Astrophysics and Astronomy Commons^™

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

Faculty Publications

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

Chromospherically Active Stars. Xiv. A Rediscussion Of The Properties And Evolutionary State Of Hd 181943, Francis C. Fekel, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

The chromospherically active single star HD 181943 was previously proposed as either a pre-main-sequence star seen pole-on or a post-main-sequence subgiant that evolved from an Ap star similar to 53 Cam. It also was found to be a variable star with a 385 day period. We have used new spectroscopic and photometric observations to reevaluate the properties and evolutionary state of this unusual system. We conclude that HD 181943 is a single K1 V star that has recently arrived on the ZAMS. Its emission line fluxes are nearly identical to those of HD 82558= LQ Hya, while its log lithium …

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

Physics and Astronomy Faculty Publications

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

Transitions In Masculinity And Hemingway's Developed "Code", Daniel Polk

Honors Theses

The "Hemingway Code" is much more than two words that fit nicely together for a scholar's usage; the words signify a much deeper championing of masculinity, almost a haunting presence. For Ernest Hemingway living life every day, every moment with its fullest masculine fervor, became an obsession, a never-ending quest to be at one with the attitude of never complaining, never crying out, panicking, thinking too much, or regretting. To live a manly life in a series of tactical victories, performed with steadfast ritualistic mannerisms, is to embody masculinity, and therefore the "Hemingway Code."

Ubvri Photometry Of The Type Ia Sn 1994d In Ngc 4526, Michael W. Richmond, Richard R. Treffers, Alexei V. Filippenko, Schuyler D. Van Dyk, Young Paik, Chien Peng, Laurence A. Marschall, Bentley D. Laaksonen, Bruce Macintosh, Ian S. Mclean

Physics and Astronomy Faculty Publications

We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 starting 13 days before B-band maximum. The light curves of this SN resemble closely those of the "normal" type Ia events SNe 1989B and 1980N, differing only in a slightly faster decline after maximum in VRI. The optical absolute magnitudes of SN 1994D, however, are significantly brighter than those of its near twins, and brighter than those predicted by Phillips' [ApJ, 413, L105 (1993)] relationship between decline rate and luminosity. Our small amount of IR photometry of SN 1994D …

Starspot Evolution, Differential Rotation, And Magnetic Cycles In The Chromospherically Active Binaries Lambda Andromedae, Sigma Geminorum, Ii Pegasi, And V711 Tauri, Gregory W. Henry, Joel A. Eaton, Jamesia Hamer, Douglas S. Hall

Information Systems and Engineering Management Research Publications

We have analyzed 15-19 yr of photoelectric photometry, obtained manually and with automated telescopes, of the chromospherically active binaries lambda And, sigma Gem, II Peg, and V711 Tau. These observations let us identify individual dark starspots on the stellar surfaces from periodic dimming of the starlight, follow the evolution of these spots, and search for long-term cyclic changes in the properties of these starspots that might reveal magnetic cycles analogous to the Sun's 11 yr sunspot cycle. We developed a computer code to fit a simple two-spot model to our observed light curves that allows us to extract the most …

The Black-Hole Candidate Gro J0422+32: Mev Emission Measured With Comptel., R Van Dijk, K Bennett, W Collmar, R Diehl, W Hermsen, G G. Lichti, Mark L. Mcconnell, James M. Ryan, V. Schonfelder, A W. Strong, J Van Paradijs, C Winkler

Physics & Astronomy

On Aug. 5, 1992, BATSE detected the bright soft X-ray transient GRO J0422+32,also known as Nova Per 1992. The COMPTEL instrument (0.75-30MeV) aboard the Compton Gamma-Ray Observatory (CGRO) observed this black-hole candidate twice. During the first observation, which started when the X-ray flux was at its maximum, GRO J0422+32 was detected between 1 and 2MeV. The flux in this energy range was higher than expected from an extrapolation of the standard Sunyaev-Titarchuk Comptonisation model fits to the contemporaneous OSSE and SIGMA data. We discuss several models that may explain the total hard-X/γ-ray spectrum, including the generalised Comptonisation model from Titarchuk. …

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

Physics and Astronomy Faculty Publications

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

Experiences Of Wfpc-2 Photometry And Psf Modelling, Nial Tanvir, David Robinson, Ted Von Hippel

