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2002

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Articles 31 - 60 of 94

Full-Text Articles in Astrophysics and Astronomy

X-Ray And Optical Variations In The Classical Be Star Γ Cassiopeia: The Discovery Of A Possible Magnetic Dynamo, Richard D. Robinson, Myron A. Smith, Gregory W. Henry Aug 2002

X-Ray And Optical Variations In The Classical Be Star Γ Cassiopeia: The Discovery Of A Possible Magnetic Dynamo, Richard D. Robinson, Myron A. Smith, Gregory W. Henry

Information Systems and Engineering Management Research Publications

The classical B0.5e star γ Cassiopeia is known to be a unique X-ray source by virtue of its moderate LX (1033 ergs s-1), hard X-ray spectrum, and light curve punctuated by ubiquitous flares and slow undulations. The peculiarities of this star have led to a controversy concerning the origin of these emissions: whether they are from wind infall onto a putative degenerate companion, as in the case of normal Be/X-ray binaries, or from the Be star itself. Recently, much progress has been made to resolve this question: (1) the discovery that γ Cas is a moderately eccentric binary system (P …

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Discovery Of Spectral Variability Of Markarian 421 At Tev Energies, P. T. Reynolds, Et. Al. Aug 2002

Discovery Of Spectral Variability Of Markarian 421 At Tev Energies, P. T. Reynolds, Et. Al.

Physical Sciences Publications

The detection of spectral variability of the γ-ray blazar Mrk 421 at TeV energies is reported. Observations with the Whipple Observatory 10 m γ-ray telescope taken in 2000/2001 revealed exceptionally strong and long-lasting flaring activity. Flaring levels of 0.4-13 times that of the Crab Nebula flux provided sufficient statistics for a detailed study of the energy spectrum between 380 GeV and 8.2 TeV as a function of the flux level. These spectra are well described by a power law with an exponential cutoff: dN/dE ∝ E-αeimg1.gif m-2 s-1 TeV-1. There is no evidence for variation in the cutoff energy with …

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Automated Stellar Spectral Classification And Parameterization For The Masses, Ted Von Hippel, Carlos Allende Prieto, Chris Sneden Aug 2002

Automated Stellar Spectral Classification And Parameterization For The Masses, Ted Von Hippel, Carlos Allende Prieto, Chris Sneden

Publications

Stellar spectroscopic classification has been successfully automated by a number of groups. Automated classification and parameterization work best when applied to a homogeneous data set, and thus these techniques primarily have been developed for and applied to large surveys. While most ongoing large spectroscopic surveys target extragalactic objects, many stellar spectra have been and will be obtained. We briefly summarize past work on automated classification and parameterization, with emphasis on the work done in our group. Accurate automated classification in the spectral type domain and parameterization in the temperature domain have been relatively easy. Automated parameterization in the metallicity domain, …

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Chromospherically Active Stars. Xxi. The Giant, Single-Lined Binaries Hd 89546 And Hd 113816, Francis C. Fekel, Gregory W. Henry, Joel A. Eaton, Julius Sperauskas, Douglas S. Hall Aug 2002

Chromospherically Active Stars. Xxi. The Giant, Single-Lined Binaries Hd 89546 And Hd 113816, Francis C. Fekel, Gregory W. Henry, Joel A. Eaton, Julius Sperauskas, Douglas S. Hall

Information Systems and Engineering Management Research Publications

We have obtained spectroscopy and photometry of the chromospherically active, single-lined spectroscopic binaries HD 89546 and HD 113816. HD 89546 has a circular orbit with a period of 21.3596 days. Its primary has a spectral type of G9 III and is somewhat metal-poor with [Fe/H]~-0.5. HD 113816 has an orbit with a period of 23.6546 and a low eccentricity of 0.022. Its mass function is extremely small, 0.0007 Msolar, consistent with a very low inclination. The primary is a slightly metal-poor K2 III. A decade or more of photometric monitoring with an automatic telescope demonstrates that both systems display brightness …

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Spectral Properties Of He And Heavy Ions In ³He-Rich Solar Flares, Glenn M. Mason, Joseph R. Dwyer Aug 2002

Spectral Properties Of He And Heavy Ions In ³He-Rich Solar Flares, Glenn M. Mason, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

