Physical Sciences and Mathematics Commons^™

The Optical-Ultraviolet-Γ-Ray Spectrum Of 3c 279, Hagai Netzer, D. Kazanas, Beverley J. Wills, D. Wills, Han Mingsheng, M. S. Brotherton, J A. Baldwin, Gary J. Ferland, I. W. A. Browne

Physics and Astronomy Faculty Publications

We have obtained spectrosocpy of the violently variable quasar 3C 279, simultaneous with γ-ray observations, in 1992 April. Our combined optical (McDonald Observatory and Cerro Tololo InterAmerican Observatory (CTIO) and ultraviolet (HST) observations, made when the source was faint, show a very steep power-law continuum (F_ν∝ν^-1.95) and strong broad emission lines. This is the first time that the broad ultraviolet lines of this object have been measured, and we note several unusual properties of the spectrum. In particular, the profiles of C IV λ1549 and Mg II λ …

Mesostructure Of Photoluminescent Porous Silicon, David D. Allred, F. Ruiz, C. Vázquez-López, Jesus González-Hernández, G. Romero-Paredes, R. Peña-Sierra, G. Torres-Delgado

Faculty Publications

Scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to characterize the microstructure of photoluminescent porous silicon (PS) layers formed by the anodic etching (HF:H2O:ethanol), at various current densities, of p-type (100) silicon wafers possessing resitivity in the range 1-2 Ω cm. Existing models for the origin of luminescence in PS are not supported by our observations. Cross-sectional as well as surface atomic force micrographs show the material to be clumpy rather than columnar; rodlike structures are not observed down to a scale of 40 nm. A three-dimensional model of the mesostructure of porous silicon is discussed. Room-temperature …

Raman Spectroscopic Study Of The Formation Of T-Mosi2 From Mo/Si Multilayers, Ming Cai, David D. Allred, A. Reyes-Mena

Faculty Publications

We have used Raman spectroscopy, large- and small-angle x-ray diffraction spectroscopy of sputter-deposited, vacuum-annealed, soft x-ray Mo/Si thin-film multilayers to study the physics of silicide formation. Two sets of multilayer samples with d-spacing 8.4 and 2.0 nm have been studied. Annealing at temperatures above 800 °C causes a gradual formation of amorphous MoSi2 interfaces between the Si and Mo layers. The transition from amorphous to crystalline MoSi2 is abrupt. The experimental results indicate that nucleation is the dominant process for the early stage and crystallization is the dominant process after nucleation is well advanced. In the thicker multilayer, a portion …

Emitted Current Instability From Silicon Field Emission Emitters Due To Sputtering By Residual Gas Ions, W.I. Karain, Larry V. Knight, David D. Allred, A. Reyes-Mena

Faculty Publications

We have fabricated arrays of silicon field emitters using semiconductor lithography techniques. The density of the tips was 10^5/cm^2. The maximum current that can be extracted from each emitter is limited by resistive heating. We have investigated how the electron current emitted changes under constant applied voltage. We found that the current is very sensitive to the vacuum conditions. We attribute this to sputtering of the emitters due to ionized residual gas molecules. The poorer the vacuum, the higher the instability in the current. We studied this phenomenon at 10^6 and 10-x Torr. The model of two concentric spherical shells …

Automated Classification Of Stellar Spectra - I. Initial Results With Artificial Neural Networks, Ted Von Hippel, L.J. Storrie-Lombardi, M.C. Storrie-Lombardi, M.J. Irwin

Publications

We have initiated a project to classify stellar spectra automatically from high-dispersion objective prism plates. The automated technique presented here is a simple back propagation neural network and is based on the visual classification work of Houk. The plate material (Houk’s) is currently being digitized, and contains « 105 stars down to K æ 11 at æ 2-Â resolution from « 3850 to 5150 Â. For this first paper in the series, we report on the results of 575 stars digitized from 6 plates. We find that even with the limited data set now in hand we can determine the …

Strong Magnetic Field Effects And Molecular Processes With Applications To White Dwarfs, Phillip C. Stancil

Physics Theses & Dissertations

Radiative transitions of hydrogenlike atoms in external magnetic fields of strength applicable to magnetic white dwarfs, i.e. B < 10³ megagauss, have been investigated for field-free principal quantum numbers n < 6. Finite proton mass corrections are included. Relativistic corrections are also investigated. Transition probabilities are determined using the length, velocity, and acceleration forms of the electric dipole operator. Discrepancies between previous calculations and magnetic white dwarf observations of low-lying boundbound transitions have been studied. New results for high-lying transitions are also obtained.

