Astrophysics and Astronomy Commons^™

Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson

Theses and Dissertations

Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist …

Debris Disks Around White Dwarfs: The Daz Connection, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We present near-infrared spectroscopic observations of 20 previously known DAZ white dwarfs obtained at the NASA Infrared Telescope Facility. Two of these white dwarfs (G29-38 and GD 362) are known to display significant K-band excesses due to circumstellar debris disks. Here we report the discovery of excess K-band radiation from another DAZ white dwarf WD0408041 (GD56). Using spectroscopic observations, we show that the excess radiation cannot be explained by a stellar or substellar companion, and is likely to be caused by a warm debris disk. Our observations strengthen the connection between the debris disk phenomena and the observed …

Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A Bayesian Approach, Ted Von Hippel, Et Al.

Publications

We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main-sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, metallicity, and line-of-sight absorption, as well as individual stellar masses. The advantages our technique has over traditional analyses of color-magnitude diagrams are objectivity, precision, and explicit dependence on prior knowledge of cluster parameters. Within the confines of a given set of often-used models of stellar evolution, a single mapping of initial to final masses, and white dwarf cooling, and assuming photometric errors that one could reasonably achieve with the Hubble Space Telescope, our technique …

A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose

Theses and Dissertations

The detection of variable stars in open clusters is an essential component of testing stellar structure and evolution theories. The ability to detect low-amplitude variability among cluster members is directly related to the quality of the photometric results. Point Spread Function (PSF) fitting is the best method available for measuring accurate magnitudes within crowded fields of stars, while high-precision differential photometry is the preferred technique for removing the effects of atmospheric extinction and variable seeing. In the search for new variable stars among hundreds or thousands of stars, the Robust Median Statistic (RoMS) is proven more effective for finding low-amplitude …

Xmm-Newton Discovery Of The X-Ray Transient Xmmu J181227.8-181234 In The Galactic Plane, Edward M. Cackett, Rudy Wijnands, Ron Remillard

Physics and Astronomy Faculty Research Publications

We report the discovery of an X-ray transient, observed in outburst with XMM-Newton on 2003 March 20, and with position (J2000, approximate positional error 2arcsec). No known source is present at this position and the source was not detected during published ROSAT or ASCA observations of that region. However, the source may be associated with 1H1812-182 detected by HEAO 1, although the error bars on the HEAO 1 position are very large and the two sources could also be unrelated. Therefore, we name the source XMMU J181227.8-181234. Initially, the source was not detected using the All-Sky Monitor (ASM) on-board the …

Dust Stratification In Young Circumstellar Disks, Terrence Rettig, Sean D. Brittain, Theodore Simon, Erika Gibb, Dinshaw S. Balsara, David A. Tilley, Craig Kulesa

Publications

We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S, RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO, and C18O, as well as broad emission lines of gas-phase 12CO. The narrow absorption lines of CO are shown to originate from the colder circumstellar gas. We find that the line-of-sight gas column densities resulting from the CO absorption lines are much higher than expected for the measured extinction for each source and suggest the gas/dust ratio is measuring the dust settling and/or grain coagulation in these extended disks. We provide a …

Solar Cycle Variations In The Composition Of The Suprathermal Heavy-Ion Population Near 1 Au, Mihir I. Desai, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

We have measured the annual variation in the quiet-time composition of interplanetary suprathermal ions between 0.04 and 1 MeV nucleon-1 from 1994 November 20 through 2006 January 1. Our results show the following: (1) The C/O and Fe/O ratios are similar to the corresponding values measured in the solar wind and corotating interaction regions (CIRs) during solar minimum conditions of 1994-1997 and 2005. (2) During periods of increased solar activity between 1998 and 2002, the C/O ratio is similar to that measured in solar energetic particle (SEP) events, while the Fe/O ratio lies between the values measured in coronal mass …