Using advanced instrumentation on the ACE spacecraft, we have conducted a survey of solar energetic particle spectra in ³He-rich events over a broad energy range ∼80 keV nucleon-1 to 15 MeV nucleonˉ¹ during the period 1997 September-2001 March. The spectra of ⁴He and heavy ions (C, N, O, Ne, Mg, Si, S, Ca, Fe) were generally similar over this range but often hardened below ∼1 MeV nucleonˉ¹. In most of the events there was even stronger hardening of the ³He spectrum below ∼1 MeV nucleonˉ¹, leading to an energy-dependent ³He: ⁴He ratio. These observations point to unique and distinct properties …

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Wide Binary Systems And The Nature Of High-Velocity White Dwarfs, Nicole M. Silvestri, Terry D. Oswalt, Suzanne L. Hawley Aug 2002

Wide Binary Systems And The Nature Of High-Velocity White Dwarfs, Nicole M. Silvestri, Terry D. Oswalt, Suzanne L. Hawley

Aerospace, Physics, and Space Science Faculty Publications

We present measured radial velocities and complete space motions for 116 white dwarf stars with M dwarf companions. Thirteen pairs have " halo-like " velocities. According to a recent study by Oppenheimer et al., all these high-velocity white dwarfs should be considered part of the dark matter heavy halo of the Galaxy, based on their kinematics. Based on the near-solar abundance levels of the M dwarf companions, we conclude that 12 of our 13 high-velocity white dwarfs are actually part of the high-velocity tail of the thick disk, rather than the dark matter halo of the Galaxy, in agreement with …

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Metal Abundances And Kinematics Of Bright Metal-Poor Giants Selected From The Lse Survey: Implications For The Metal-Weak Thick Disk, Timothy C. Beers, John S. Drilling, Silvia Rossi, Masashi Chiba, Jaehyon Rhee, Birgit Fṻhrmeister, John E. Norris, Ted Von Hippel Aug 2002

Metal Abundances And Kinematics Of Bright Metal-Poor Giants Selected From The Lse Survey: Implications For The Metal-Weak Thick Disk, Timothy C. Beers, John S. Drilling, Silvia Rossi, Masashi Chiba, Jaehyon Rhee, Birgit Fṻhrmeister, John E. Norris, Ted Von Hippel

Publications

We report medium-resolution (1–2A ˚ ) spectroscopy and broadband (UBV) photometry for a sample of 39 bright stars (the majority of which are likely to be giants) selected as metal-deficient candidates from an objective-prism survey concentrating on Galactic latitudes below |b| = 30, the Luminous Stars Extension (LSE) survey of Drilling & Bergeron. Although the primary purpose of the LSE survey was to select OB stars (hence the concentration on low latitudes), the small number of bright metal-deficient giant candidates noted during this survey provide interesting information on the metal-weak thick disk (MWTD) population. Metal abundance estimates are obtained from …

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Simulations Of The Instability Of The M = 1 Self-Shielding Diocotron Mode In Finite-Length Non-Neutral Plasmas, Grant W. Mason, Ross L. Spencer Aug 2002

Simulations Of The Instability Of The M = 1 Self-Shielding Diocotron Mode In Finite-Length Non-Neutral Plasmas, Grant W. Mason, Ross L. Spencer

Faculty Publications

The "self-shielding" m = 1 diocotron mode in Malmberg-Penning traps has been known for over a decade to be unstable for finite length non-neutral plasmas with hollow density profiles. Early theoretical efforts were unsuccessful in accounting for the exponential growth and/or the magnitude of the growth rate. Recent theoretical work has sought to resolve the discrepancy either as a consequence of the shape of the plasma ends or as a kinetic effect resulting from a modified distribution function as a consequence of the protocol used to form the hollow profiles in experiments. Both of these finite length mechanisms have been …

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Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt Jul 2002

Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt

Dartmouth Scholarship

We analyze the evolution of energy density fluctuations in cosmological scenarios with a mixture of cold dark matter and quintessence, in which the quintessence field is modeled by a constant equation of state. We obtain analytic expressions for the time evolution of the quintessence perturbations in models with light fields. The fluctuations behave analogously to a driven harmonic oscillator, where the driving term arises from the inhomogeneities in the surrounding cosmological fluid. We demonstrate that the homogeneous solution, determined by the initial conditions, is completely subdominant to the inhomogeneous solution for physically realistic scenarios. Thus we show that the cosmic …

