Astrophysics and Astronomy Commons^™

Upper Limits On Gravitational Wave Emission From 78 Radio Pulsars, B. P. Abbott, R. Abbott, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Cristina V. Torres

Physics & Astronomy Faculty Publications

We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors. The data from both runs have been combined coherently to maximize sensitivity. For the first time, pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor …

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 …

On Stability And Evolution Of Solutions In General Relativity, Stephen M. Taylor

Theses and Dissertations

This thesis is concerned with several problems in general relativity and low energy string theory that are pertinent to the time evolution of the gravitational field. We present a formulation of the Einstein field equations in terms of variational techniques borrowed from geometric analysis. These equations yield the evolution equations for the Cauchy problems of both general relativity and low energy string theory. We then proceed to investigate the evolutionary linear stability of Schwarzschild-like solutions in higher dimensional relativity called black strings. These objects are determined to be linearly unstable. This motivates a further stability analysis of the charged p-brane …

Development Of A Mevva Based Beryllium-7 Plasma Source, David K. Olson

Theses and Dissertations

We have designed a new type of plasma gun ion source for a Malmberg-Penning trap based on Metal Vapor Vacuum Arc (MeVVA) ion source designs. Our primary intent with this MeVVA-type source is to create a confinable beryllium-7 (7-Be) plasma. 7-Be is a peculiar isotope due to its varying radioactive decay half-life in different electro-chemical configurations. It is also found in an unexpected abundance at high altitudes of the Earth's atmosphere. It is possible ioniziation affects the radioactivity of the isotope, partly explaining this discrepancy with atmospheric models. The short half-life of 7-Be requires us to replace the sample inside …

The Mid-Infrared Emission Of M87, Eric S. Perlman, R. E. Mason, Christopher Packham, N. A. Levenson, Moshe Elitzur, Justin J. Schaefer, Masatoshi Imanishi, William B. Sparks, James Radomski

Physics and Astronomy Faculty Publications

We discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87 in the mid-infrared (mid-IR) from 5 to 35 μm. These observations allow us to investigate mid-IR emission mechanisms in the core of M87 and to establish that the flaring, variable jet component HST-1 is not a major contributor to the mid-IR flux. The Spitzer data include a high signal-to-noise ratio 15-35 μm spectrum of the knot A/B complex in the jet, which is consistent with synchrotron emission. However, a synchrotron model cannot account for the observed nuclear spectrum, even when contributions from the jet, necessary due …

Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics, Nicole Brimhall

Theses and Dissertations

We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux directional EUV source has available wavelengths between 8 nm and 62 nm and easily rotatable linear polarization. The polarimeter will aid researchers at BYU in characterizing EUV thin films and improving their understanding of materials for use in EUV optics. This first-time workhorse application of laser high harmonics enables polarization-sensitive reflection measurements not previously available in the EUV. We have constructed a versatile positioning system that places harmonics on the microchannel plate detector with an accuracy of 0.3 mm, which allows …

The Cosmic Ray Observatory Project: A Statewide Outreach And Education Ex-Periment In Nebraska, Daniel Claes, Gregory Snow

Gregory Snow Publications

Abstract: The Cosmic Ray Observatory Project (CROP) is a statewide education and research ex-periment involving Nebraska high school students, teachers and university undergraduates in the study of extensive cosmic-ray air showers. A network of high school teams construct, install, and op-erate school-based detectors in coordination with University of Nebraska physics professors and graduate students. The detector system at each school is an array of scintillation counters recycled from the Chicago Air Shower Array in weather-proof enclosures on the school roof, with a GPS re-ceiver providing a time stamp for cosmic-ray events. The detectors are connected to triggering elec-tronics and a …

Optically Thick [O I] And [C Ii] Emission Toward Ngc 6334a, N. P. Abel, A. P. Sarma, Thomas H. Troland, Gary J. Ferland

