Astrophysics and Astronomy Commons^™

Energetics Of Magnetic Storms Driven By Corotating Interaction Regions: A Study Of Geoeffectiveness, Niescja E. Turner, E J. Mitchell, D J. Knipp, B A. Emery

Physics and Astronomy Faculty Research

We investigate the energetics of magnetic storms associated with corotating interaction regions (CIRs). We analyze 24 storms driven by CIRs and compare to 18 driven by ejecta-related events to determine how they differ in overall properties and in particular in their distribution of energy. To compare these different types of events, we look at events with comparable input parameters such as the epsilon parameter and note the properties of the resulting storms. We estimate the energy output by looking at the ring current energy along with ionospheric Joule heating derived from the PC and Dst indices. We also include the …

A Catalog Of Edge-On Disk Galaxies: From Galaxies With A Bulge To Superthin Galaxies, Stefan Kautsch, E. K. Grebel, F. D. Barazza, J. S. Gallagher

Chemistry and Physics Faculty Articles

Spiral galaxies range from bulge-dominated early-type galaxies to late types with little or no bulge. Cosmological models do not predict the formation of disk-dominated, essentially bulgeless galaxies, yet these objects exist. A particularly striking and poorly understood example of bulgeless galaxies are flat or superthin galaxies with large axis ratios. We therefore embarked on a study aimed at a better understanding of these enigmatic objects, starting by compiling a statistically meaningful sample with well-defined properties. The disk axis ratios can be most easily measured when galaxies are seen edge-on. We used data from the Sloan Digital Sky Survey (SDSS) in …

Optimization Of Single-Sided Charge-Sharing Strip Detectors, L A. Hamel, M Benoit, B Donmez, John R. Macri, Mark L. Mcconnell, T Narita, James M. Ryan

Space Science Center

Simulation of the charge sharing properties of single-sided CZT strip detectors with small anode pads are presented. The effect of initial event size, carrier repulsion, diffusion, drift, trapping and detrapping are considered. These simulations indicate that such a detector with a 150 µm pitch will provide good charge sharing between neighboring pads. This is supported by a comparison of simulations and measurements for a similar detector with a coarser pitch of 225 µm that could not provide sufficient sharing. The performance of such a detector used as a gamma-ray imager is discussed.

Prospects For Grb Polarimetry With Grape, Mark L. Mcconnell, Peter F. Bloser, Jason S. Legere, John R. Macri, T Narita, James M. Ryan

Space Science Center

This paper discusses the latest progress in the development of GRAPE (Gamma‐Ray Polarimeter Experiment), a hard X‐ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X‐rays in the 50–300 keV energy range. We are particularly interested in X‐rays that are emitted from solar flares and gamma‐ray bursts (GRBs). Accurately measuring the polarization of the emitted radiation from these sources will lead to a better understating of both the emission mechanisms and source geometries. The GRAPE design consists of an array of plastic scintillators surrounding a central high‐Z crystal scintillator. We can monitor individual Compton scatters …

Position Resolution In Labr3 And Lacl3 Scintillators Using Position-Sensitive Photomultiplier Tubes, Peter F. Bloser, Mark L. Mcconnell, John R. Macri, James M. Ryan, Justin Baker

Space Science Center

Advanced scintillator materials such as LaBr3:Ce and LaCl3:Ce hold great promise for future hard X-ray and gamma-ray astrophysics missions due to their high density, high light output, good linearity, and fast decay times. Of particular importance for future space-based imaging instruments, such as coded-aperture telescopes, is the precise spatial location of individual gamma-ray interactions. We have investigated the position and energy resolution achievable within monolithic (5 cm × 5 cm × 1 cm) LaBr3:Ce and LaCl3:Ce crystals using position-sensitive light readout devices, including a position-sensitive photomultiplier tube and a multi-anode photomultiplier tube. We present the results of these tests and …

Medium-Energy Gamma-Ray Astrophysics With The 3-Dti Gamma-Ray Telescope, Stanley D. Hunter, Robert G. Baker, Louis M. Barbier, Peter F. Bloser, La Vida Cooper, John F. Krizmanic, Jason T. Link, Mark L. Mcconnell, Geoergia A. De Nolfo, James M. Ryan, Satpal Singh, Seunghee Son

Space Science Center

Gamma-ray observations in the medium energy range (0.50-50.0 MeV) are central to unfolding many outstanding questions in astrophysics. The challenges of medium-energy gamma-ray observations, however, are the low photon statistics and large backgrounds. We review these questions, address the telescope technology requirements, and describe our development of the 3-Dimensional Track Imaging (3-DTI) Compton telescope and its performance for a new mediumenergy gamma-ray mission. The 3-DTI is a large-volume time projection chamber (TPC) with a 2-dimensional gas micro-well detector (MWD) readout.