Consequences Of Disk Scale Height On Lisa Confusion Noise From Close White Dwarf Binaries, M. Benacquista, K. Holley-Bockelmann

Physics & Astronomy Faculty Publications

Gravitational radiation from the Galactic population of close white dwarf binaries (CWDBs) is expected to produce a confusion-limited signal at the lower end of the sensitivity band of the Laser Interferometer Space Antenna (LISA). The canonical scale height of the disk population has been taken to be 90 pc for most studies of the nature of this confusion-limited signal. This estimate is probably too low, and the consequences of a more realistic scale height are investigated with a model of the LISA signal due to populations of CWDBs with different scale heights. If the local space density of CWDBs is …

Book Review: Evolution Of Stars And Stellar Populations, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Evolution of Stars and Stellar Populations by Maurizio Salaris and Santi Cassisi Wiley, 2005 374p, 047009219X $150.00, 047009219X $60.00

Measurement Of Orbital Decay In The Double Neutron Star Binary Psr B2127+11c, B. A. Jacoby, P. B. Cameron, F. A. Jenet, S. B. Anderson, R. N. Murty, S. R. Kulkarni

Physics & Astronomy Faculty Publications

We report the direct measurement of orbital period decay in the double neutron star pulsar system PSR B2127 + 11C in the globular cluster M15 at the rate of (-3.95 ± 0.13) × 10-12, consistent with the prediction of general relativity at the ∼3% level. We find the pulsar mass to be mp = 1.358 ± 0.010 M⊙ and the companion mc = 1.354 ± 0.010 M⊙. We also report long-term pulse timing results for the pulsars PSR B2127+11A and PSR B2127+11B, including confirmation of the cluster proper motion.

Probing The Universe On Gigaparsec Scales With Remote Cosmic Microwave Background Quadrupole Measurements, Emory F. Bunn

Physics Faculty Publications

Scattering of cosmic microwave background (CMB) radiation in galaxy clusters induces a polarization signal proportional to the CMB quadrupole anisotropy at the cluster’s location and lookback time. A survey of such remote quadrupole measurements provides information about large-scale cosmological perturbations. This paper presents a formalism for calculating the correlation function of remote quadrupole measurements in spherical harmonic space. The number of independent modes probed by both single-redshift and volume-limited surveys is presented, along with the length scales probed by these modes. In a remote quadrupole survey sparsely covering a large area of sky, the largest-scale modes probe the same-length scales …

The Advanced Compton Telescope, S E. Boggs, J Kurfess, James M. Ryan, Elena Aprile, Neil Gehrels, R M. Kippen, Marc Leising, U Oberlack, Cornelia B. Wunderer, Allen Zych, Peter F. Bloser, M Harris, A Hoover, Alexei Klimenk, Dan Kocevski, Mark L. Mcconnell, Peter Milne, E I. Novikova, B F. Phlips, Mark Polsen, Steven Sturner, Derek Tournear, G Weidenspointer, Eric Wulf, A Zoglauer, Matthew Baring, John Beacom, Lars Bildsten, Charles Dermer, Dieter H. Hartman, Margarita Hernanz, David Smith, Sumner Starrfield

Space Science Center

The Advanced Compton Telescope (ACT), the next major step in gamma-ray astronomy, will probe the fires where chemical elements are formed by enabling high-resolution spectroscopy of nuclear emission from supernova explosions. During the past two years, our collaboration has been undertaking a NASA mission concept study for ACT. This study was designed to (1) transform the key scientific objectives into specific instrument requirements, (2) to identify the most promising technologies to meet those requirements, and (3) to design a viable mission concept for this instrument. We present the results of this study, including scientific goals and expected performance, mission design, …

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 …

Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter

Theses and Dissertations

We studied the wurtzite to rock salt phase transition in gallium nitride ( GaN ). Using the mapping algorithm of COMSUBS we found 435 possible mechanisms for this transition. We then used FIREBALL to do density functional theory calculations and found enthalpy barrier heights for the transition pathway. We used this to determine the mechanisms that are the most favorable for GaN. The most favorable mechanisms for GaN are those that break no bonds during the phase transition. The bond-preserving mechanisms involve bilayer sliding of (010) hexagonal plane in the plus or minus [100] hexagonal direction.