Physics and Astronomy Faculty Publications

This work focuses on [O I] and [C II] emission toward NGC 6334A, an embedded H⁺ region/PDR only observable at infrared or longer wavelengths. A geometry in which nearly all the emission escapes out the side of the cloud facing the stars, such as Orion, is not applicable to this region. Instead, we find the geometry to be one in which the H⁺ region and associated PDR is embedded in the molecular cloud. Constant-density PDR calculations are presented which predict line intensities as a function of A_V [or N(H)], hydrogen density (n_H), and …

Gravitational Wave Bursts From The Galactic Massive Black Hole, Clovis Hopman, Marc Freitag, Shane L. Larson

All Physics Faculty Publications

The Galactic massive black hole (MBH), with a mass of M_•= 3.6 × 10⁶ M_⊙, is the closest known MBH, at a distance of only 8 kpc. The proximity of this MBH makes it possible to observe gravitational waves (GWs) from stars with periapse in the observational frequency window of the Laser Interferometer Space Antenna (LISA). This is possible even if the orbit of the star is very eccentric, so that the orbital frequency is many orders of magnitude below the LISA frequency window, as suggested by Rubbo, Holley-Bockelmann & Finn (2006). …

Depleted Carbon Monoxide In Fragment C Of The Jupiter-Family Comet 73p/Schwassmann-Wachmann 3, M. Disanti, W. Anderson, G. Villanueva, B. Bonev, K. Magee-Sauer, E. Gibb, M. Mumma

Physics Faculty Works

Carbon monoxide emission was targeted in fragment C of the recently split Jupiter-family comet 73P/Schwassmann-Wachmann 3 during its 2006 apparition, using the Cryogenic Echelle Spectrograph (CSHELL) at the NASA IRTF on Mauna Kea, Hawaii. Simultaneous sounding with H2O near 4.65 μm revealed highly depleted CO, consistent with a mixing ratio of 0.5% ± 0.13%. Along with depleted CH3OH but nearly normal HCN, this may indicate that this comet formed in the inner giant planets' region or, alternatively, that it formed relatively late, after significant clearing of the protosolar nebula.

An Investigation Into The Effects Of Luminosity On The Mid-Infrared Spectral Energy Distributions Of Radio-Quiet Quasars, S. C. Gallagher, G. T. Richards, M. Lacy, D. C. Hines, Moshe Elitzur, L. J. Storrie-Lombardi

Physics and Astronomy Faculty Publications

We present an analysis of the effects of luminosity on the shape of the mid-infrared spectral energy distributions (SEDs) of 234 radio-quiet quasars originally presented by Richards et al. In quasars without evident dust extinction, the spectrally integrated optical and infrared luminosities are linearly correlated over nearly three decades in luminosity. We find a significant (≳99.99\% confidence) correlation between the 1.8-8.0 μm spectral index and infrared luminosity that indicates an enhancement of the mid-infrared continuum with increasing luminosity. Coupled with strong evidence for spectral curvature in more luminous quasars, we conclude that this trend is likely a manifestation of …

Gemini Mid-Ir Polarimetry Of Ngc 1068: Polarized Structures Around The Nucleus, C. Packham, S. Young, S. Fisher, K. Volk, R. Mason, J. H. Hough, P. F. Roche, Moshe Elitzur, J. Radomski, E. Perlman

Physics and Astronomy Faculty Publications

We present diffraction-limited, 10 μm imaging polarimetry data for the central regions of the archetypal Seyfert active galactic nucleus NGC 1068. The position angle of polarization is consistent with three dominant polarizing mechanisms. We identify three distinct regions of polarization: (1) north of the nucleus, arising from aligned dust in the narrow emission line region, (2) south, east, and west of the nucleus, consistent with dust being channeled toward the central engine, and (3) a central minimum of polarization consistent with a compact (≤22 pc) torus. These observations provide continuity between the geometrically and optically thick torus and the …

The Shape Of Galaxy Cluster Dark Matter Haloes: Systematics Of Its Imprint On Cluster Gas And Comparison To Observations, Ricardo Flores, Brandon Allgood, Andrey Kravtsov, Joel Primack, David Buote, James Bullock

