Physical Sciences and Mathematics Commons^™

Plasma Oscillations And Expansion Of An Ultracold Neutral Plasma, Scott D. Bergeson, S. Kulin, T. C. Killian, S. L. Rolston

Faculty Publications

We report the observation of plasma oscillations in an ultracold neutral plasma. With this collective mode we probe the electron density distribution and study the expansion of the plasma as a function of time. For classical plasma conditions, i.e., weak Coulomb coupling, the expansion is dominated by the pressure of the electron gas and is described by a hydrodynamic model. Discrepancies between the model and observations at low temperature and high density may be due to strong coupling of the electrons.

Orbital Period Of The Low‐Inclination Sw Sextantis Star V442 Ophiuchi, D. W. Hoard, John R. Thorstensen, Paula Szkody

Dartmouth Scholarship

V442 Ophiuchi is a low-inclination (noneclipsing) nova-like cataclysmic variable. We have obtained medium resolution (1-3.5 Å), time-resolved optical spectroscopy of this interacting binary star spanning an interval of 4 yr, from 1995 August to 1999 June. Using an Hα radial velocity curve constructed from our combined spectroscopic data sets, we have determined that Porb = 0.1243 days for V442 Oph, breaking the long-standing 1 day alias ambiguity in its orbital period. V442 Oph shares many of the characteristics of the group of cataclysmic variables known as the SW Sextantis stars. Its Doppler tomograms and orbital phase-dependent emission-line behavior, including …

Analytic Inversion Of Emission Lines Of Arbitrary Optical Depth For The Structure Of Supernova Ejecta., R. Ignace, M. A. Hendry

Richard Ignace

We derive a method for inverting emission line profiles formed in supernova ejecta. The derivation assumes spherical symmetry and homologous expansion (i.e., v(r)∝r), is analytic, and even takes account of occultation by a pseudo-photosphere. Previous inversion methods have been developed which are restricted to optically thin lines, but the particular case of homologous expansion permits an analytic result for lines of arbitrary optical depth. In fact, we show that the quantity that is generically retrieved is the run of line intensity Iλ with radius in the ejecta. This result is quite general, and so could be applied to resonance lines, …

The University Of Nebraska At Omaha Center For Space Data Use In Teaching And Learning, Neal Grandgenett, Uno Aviation Institute

Faculty Books and Monographs

UNOAI Report 2000-4

Within the context of innovative coursework and other educational activities, we are proposing the establishment of a University of Nebraska at Omaha Center for the Use of Space Data in Teaching and Learning. This Center will provide an exciting and motivating process for educators at all levels to become involved in professional development and training which engages real life applications of mathematics, science, and technology. The Center will facilitate innovative courses (including online and distance education formats), systematic degree programs, classroom research initiatives, new instructional methods and tools, engaging curriculum materials, and various symposiums. It will involve …

1237+6526_Opt_Lris, Adam J. Burgasser

Publications and Research

No abstract provided.

Redshift-Distance Survey Of Early-Type Galaxies. I. Sample Selection, Properties, And Completeness, L. N. Da Costa, M. Bernardi, M. V. Alonso, G. Wegner

Dartmouth Scholarship

This is the first in a series of papers describing the recently completed all-sky redshift-distance survey of Early-type NEARby galaxies (ENEAR) carried out for peculiar velocity analysis. The sample is divided into two parts and consists of 1607 elliptical and lenticular galaxies with cz ≤ 7000 km s^-1 and with blue magnitudes brighter than m_B = 14.5 (ENEARm) and of galaxies in clusters (ENEARc). Galaxy distances based on the D_n-σ and fundamental plane (FP) relations are now available for 1359 and 1107 ENEARm galaxies, respectively, with roughly 80% based on new data gathered by …

Enear Redshift-Distance Survey: Cosmological Constraints, Stefano Borgani, Mariangela Bernardi, Luiz N. Da Costa, Gary Wegner

Dartmouth Scholarship

We present an analysis of the ENEAR sample of peculiar velocities of field and cluster elliptical galaxies, obtained with Dn-σ distances. We use the velocity correlation function ψ1(r) to analyze the statistics of the field object's velocities, while the analysis of the cluster data is based on the estimate of their rms peculiar velocity Vrms. The results are compared with predictions from cosmological models using linear theory. The statistics of the model velocity field is parameterized by the amplitude η8 = σ8Ω and by the shape parameter Γ of the cold dark matter-like power spectrum. …

