Physical Sciences and Mathematics Commons^™

Comptel Solar Flare Measurements, James M. Ryan, Mark L. Mcconnell

Space Science Center

We review some of the highlights of the COMPTEL measurements of solar flares. These include images of the Sun in γ rays and neutrons. One of the important features of the COMPTEL instrument is its capability to measure weak fluxes of γ rays and neutrons in the extended phase of flares. These data complement the spectra taken with the COMPTEL burst spectrometer and the telescope during the impulsive phase of flares. We focus our attention on some of these general capabilities of the instrument and the latest results of two long‐duration γ‐ray flares, i.e., 11 and 15 June 1991

The Δ Scuti Star Fg Virginis Ii. A Search For High Pulsation Frequencies, Michel Breger, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

Although the δ Scuti and roAp variables occupy similar positions on and near the main sequence, δ Scuti variables pulsate with lower radial and nonradial overtones and lower frequencies. To test whether high frequencies (as found in the roAp stars) are also present in δ Scuti stars, a multisite campaign with the Whole Earth Telescope (WET) was carried out for the star FG Vir. The 96.7 hours of WET photometry were supplemented by measurements made with the Delta Scuti Network (DSN), because the DSN technique includes regular measurements of comparison stars and is better suited to monitoring the low frequencies …

Space, Time, And Matter, Henry G. Schwarz

History Faculty and Staff Publications

One of the principal tasks of current cosmology is to determine the amount of matter in the present universe. This task, however, is hampered by two basic errors, one the present method of measuring distances, particularly the reliance on the notion of a "standard candle," and the other the way the amount of matter is estimated, namely, by counting objects in the visi­ble universe and estimating the amount of invisible matter. Underlying these two errors is the failure to study the universe in terms of space-time.

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

Alejandro Garcia

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.

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

Physics and Astronomy Faculty Publications and Presentations

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 …

A Survey For Millisecond Pulsars, P. S. Ray, S. E. Thorsett, F. A. Jenet, M. H. Van Kerkwuk, S. R. Kulkarni, T. A. Prince, J. S. Sandhu, D. J. Nice

Physics and Astronomy Faculty Publications and Presentations

We have searched 960 square degrees of sky for radio pulsars, using the 305 m telescope at Arecibo, Puerto Rico. The 430 MHz survey reached a limiting sensitivity for slow pulsars of 0.7 mJy using a dual-polarization, 32 channel filter bank over 8 MHz of bandwidth. We have detected one new millisecond pulsar, 11 new slow pulsars, one previously known millisecond pulsar, and eight previously known slow pulsars. The new millisecond pulsar, PSR J2033 + 17, with a period of 5.9 ms, has been found to be in a binary system. The Keplerian circular orbital solution has a period of …

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. …

High-Sensitivity Absorption Spectroscopy In Fe Ii, Scott D. Bergeson, K. L. Mullman, J. E. Lawler

Faculty Publications

We report the first measurements of UV oscillator strengths (ƒ-values) in Fe II from a high-sensitivity absorption experiment developed at the University of Wisconsin. The accuracy of our measurements is demonstrated by our reproducing well-known ƒ-value ratios in Fe I and Fe II. The first laboratory ƒ-value measurement of the 160.845 nm transition in Fe II is presented and compared to values in the literature. While this paper focuses on Fe II, the high-sensitivity absorption method that we have developed is applicable to essentially every element in the periodic table, for both neutral and ionized species, over a broad range …

Branching Fractions And Oscillator Strengths For Fe Ii Transitions From The 3d6(5D)4p Subconfiguration, Scott D. Bergeson, K. L. Mullman, M. E. Wickliffe, J. E. Lawler

Faculty Publications

New experimental branching fractions and transition probabilities are reported for 56 transitions in Fe II. The branching fractions are measured with a Fourier transform spectrometer and also with a high-resolution grating spectrometer on a n optically thin hollow cathode discharge. Highly accurate experimental radiative lifetimes from the recent literature provide the normalization required to convert our branching fractions into absolute transition probabilities. Results are compared with experimental and theoretical values in the literature. Our new transition probabilities will establish the absolute scale for relative absorption oscillator strengths of vacuum ultraviolet lines measured using a new high-sensitivity absorption experiment at the …

Ion Viscosity Mediated By Tangled Magnetic Fields: An Application To Black Hole Accretion Disks, P. Subramanian, P. A. Becker, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