Physics Faculty Works

We study predictions for galaxy cluster observables that can test the statistics of dark matter halo shapes expected in a flat Λ cold dark matter (CDM) universe. We present a simple analytical model for the prediction of cluster-scale X-ray observations, approximating clusters as isothermal systems in hydrostatic equilibrium, and dark matter haloes as ellipsoids with uniform axial ratios (homeoidal ellipsoids). We test the model against high-resolution, hydrodynamic cluster simulations to gauge its reliability. We find that this simple prescription does a good job of predicting cluster X-ray ellipticities compared to the simulations as long as one focuses on cluster regions …

Warm Hcn, C2h2, And Co In The Disk Of Gv Tau, Erika Gibb, K. Van Brunt, S. Brittain, T Rettig

Physics Faculty Works

We present the first high-resolution, ground-based observations of HCN and C2H2 toward the T Tauri binary star system GV Tau. We detected strong absorption due to HCN ν3 and weak C2H2 [ν3 and ν2 + (ν4 + ν5)img1.gif] absorption toward the primary (GV Tau S) but not the infrared companion. We also report CO column densities and rotational temperatures, and present abundances relative to CO of HCN/CO ~ 0.6% and C2H/CO ~ 1.2% and an upper limit for CH4/CO < 0.37% toward GV Tau S. Neither HCN nor C2H2 were detected toward the infrared companion, and results suggest that abundances may differ between the two sources.

Determination Of The Physical Conditions Of The Knots In The Helix Nebula From Optical And Infrared Observations, C. R. O'Dell, W. J. Henney, Gary J. Ferland

Physics and Astronomy Faculty Publications

We use new Hubble Space Telescope and archived images to clarify the nature of the ubiquitous knots in the Helix Nebula, which are variously estimated to contain a significant to majority fraction of the material ejected by its central star. We employ published far-infrared spectrophotometry and existing 2.12 μm images to establish that the population distribution of the lowest rovibrational states of H2 is close to the distribution of a gas in local thermodynamic equilibrium at 988 ± 119 K. In addition, we present calculations that show that the weakness of the H₂ 0-0 S(7) line is not …

A Photon Dominated Region Code Comparison Study, M. Röllig, Nicholas Paul Abel, T. Bell, F. Bensch, J. Black, Gary J. Ferland, B. Jonkheid, I. Kamp, M. J. Kaufman, J. Le Bourlot, F. Le Petit, R. Meijerink, O. Morata, V. Ossenkopf, E. Roueff, Gargi Shaw, M. Spaans, A. Sternberg, J. Stutzki, W.-F. Thi, E. F. Van Dishoeck, P. A. M. Van Hoof, S. Viti, M. G. Wolfire

Physics and Astronomy Faculty Publications

Aims. We present a comparison between independent computer codes, modeling the physics and chemistry of interstellar photon dominated regions (PDRs). Our goal was to understand the mutual differences in the PDR codes and their effects on the physical and chemical structure of the model clouds, and to converge the output of different codes to a common solution.

Methods. A number of benchmark models have been created, covering low and high gas densities n = 10³,10^5.5 cm^-3 and far ultraviolet intensities χ = 10, 10⁵ in units of the Draine field (FUV: 6 < h_ν < 13.6 eV). The benchmark models were computed in two ways: one set assuming constant temperatures, thus testing the consistency of the chemical network and photo-processes, and a second set determining the temperature self consistently by solving the thermal balance, thus testing the modeling of the heating and cooling mechanisms accounting for the detailed energy balance throughout the clouds.

Results. …

Anomalous Magnetic Field Dependence Of The T1 Spin Lifetime In A Lightly Doped Gaas Sample, John S. Colton, M. E. Heeb, P. Schroeder, A. Stokes, L. R. Wienkes, A. S. Bracker

Faculty Publications

The T1 spin lifetime of a lightly doped n-type GaAs sample has been measured via time-resolved polarization spectroscopy under a number of temperature and magnetic field conditions. Lifetimes up to 19 μs have been measured. The magnetic field dependence of T1 shows a nonmonotonic behavior, where the spin lifetime first increases, then decreases, then increases again with field. The initial increase in T1 is understood to be due to correlation between electrons localized on donors. The decrease in T1 is likely due to phonon-related spin-orbit relaxation. The final increase in T1 with B indicates a suppression of the spin-orbit relaxation …

Coupling Down Converted Light Into Single Mode Fibers, David A. Niemi

Theses and Dissertations

We investigate the influence of the pump and collection mode parameters on the collection efficiency of Type I down converted photons into single mode fibers. For best single and coincidence counting rates, we find that the mode sizes should be close to the same size and that the mode waists should be located near the down-conversion crystal. Larger collection waists give higher collection efficiencies, but lower singles counts.