The Primordial Helium Abundance: Toward Understanding And Removing The Cosmic Scatter In The Dy/Dz Relation, D. R. Ballantyne, Gary J. Ferland, P. G. Martin

Physics and Astronomy Faculty Publications

We present results from photoionization models of low-metallicity H II regions. These nebulae form the basis for measuring the primordial helium abundance. Our models show that the helium ionization correction factor (ICF) can be nonnegligible for nebulae excited by stars with effective temperatures larger than 40,000 K. Furthermore, we find that when the effective temperature rises to above 45,000 K, the ICF can be significantly negative. This result is independent of the choice of stellar atmosphere. However, if an H II region has an [O III] λ5007/[O I] λ6300 ratio greater than 300, then our models show that, regardless of …

Electronic Structure Of Bas And Boride Iii-V Alloys, Gus L. W. Hart, Alex Zunger

Faculty Publications

Boron arsenide, the typically ignored member of the Group-III–V arsenide series BAs-AlAs-GaAs-InAs is found to resemble silicon electronically: its Γ conduction-band minimum is p-like (Γ15), not s-like (Γ1c), it has an X1c-like indirect band gap, and its bond charge is distributed almost equally on the two atoms in the unit cell, exhibiting nearly perfect covalency. The reasons for these are tracked down to the anomalously low atomic p orbital energy in the boron and to the unusually strong s–s repulsion in BAs relative to most other Group-III–V compounds. We find unexpected valence-band offsets of BAs with respect to GaAs and …

Grb 991216 Joins The Jet Set: Discovery And Monitoring Of Its Optical Afterglow, J. P. Halpern, R. Uglesich, N. Mirabal, S. Kassin, J. Thorstenson, W. C. Keel, A. Diercks, J. S. Bloom, F. Harrison, J. Mattox, M. Eracleous

Dartmouth Scholarship

The optical light curve of the energetic γ-ray burst GRB 991216 is consistent with jetlike behavior in which a power-law decay steepens from t^-1.22+-0.04 at early times to t^{-1.53 +- 0.05} in a gradual transition at around 2 days. The derivation of the late-time decay slope takes into account the constant contribution of a host or intervening galaxy, which was measured 110 days after the event at R = 24.56 +- 0.14, although the light curve deviates from a single power law whether or not a constant term is included. The early-time spectral energy distribution of the afterglow …

Search For Transits Of A Short-Period, Sub-Saturn Extrasolar Planet Orbiting Hd 46375, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Precise brightness measurements of HD 46375 have been acquired with an automatic telescope to search for transits of its short-period, sub-Saturn extrasolar planet. Transits of the companion do not occur, indicating that the inclination of the orbit i is less than 83° and sin i is less than 0.992. This upper limit on sin i still preserves the possibility that the mass of the planet is less than Saturn's. Analysis of the photometry for HD 46375 reveals no photometric variability larger than 0.0001 ± 0.0002 mag at the orbital period of the planet. This effectively eliminates starspots and stellar pulsations …

Long‐Term Vri Photometry Of 89 (V441) Herculis, John R. Percy, Akos G. Bakos, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We report 4500 days of VRI photometry of the peculiar high‐latitude F2 Ibe star 89 (V441) Herculis, from a robotic photometric telescope, and the American Association of Variable Star Observers photoelectric photometry program. We detected the previously known photometric period of 65.2 days and also the 283 day period which was previously observed in radial velocity only and ascribed to binarity. We have determined the relative amplitudes and phases of light, color, and radial velocity for each period. The 65.2 day period appears to be due to pulsation—probably radial. The nature of the 283 day variations is unclear; we discuss …

The Peculiar Type Ic Supernova 1997ef: Another Hypernova, Koichi Iwamoto, Takayoshi Nakamura, Ken’Ichi Nomoto, Paolo A. Mazzali, I. John Danziger, Peter Garnavich, Robert Kirshner, Saurabh Jha, David Balam, John Thorstensen