Radiation Damage And Activation From Proton Irradiation Of Advanced Scintillators, Peter F. Bloser, Mark L. Mcconnell, John R. Macri, P J. Bruillard, James M. Ryan, W Hajdas

Space Science Center

We present results from a proton accelerator beam test to measure radiation damage and activation in advanced scintillator materials. Samples of LaBr3:Ce and LaCl3:Ce were exposed to protons from 40-250 MeV at the Proton Irradiation Facility of the Paul Scherrer Institute in Switzerland. Twelve energy bands were used to simulate the spectrum of the South Atlantic Anomaly (SAA), with different samples exposed to the equivalent of 4 months, 1 year, and 5 years of SAA passage. No significant decrease in light output was found due to radiation damage, indicating that these new scintillator materials are radiation tolerant. High-resolution spectra of …

The Caster Black Hole Finder Probe, Mark L. Mcconnell, Peter F. Bloser, G L. Case, M L. Cherry, J Cravens, T G. Guzik, K Hurley, R M. Kippen, John R. Macri, R S. Miller, W Paciesas, James M. Ryan, B Schaefer, J G. Stacy, W T. Vestrand, J P. Wefel

Space Science Center

The primary scientific mission of the Black Hole Finder Probe (BHFP), part of the NASA Beyond Einstein program, is to survey the local Universe for black holes over a wide range of mass and accretion rate. One approach to such a survey is a hard X‐ray coded‐aperture imaging mission operating in the 10–600 keV energy band. The development of new inorganic scintillator materials provides improved performance that is well suited to the BHFP science requirements. Detection planes formed with these materials coupled with a new generation of readout devices represent a major advancement in the performance capabilities of scintillator‐based gamma …

Simulated Performance Of 3-Dti Gamma-Ray Telescope Concepts, Peter F. Bloser, Mark L. Mcconnell, James M. Ryan, Louis M. Barbier, Alan Centa, Stanley D. Hunter, John F. Krizmanic, Jason T. Link, Geoergia A. De Nolfo, Seunghee Son

Space Science Center

We present Monte Carlo simulations of two astronomical gamma-ray telescope concepts based on the ThreeDimensional Track Imager (3- DTI) detector. The 3-DTI consists of a time projection chamber with two-dimensional, crossedstrip micro-well detector readout. The full three- dimensional reconstruction of charged-particle tracks in the gas volume is obtained from transient digitizers, which record the time signature of the charge collected in the wells of each strip. Such detectors hold great promise for advanced Compton telescope (ACT) and advanced pair telescope (APT) concepts due to the very precise measurement of charged particle momenta that is possible (Compton recoil electrons and electron-positron …

An Explicit Scheme For Multifluid Magnetohydrodynamics, Stephen O'Sullivan, Turlough Downes

Articles

When modelling astrophysical fluid flows, it is often appropriate to discard the canonical magnetohydrodynamic approximation, thereby freeing the magnetic field to diffuse with respect to the bulk velocity field. As a consequence, however, the induction equation can become problematic to solve via standard explicit techniques. In particular, the Hall diffusion term admits fast-moving whistler waves which can impose a vanishing time-step limit.Within an explicit differencing framework, a multifluid scheme for weakly ionized plasmas is presented which relies upon a new approach to integrating the induction equation efficiently. The first component of this approach is a relatively unknown method of accelerating …

The Solar Flare Of The 14th Of July 2000 (L3+C Detector Results), Pablo Achard, Gyöngyi Baksay, László A. Baksay, K Dehmelt, Marcus Hohlmann, D Rembeczki, Z Szillasi, I Vodopianov, The L3 Collaboration

Aerospace, Physics, and Space Science Faculty Publications

Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods.The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary …

The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston

Aerospace, Physics, and Space Science Faculty Publications

We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the presence of (at least) 15 periodicities in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557, Paper I). Based on high-S/N, medium-resolution spectra obtained at the Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT Telescope, new NLTE spectroscopic derivations of the atmospheric parameters of PG 1325+101 are presented. The mean values of T eff = 35 050 ± 220 K, log …

Runaway Breakdown In The Jovian Atmospheres, Joseph R. Dwyer, Lee M. Coleman, Ramon E. Lopez, Ziad H. Saleh, D. Concha, Michael G. Brown, Hamid K. Rassoul