We examine the viscosity associated with the shear stress exerted by ions in the presence of a tangled magnetic field. As an application, we consider the effect of this mechanism on the structure of black hole accretion disks. We do not attempt to include a self-consistent description of the magnetic field. Instead, we assume the existence of a tangled field with coherence length λcob• which is the average distance between the magnetic "kinks" that scatter the particles. For simplicity, we assume that the field is self-similar, and take λcob to be a fixed fraction ξ of the local disk height …

A New Archaeoastronomical Investigation Of The Irish Axial-Stone Circles, Frank T. Prendergast, Clive L. Ruggles

Conference Papers

This paper presents the preliminary results of a project undertaken in 1994 to investigate the astronomical potential of the axial-stone circles (ASCs) of seven or more stones in Counties Cork and Kerry, south-west Ireland. This group of sites is of particular interest in that the monuments in the group bear a striking resemblance to the recumbent stone circles (RSCs) of Aberdeenshire, eastern Scotland, which appear to exhibit a strong pattern of alignment in relation to prominent hilltop summits and the rising and setting position of the moon. The first indications from the Irish data are that similar patterns of alignment …

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 …

The Application Of Artificial Neural Networks To Stellar Classification, Coryn A. L. Jones, Mike Irwin, Ted Von Hippel

Publications

We are working on a project to automate the multi-parameter classification of stellar spectra using Principal Components Analysis (PCA) and Artificial Neural Networks. We present here the usefulness of PCA as a form of spectral data compression, and our results to date of classification on the MK system.

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

Physics and Astronomy Faculty Publications and Presentations

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 …

The Orbital Period Of Bk Lyncis (Pg 0917 + 342), F. A. Ringwald, J. R. Thorstensen, R. K. Honeycutt, J. W. Robertson

Dartmouth Scholarship

Long-term light curves of the cataclysmic variable BK Lyn = PG 0917 + 342 from the Indiana Automated CCD photometric telescope (‘RoboScope’) and the Harvard College Observatory plate archive reveal no dwarf nova outbursts. Two radial velocity studies show its orbital period to be 107.97 ;1 0.07 min, confirming that it does have an orbital period shorter than the period gap for cataclysmic variables. Whether this is the first nova-like variable below the period gap or a dwarf nova with rare outbursts resembling WZ Sge is still unclear, however.

Estimating Milky-Way Dark Matter: Its Amount And Distribution, Jeffery E. Clayton, Sue Ellen Mccloskey, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

No abstract provided.

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 …

An Automated Search For Variability In Chromospherically Active Stars, Gregory W. Henry, Francis C. Fekel, Douglas S. Hall

Information Systems and Engineering Management Research Publications

We have completed an automated photometric survey of 66 potential or known chromospherically active late-type stars with the 0.4 m Vanderbilt/Tennessee State robotic telescope. The precision of the observations from this telescope matches that predicted from photon and scintillation noise alone and represents a significant improvement in the precision of previous robotic telescope surveys of chromospherically active stars. Light variability has been detected and its period has been determined for 47 stars, 41 of which are newly discovered variables. The primary mechanism of variability is rotational modulation of a spotted surface. In addition we have detected eclipses in HD 62668 …

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 Lyman Continuum In Starburst Galaxies Observed With The Hopkins Ultraviolet Telescope, Claus Leitherer, Henry C. Ferguson, Timothy M. Heckman, James D. Lowenthal

Astronomy: Faculty Publications

The starburst galaxies IRAS 08339+6517, Mrk 1267, Mrk 66, and Mrk 496 (=NGC 6090) were observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission. All four galaxies have radial velocities larger than 5000 km s-1, permitting the measurement of their intrinsic Lyman continuum fluxes redward of the H I absorption edge in our Galaxy. The sample was selected on the basis of having the most favorable conditions for the escape of Lyman continuum photons. Two a upper limits of Fk < 7 X 10-16 ergs s-1 cm-2 A-1 were obtained for the flux around 900 A within the rest frame of each galaxy.A set of theoretical spectral energy distributions has been calculated. We show that there exists a tight correlation between the continuum luminosity at 900 A and the total number of photons emitted in the Lyman continuum, which is valid for high- and low-metallicity galaxies and essentially all relevant initial mass functions and star formation histories. Comparison with the observed values suggests that, on average, less than 3% of the intrinsic Lyman continuum photons escape from the program galaxies. Models for the ionization of the intergalactic medium at high 2 by young starbursts require a significant fraction of the ionizing radiation to escape from the galaxy. If the four galaxies observed by us have properties similar to young galaxies at redshift 2 2 3, such galaxies are not likely to provide Lyman continuum photons for the ionization of the early universe.

