlations of fluctuations in nonequilibrium fluid systems. Illustration of model through analysis of flat-car trains running on parallel tracks; Simulation of train model in computers; Theoretical analysis for fluctuations in the train model; Relationship between train model and the fluctuating hydrodynamic theory of fluids.

Theoretical Hei Line Intensities In Gaseous Nebulae: Ngc 1976, 6572 And Ic 4997, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Smits has recently calculated theoretical He I intensities for a large number of lines for conditions appropriate to gaseous nebulae. These are likely to remain the definitive calculations for some time to come. A comparison of these line ratios with observed values in three nebulae reveals some discrepancies. We show that these discrepancies are reduced when collisional effects from the metastable 2₃S level are included, and that it is not necessary to invoke an unknown depopulation mechanism for the He I2₃S level.

Polymers Interacting With Spherical And Rodlike Particles, E. Eisenriegler, Andreas Hanke, S. Dietrich

Physics & Astronomy Faculty Publications

The interaction of a long flexible polymer chain with mesoscopic particles of spherical or elongated cylindrical shape is investigated by field-theoretic methods using the polymer-magnet analogy. In the case that these particles are immersed in a dilute polymer solution and exhibit purely repulsive surfaces we study density profiles for monomers and chain ends near such a particle, the change of configurational entropy by immersing a particle into the solution, and the depletion interaction between a particle and a distant planar wall. Both ideal chains and chains with an excluded-volume interaction are considered. We also analyze particle surfaces with a short-ranged …

Basic Astronomy Labs, Terry L. Smith, Michael D. Reynolds, Jay S. Huebner

Physics Faculty Research and Scholarship

Providing the tools and know-how to apply the principles of astronomy first-hand, these 43 laboratory exercises each contain an introduction that clearly shows budding astronomers why the particular topic of that lab is of interest and relevant to astronomy. About one-third of the exercises are devoted solely to observation, and no mathematics is required beyond simple high school algebra and trigonometry.Organizes exercises into six major topics—sky, optics and spectroscopy, celestial mechanics, solar system, stellar properties, and exploration and other topics—providing clear outlines of what is involved in the exercise, its purpose, and what procedures and apparatus are to be used. …

Model Equations From Gyrokinetic Theory For A Non-Neutral Plasma To Include Temperature Effects And Applications To A Plasma Of Infinite Length, S. Neil Rasband

Faculty Publications

Gyrokinetic equations are derived for applications to non-neutral plasmas in constant, straight magnetic fields wherein E X B drift velocities are of the same order as thermal velocities. The ratio of the E X B rotation frequency to the cyclotron frequency and the ratio of the gyroradius to a plasma scale length are assumed to be of order epsilon and terms are retained in the gyrokinetic expansion to second order to include finite-Larmor-radius (FLR) effects. A mode equation is obtained for a non-neutral plasma in the infinite-length approximation. The singularities of this equation are compared and contrasted with the familiar …

Hierarchical Search Strategy For The Detection Of Gravitational Waves From Coalescing Binaries, Soumya Mohanty, S. Dhurandhar

Physics & Astronomy Faculty Publications

The detection of gravitational waves from coalescing compact binaries would be a computationally intensive process if a single bank of template wave forms (i.e., a one-step search) is used. We present, in this paper, a method which leads to a large reduction in the computational power required as compared to a one-step search. This method is a hierarchical search strategy involving two template banks. We show that the computational power required by such a two-step search, for an on-line detection of the one-parameter family of Newtonian signals, is 18 of that required when an on-line one-step search is used. This …

Measured Stark Widths Of A 425,94 Nm Ari Spectral Line, Ljiljana Skuljan, Vladimir Milosavljevic, Aleksandar Sreckovic, Stevan Djenize

Articles

No abstract provided.

Locally Optimally Emitting Clouds And The Origin Of Quasar Emission Lines, Jack Baldwin, Gary J. Ferland, Kirk Korista, Dima Verner

Physics and Astronomy Faculty Publications

The similarity of quasar line spectra has been taken as an indication that the emission line clouds have preferred parameters, suggesting that the environment is subject to a fine-tuning process. We show here that the observed spectrum is a natural consequence of powerful selection effects. We computed a large grid of photoionization models covering the widest possible range of cloud gas density and distance from the central continuum source. For each line only a narrow range of density and distance from the continuum source results in maximum reprocessing efficiency, corresponding to "locally optimally emitting clouds" (LOCs). These parameters depend on …

Broad Ne Viii Λ744 Emission From The Quasar Pg 1148+549, Fred Hamann, Joseph C. Shields, Gary J. Ferland, Kirk T. Korista

Physics and Astronomy Faculty Publications

We discuss the probable detection of broad Ne VIII λ774 emission from the z_ɛ = 0.978 quasar PG 1148+549, and we use spectral synthesis calculations to study the physical conditions in the line-forming gas. The theoretical predictions and the measured line wavelength both support Ne VIII λ774 as the most likely identification.

