Open Access. Powered by Scholars. Published by Universities.®

Astrophysics and Astronomy Commons™

Open Access. Powered by Scholars. Published by Universities.®

Discipline
Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 5611 - 5640 of 8864

Full-Text Articles in Astrophysics and Astronomy

High Order Finite Difference Methods With Subcell Resolution For Advection Equations With Stiff Source Terms, Wei Wang, Chi-Wang Shu, H.C. Yee, Björn Sjögreen Sep 2011

High Order Finite Difference Methods With Subcell Resolution For Advection Equations With Stiff Source Terms, Wei Wang, Chi-Wang Shu, H.C. Yee, Björn Sjögreen

United States National Aeronautics and Space Administration: Publications

A new high order finite-difference method utilizing the idea of Harten ENO subcell resolution method is proposed for chemical reactive flows and combustion. In reaction problems, when the reaction time scale is very small, e.g., orders of magnitude smaller than the fluid dynamics time scales, the governing equations will become very stiff. Wrong propagation speed of discontinuity may occur due to the underresolved numerical solution in both space and time. The present proposed method is a modified fractional step method which solves the convection step and reaction step separately. In the convection step, any high order shock-capturing method can be …

Go to article

Early Magnetic B-Type Stars: X-Ray Emission And Wind Properties., L. Oskinova, H. Todt, Richard Ignace, J. Brown, J. Cassinelli, W.-R. Hamann Sep 2011

Early Magnetic B-Type Stars: X-Ray Emission And Wind Properties., L. Oskinova, H. Todt, Richard Ignace, J. Brown, J. Cassinelli, W.-R. Hamann

ETSU Faculty Works

We present a comprehensive study of X-ray emission by, and wind properties of, massive magnetic early B-type stars. Dedicated XMM–Newton observations were obtained for three early-type B-type stars, ξ1 CMa, V2052 Oph and ζ Cas, with recently discovered magnetic fields. We report the first detection of X-ray emission from V2052 Oph and ζ Cas. The latter is one the softest X-ray sources among the early-type stars, while the former is one of the X-ray faintest. The observations show that the X-ray spectra of our programme stars are quite soft with the bulk of X-ray emitting material having a temperature of …

Go to article

Multiwavelength Observations Of The Very High Energy Blazar 1es 2344+514, P. T. Reynolds, Et. Al. Sep 2011

Multiwavelength Observations Of The Very High Energy Blazar 1es 2344+514, P. T. Reynolds, Et. Al.

Physical Sciences Publications

Multiwavelength observations of the high-frequency-peaked blazar 1ES 2344+514 were performed from 2007 October to 2008 January. The campaign represents the first contemporaneous data on the object at very high energy (VHE, E >100 GeV) γ-ray, X-ray, and UV energies. Observations with VERITAS in VHE γ-rays yield a strong detection of 20σ with 633 excess events in a total exposure of 18.1 hr live time. A strong VHE γ-ray flare on 2007 December 7 is measured at F(>300 GeV) = (6.76 ± 0.62) × 10–11 photons cm–2 s–1, corresponding to 48% of the Crab Nebula flux. Excluding this flaring episode, …

Go to article

Energy Spectrum Of Energetic Particles Accelerated By Shock Waves: From Focused Transport To Diffusive Acceleration, Pingbing Zuo, Ming Zhang, Konstantin V. Gamayunov, Hamid K. Rassoul, Xi Luo Sep 2011

Energy Spectrum Of Energetic Particles Accelerated By Shock Waves: From Focused Transport To Diffusive Acceleration, Pingbing Zuo, Ming Zhang, Konstantin V. Gamayunov, Hamid K. Rassoul, Xi Luo

Aerospace, Physics, and Space Science Faculty Publications

The focused transport equation (FTE) includes all the necessary physics for modeling the shock acceleration of energetic particles with a unified description of first-order Fermi acceleration, shock drift acceleration, and shock surfing acceleration. It can treat the acceleration and transport of particles with an anisotropic distribution. In this study, the energy spectrum of pickup ions accelerated at shocks of various obliquities is investigated based on the FTE. We solve the FTE by using a stochastic approach. The shock acceleration leads to a two-component energy spectrum. The low-energy component of the spectrum is made up of particles that interact with shock …

Go to article

Cluster Observations Of Bow Shock Energetic Ion Transport Through The Magnetosheath Into The Cusp, K. J. Trattner, S. M. Petrinec, S. A. Fuselier, K. Nykyri, E. Kronberg Sep 2011