Dartmouth Scholarship

SN 1997ef has been recognized as a peculiar supernova from its light curve and spectral properties. The object was classified as a Type Ic supernova (SN Ic) because its spectra were dominated by broad absorption lines of oxygen and iron, lacking any clear signs of hydrogen or helium line features. The light curve is very different from that of previously known SNe Ic, showing a very broad peak and a slow tail. The strikingly broad line features in the spectra of SN 1997ef, which were also seen in the hypernova SN 1998bw, suggest the interesting possibility that SN 1997ef may …

64 Orionis: Three-Dimensional Orbit And Physical Parameters, Colin D. Scarfe, David J. Barlow, Francis C. Fekel

Information Systems and Engineering Management Research Publications

We have obtained radial velocities of the components of the short-period subsystem of the B-type triple star 64 Orionis, covering a full cycle of the long-period orbit since the date of our earlier paper by Fekel & Scarfe. We use all of our radial velocities, together with available speckle interferometry, to derive a three-dimensional orbit for the long-period system. The system has orbital periods of 14.57213 days and 12.98 yr. We also determine spectroscopically a magnitude difference at 4500 Å of 1.0 ± 0.1 between the components of the close pair. Although radial velocities of the third component continue to …

A Spectroscopic Redshift For The Cl 0024+16 Multiple Arc System: Implications For The Central Mass Distribution, Tom Broadhurst, Xiaosheng Huang, Brenda Frye, Richard Ellis

Physics and Astronomy

We present a spectroscopic redshift of z = 1.675 for the well-known multiply lensed system of arcs seen in the z = 0.39 cluster Cl 0024+16. In contrast to earlier work, we find that the lensed images are accurately reproduced by a projected mass distribution which traces the locations of the brightest cluster elliptical galaxies, suggesting that the most significant minima of the cluster potential are not dynamically erased. The averaged mass profile is shallow and consistent with predictions of recent numerical simulations. The source redshift enables us to determine an enclosed cluster mass of M(<100 kpc h-1) = …

Infrared Classification Of Galactic Objects, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

Unbiased analysis shows that IRAS data reliably differentiate between the early and late stages of stellar evolution because objects at these stages clearly segregate in infrared color-color diagrams. Structure in these diagrams is primarily controlled by the density distribution of circumstellar dust. The density profile around older objects is the steepest, declining as r^-2, while young objects have profiles that vary as r^-3/2 and flatter. The different density profiles reflect the different dynamics that govern the different environments. Our analysis also shows that high-mass star formation is strongly concentrated within ~5 kpc around the Galactic center, in …

The Warps Survey. Iii. The Discovery Of An X‐Ray Luminous Galaxy Cluster At Z = 0.833 And The Impact Of X‐Ray Substructure On Cluster Abundance Measurements, H. Ebeling, L. R. Jones, E. Perlman, C. Scharf, D. Horner, G. Wegner

Dartmouth Scholarship

The Wide Angle ROSAT Pointed Survey team reviews the properties and history of the discovery of Cl J0152.7-1357, an X-ray luminous, rich cluster of galaxies at a redshift of z = 0.833. At LX = 8 × 1044h ergs s-1 (0.5-2.0 keV) Cl J0152.7-1357 is the most X-ray luminous cluster known at redshifts z > 0.55. The high X-ray luminosity of the system suggests that massive clusters may begin to form at redshifts considerably greater than unity. This scenario is supported by the high degree of optical and X-ray substructure in Cl J0152.7-1357, which is similarly complex as that …

Dust Emissions From High-Redshift Qsos, C L. Carilli, K M. Bertoldi, K M. Menten, M P. Rupen, E Kreysa, Xiaohui Fan, Michael A. Strauss, Donald P. Schneider, A Bertarini, Min S. Yun, R Zylka

Min S. Yun

We present detections of emission at 250 GHz (1.2 mm) from two high-redshift QSOs from the Sloan Digital Sky Survey sample using the bolometer array at the IRAM 30 m telescope. The sources are SDSSp 015048.831004126.2 at z = 3.7 and SDSSp J033829.311002156.3 at z = 5.0; the latter is the third highest redshift QSO known and the highest redshift millimeter-emitting source yet identified. We also present deep radio continuum imaging of these two sources at 1.4 GHz using the Very Large Array. The combination of centimeter and millimeter observations indicate that the 250 GHz emission is most likely thermal …