The transition probability for the hydrogenlike 2s two-photon decay has been investigated and shown to increase substantially with field strength. The computed two-photon spectra show resonances and interference minima. Anomalous Zeeman depolarization features are found in computed two-photon polarization spectra of alkali atoms in laboratory strength magnetic fields. A previously observed fine structure depolarization feature is shown to decay with decreasing field strength.

Experimental Stark Shift Of Several Nii And Oii Spectral Lines, Mara Scepanovic, Vladimir Milosavljevic, Stevan Djenize, Mihajlo Platisa, Jaroslav Labat

Articles

Stark shift of four NII and seven OII spectral lines have been measured for the first time in the linear low pressure pulsed arc plasma and compared with existing theoretical values.

Comptel Imaging Of The Galactic Disk And The Separation Of Diffuse Emission And Point Sources, H Bloemen, W Hermsen, B Swanenburg, C De Vries, R Diehl, V. Schonfelder, H Steinle, A W. Strong, A Connors, Mark L. Mcconnell, D Morris, G Stacy, K Bennett, C Winkler

Physics & Astronomy

The first MeV image of the inner Galaxy obtained with the COMPTEL telescope aboard the Compton Gamma-Ray Observatory shows a structured ridge of emisssion along the Galactic equator which probably consists of diffuse radiation and unresolved discrete sources. The intensity distribution of this ridge distinctly differs from the expected distribution for a simple model of the diffuse radiation. Most remarkable are the observed excursions out of the disk, which may hint at the presence of gamma-ray point sources located several degrees away from the mid-plane, but a diffuse origin cannot be excluded. If these are indeed discrete sources, a substantial …

A Protostellar Jet Model For The Water Masers In W49n, Mordecai-Mark Mac Low, Moshe Elitzur, James M. Stone, Arieh Königl

Physics and Astronomy Faculty Publications

Observations by Gwinn, Moran, & Reid of the proper motions of water masers in W49N show that they have elongated distribution expanding from a common center. Features with high space velocity only occur far from the center, while low-velocity features occur at all distances. We propose that these observations can be interpreted in terms of a shell of shocked molecular gas that is driven by the expanding cocoon of a high-velocity protostellar jet. We present three-dimensional numerical simulations in support of this interpretation and argue that this source provides a unique oppurtunity for a detailed study of jet-driven cocoons.

Observations Of Gamma-Ray Bursts By Comptel, L O. Hanlon, K Bennett, W Collmar, A Connors, R Diehl, R Van Dijk, J Greiner, J W. Den Herder, W Hermsen, R M. Kippen, L Kuiper, Mark L. Mcconnell, James M. Ryan, V. Schonfelder, H Steinle, A W. Strong, M Varendorff, C Winkler

Physics & Astronomy

During the first year of operation, 22 cosmic gamma-ray bursts were detected within the field of view of the COMPTEL instrument on board the Compton Gamma Ray Observatory. Spectra and time histories for the strongest of these bursts have been obtained from both the main instrument (0.75-30 MeV) and the burst modules (0.3-10 MeV). The deconvolved photon spectra for the majority of bursts are fit by a single power law model with spectral index between -1.6 and -2.8. One strong burst, GRB 910814, exhibited significant curvature and could not be fit by a single power law model. A broken power …

Nebular Properties And The Ionizing Radiation Field In The Galactic Center, Joseph C. Shields, Gary J. Ferland

Physics and Astronomy Faculty Publications

Nebulosity in the central parsec of the Milky Way exhibits a low-ionization spectrum that has led previous analyses of this region to conclude that this material is photoionized by a relatively soft continuum. We have reanalyzed the infrared emission-line spectrum of te Galactic center in order to consider whether the data could actually be explained with photoionization by a relatively hard, yet dilute continuum, and additionally to constrain the properties of the reaiating plasma. We conclude that the composite infrared spectrum does not place strong restrictions on the nature of the ionizing continuum and that much of the ionized gas …

Hot Gas And The Origin Of The Nebular Continuum In Novae, Pedro Saizar, Gary J. Ferland