A Rosat Hri Observation Of The Supernova Remnant G109.1 – 1.0, Alan P. Hurford, Robert A. Fesen

Dartmouth Scholarship

We present results of a search using ROSAT HRI data for X-ray spatial substructures in the galactic supernova remnant G109.1 – 1.0 which might indicate a connection between the remnant’s bright X-ray blob and its X-ray pulsar, 1E2259 + 586. A 0.1 – 2.4 keV HRI image, created by combining separate 28- and 22-ks pointings, reveals the presence of a few small-scale X-ray features, including a NE-SW emission ridge in the remnant’s X-ray blob. Two diffuse knots in the X-ray blob, previously suggested as being aligned with the X-ray pulsar, appear to be statistical fluctuations in the Einstein HRI data. …

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 …

Extended Molecular Gas Distribution In Mrk 273 And Merger-Luminosity Evolution, Min S. Yun, N Z. Scoville

Min S. Yun

We present the first interferometric measurement of CO emission (θ ~ 2'') from the ultraluminous infrared galaxy Mrk 273. A total H2 mass of 3.6 × 1010 Msun is inferred from the CO observations, half of which belongs to an extended component with deconvolved size 5.1 × 2.5 kpc. In addition, an unresolved molecular gas complex is found to be coincident with the optical nucleus. The inferred H2 mass, size (R ~ 380 pc), and mean surface mass density (ΣH2 ≥ 4 × 104 Msun pc-3) of this complex, as well as the IR luminosity, are very similar to those …

Imaging And Spectroscopy Of Damped Lyα Quasi-Stellar Object Absorption-Line Clouds, James Lowenthal, Craig J. Hogan, Richard F. Green, Bruce Woodgate, Adeline Caulet, Larry Brown, Jill Bechtold

Astronomy: Faculty Publications

We present the results of a multifaceted search for line emission from the vicinities of high-redshift quasi-stellar object (QSO) absorption-line clouds, most of them damped Lyα systems at z ≳ 2. Seven fields containing QSOs with known intervening damped Lyα absorbers were imaged with the GSFC Fabry-Perot Imager to search for diffuse redshifted Lyα. Apart from the one Lyα companion galaxy reported previously, no confirmed extended Lyα emission was detected down to 3 σ flux levels of around 3 x 10-17 ergs s-1 cm-2, corresponding to star formation rates ≲1 M⊙ yr-1, assuming case B recombination, a reasonable initial mass …

Development Of An Orthogonal-Stripe Cdznte Gamma Radiation Imaging Spectrometer, John R. Macri, Boris A. Apotovsky, J F. Butler, M L. Cherry, Brian K. Dann, A Drake, F P. Doty, T G. Guzik, K Larson, M Mayer, Mark L. Mcconnell, James M. Ryan

Space Science Center

We report performance measurements of a sub-millimeter resolution CdZnTe strip detector developed as a prototype for astronomical instruments operating with good efficiency in the 30-300 keV photon energy range. The prototype is a 1.4 mm thick, 64×64 contact stripe CdZnTe array of 0.375 mm pitch in both dimensions. Pulse height spectra were recorded in orthogonal-stripe coincidence mode which demonstrate room-temperature energy resolution <10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio >5:1. Good response is also demonstrated at higher energies using a coplanar grid readout configuration. Spatial resolution capabilities finer than the stripe pitch are demonstrated. We present the image of a ¹³³Ba source viewed through a collimator …

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 …

Large-Area Submillimeter Resolution Cdznte Strip Detector For Astronomy, James M. Ryan, John R. Macri, Mark L. Mcconnell, Brian K. Dann, M L. Cherry, T G. Guzik, F P. Doty, Boris A. Apotovsky, J F. Butler

Space Science Center

We report the first performance measurements of a sub-millimeter CdZnTe strip detector developed as a prototype for space-borne astronomical instruments. Strip detector arrays can be used to provide two-dimensional position resolution with fewer electronic channels than pixellated arrays. Arrays of this type and other candidate technologies are under investigation for the position-sensitive backplane detector for a coded-aperture telescope operating in the range of 30 - 300 keV. The prototype is a 1.4 mm thick, 64 multiplied by 64 stripe CdZnTe array of 0.375 mm pitch in both dimensions, approximately one square inch of sensitive area. Pulse height spectra in both …