Erratum: 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

Erratum

[Accepted Article Manuscript Version (Postprint)] Testing The Inverse-Compton Catastrophe Scenario In The Intra-Day Variable Blazar S5 0716+71. I. Simultaneous Broadband Observations During November 2003, Bruce Wilking, L. Ostorero, S Wagner, J. Gracia, E. Ferrero, T Krichbaum, S. Britzen, A. Witzel, K. Nilsson, M. Villata, U. Bach, D. Barnaby, S. Bernhart, M Carini, C Chen, W. Chen, S. Ciprini, S. Crapanzano, V. Doroshenko, N Efimova, D. Emmanoulopoulos, L. Fuhrmann, K Gabanyi, A. Giltinan, V. Hagen-Thorn, M. Hauser, J. Heidt, A Hojaev, T. Hovatta, F. Hroch, M. Ibrahimov, V. Impellizzeri, R Ivanidze, D. Kachel, A. Kraus, O. Kurtanidze, A. Lähteenmäki, L. Lanteri, V. Larionov, Z Lin, E. Lindfors, F. Munz, M. Nikolashvili, G. Nucciarelli, A. O’Connor, J. Ohlert, M. Pasanen, C. Pullen, C. Raiteri, T Rector, R. Robb, L. Sigua, A. Sillanpää, L. Sixtova, N. Smith, P. Strub, S. Takahashi, L. Takalo, C. Tapken, J. Tartar, M. Tornikoski, G. Tosti, M. Tröller, R. Walters, W. Wills, I. Agudo, H. Aller, M. Aller, E. Angelakis, J. Klare, E. Körding, R Strom, H. Teräsranta, H. Ungerechts, B. Vila-Vilaró

Physics Faculty Works

Context. Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding 1012 K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The violation of the IC limit, actually possible under non-stationary conditions, would lead to IC avalanches in the soft-γ-ray energy band during transient periods.Aims. For the first time, broadband signatures of possible IC catastrophes were searched for in a prototypical source, S5 0716+71.Methods. A multifrequency observing campaign targetting S5 0716+71 was carried out during November 06-20, 2003. The observations, organized under the framework of the European Network for the Investigation of …

Probing Cosmic Chemical Evolution With Gamma-Ray Bursts: Grb060206 At Z=4.048, J. P. U. Frynbo, R. L. C. Starling, C. Ledoux, K. Wiersema, C. C. Thöne, J. Sollerman, P. Jakobsson, J. Hjorth, D. Watson, P M. Vreeswijk, P Møller, E Rol, J Gorosabel, J Näränen, R.A.M.J. Wijers, G Björnsson, J M. Castro Cerón, P Curran, Dieter H. Hartmann, S T. Holland, B L. Jensen, A J. Levan, M Limousin, C Kouveliotou, G Nelemans, K Pedersen, R S. Priddey, N R. Tanvir

Publications

Aims. We present early optical spectroscopy of the afterglow of the gamma-ray burst GRB 060206 with the aim of determining the metallicity of the GRB absorber and the physical conditions in the circumburst medium. We also discuss how GRBs may be important complementary probes of cosmic chemical evolution. Methods. Absorption line study of the GRB afterglow spectrum. Results. We determine the redshift of the GRB to be z =4.04795 ±0.00020. Based on the measurement of the neutral hydrogen column density from the damped Lyman-αline and the metal content from weak, unsaturated S ii lines we derive a metallicity of [S/H] …

Wind Signatures In The X-Ray Emission-Line Profiles Of The Late-O Supergiant Zeta Orionis, David H. Cohen, M. A. Leutenegger, K. T. Grizzard, Catherine Lois Reed , '05, Roban Hultman Kramer , '03, S. P. Owocki