Physics and Astronomy Faculty Publications

A featureless blue continuum (with constant f_ν) is a defining feature of declining classical novae. The fact that f_ν is constant into the infrared, and the absence of a Balmer jump, suggests that this continuum originates in hot tenous gas. The electron temperature and density of the hot gas phase of classical nova QU Vul 1984 are estimated from ground-based optical and IUE ultraviolet observations. This region has a temperature of 10⁵ - 10⁶, and a density in the range of 2 x 10⁴ to 3 x 10⁵cm^-3. …

Optical Variability In The Unusual K5 V Infrared-Excess Star Hd 98800, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

The dusty infrared-excess star HD 98800 (K5 V) was observed for several weeks in the spring of 1993 by the Vanderbilt/Tennessee State 0.4 m automatic photoelectric telescope. It was found to be a variable star with an amplitude of 0.07 mag in V and a period of 14.7 days. We show, by comparison with other chromospherically active variable stars and constant stars with good observational histories, that the Rossby number for HD 98800, determined to be 0.30, places it well within the regime of stars whose convective envelopes and rotation rates combine to drive a magnetic dynamo strong enough to …

The Two Variables In The Triple System Hr 6469=V819 Her: One Eclipsing, One Spotted, Walter V. Van Hamme, Douglas S. Hall, Adam W. Hargrove, Gregory W. Henry, Rick Wasson, William S. Barksdale, Sandy Chang, Robert E. Fried, Charles L. Green, Helen C. Lines, Richard D. Lines, Paul Nielsen, Harry D. Powell, Robert C. Reisenweber, Charles W. Rogers, Steve Shervais, Randy Tatum

Information Systems and Engineering Management Research Publications

A complete BV light curve, from 14 nights of good data obtained with the Vanderbilt University-Tennessee State University (VU-TSU) automatic telescope, are presented and solved with the Wilson-Devinney program. Third light is evaluated, with the companion star brighter by 0.58m in V and 0.11m in B. The eclipses are partial. Inferred color indices yield F2 V and F8 V for the eclipsing pair and G8 IV-III for the distant companion star. After removing the variability due to eclipses, we study the residual variability of the G8 IV-III star over the ten years 1982 to 1992. Each yearly light curve is …

The Spectroscopic-Speckle Triple System Hr 6469, Colin D. Scarfe, David J. Barlow, Francis C. Fekel, Richard F. Rees, R. W. Lyons, Charles Thomas Bolton, Harold A. Mcalister, William I. Hartkopf

Information Systems and Engineering Management Research Publications

HR 6469 consists of an evolved G star and a close pair of stars, believed to be on the main sequence, the brighter of which is an early F star. Shallow eclipses have been detected in the close pair and the components of the wide system have been resolved over most of the orbit by speckle interferometry (McAlister & Hartkopf, Second Catalog of Interferometric Observations of Binary Stars, Center for High Angular Resolution Astronomy, Contribution No. 2 (CHARA), 1988). This paper presents radial velocities, obtained at the David Dunlap, McDonald, Kitt Peak and Dominion Astrophysical Observatories, for the G star …

Observations Of Cygnus X-1 Comptel During 1991, Mark L. Mcconnell, D J. Forrest, James M. Ryan, W Collmar, V. Schonfelder, H Steinle, A W. Strong, R Van Dijk, W Hermsen, K Bennett

Physics & Astronomy

The Compton Telescope (COMPTEL) experiment on the Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on two occasions during the first (sky survey) phase of its mission. These data represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. The observations in 1991 June and August both showed evidence for emission in the 0.75-2 MeV energy range. The flux level was larger by about a factor of 2 during the August observation. The spectral data were analyzed in the context of a Wien spectral model (the high-energy limit of the Sunyaev-Titarchuk Comptonization spectrum). Fits …

On The Theory Of Astronomical Masers In Three Dimensions, Moshe Elitzur

Physics and Astronomy Faculty Publications

In the standard theory of three-dimensional astronomical masers, the radiation field is described as if the source were comprised of a collection of linear masers. To leading order, the standard theory is shown to provide the correct description of three-dimensional masers and its results remain intact, but only within a frequency core whose half-width is χ_sΔν_D, where Δν_D is the Doppler width and χ_s is a dimensionless parameter. For any given geometry, χ_s is ~1θ_sat, where θ_sat is the beaming angle of a maser with that geometry that has …

Space Venture, Edward E. Chipman

Humanistic Mathematics Network Journal

No abstract provided.