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Pumping Or Mixing System Using A Levitating Magnetic Element, Aexandre N. Terentiev Jul 2002

Pumping Or Mixing System Using A Levitating Magnetic Element, Aexandre N. Terentiev

Physics and Astronomy Faculty Patents

A system capable of pumping or mixing relatively warm fluids using a rotating magnetic element or bearing levitated by a cold superconducting element is disclosed. The magnetic element or bearing carries at least one impeller and is placed in a fluid vessel positioned external to the outer wall of a cryostat or other housing for the superconducting element. A separate cooling source thermally linked to the superconducting element provides the necessary cooling to create the desired superconductive effects and induce levitation in the magnetic element or bearing. The outer wall or housing defines a chamber around the cold superconducting element …

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Genetic Optimization Of A Tensegrity Structure, Jaime R. Taylor Jul 2002

Genetic Optimization Of A Tensegrity Structure, Jaime R. Taylor

Physics Faculty Research

Marshall Space Flight Center (MSFC) is charged with developing advanced technologies for space telescopes. The next generation of space optics will be very large and lightweight. Tensegrity structures are built of compressive members (bars), and tensile members (strings). For most materials, the tensile strength of a longitudinal member is larger than its buckling strength; therefore a large stiffness to mass ratio can be achieved by increasing the use of tensile members. Tensegrities are the epitome of lightweight structures, since they take advantage of the larger tensile strength of materials. The compressive members of tensegrity structures are disjoint allowing compact storage …

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The Physical Conditions Within Dense Cold Clouds In Cooling Flows - Ii, Gary J. Ferland, A. C. Fabian, R. M. Johnstone Jul 2002

The Physical Conditions Within Dense Cold Clouds In Cooling Flows - Ii, Gary J. Ferland, A. C. Fabian, R. M. Johnstone

Physics and Astronomy Faculty Publications

This is a progress report on our numerical simulations of conditions in the cold cores of cooling flow condensations. The physical conditions in any non-equilibrium plasma are the result of a host of microphysical processes, many involving reactions that are research areas in themselves. We review the dominant physical processes in our previously published simulations, to clarify those issues that have caused confusion in the literature. We show that conditions in the core of an X-ray-illuminated cloud are very different from those found in molecular clouds, largely because carbon remains substantially atomic and provides powerful cooling through its far infrared …

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Vibrational Modes Of Thin Oblate Clouds Of Charge, Thomas G. Jenkins, Ross L. Spencer Jul 2002

Vibrational Modes Of Thin Oblate Clouds Of Charge, Thomas G. Jenkins, Ross L. Spencer

Faculty Publications

A numerical method is presented for finding the eigenfunctions (normal modes) and mode frequencies of azimuthally symmetric non-neutral plasmas confined in a Penning trap whose axial thickness is much smaller than their radial size. The plasma may be approximated as a charged disk in this limit; the normal modes and frequencies can be found if the surface charge density profile sigma(r) of the disk and the trap bounce frequency profile wz(r) are known. The dependence of the eigenfunctions and equilibrium plasma shapes on nonideal components of the confining Penning trap fields is discussed. The results of the calculation are compared …

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Chasing Solar Eclipses Around The World, Martina B. Arndt Jun 2002

Chasing Solar Eclipses Around The World, Martina B. Arndt

Bridgewater Review

No abstract provided.