Physics & Astronomy Faculty Works

X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper, we apply several analysis techniques to the emission lines in the Chandra High Energy Transmission Grating Spectrometer (HETGS) spectrum of the late-O supergiant zeta Ori (O9.7 Ib), including the fitting of a …

A Chandra X-Ray Observation Of The Globular Cluster Terzan 1, E. M. Cackett, R. Wijnands, C. O. Heinke, D. Pooley, W. H. G. Lewin, J. E. Grindlay, P. D. Edmonds, P. G. Jonker, J. M. Miller

Physics and Astronomy Faculty Research Publications

We present a ~19-ks Chandra Advanced CCD Imaging Spectrometer (ACIS)-S observation of the globular cluster Terzan 1. 14 sources are detected within 1.4arcmin of the cluster centre with two of these sources predicted to be not associated with the cluster (background active galactic nuclei or foreground objects). The neutron star X-ray transient, X1732-304, has previously been observed in outburst within this globular cluster with the outburst seen to last for at least 12yr. Here, we find four sources that are consistent with the ROSAT position for this transient, but none of the sources are fully consistent with the position of …

Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adéla Kawka, Stéphane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri

Aerospace, Physics, and Space Science Faculty Publications

We report the identification of LP 400-22 (WD 2234+222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080 ± 140 K and a surface gravity of log g = 6.32 ± 0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 M⊙. The tangential velocity of this white dwarf is 414 ± 43 km s-1, making it one of the fastest moving white dwarfs known. We discuss probable evolutionary scenarios for this …

Grb 060218/Sn 2006aj: A Gamma-Ray Burst And Prompt Supernova Atz= 0.0335, N. Mirabal, J. P. Halpern, D. An, J. R. Thorstensen, D. M. Terndrup

Dartmouth Scholarship

We report the imaging and spectroscopic localization of GRB 060218 to a low-metallicity dwarf starburst galaxy at z = 0.03345 ± 0.00006. In addition to making it the second nearest gamma-ray burst known, optical spectroscopy reveals the earliest detection of weak, supernova-like Si II near 5720 Å (~0.1c), starting 1.95 days after the burst trigger. UBVRI photometry obtained between 1 and 26 days postburst confirms the early rise of supernova light, and suggests a short time delay between the gamma-ray burst and the onset of SN 2006aj if the early appearance of a soft component in the X-ray …

Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adela Kawka, Stephane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri

Publications

We report the identification of LP 400-22 (WD 2234 + 222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080 ± 140 K and a surface gravity of log g p 6.32 ± 0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 M_Ꙩ. The tangential velocity of this white dwarf is 414 ± 43 km s^-1, making it one of the fastest moving white dwarfs known. We …

Fnit: The Fast Neutron Imaging Telescope For Snm Detection, U Bravar, P J. Bruillard, E O. Fluckiger, John R. Macri, Mark L. Mcconnell, M R. Moser, James M. Ryan

Space Science Center

We report on recent progress in the development of the Fast Neutron Imaging Telescope (FNIT), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV range. FNIT was initially conceived to study solar neutrons as a candidate design for the Solar Sentinels program under formulation at NASA. This instrument is now being configured to locate fission neutron sources for homeland security purposes. By accurately identifying the position of the neutron source with imaging techniques and reconstructing the energy spectrum of fission neutrons, FNIT can locate problematic amounts of Special Nuclear Material (SNM), including heavily …

Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix

Theses and Dissertations

Highly directive loudspeakers have long been important tools for sound system designers, experimental acousticians, and many other professionals in the audio industry. They allow sound engineers to more easily manipulate the radiation pattern of their loudspeakers to accommodate the purpose of the venue. Many commercially available products, while exhibiting good directivity at mid and high frequencies, generally lack control in the low frequency range. A new method for controlling the radiation pattern of a loudspeaker at low frequencies has been developed and modeled extensively. Prototypes have been built and tested in an anechoic chamber. Results from computer modeling and experimental …