Ua66 2007 Student Awards Ceremony, Wku Ogden College Of Science & Engineering

WKU Administration Documents

Program recognizing Ogden College students with brief list of activities for each student.

Dust And Pah Emission In The Star-Forming Active Nucleus Of Ngc 1097, R. E. Mason, N. A. Levenson, C. Packham, Moshe Elitzur, J. Radomski, A. O. Petric, G. S. Wright

Physics and Astronomy Faculty Publications

The nucleus of the nearby galaxy NGC 1097 is known to host a young, compact (r < 9 pc) nuclear star cluster, as well as a low-luminosity active galactic nucleus (AGN). It has been suggested both that the nuclear stellar cluster is associated with a dusty torus and that low-luminosity AGNs like NGC 1097 do not have the torus predicted by the unified model of AGNs. To investigate these contradictory possibilities we have acquired Gemini/T-ReCS 11.7 and 18.3 μm images of the central few hundred parsecs of this galaxy at <45 pc angular resolution, in which the nucleus and spectacular, kiloparsec-scale star-forming ring are detected in both bands. The small-scale mid-IR luminosity implies thermal emission from warm dust close to the central engine. Fitting of torus models shows that the observed mid-IR emission cannot be accounted for by dust heated by the central engine. Rather, the principal source heating the dust in this object is the nuclear star cluster itself, suggesting that the detected dust is not the torus of AGN unified schemes (although it is also possible that the dusty starburst itself could provide the obscuration invoked by the unified model). Comparison of Spitzer IRS and Gemini GNIRS spectra shows that, although PAH bands are strong in the immediate circumnuclear region of the galaxy, PAH emission is weak or absent in the central 19 pc. The lack of PAH emission can probably be explained largely by destruction/ionization of PAH molecules by hard photons from the nuclear star cluster. If NGC 1097 is typical, PAH emission bands may not be a useful tool with which …

A Magnetically Supported Photodissociation Region In M17, E. W. Pellegrini, J. A. Baldwin, C. L. Brogan, M. M. Hanson, N. P. Abel, Gary J. Ferland, H. B. Nemala, G. Shaw, Thomas H. Troland

Physics and Astronomy Faculty Publications

The southwestern (SW) part of the Galactic H II region M17 contains an obscured ionization front that is most easily seen at infrared and radio wavelengths. It is nearly edge-on, thus offering an excellent opportunity to study the way in which the gas changes from fully ionized to molecular as radiation from the ionizing stars penetrates into the gas. M17 is also one of the very few H II regions for which the magnetic field strength can be measured in the photodissociation region ( PDR) that forms the interface between the ionized and molecular gas. Here we model an observed …

An Isotropic Metric, Joseph D. Rudmin

Virginia Journal of Science

An isotropic metric for a black hole and a better vacuum condition \nabla^2 V_G =0 are presented which yield distinct terms for the energy densities of ordinary matter and gravitational fields in the Einstein tensor (G^44 =-g^2 (2\nabla^2 V_G +(\nabla V_G)^2)). This model resolves an inconsistency between electromagnetism and gravity in the calculation of field energy. Resolution of this inconsistency suggests a slight modification of the Einstein equation to gG^\mu\nu = 8\pi G T^\mu\nu.