Publications

The wide-field chips in WFPC-2 have ~0.0996 arcsec pixels, which is larger than the FWHM of the point spread function (PSF). This poor sampling of WFPC-2 images, means that simple stellar aperture photometry is competitive with profile fitting for moderately crowded fields. One of the problems which must be addressed with profile fitting photometry is that of allowing for variations of the PSF as a function of position on the image. The equivalent problem for aperture photometry is obtaining aperture corrections as a function of position. The aperture correction must be added to each aperture magnitude in order to account …

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

Physics and Astronomy Faculty Publications

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

A …

A Spectroscopic And Photometric Study Of 12 Bm Camelopardalis, Douglas S. Hall, Francis C. Fekel, Gregory W. Henry, Joel A. Eaton, William S. Barksdale, Virgiljus Dadonas, Zeki Eker, Peep Kalv, Carlson R. Chambliss, Robert E. Fried, George L. Fortier, Howard J. Landis, Howard P. Louth, Harry D. Powell, Thomas G. Mcfaul, Richard Miles, Paul Nielsen, Thomas R. Renner, Stephen P. Robb, Douglas M. Slauson, Harold J. Stelzer, Rick Wasson, James E. Wood

Information Systems and Engineering Management Research Publications

Radial velocities from 1916.95 to 1991.95 and photometry from l979.25, both published and new in this paper, are presented and analyzed. A new solution of the radial velocity curve reveals a new period of 80.90 days and an eccentricity of e = 0.05 +/- 0.02, both very different from the 80.17 days and 0.35 found by Abt et al. (1969). An alternative solution with e = 0 is given because we cannot decide firmly whether or not the small eccentricity is real. We find V sin i = 11.3 +/- 0.3 km/s from Maidanak and 10 unequal depth. 0.048 mins …

Starspots Found On The Ellipsoidal Variable V350 Lacertae = Hr 8575, Lionel J. Crews, Douglas S. Hall, Gregory W. Henry, Richard D. Lines, Helen C. Lines, Robert E. Fried

Information Systems and Engineering Management Research Publications

It has been a puzzle why this chromospherically active, strong-dynamo K2 IV-III star is not known to have the large starspots characteristic of other such stars. Published individual radial velocities, which had never been analyzed, are used to derive an orbital solution. Combined with the one older existing orbital solution, this yields an improved orbital ephemeris: time of conjunction (K star behind) = JD 2445255.47 +/- 0.11 days and period = 17.75346 +/- 0.00016 days. All available photoelectric photometry, from 1970.9 to 1992.5, is collected A cos 2 theta fit of the ellipticity effect yields JD 2445255.60 +/- 0.06 days …

Rotation Periods Of Open Cluster Stars, Iii, Charles F. Prosser, Matthew D. Shetrone, Amil Dasgupta, Dana E. Backman, Bentley D. Laaksonen, Shawn W. Baker, Laurence A. Marschall, Barbara A. Whitney, Konrad Kuuken, John R. Stauffer

Physics and Astronomy Faculty Publications

We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several slow rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleiades stars with photometric periods together with current X-ray flux measurements, we illustrate the X-ray activity/rotation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P~6-7 days-in general accordance with previous results using more heterogeneous samples of G/K stars.

An Independent Calibration Of Stellar Ages: Hst Observations Of White Dwarfs At V=25, Ted Von Hippel, Gerard Gilmore, D.H.P. Jones

Publications

The white dwarf luminosity function of a stellar cluster will have a sharp trunca- tion at a luminosity which is determined by the time since formation of the first white dwarfs in that cluster. Calculation of the dependence of this limiting luminosity on age requires relatively well-understood physics and is independent of stellar evolutionary models. Thus, measurement of the termination of the white dwarf luminosity func- tion provides an independent method to determine the age of a cluster, and thereby to calibrate stellar evolutionary ages. We have obtained HST WFPC2 data in two open clusters, identified the white dwarf sequence, …

Hubble Space Telescope Observations Of Cool White Dwarf Stars: Detection Of New Species Of Heavy Elements, Harry Shipman, Terry D. Oswalt

Aerospace, Physics, and Space Science Faculty Publications

Observations of cool white dwarf stars with the Hubble Space Telescope has uncovered a number of spectral features from previously unobserved species. In this paper we present the data on four cool white dwarfs. We present line identifications, equivalent width measurements, and brief summaries of the significance of our findings. The four stars observed are GD 40 (DBZ3), G 74-7 (DAZ), L 745-46A (DZ), and LDS 749 B (DBA). Many additional species of heavy elements were detected in GD 40 and G 74-7. In L 745-46A,while the detections are limited to Fe I, Fe II, and Mg II, the quality …

On The Current Status Of Maser Polarization Theory, Moshe Elitzur

Physics and Astronomy Faculty Publications

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

To Stephen W. Hawking, Lillia N. Apostolova

Humanistic Mathematics Network Journal

No abstract provided.