Time-Series Photometric Spot Modeling. Ii. Fifteen Years Of Photometry Of The Bright Rs Cvn Binary Hr 7275., Klaus G. Strassmeier, Douglas S. Hall, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present a time-dependent spot modeling analysis of 15 consecutive years of V-band photometry of the long-period (Porb = 28.6 days) RS CVn binary HR 7275. This baseline in time is one of the longest, uninterrupted intervals a spotted star has been observed. The spot modeling analysis yields a total of 20 different spots throughout the time span of our observations. The distribution of the observed spot migration rates is consistent with solar-type differential rotation and suggests a lower limit of the differential-rotation coefficient of 0.022 +/-0.004. The observed, maximum lifetime of a single spot (or spot group) is 4.5 …

Comptel Measurements Of The Gamma-Ray Burst Grb 930131, James M. Ryan, K Bennett, W Collmar, A Connors, Gerald J. Fishman, J Greiner, L O. Hanlon, W Hermsen, R M. Kippen, C Kouveliotou, L Kuiper, G G. Lichti, John R. Macri, J. Mattox, Mark L. Mcconnell, B Mcnamara, C Meegan, V. Schonfelder, R Vandijk, M Varendorff, W Webber, C Winkler

Physics & Astronomy

On 1993 January 31 at 1857:12 Universal Time (UT), the Imaging Compton Telescope COMPTEL onboard the Compton Gamma Ray Observatory (CGRO) detected the cosmic gamma-ray burst GRB 930131. COMPTEL's MeV imaging capability was employed to locate the source to better than 2 deg (1 sigma error radius) within 7 hr of the event, initiating a world-wide search for an optical and radio counterpart. The maximum likelihood position of the burst from the COMPTEL data is alpha₂₀₀₀ = 12h 18m, delta₂₀₀₀ = -9 deg 42 min, consistent with independent CGRO-Burst and Transient Source Experiment (CGRO-BATSE) and Energetic Gamma Ray …

The Three-Dimensional Structure Of The Infrared Cirrus, John E. Gaustad

Physics & Astronomy Faculty Works

This project was carried out over a period of four years, beginning 6/15/89 and continuing through 9/15/93. Intermediate results have been reported as poster papers at several meetings of the American Astronomical Society. A brief summary was presented in April 1993 at a symposium on the infrared cirrus. The final results were published in late 1993. The measurements have been deposited in NASA's Astronomical Data Center. Briefly, the results are as follows: Using the IRAS data base, we surveyed the 1808 06-B9.5 stars in the Bright Star Catalog for extended excess emission at 60 micrometers, indicating the presence of heated …

Gravity And Electromagnetism In Noncommutative Geometry, Giovanni Landi, Nguyen Ai Viet, Kameshwar C. Wali

Physics - All Scholarship

We present a unified description of gravity and electromagnetism in the framework of a Z 2 non-commutative differential calculus. It can be considered as a “discrete version” of Kaluza-Klein theory, where the fifth continuous dimension is replaced by two discrete points. We derive an action which coincides with the dimensionally reduced one of the ordinary Kaluza-Klein theory.

An Overview Of Solar Flare Results From Comptel, Mark L. Mcconnell

Space Science Center

The COMPTEL experiment on the Compton Gamma Ray Observatory (CGRO) has been operating in orbit since April of 1991. During that time, COMPTEL has observed several large flares, the most notable of which were several X‐class flares which took place in June of 1991. As a solar instrument, COMPTEL has the capability to measure solar flare radiation in two parallel observing modes. In its telescope mode, COMPTEL is capable of measuring both solar flare photons (in the 0.75–30 MeV range) and solar flare neutrons (in the 20–150 MeV range) using the double scatter technique with a field‐of‐view of ∼1 steradian. …

First Results Of The Batse/Comptel/Nmsu Rapid Burst Response Campaign, R M. Kippen, A Connors, John R. Macri, Mark L. Mcconnell, James M. Ryan, W Collmar, J Greiner, V Schonfelder, M Varendorff, Gerald J. Fishman, C Meegan, C Kouveliotou, B Mcnamara, T Harrison, W Hermsen, L Kuiper, K Bennett, L O. Hanlon, C Winkler