A Single Circumbinary Disk In The Hd 98800 Quadruple System, D. W. Koerner, Eric L.N. Jensen, K. L. Cruz, T. B. Guild, K. Gultekin

Physics & Astronomy Faculty Works

We present subarcsecond thermal infrared imaging of HD 98800, a young quadruple system composed of a pair of low-mass spectroscopic binaries separated by 0".8 (38 AU), each with a K-dwarf primary. Images at wavelengths ranging from 5 to 24.5 mu m show unequivocally that the optically fainter binary, HD 98800B, is the sole source of a comparatively large infrared excess on which a silicate emission feature is superposed. The excess is detected only at wavelengths of 7.9 mu m and longer, peaks at 25 mu m, and has a best-fit blackbody temperature of 150 K, indicating that most of the …

Hot Star Polarimetric Variability And The Nature Of Wind Inhomogeneities., J. C. Brown, R. Ignace, J. P. Cassinelli

Richard Ignace

The problem is addressed of how much hot star polarisation variability can result from density redistribution processes within the wind as opposed to localised enhancement of stellar mass loss rate, such as ejections of wind inhomogeneities. For optically thin electron scattering, we present a theory for the relative polarisation arising from particle redistribution and consider several specific cases relevant to interpreting observations of wind variability. It is concluded that, allowing for partial cancellation of the contribution from compressed and evacuated regions, density redistribution internal to the wind can produce significant polarisation but only for processes that redistribute wind material over …

The Size Distribution Of Dust Toward Hd 210121 As Determined From Extinction, Kristen A. Larson, M. J. Wolff, W. G. Roberge, D. C. B. Whittet, L. He

Physics & Astronomy

Several observations suggest that the molecular cloud toward HD 210121 contains an enhanced relative abundance of small dust grains. In particular, the value of the ratio of total-to-selective extinction (R_v) is unusually low. In this paper, we estimate the size distribution of dust grains in this line of sight from the extinction curve observed in the near-infrared through the ultraviolet. We use the maximum entropy method (MEM) to find the smoothest possible size distribution consistent within a χ² confidence level fit to the extinction data. While MEM has been shown to be a powerful tool in …

Properties Of Dust Grains In Planetary Nebulae. I. The Ionized Region Of Ngc 6445, Peter A. M. Van Hoof, Griet C. Van De Steene, Douwe A. Beintema, P. G. Martin, Stuart R. Pottasch, Gary J. Ferland

Physics and Astronomy Faculty Publications

One of the factors influencing the spectral evolution of a planetary nebula is the fate of the dust grains that are emitting the infrared continuum. Several processes have been proposed that either destroy the grains or remove them from the ionized region. To test whether these processes are effective, we study new infrared spectra of the evolved nebula NGC 6445. These data show that the thermal emission from the grains is very cool and has a low flux compared to Hβ. A model of the ionized region is constructed, using the photoionization code CLOUDY 90.05. Based on this model, we …

Average Energy Flow Of Optical Pulses In Dispersive Media, Scott Glasgow, Michael Ware, Justin Peatross

Faculty Publications

The arrival time of a light pulse at a point in space is defined using a time expectation integral over the Poynting vector. The delay between pulse arrival times at two distinct points is shown to consist of two parts: a spectral superposition of group delays (inverse of group velocity) and a delay due to spectral reshaping via absorption or amplification. The result provides a context wherein group velocity is always meaningful even for broad band pulses and when the group velocity is superluminal or negative. The result imposes luminality on sharply defined pulses.

Neutral Hydrogen Distribution In Merging Galaxies: Differences Between Stellar And Gaseous Tidal Morphologies, J E. Hibbard, W D. Vacca, Min S. Yun

Min S. Yun

As part of several H I synthesis-mapping studies of merging galaxies, we have mapped the tidal gas in the three disk-disk merger systems Arp 157 (NGC 520), Arp 220, and Arp 299 (NGC 3690). These systems differ from the majority of the mergers mapped in H I in that their stellar and gaseous tidal features do not coincide. In particular, they exhibit large stellar tidal features with little if any accompanying neutral gas and large gas-rich tidal features with little if any accompanying starlight. On smaller scales, there are striking anticorrelations in which the gaseous and stellar tidal features appear …

An Interpretation Of Martian Thermospheric Waves Based On Analysis Of A General Circulation Model, Manoj Joshi, Jeffery Hollingsworth, Robert Haberle, Alison Bridger