Our calculations show that Ne VIII λ774 forms in hotter and more highly ionized gas than previously recognized in the broad emission line region. If the gas is photoionized by a standard active galactic nucleus continuum, the observed Ne VIII equivalent width, the Ne VIII/O VI flux …

Observation Of Beam-Induced Changes In The Polarization Of Balmer-Α Radiation Emitted Following Beam--Tilted-Foil Transmission, Wang Qi, David D. Allred, Larry V. Knight, Douglas L. Harper, Royal G. Albridge, Norman H. Tolk

Faculty Publications

Measurements of the circular polarization of Balmer-α radiation emitted by excited hydrogen atoms, following the transmission of (20-50)-keV protons through thin, tilted amorphous carbon foils, exhibit markedly unexpected behavior as a function of exposure of the foil to the proton beam. Specifically, the circular polarization changes from an initially well understood tilt-angle dependence to a behavior which, for low tilt angles, gives the opposite handedness of circular polarization from that predicted. In addition, the degree of alignment, indicated by the linear Stokes parameter M/I, is enhanced also as a function of dose. These changes in the tilt-angle dependence of the …

The Geometry And Kinematics Of The Broad-Line Region In Ngc 5548 From Hst And Iue Observations, Ignaz Wanders, Mike R. Goad, Kirk T. Korista, Bradley M. Peterson, Keith Horne, Gary J. Ferland, Anuradha P. Koratkar, Richard W. Pogge, Joseph C. Sheilds

Physics and Astronomy Faculty Publications

The spatial and radial velocity distribution of broad-line-emitting gas in the Seyfert 1 galaxy NGC 5548 is examined through the process of reverberation mapping, which is done by detailed comparison of continuum and emission-line variations. Recent spectroscopic monitoring of NGC 5548 with HST and IUE allows us to resolve the "transfer function" (TF) that relates the continuum and emission-line variability. We also examine the radial velocity-resolved TFs, and confirm that predominantly radial motions of the line-emitting clouds can be excluded. We find that a broad-line region comprised of clouds that are orbiting a central source of mass ~10⁸ M …

Aliasing Reduction In Staring Infrared Imagers Utilizing Subpixel Techniques, Joseph C. Gillette, Thomas M. Stadtmiller, Russell C. Hardie

Electrical and Computer Engineering Faculty Publications

We introduce and analyze techniques for the reduction of aliased signal energy in a staring infrared imaging system. A standard staring system uses a fixed two-dimensional detector array that corresponds to a fixed spatial sampling frequency determined by the detector pitch or spacing. Aliasing will occur when sampling a scene containing spatial frequencies exceeding half the sampling frequency. This aliasing can significantly degrade the image quality. The aliasing reduction schemes presented here, referred to as microscanning, exploit subpixel shifts between time frames of an image sequence. These multiple images are used to reconstruct a single frame with reduced aliasing. If …

Temperature Fluctuations In Photoionized Nebulae, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Recombination lines in gaseous nebulae frequently yield parent-ion abundances that are several times larger than abundances derived from forbidden lines. One possible explanation for this discrepancy is the presence of temperature fluctuations. We examine temperature fluctuations in model nebulae by utilizing Peimbert's t² parameter. We have run large grids of models, varying the stellar temperature and the total hydrogen density. We consider two abundance sets: The first uses "typical" planetary nebulae abundances, while the second examines the effect of increasing the metals and grains by a factor of 3. We also consider both a constant density distribution and one …

Trajectory Mapping And Applications To Data From The Upper Atmosphere Research Satellite, Gary A. Morris, Mark R. Schoeberl, Lynn C. Sparling, Paul A. Newman, Leslie R. Lait, Lee Elson, Joe Waters, Robert A. Suttie, Aidan Roche, Jack Kumer, James M. Russell Iii

Physics and Astronomy Faculty Publications

The problem of creating synoptic maps from asynoptically gathered trace gas data has prompted the development of a number of schemes. Most notable among these schemes are the Kalman filter, the Salby-Fourier technique, and constituent reconstruction. This paper explores a new technique called "trajectory mapping." Trajectory mapping creates synoptic maps from asynoptically gathered data by advecting measurements backward or forward in time using analyzed wind fields. A significant portion of this work is devoted to an analysis of errors in synoptic trajectory maps associated with the calculation of individual parcel trajectories. In particular, we have considered (1) calculational errors; (2) …

The Hubble Space Telescope Sample Of Radio-Loud Quasars: The LyΑ/HΒ Ratio, Hagai Netzer, M. S. Brotherton, Beverley J. Wills, Mingsheng Han, D. Wills, J. A. Baldwin, Gary J. Ferland, I. W. A. Browne