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The Warps Survey. Vi. Galaxy Cluster And Source Identifications From Phase I, Eric S. Perlman, Donald J. Horner, Laurence R. Jones, Caleb A. Scharf, Harald Ebeling, Gary Wegner, Matthew Malkan Jun 2002

The Warps Survey. Vi. Galaxy Cluster And Source Identifications From Phase I, Eric S. Perlman, Donald J. Horner, Laurence R. Jones, Caleb A. Scharf, Harald Ebeling, Gary Wegner, Matthew Malkan

Dartmouth Scholarship

We present in catalog form the optical identifications for objects from the first phase of the Wide Angle ROSAT Pointed Survey (WARPS). WARPS is a serendipitous survey of relatively deep, pointed ROSAT observations for clusters of galaxies. The X-ray source detection algorithm used by WARPS is Voronoi Tessellation and Percolation (VTP), a technique which is equally sensitive to point sources and extended sources of low surface brightness. WARPS-I is based on the central regions of 86 ROSAT PSPC fields, covering an area of 16.2 square degrees. We describe here the X-ray source screening and optical identification process for WARPS-I, which …

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Redshift-Distance Survey Of Early-Type Galaxies. I. The Enearc Cluster Sample*, M. Bernardi, M. V. Alonso, L. N. Da Costa, C. N. A. Willmer, A. Wegner Jun 2002

Redshift-Distance Survey Of Early-Type Galaxies. I. The Enearc Cluster Sample*, M. Bernardi, M. V. Alonso, L. N. Da Costa, C. N. A. Willmer, A. Wegner

Dartmouth Scholarship

This paper presents data on the ENEARc subsample of the larger ENEAR survey of nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a D-n-sigma template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg-2, and the angular diameter d(n)), as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to …

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A Determination Of The Local Density Of White Dwarf Stars, Jay B. Holberg, Terry D. Oswalt, Edward M. Sión May 2002

A Determination Of The Local Density Of White Dwarf Stars, Jay B. Holberg, Terry D. Oswalt, Edward M. Sión

Aerospace, Physics, and Space Science Faculty Publications

The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based distance moduli that place them at a distance within 20 pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such well-known systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is largely complete …

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Equilibrium Shapes Of Flat Knots, Ralf Metzler, Andreas Hanke, Paul G. Dommersnes, Yacov Kantor, Mehran Kardar May 2002

Equilibrium Shapes Of Flat Knots, Ralf Metzler, Andreas Hanke, Paul G. Dommersnes, Yacov Kantor, Mehran Kardar

Physics & Astronomy Faculty Publications

The equilibrium shapes of prime and composite knots were studied. It was showed that the topological details of prime knots were localized on a small portion of the larger ring polymer due to self-avoiding effects. The original knot configuration could assume a hierarchy of contracted shape, the dominating one given by one small loop, within this region. For the flat trefoil knot, this hierarchy was studied in detail and corroborated by Monte Carlo simulations.

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Communicator-In-Chief: Presidential Use Of Television Past, Present, And Future, Jenna Wasson May 2002

Communicator-In-Chief: Presidential Use Of Television Past, Present, And Future, Jenna Wasson

Honors Theses

This thesis seeks to determine how television has changed as a communication medium for presidents over the past half century. An evaluation of the evolving ways presidents use television to communicate with and to build support from the American people has been conducted. Presidential communication strategies have been identified by drawing primarily from primary sources written by presidents and White House staff. Television technology and the television audience have changed over the years. Presidents have taken a more pro-active, aggressive role in their efforts to harness television for their own purposes. Why have these changes occurred? What impact have these …

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Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres May 2002

Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres

Physics & Astronomy Faculty Works

Present-day Z-pinch experiments generate 200 TW peak power, 5–10 ns duration x-ray bursts that provide new possibilities to advance radiation science. The experiments support both the underlying atomic and plasma physics, as well as inertial confinement fusion and astrophysics applications. A typical configuration consists of a sample located 1–10 cm away from the pinch, where it is heated to 10–100 eV temperatures by the pinch radiation. The spectrally-resolved sample-plasma absorption is measured by aiming x-ray spectrographs through the sample at the pinch. The pinch plasma thus both heats the sample and serves as a backlighter. Opacitymeasurements with this source are …

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Dust Emission From Active Galactic Nuclei, Maia Nenkova, Željko Ivezić, Moshe Elitzur May 2002

Dust Emission From Active Galactic Nuclei, Maia Nenkova, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

Unified schemes of active galactic nuclei require an obscuring dusty torus around the central source, giving rise to a Seyfert 1 line spectrum for pole-on viewing and Seyfert 2 characteristics in edge-on sources. Although the observed IR is in broad agreement with this scheme, the behavior of the 10 μm silicate feature and the width of the far-IR emission peak remained serious problems in all previous modeling efforts. We show that these problems find a natural explanation if the dust is contained in approximately five to 10 clouds along radial rays through the torus. The spectral energy distributions of …