Spectroscopic Identification Of Cool White Dwarfs In The Solar Neighborhood, Adela Kawka, Stéphane Vennes

Aerospace, Physics, and Space Science Faculty Publications

The New Luyten Two-Tenths catalog contains a large number of high proper motion white dwarf candidates that remain to be spectroscopically confirmed. We present new spectroscopic observations, as well as SDSS archival spectra of 49 white dwarf candidates selected from the revised NLTT catalog of Salim & Gould. Of these, 34 are cool DA white dwarfs with temperatures ranging from approximately 5000 up to 11,690 K, and 11 are DC white dwarfs with temperatures ranging from 4300 K (NLTT 18555) up to 11,000 K. Three of the DA white dwarfs also display abundances of heavy elements (NLTT 3915, NLTT 44986, …

Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter

Theses and Dissertations

We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, …

The Mystery Deepens: Spitzer Observations Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We present 4.5 and 8 µm photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with Teᶠᶠ < 6000 K show slightly depressed mid-infrared fluxes relative to white dwarf models. In addition, another white dwarf with a peculiar optical and near-infrared spectral energy distribution (LHS 1126) is found to display significant flux deficits in Spitzer observations. These mid-infrared flux deficits are not predicted by the current white dwarf models including collision-induced absorption due to molecular hydrogen. We postulate that either the collision-induced absorption calculations are incomplete or there are other unrecognized physical processes occurring in cool white dwarf atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with effective temperature well in excess of 105 K. This implies that the source of this flux deficit is probably not molecular absorption but some other process.

Nonlinear Filtering In Compact High-Order Schemes, H. C. Yee, Björn Sjögreen

United States National Aeronautics and Space Administration: Publications

The adaptive nonlinear filtering approach for shock/turbulence gas dynamics and magnetohydrodynamics (MHD) flows adopted in our previous work is employed in conjunction with compact high-order methods as the spatial base scheme. The objective is to compare the performance of nonlinear filtering in compact high-order schemes with nonlinear filtering in standard central (non-compact) schemes for multiscale problems containing shock waves.

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. I. Rr Lyncis, 12 Bootis, And Hr 6169, Jocelyn Tomkin, Francis C. Fekel

Information Systems and Engineering Management Research Publications

Radial velocities from the 2.1 m telescope at McDonald Observatory supplemented with radial velocities from the coudé feed telescope at Kitt Peak National Observatory provide new precise orbits for the double-lined spectroscopic binaries RR Lyn (A3/A8/A6), 12 Boo (F8 IV), and HR 6169 (A2 V). We derive orbital dimensions (a1 sin i and a2 sin i) and minimum masses (m1 i and m2 i) with accuracies of 0.06%-0.9%. The three systems, which have V magnitudes of 5.53, 4.82, and 6.42, respectively, are all sufficiently bright that they are easily within the grasp of modern optical interferometers and so afford the …

Are Ti44-Producing Supernovae Exceptional?, L.-S. The, Donald D. Clayton, R Diehl, Dieter H. Hartmann, A F. Iyudin, M D. Leising, B S. Meyer, Y Motizuki, V Schönfelder

Publications

According to standard models supernovae produce radioactive ⁴⁴Ti, which should be visible in gamma-rays following decay to ⁴⁴Ca for a few centuries. ⁴⁴Ti production is believed to be the source of cosmic ⁴⁴Ca, whose abundance is well established. Yet, gamma-ray telescopes have not seen the expected young remnants of core collapse events. The ⁴⁴Ti mean life of 89 y and the Galactic supernova rate of 3/100 y imply several detectable ⁴⁴Ti gamma-ray sources, but only one is clearly seen, the 340-year-old Cas A SNR. Furthermore, supernovae which produce much ⁴⁴Ti are expected …