Physics and Astronomy Faculty Publications

We have used the first Hubble Space Telescope Faint Object Spectrograph spectra of our sample of radio- loud quasars, and quasi-simultaneous ground-based spectrophotometry, to investigate the intensity ratio Lyα/Hβ, whose small observed values are one of the outstanding problems of active galactic nuclei research. The present sample of 20 quasars with complete flux and profile data shows the first significant correlations of this ratio with other observed properties. The strongest correlations are with various continuum slope indicators: we find smaller Lyα/Hβ ratios in quasars whose continua rise more steeply into the red. The …

The Hubble Space Telescope Sample Of Radio-Loud Quasars: Ultraviolet Spectra Of The First 31 Quasars, Beverley J. Wills, Keith L. Thompson, Mingsheng Han, H. Netzer, D. Wills, J. A. Baldwin, Gary J. Ferland, I W. A. Browne, M. S. Brotherton

Physics and Astronomy Faculty Publications

We report the first results from a continuing program to investigate the multifrequency spectrophotometric and other properties of a sample of about 50 radio-loud quasars in the redshift range ˜0.3-1.3. Here we present spectrophotometric data of high signal-to-noise ratio (≳20 in the continuum) of the first 31 radio-loud quasars, over the wavelength range from below Lyα to an observed wavelength of 3250 or 4800 Å, obtained using the Faint Object Spectrograph on the Hubble Space Telescope. We have also made quasi-simultaneous observations to extend these spectra beyond the Balmer lines -- either Hβ or Hα -- …

Numerical Calculation Of Axisymmetric Electrostatic Modes For Cold Finite-Length Non-Neutral Plasmas, Johnny K. Jennings, Ross L. Spencer, K. C. Hansen

Faculty Publications

A numerical calculation of mode frequencies for cold, non-neutral plasmas is reported. The numerical method can be applied to any axisymmetric plasma shape in a trap. Here, it is used to study axisymmetric electrostatic modes in a long conducting cylinder. These modes were previously studied by Prasad and O'Neil [Phys. Fluids 26, 665 (1983)] and by Dubin [Phys. Rev. Lett. 66, 2076 (1991)]. In contrast to Dubin's calculation, the effects of a nearby cylindrical wall, including its influence on the shape of the plasma equilibrium, are considered. It is found that for plasmas with aspect ratios (length divided by diameter) …

Infrared Emission And Dynamics Of Outlfows In Late-Type Stars, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

The dynamical structure and infrared emission of winds around late-type stars are studied in a self-consistent model that couples the equations of motion and radiative transfer. Thanks to its scaling properties, both the dynamics and IR spectrum of the solution are fully characterized by τ_F, the flux-averaged optical depth of the wind. Five types of dust grains are considered: astronomical silicate, crystalline olivine, graphite, amorphous carbon and SiC, as well as mixtures. Analysis of infrared signatures provides constraints on the grain chemical composition and indications for the simultaneous existence of silicate and carbon grains. The abundances of crystalline …

Collisional Effects In He I: An Observational Analysis, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosynthesis. Unfortunately, there is some question whether current theory can account for collisional contributions to He I. We present new observations of two planetary nebulae (PNs) in the range λ850-λ9650, which we use to assess the importance of collisonal effects in the He I spectrum. The first object, NGC 7027, is expected to show relatively strong collisional enhancement, while the second, NGC 7026, should display only small effects. We derive new collision-to-recombination correction factors, based on new collision strengths from the 29-state quantal calculation …

Optically Thin Broad-Line Clouds In Active Galactic Nuclei, Joseph C. Shields, Gary J. Ferland, Bradley M. Peterson

Physics and Astronomy Faculty Publications

The broad-line region (BLR) in Seyfert galaxy nuclei exhibits correlated variations in continuum and emission-line luminosity that are qualitatively consistent with photoionization of ionization-bounded (optically thick) clouds. However, evidence is growing that a nonnegligible fraction of the BLR cloud population is optically thin to the Lyman continuum and fully ionized in hydrogen. We consider the implications of this nebular component for observed line emission and find that inclusion of thin clouds in photoionization calculations can resolve several outstanding puzzles of Seyfert variability, notably the behavior of the C IV λ1549/Lyα ratio as a function of continuum luminosity.

A …

On The Current Status Of Maser Polarization Theory, Moshe Elitzur

Physics and Astronomy Faculty Publications

Despite recent criticism, past conflicts among theoretical studies of maser polarization are by now resolved and clarified. All analytical methods proposed thus far produce the same polarization solutions, solutions that agree with observations. Current numerical studies do not reproduce these solutions. Instead, for any pumping employed, their results are in direct conflict with both analytical theory and observations. These problems reflect the fact that the basic formulation of numerical modeling has yet to incorporate the statistical nature of the radiation field.