Faculty Publications, Meteorology and Climate Science

Planetary‐scale longitudinal variations in density observed by the Mars Global Surveyor accelerometer in the 125 km region can be qualitatively reproduced by the NASA Ames Mars general circulation model in the 80 km altitude region, but only when locations having specific local times are used in the analysis. If the model results are averaged over all local times, the high‐altitude longitudinal variations nearly disappear, leaving only a small stationary wave 1 pattern, consistent with theory and previous modeling studies. This analysis suggests that the observed wavelike structures are a result of sampling tidal modes at a limited range of local …

Infrared Spectroscopy Of Symbiotic Stars. I. Orbits For Well-Known S-Type Systems, Francis C. Fekel, Richard Joyce, Kenneth H. Hinkle, Michael F. Skrutskie

Information Systems and Engineering Management Research Publications

First results are reported for a program of monitoring symbiotic-star velocities in the 1.6 μm region with infrared-array technology. Infrared radial velocities have been used to determine single-lined spectroscopic orbits for six well-known symbiotic stars, EG And, T CrB, CI Cyg, BX Mon, RS Oph, and AG Peg. The new orbits are in general agreement with previous orbits derived from optical velocities. From the combined optical and infrared velocities improved orbital elements for the six systems have been determined. Each of the orbital periods has been determined solely from the radial-velocity data. With the addition of our new velocities, the …

Long‐Term Vri Photometry Of Ρ Cassiopeiae, John R. Percy, David L. Kolin, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We report over 5700 days (15 years) of VRI photometry of the yellow hypergiant variable star ρ Cassiopeiae. The V−I color curve is generally in phase with the V light curve on timescales of a few hundred days, but there is a 4000 day variation in V−I which is absent from the light curve. The approximate ratio of Δ(V−I)/ΔV is 0.46. The most conspicuous period in the light curve, in the autocorrelation diagram, and in the power spectrum is about 820 days. Less significant periods of 380, 510, and 645 days also appear in the power spectrum, …

Photometric And Ca Ii H And K Spectroscopic Variations In Nearby Sun-Like Stars With Planets. Iii., Gregory W. Henry, Sallie L. Baliunas, Robert A. Donahue, Francis C. Fekel, Willie Soon

Information Systems and Engineering Management Research Publications

We present the results of an analysis of time-series photometry, Ca II H and K spectrophotometry, and high-dispersion visible spectra of nine nearby Sun-like stars recently identified as having planets. For the six stars whose presumed planets have orbital periods of less than 4 months (τ Boo, 51 Peg, υ And, ρ¹ Cnc, ρ CrB, and 70 Vir), sine-curve fits to the photometric data show no variations with semiamplitude greater than 1 or 2 parts in 10⁴. Photometric variations in 47 UMa are similarly small, although our photometric data of this star are slightly affected by variability …

Testing Of The New Usgs K Index Algorithm At Bear Lake, Ariel O. Acebal

All U.S. Government Documents (Utah Regional Depository)

The K index was developed by Bartels in 1939 as an estimate of the level of geomagnetic activity caused by the Sun. This index was computed manually every three hours at geomagnetic observatories using the magnetic traces of the surface planetary magnetic field. In 1991, the International Association of Geomagnetism and Aeronomy approved four additional methods to compute the K index; all of them were computer algorithms. One of the approved methods, the Wilson code, recently underwent some modifications. The new algorithm is now part of a Windows-based computer program being developed by the United States Geological Survey (USGS). After …

Spectroscopy And Orbital Periods Of The Old Novae V533 Herculis, V446 Herculis And X Serpentis, J. R. Thorstensen, C. J. Taylor

Dartmouth Scholarship

We report spectroscopic orbital periods of 0.147 d (= 3.53 h) for V533 Her, 0.207 d (= 4.97 h) for V446 Her and 1.478 d for X Ser. V533 Her (Nova Herculis 1963) shows absorption features in its He i and Balmer lines which appear only in a limited range of orbital phase, suggesting that it is a low-inclination SW Sextantis star. V446 Her is unusual in that it has started normal dwarf nova eruptions after a nova outburst, but we find nothing else unusual about it — in particular, a distance estimate based on its dwarf nova outbursts agrees …