Aerospace, Physics, and Space Science Faculty Publications

Using detailed Monte Carlo calculations, the properties of runaway breakdown in the atmospheres of the four gas giant planets in our solar system are investigated, and the runaway avalanche lengths and average runaway electron kinetic energies are presented as a function of atmospheric electric field strengths. The runaway breakdown threshold field for the Jovian atmospheres is found to be 10 times smaller than the conventional breakdown field when hydrometeors are present, compared to 3 times smaller for Earth's atmosphere, indicating that runaway breakdown processes may be much more efficient in the gas giants than on Earth. In the Earth's atmosphere, …

A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt

Aerospace, Physics, and Space Science Faculty Publications

We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination …

Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri

Aerospace, Physics, and Space Science Faculty Publications

This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 μHz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after …

The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston

Aerospace, Physics, and Space Science Faculty Publications

In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff - 35 000 K, log g = 5.8, log N(Hs)/N(H) = -1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies …

Constraints On The Nucleon Strange Form Factors At Q2 ∼ 0.1 Gev2, K. A. Aniol, D. S. Armstrong, T. Averett, H. Benaoum, P. Y. Bertin, E. Burtin, J. Cahoon, G. D. Cates, C. C. Chang, Y.-C. Chao, D. Deepa, H. Ibrahim

Mechanical & Aerospace Engineering Faculty Publications

We report the most precise measurement to date of a parity-violating asymmetry in elastic electron–proton scattering. The measurement was carried out with a beam energy of 3.03 GeV and a scattering angle (θ_lab) = 6.0○ , with the result A PV = ( − 1.14 ± 0.24 ( stat ) ± 0.06 ( syst ) ) × 10⁻⁶ . From this we extract, at Q² = 0.099 GeV² , the strange form factor combination G^s_E + 0.080 G^s_M = 0.030 ± 0.025 ( stat ) ± 0.006 ( syst ) ± …

Measurement Of The X- And Q2 -Dependence Of The Asymmetry A1 On The Nucleon, K. V. Dharmawardane, S. E. Kuhn, P. Bosted, Y. Prok, G. Adams, P. Ambrozewicz, M. Anghinolfi, G. Asryan, H. Avakian, H. Bagdasaryan, M. Bektasoglu, S. Bültmann, S. L. Careccia, G. E. Dodge, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. Klein, J. Lachniet, M. R. Niroula, R. A. Niyazov, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Zhang

Physics Faculty Publications

We report results for the virtual photon asymmetry A₁ on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton (¹⁵NH₃) and deuteron (¹⁵ND₃) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present Letter, we concentrate on our results for A₁ ( x , Q² ) and the related ratio g1 / F₁ ( x , Q² ) in the resonance and the deep inelastic …

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 …

Unfolding The Labyrinth: Open Problems In Physics, Mathematics, Astrophysics, And Other Areas Of Science, Florentin Smarandache, Victor Christianto, Fu Yuhua, Radi Khrapko, John Hutchison

Branch Mathematics and Statistics Faculty and Staff Publications

The reader will find herein a collection of unsolved problems in mathematics and the physical sciences. Theoretical and experimental domains have each been given consideration. The authors have taken a liberal approach in their selection of problems and questions, and have not shied away from what might otherwise be called speculative, in order to enhance the opportunities for scientific discovery. Progress and development in our knowledge of the structure, form and function of the Universe, in the true sense of the word, its beauty and power, and its timeless presence and mystery, before which even the greatest intellect is awed …

Growth And Thermal Properties Of Sr W O 4 Single Crystal, J. D. Fan, H. J. Wang, M. H. Jiang, Robert I. Boughton, D. G. Ran, S. Q. Sun, H. R. Xia

Physics and Astronomy Faculty Publications

A strontium tungstate SrWO4 single crystal with dimensions of 25 40 mm2 has been grown by the Czochralski method using an iridium crucible. X-ray powder diffraction results show that as grown the SrWO4 crystal belongs to the tetragonal system in the scheelite structure. The effective segregation coefficients of elemental W and Sr in the crystal growth are measured by x-ray fluorescence, and the respective values are close to 1. The thermal properties of the SrWO4 crystal were systemically studied by measuring the thermal expansion, specific heat, and thermal diffusion coefficient. These results show that the crystal possesses a large anisotropic …

Near-Infrared Observations Of Comet-Asteroid Transition Objects, Julie Elaine Ziffer

Electronic Theses and Dissertations

The primary objective of this research is to characterize the surface composition of five comet-asteroid transition objects via near-infrared spectroscopy. The five targets include two asteroids with Tisserand invariants lower than 3.0 (1373 Cincinnati and 2906 Caltech), one asteroid that is likely an extinct comet (944 Hidalgo), one intermittent activity comet (162P/Siding Spring), and one nearly dormant comet (28P/Neujmin1). Previous research regarding cometary end states and dynamical and physical properties of comets and asteroids provides the foundation for this work. Focusing primarily on the 1-2.5 µm spectral region of the five target objects, this project specifically searches for mineral species …