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Dissipative Heating And Quasar Emission Lines, Mark Bottorff, Gary J. Ferland Apr 2002

Dissipative Heating And Quasar Emission Lines, Mark Bottorff, Gary J. Ferland

Physics and Astronomy Faculty Publications

Recent observations reveal that the profiles of emission lines of active galactic nuclei are too smooth to be produced by discrete thermal (T~104 K) clouds. The lines may also be too bright to be powered by the continuum unless a large covering factor or additional heating mechanisms are present. We have been investigating one possible explanation of these observations, namely, that the clouds are turbulent. This paper focuses on observational effects caused by dissipation of turbulent energy into cloud heating. We find that internal heating can explain these observations. Clouds energized by both the ionizing continuum and …

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Infrared Spectra Of The Subluminous Type Ia Supernova Sn 1999by, Peter Hoflich, Christopher L. Gerardy, Robert A. Fesen, Shoko Sakai Apr 2002

Infrared Spectra Of The Subluminous Type Ia Supernova Sn 1999by, Peter Hoflich, Christopher L. Gerardy, Robert A. Fesen, Shoko Sakai

Dartmouth Scholarship

Near-infrared (NIR) spectra of the subluminous Type Ia supernova SN 1999by are presented that cover the time evolution from about 4 days before to 2 weeks after maximum light. Analysis of these data was accomplished through the construction of an extended set of delayed detonation (DD) models covering the entire range of normal to subluminous SNe Ia. The explosion, light curves, and time evolution of the synthetic spectra were calculated self-consistently for each model, with the only free parameters being the initial structure of the white dwarf and the description of the nuclear burning front during the explosion. From these, …

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Measuring The Speed Of Sound Of Quintessence, Joel K. Erickson, R. R. Caldwell, Paul J. Steinhardt, C. Armendariz-Picon, V. Mukhanov Mar 2002

Measuring The Speed Of Sound Of Quintessence, Joel K. Erickson, R. R. Caldwell, Paul J. Steinhardt, C. Armendariz-Picon, V. Mukhanov

Dartmouth Scholarship

Quintessence, a time-varying energy component that may account for the accelerated expansion of the universe, can be characterized by its equation of state and sound speed. In this paper, we show that if the quintessence density is at least 1% of the critical density at the surface of last scattering the cosmic microwave background anisotropy can distinguish between models whose sound speed is near the speed of light versus near zero, which could be useful in distinguishing competing candidates for dark energy.

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The Quadruple System Μ Orionis: Three-Dimensional Orbit And Physical Parameters, Francis C. Fekel, Colin D. Scarfe, David J. Barlow, William I. Hartkopf, Brian D. Mason, Harold Mcalister Mar 2002

The Quadruple System Μ Orionis: Three-Dimensional Orbit And Physical Parameters, Francis C. Fekel, Colin D. Scarfe, David J. Barlow, William I. Hartkopf, Brian D. Mason, Harold Mcalister

Information Systems and Engineering Management Research Publications

The star μ Orionis is a spectroscopic visual quadruple system in which each visual component is a short-period spectroscopic binary. The visual orbit has a period of 18.644 yr, a high eccentricity of 0.7426, and a high inclination of 962. The visual primary consists of an Am star and probably a G or early K dwarf that orbit each other in a nearly circular orbit with a period of 4.4475858 days. The visual secondary consists of a pair of F5: V stars in a circular orbit with a period of 4.7835361 days. While the masses of the two stars are …

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Tip Of The Red Giant Branch Distances To Ngc 4214, Ugc 685, And Ugc 5456, Jesús Maíz Apellániz, Lucas Cieza, John W. Mackenty Mar 2002

Tip Of The Red Giant Branch Distances To Ngc 4214, Ugc 685, And Ugc 5456, Jesús Maíz Apellániz, Lucas Cieza, John W. Mackenty

Aerospace, Physics, and Space Science Faculty Publications

We have used WFPC2 VRI observations to calculate the distances to three nearby galaxies, NGC 4214, UGC 685, and UGC 5456, using the tip of the red giant branch method. Our values for NGC 4214 (2.94 ± 0.18 Mpc) and UGC 685 (4.79 ± 0.30 Mpc) are the most precise measurements of the distances to these objects ever made. For UGC 5456 the data do not allow us to reach a decisive conclusion since there are two possible solutions, one leading toward a short distance around 3.8 Mpc and another one toward a long distance of 5.6 Mpc or more.