Grains In Ionized Nebulae: Spectral Line Diagnostics, J. B. Kingdon, Gary J. Ferland, W. A. Feibelman

Physics and Astronomy Faculty Publications

The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the [Ca II] λλ7291, 7324 doublet and the detection of …

Imaging The Host Galaxies Of High-Redshift Radio-Quiet Qsos, James D. Lowenthal, Timothy M. Heckman, Matthew D. Lehnert, J. H. Elias

Astronomy: Faculty Publications

We present new deep K-band and optical images of four radio-quiet QSOs at z ≈ 1 and six radio-quiet QSOs at z ≈ 2.5, as well as optical images only of six more at z ≈ 2.5. We have examined the images carefully for evidence of extended "fuzz" from any putative QSO host galaxy. None of the z ≈ 2.5 QSOs shows any extended emission, and only two of the z ≈ 1 QSOs show marginal evidence for extended emission. Our 3 σ detection limits in the K images, mK ≃ 21 for an isolated source, would correspond approximately to …

The Contribution Of Low Surface Brightness Galaxies To Faint Galaxy Counts, Stacy S. Mcgaugh

Faculty Scholarship

Recent observations have revealed a population of blue galaxies at intermediate redshift with a space density well in excess of expectations from the local luminosity function and standard cosmology. The colors and luminosities of these faint blue galaxies are similar to nearby low surface brightness (LSB) galaxies. Such galaxies are severely underrepresented in surveys used to define the local luminosity function, but could in principle be detected in deep surveys. If LSB galaxy density is high enough, the faint-galaxy counts could be explained without requiring rapid galaxy evolution. To explore the consequences of including LSB galaxies, we construct catalogs of …

The Orbital Period Of The Pre-Cataclysmic Binary Re 2013+400 And A Study Of The Atmosphere Of The Dao White Dwarf Primary, M. A. Barstow, M. R. Burleigh, T. A. Fleming, J. B. Holberg, D. Koester, M. C. Marsh, S. R. Rosen, R. G.M. Rutten, S. Sakai, R. W. Tweedy, G. Wegner

Dartmouth Scholarship

Several pre-cataclysmic binaries, comprising a hot white dwarf with a red dwarf companion, have been discovered as a result of the optical identification of EUV sources from the ROSAT all-sky survey. The optical spectra have the steep blue continuum and Balmer absorption typical of a hot white dwarf, but there are bright, narrow emission lines of H I (and sometimes He I and Ca II) superimposed. An intense campaign of follow-up observations has been devoted to these binary systems. So far, only RE 2013+400 has exhibited any measurable changes in the radial velocities of the emission components, from which it …

The Origin Of N Iii Λ990 And C Iii Λ977 Emission In Agn Narrow-Line Region Gas, Jason W. Ferguson, Gary J. Ferland, A. K. Pradham

Physics and Astronomy Faculty Publications

We discuss implications of Hopkins Ultraviolet Telescope (HUT) detections of C III λ977 and N III λ990 emission from the narrow-line region of the Seyfert 2 galaxy NGC 1068. In their discovery paper Kriss et al. showed that the unexpectedly great strength of these lines implies that the emitting gas must be shock-heated if the lines are collisionally excited. Here we investigate other processes which excite these lines in photoionization equilibrium. Recombination, mainly dielectronic, and continuum fluorescence are strong contributors to the line. The resulting intensities are sensitive to the velocity field of the emitting gas and require …

The Wall Of Reconnection-Driven Magnetohydrodynamic Turbulence In A Large Solar-Flare, Ronald L. Moore, Ted N. La Rosa, L. E. Orwig

Faculty Articles

LaRosa & Moore (1993) recently proposed that the bulk dissipation of magnetic field that is required for the electron energization in the explosive phase of solar flares occurs in a ''fat current sheet,'' a wall of cascading MHD turbulence sustained by highly disordered driven reconnection of opposing magnetic fields impacting at a turbulent boundary layer. In two-ribbon eruptive flares, this turbulent reconnection wall is supposed to develop at the usual reconnection site in the standard model for these flares; that is, the reconnection wall stands in the vertical magnetic rent made by the eruption of the sheared core of the …

Creation And Implementation Of A Tracking Module For A Small-Geometry, Vertex Time Projection Chamber, Christine A. Byrd, Wilson H. Howe, Amber D. Climer, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

A charged-particle tracking module was written and tested using pixel data generated from CERN's Monte Carlo detector-modeling program GEANT. This tracking module was customized for testing the design of a micro-strip gas time project chamber, designed by Drs. Margetis and Wieman of the Relativistic Nuclear Collisions Group at Lawrence Berkeley Laboratory. This low-mass, high-resolution, small-geometry vertex time projection chamber was designed for possible use with a larger instrument in an experiment using the relativistic heavy ion collider, RHIC, under construction at Brookhaven National Laboratory in New York. Implementing this tracking module involved generating tables and source code in a manner …

Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

No abstract provided.