Space Science Center

The Imaging Compton Telescope (COMPTEL) on board the Compton Gamma Ray Observatory regularly observes gamma‐ray bursts which occur inside the instrument’s ∼1 sr field‐of‐view. COMPTEL images bursts in the 0.75–30 MeV energy range with a typical location accuracy of 1–3 degrees, depending on burst strength, position, duration, and spectrum. COMPTEL’s imaging capability has been exploited in order to search for fading gamma‐ray burst counterparts at other wavelengths through the establishment of a BATSE/COMPTEL/NMSU rapid burst response campaign. This campaign utilizes near real‐time identification and preliminary burst location by BATSE, accelerated COMPTEL imaging, and a world‐wide network of observers to search …

Interstellar Gas And Dust In The Young Cluster Ic 348, Theodore P. Snow, Margaret Murray Hanson, C Gregory Seab, Jon M. Saken

Physics Faculty Publications

We have completed a multiband absorption- and emission-line study of a star embedded in the young cluster IC 348, to determine the environmental effect of star formation on the interstellar medium (ISM) local to the region. The hottest and youngest star in IC 348 is BD+31°643, a B5 V star which samples the inner bright nebular region. The nearby star o Per, which lies only 8 to the north and is thought to lie beyond IC 348, samples the gas and dust which has not been processed by very recent star formation. We speculate that the ISM throughout the region …

Velocity Distribution Among Colliding Asteroids, W F. Bottke, M C. Nolan, R Greenberg, Robert A. Kolvoord

Robert A Kolvoord

No abstract provided.

Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander

Faculty Publications

The direct simulation Monte Carlo (DSMC) scheme is used to study the gas flow under a read/write head positioned nanometers above a moving disk drive platter (the slider bearing problem). In most cases, impressive agreement is found between the particle-based simulation and numerical solutions of the continuum hydrodynamic Reynolds equation which has been corrected for slip. However, at very high platter speeds the gas is far from equilibrium, and the load capacity for the slider bearing cannot be accurately computed from the hydrodynamic pressure.

Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

The Bird algorithm is a computationally efficient method for simulating dilute gas flows. However, due to the relatively large transport coefficients at low densities, high Rayleigh or Reynolds numbers are difficult to achieve by this technique. We present a modified version of the Bird algorithm in which the relaxation processes are enhanced and the transport coefficients reduced, while preserving the correct equilibrium and nonequilibrium fluid properties. The present algorithm is found to be two to three orders of magnitude faster than molecular dynamics for simulating complex hydrodynamical flows.

Variations In Meteorological Elements During Three Minnesota Partial Eclipses, L. E. Newman, J. E. Ljungkull, D. G. Baker, D. L. Ruschy, J. A. Zandlo

Journal of the Minnesota Academy of Science

The University of Minnesota climatological observatory on the St. Paul campus has been in the path of four partial eclipses, ranging from 500/4 to 91 % of totality (the area of the covered sun) since operations began in 1960. Three of the four partial eclipses occurred while the atmosphere at St. Paul was essentially cloud-free. Measurements made during the three partial eclipses include incoming and reflected solar radiation, incoming and outgoing longwave radiation, air and soil temperatures, relative humidity, and wind speed and direction. Of the partial eclipses for which the effects could be measured, only the one of 30 …

Observations Of The 1991 June 11 Solar Flare With Comptel, G Rank, R Diehl, G G. Lichti, V Schonfelder, M Varendorff, B Swanenburg, R Vandijk, D J. Forrest, John R. Macri, Mark L. Mcconnell, M Loomis, James M. Ryan, K Bennett, C Winkler

Space Science Center

The COMPTEL instrument onboard of the Compton Gamma‐Ray Observatory (CGRO) is sensitive to γ‐rays in the energy range from 0.75 to 30 MeV and to neutrons in the energy range from 10 to 100 MeV.

During the period of unexpectedly high solar activity in June 1991, several flares from active region 6659 were observed by COMPTEL. For the flare on June 11, we have analyzed the COMPTEL telescope data, finding strong 2.223 MeV line emission, that declines with a time constant of 11.8 minutes during the satellite orbit in which the flare occurs. It remains visible for at least 4 …