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Modeling The Galactic Center Nonthermal Filaments As Magnetized Wakes, Russell B. Dahlburg, Giorgio Einaudi, Ted N. La Rosa, Steven N. Shore Mar 2002

Modeling The Galactic Center Nonthermal Filaments As Magnetized Wakes, Russell B. Dahlburg, Giorgio Einaudi, Ted N. La Rosa, Steven N. Shore

Faculty Articles

We simulate the Galactic center nonthermal laments as magnetized wakes formed dynamically from amplification of a weak ( tens of l G) global magnetic field through the interaction of molecular clouds with a Galactic center wind. One of the key issues in this cometary model is the stability of the lament against dynamical disruption. Here we show two-dimensional MHD simulations for interstellar conditions that are appropriate for the Galactic center. The structures eventually disrupt through a shear-driven nonlinear instability but maintain coherence for lengths up to 100 times their width as observed. The final instability, which destroys the lament through …

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Theoretical Uncertainties In The Subgiant--Mass Age Relation And The Absolute Age Of Omega Cen, Brian Chaboyer, Lawrence M. Krauss Mar 2002

Theoretical Uncertainties In The Subgiant--Mass Age Relation And The Absolute Age Of Omega Cen, Brian Chaboyer, Lawrence M. Krauss

Dartmouth Scholarship

The theoretical uncertainties in the calibration of the relationship between the subgiant mass and age in metal-poor stars are investigated using a Monte Carlo approach. Assuming that the mass and iron abundance of a subgiant star are known exactly, uncertainties in the input physics used to construct stellar evolution models and isochrones lead to a Gaussian 1 σ uncertainty of ±2.9% in the derived ages. The theoretical error budget is dominated by the uncertainties in the calculated opacities. Observations by Kałużny et al. of detached double-lined eclipsing binary OGLEGC 17 in the globular cluster ω Centauri have found that the …

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Negative Band Gap Bowing In Epitaxial Inas/Gaas Alloys And Predicted Band Offsets Of The Strained Binaries And Alloys On Various Substrates, Gus L. W. Hart, Kwiseon Kim, Alex Zunger Feb 2002

Negative Band Gap Bowing In Epitaxial Inas/Gaas Alloys And Predicted Band Offsets Of The Strained Binaries And Alloys On Various Substrates, Gus L. W. Hart, Kwiseon Kim, Alex Zunger

Faculty Publications

We use pseudopotential theory to provide (1) the band offsets of strained GaAs and InAs on various substrates and (2) the energies Ev(x) of the valence and conduction bands of InxGa1-xAs alloy, as a function of composition. Results are presented for both the bulk alloy and for the alloy strained on InP or GaAs. We predict that while Ex(x) bows downward for relaxed bulk alloys, it bows upward for strained epitaxial alloys. The calculated alloy offsets are used to discuss electron and hole localization in this system.

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Keck Spectroscopy And Imaging Of Faint Galaxies Identified As Microjansky Radio Sources, Nathan D. Roche, James D. Lowenthal, David C. Koo Feb 2002

Keck Spectroscopy And Imaging Of Faint Galaxies Identified As Microjansky Radio Sources, Nathan D. Roche, James D. Lowenthal, David C. Koo

Astronomy: Faculty Publications

We investigate the nature of the faintest radio sources detected in three Very Large Array surveys, to F(8.5 GHz) ∼ 8 μJy. Using the Keck low-resolution imaging spectrograph in BRI and the near-infrared camera in K′ (2.1 μm), we image 51 radio sources, and identify probable optical counterparts for 50. With low-resolution imaging spectroscopy, we successfully acquire new redshifts for 17 sources. Combining these with nine prior redshifts, we can then analyse a sample of 26 sources with spectroscopic redshifts. Based on this sample of 26, we find the largest contribution, about 60 per cent (15), to be from disc …

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