A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder

Faculty Publications

The direct simulation Monte Carlo method for the Boltzmann equation is modified by an additional displacement in the advection process and an enhanced collision rate in order to obtain the exact hard sphere equation of state at all densities. This leads to consistent thermodynamic and transport properties in the low density (Boltzmann) regime. At higher densities transport properties are comparable to the predictions of the Enskog model. The algorithm is faster than molecular dynamics at low and moderate densities and readily run on a parallel architecture

A Theoretical Study Concerning The Solar Cycle Dependence Of The Nightside Ionosphere Of Venus, Zoltan Dobe, Andrew F. Nagy, Jane L. Fox

Physics Faculty Publications

We modeled the chemical and physical processes taking place in the nightside ionosphere of Venus by solving the one dimensional coupled continuity and momentum equations for 12 ion species [CO₂⁺, O₂⁺, O⁺, H⁺, NO⁺, CO⁺, N₂⁺, N⁺, He⁺, C⁺, O⁺ (²D) and O⁺ (²P)]. We investigated the relative importance of the two major processes responsible for maintaining the nightside plasma densities: atomic ion transport from the dayside and impact ionization due to energetic electron precipitation. …

Three-Dimensional Fabry-Perot Imaging Spectroscopy Of The Crab Nebula, Cassiopeia A, And Nova Gk Persei, Stephen S. Lawrence, Gordon M. Macalpine, Alan Uomoto, Bruce E. Woodgate, Larry W. Brown, Ronald J. Oliversen, James D. Lowenthal, Charles Liu

Astronomy: Faculty Publications

Three-dimensional spatial models of the line-emitting gas in the Crab Nebula, Cassiopeia A, and the nova remnant of GK Persei have been developed from imaging spectroscopy taken with the Goddard Fabry-Perot Imager mounted on the McGraw-Hill 1.3 m and Hiltner 2.4 m telescopes of the Michigan-Dartmouth-MIT Observatory. The spatial model of the Crab Nebula in [O III] λ5007 emission reveals the thin, annular morphology of the "high-helium torus," the association of this torus and other bright filament loops with north-south bipolar asymmetry of the remnant shell, the structure of the filamentary shell at the boundary with the inner synchrotron cavity, …

Using Geant To Model Calrimeter Response For Electromagnetic Cascades From Nucleus-Nucleus Interactions In A Cosmic Ray Detector, Kazuhiko Murai, Carlos A. Sanchez, Donald C. Wold

Journal of the Arkansas Academy of Science

Ascintillating optical fiber calorimeter (SOFCAL) is being developed by NASA/Marshall Space Flight Center for use in balloon-borne experiments to study the spectrum of high-energy cosmic rays and gamma rays. SOFCAL will not saturate for long exposures and the calorimeter willbe useful in emulsion chambers to study primary cosmic-ray nuclei with energies from 100 GeV to 1,000 TeV. The event generator FRITIOF was used to model the collision of a cosmic-ray projectile with a target nucleus inan emulsion chamber. The measurements of charged particles from the interaction in the emulsions are related to the energy of the primary cosmic ray nucleus-nucleus …

Using Fritiof To Model Nucleus-Nucleus Interactions In A Cosmic Ray Detector, Carlos A. Sanchez, Kazuhiko Murai, Donald C. Wold

Journal of the Arkansas Academy of Science

Ascintillating optical fiber calorimeter (SOFCAL) isbeing developed by NASA/Marshall Space Flight Center for use in experiments to study the spectrum of high-energy cosmic rays and gamma rays from 100 GeV to 1,000 TeV. SOFCAL willnot saturate for long exposures and this calorimeter inthese balloon-borne emulsion chambers willbe helpful for the study of the composition of primary cosmic-ray nuclei. For primary nuclei with energies much greater than 1014 eV, nucleus-nucleus interactions are likely to exhibit characteristics of a quark-gluon plasma (QGP). Aparticle event generator was used tomodel the collision of a cosmic-ray nucleus with a target nucleus inan emulsion chamber. FRITIOF …