Discovery Of Outlying High-Velocity Oxygen-Rich Ejecta In Cassiopeia A, Robert A. Fesen, Molly C. Hammell, Jon Morse, Roger A. Chevalier, Kazimierz J. Borkowski, Michael A. Dopita, Christopher L. Gerardy, Stephen S. Lawrence, John C. Raymond, Sydney Van Den Bergh

Dartmouth Scholarship

Analysis of broadband HST ACS and WFPC2 images of the young Galactic supernova remnant Cassiopeia A reveals a far larger population of outlying, high-velocity knots of ejecta with a broader range of chemical properties than previously suspected. ACS filte r flux ratios along with follow-up, ground-based spectra are used to investigate some of the kinema tic and chemical properties of these outermost ejecta. In this paper, we concentrate on a ≃ 1.5 sq arcmin region located along the eastern limb of the remnant where numerous outer emission knots are optica lly visible due to an interaction with a local circumstellar …

Observations Of Triboelectric Charging Effects On Langmuir-Type Probes In Dusty Plasma, Aroh Barjatya, Charles M. Swenson

Publications

Investigation of Earth’s mesosphere using sounding rockets equipped with a myriad of instruments has been a highly active field in the last 2 decades. This paper presents data from three separate instruments: an RF impedance probe, a DC fixed bias Langmuir probe, and an electric field probe, that were flown on a mesospheric sounding rocket flight investigating the presence of charged dust within and/or around a sporadic metal layer. The combined data set indicates a case of payload surface charging, the causes of which are investigated within this paper. A generic circuit model is developed to analyze payload charging and …

The Strength And Structure Of The Galactic Center Magnetic Field, Ted La Rosa, Steven N. Shore, T. Joseph W. Lazio, Namir E. Kassim

Faculty Articles

This paper summarizes recently obtained, strong evidence for a weak global field in the Galactic center (GC): the existence of a large-scale region of diffuse, low-frequency, nonthermal emission coincident with the central molecular zone. The overall energetics of this emission, considered along with constraints on GC cosmic ray energy density and diffusion, indicate clearly that the magnetic field pervading this region is ∼ 10 μG. For completeness, additional points on the orientation of the GC nonthermal filaments, rotation measures of extragalactic sources seen through the GC, and comparison with other normal spiral galaxies are also reviewed.

Hydrodynamic Description Of The Adiabatic Piston, Alejandro Garcia, M. M. Mansour

Faculty Publications

A closed macroscopic equation for the motion of the two-dimensional adiabatic piston is derived from standard hydrodynamics. It predicts a damped oscillatory motion of the piston towards a final rest position, which depends on the initial state. In the limit of large piston mass, the solution of this equation is in quantitative agreement with the results obtained from both hard disk molecular dynamics and hydrodynamics. The explicit forms of the basic characteristics of the piston’s dynamics, such as the period of oscillations and the relaxation time, are derived. The limitations of the theory’s validity, in terms of the main system …

Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine

Publications

A reduced proper motion diagram utilizing Sloan Digital Sky Survey (SDSS) photometry and astrometry and USNO-B plate astrometry is used to separate cool white dwarf candidates from metal-weak, high-velocity, mainsequence Population II stars (subdwarfs) in the SDSS Data Release 2 imaging area. Follow-up spectroscopy using the Hobby-Eberly Telescope, the MMT, and the McDonald 2.7 m telescope is used to demonstrate that the white dwarf and subdwarf loci separate cleanly in the reduced proper motion diagram and that the contamination by subdwarfs is small near the cool white dwarf locus. This enables large, statistically complete samples of white dwarfs, particularly the …

The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider

Publications

A sample of white dwarfs is selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 using their reduced proper motions, based on improved proper motions from combined SDSS and USNO-B data. Numerous SDSS and follow-up spectra (Kilic and coworkers) are used to quantify completeness and contamination of the sample; kinematicsmodels are used to understand and correct for velocity-dependent selection biases.A luminosity function is constructed covering the range 7 < Mbol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth and rises nearly monotonically to Mbol=15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars …

Book Review: The Amateur Astronomer's Introduction To The Celestial Sphere, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The Amateur Astronomer's Introduction to the Celestial Sphere by William Millar. Cambridge, 2006 299p, 052167123X $40.00, 9780521671231 $40.00.

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 …