Grating Lobe Reduction In Transducer Arrays Through Structural Filtering Of Supercritical Plates, Brian E. Anderson, Stephen A. Hambric, Jack W. Hughes

Faculty Publications

The effect of placing a structural acoustic filter between water and the transducer elements of an array to help reduce undesirable grating lobes is investigated. A supercritical plate is mounted to transducer elements with a thin decoupling polyurethane layer between the transducers and the plate. The plate acts as a radiation/incidence angle filter to pass energy at angles near normal incidence, but suppress energy at large incidence angles. Grating lobe reduction is achieved at the expense of limiting the available steering of the main lobe. Within this steer angle limitation, the main lobe can be steered as normal while the …

Development Of An H-Alpha Index For The Detection Of Pms Candidates In Young Open Clusters, Liberty Rae Evanko

Theses and Dissertations

One phase of formation of medium- and low-mass stars is the optically visible phase known as the pre-main-sequence or PMS phase. In order to further the understanding of this phase, more of these PMS objects need to be identified and classified. Previous techniques have used photometry to identify possible PMS objects by their characteristic Hα emission. Once identified these objects can be studied spectroscopically yielding complete PMS classification. This study develops a method to locate these emission objects that overcomes two limitations of previous techniques. The first limitation is the need for the creation of reddening maps. It is eliminated …

Large Merger Recoils And Spin Flips From Generic Black Hole Binaries, Manuela Campanelli, Carlos O. Lousto, Y. Zlochower, David Merritt

Physics & Astronomy Faculty Publications

We report the first results from the evolution of generic black hole binaries, i.e., binaries containing unequal-mass black holes with misaligned spins. Our configuration, which has a mass ratio of 2 : 1, consists of an initially nonspinning hole orbiting a larger, rapidly spinning hole (specific spin a/m = 0.885), with the spin direction oriented -45° with respect to the orbital plane. We track the inspiral and merger for ~2 orbits and find that the remnant receives a substantial kick of 454 km s-1, more than twice as large as the maximum kick from nonspinning binaries. The remnant …

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 (I_pred/I_obs-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 …

Induced Nested Galactic Bars Inside Assembling Dark Matter Halos, Clayton Heller, Isaac Shlosman, Evangelie Athanassoula

Physics & Astronomy: Faculty Publications

We investigate the formation and evolution of nested bar systems in disk galaxies in a cosmological setting by following the development of an isolated dark matter (DM) and baryon density perturbation. The disks form within the assembling triaxial DM halos, and the feedback from the stellar evolution is accounted for in terms of supernovae and OB stellar winds. Focusing on a representative model, we show the formation of an oval disk and of a first generation of nested bars with characteristic subkiloparsec sizes and a few kiloparsec sizes. The system evolves through successive dynamical couplings and decouplings, forcing the gas …

Bounds And Conditions: A Kolob In Our Solar System?, David D. Allred

Faculty Publications

In 2003, Dialogue ran adjacent essays by two scientists, David Tolman and David Allred. The two Davids had been students together at Princeton, attending the same student ward. Decades after Princeton, Tolman had left Mormonism and Allred had stayed. Their essays are a fascinating juxtaposition. In the course of his piece, David Allred ventured for a few paragraphs into a discussion of the planet Jupiter and its role as a governor and protector in our solar system—a type of Kolob. Although the other author dismissed the topic as “fanciful physics,” my own interest was piqued. I asked Dr. Allred, who …

The Distribution Of Silicate Strength In Spitzer Spectra Of Agns And Ulirgs, Lei Hao, D. W. Weedman, H. Spoon, J. A. Marshall, N. A. Levenson, Moshe Elitzur, J. R. Houck

Physics and Astronomy Faculty Publications

A sample of 196 AGNs and ULIRGs observed by the Infrared Spectrograph (IRS) on Spitzer is analyzed to study the distribution of the strength of the 9.7 μm silicate feature. Average spectra are derived for quasars, Seyfert 1 and Seyfert 2 AGNs, and ULIRGs. We find that quasars are characterized by silicate features in emission and Seyfert 1s equally by emission or weak absorption. Seyfert 2s are dominated by weak silicate absorption, and ULIRGs are characterized by strong silicate absorption (mean apparent optical depth about 1.5). Luminosity distributions show that luminosities at rest frame 5.5 μm are similar …

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 …