Cluster Observations Of Bow Shock Energetic Ion Transport Through The Magnetosheath Into The Cusp, K. J. Trattner, S. M. Petrinec, S. A. Fuselier, K. Nykyri, E. Kronberg

Publications

The observation of energetic particles by polar orbiting satellites in the magnetospheric cusp resulted in a controversy about their source region. It has been suggested that these cusp energetic particles (CEP) with significant fluxes from magnetosheath energies up to several hundred keV/e are accelerated locally in the cusp by the turbulence found in cusp diamagnetic cavities (CDC). As an alternative to the local acceleration region, the quasi‐parallel shock is successful as a source region for CEP events. Energetic ions accelerated at the bow shock can be transported downstream and enter the cusp along newly reconnected field lines. Composition and energy …

Go to article

Probing The Cosmos With Light And Gravity: Multi-Messenger Astronomy In The Gravitational Wave Era, Shane L. Larson Sep 2011

Probing The Cosmos With Light And Gravity: Multi-Messenger Astronomy In The Gravitational Wave Era, Shane L. Larson

Colloquia and Seminars

No abstract provided.

Go to article

The Initial Mass Function And Disk Frequency Of The Ρ Ophiuchi Cloud: An Extinction-Limited Sample, Kristen Erickson, Bruce Wilking, Michael Meyer, John Robinson, Lauren Stephenson Sep 2011

The Initial Mass Function And Disk Frequency Of The Ρ Ophiuchi Cloud: An Extinction-Limited Sample, Kristen Erickson, Bruce Wilking, Michael Meyer, John Robinson, Lauren Stephenson

Physics Faculty Works

We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of candidate young stars covering 1.3 deg2 of the ρ Ophiuchi star-forming region. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys are biased toward particular stages of stellar evolution and are not optimal for studies of the disk frequency and initial mass function. We have obtained over 300 optical spectra to help identify 135 association members based on the presence of Hα in emission, lithium absorption, X-ray emission, a mid-infrared excess, a common proper motion, reflection nebulosity, and/or …

Go to article

Particle Transport And Stochastic Acceleration In The Giant Lobes Of Centaurus A, Stephen O'Sullivan Sep 2011

Particle Transport And Stochastic Acceleration In The Giant Lobes Of Centaurus A, Stephen O'Sullivan

Conference papers

The conditions within the giant lobes of Centaurus A are reviewed in light of recent radio and γ‐ray observations. Data from WMAP and ground‐based telescopes in conjunction with measurements from Fermi‐LAT constrain the characteristic field strength and the maximum electron energy. The implications for the transport of energetic particles are discussed in terms of residence times and cooling times within the lobes. Acceleration of electrons and UHECR via the second order Fermi mechanism is discussed.

Go to article

Hubble Space Telescope Transmission Spectroscopy Of The Exoplanet Hd 189733b: High-Altitude Atmospheric Haze In The Optical And Near-Ultraviolet With Stis, David K. Sing, Frederic Pont, Suzanne Aigrain, David Charbonneau, Jean-Michel Désert, Neale P. Gibson, Ronald Gilliland, Wolfgang Hayek, Gregory W. Henry, Heather Knutson, Alain Lecavelier Des Etangs, Tsevi Mazeh, Avi Shporer Sep 2011

Hubble Space Telescope Transmission Spectroscopy Of The Exoplanet Hd 189733b: High-Altitude Atmospheric Haze In The Optical And Near-Ultraviolet With Stis, David K. Sing, Frederic Pont, Suzanne Aigrain, David Charbonneau, Jean-Michel Désert, Neale P. Gibson, Ronald Gilliland, Wolfgang Hayek, Gregory W. Henry, Heather Knutson, Alain Lecavelier Des Etangs, Tsevi Mazeh, Avi Shporer

Information Systems and Engineering Management Research Publications

We present Hubble Space Telescope (HST) optical and near-ultraviolet transmission spectra of the transiting hot Jupiter HD 189733b, taken with the repaired Space Telescope Imaging Spectrograph (STIS) instrument. The resulting spectra cover the range 2900–5700 Å and reach per exposure signal-to-noise ratio levels greater than 11 000 within a 500-Å bandwidth. We used time series spectra obtained during two transit events to determine the wavelength dependence of the planetary radius and measure the exoplanet’s atmospheric transmission spectrum for the first time over this wavelength range. Our measurements, in conjunction with existing HST spectra, now provide a broad-band transmission spectrum covering …

Go to article

Veritas Observations Of The Tev Binary Ls I+61 Degrees 303 During 2008-2010, P. T. Reynolds, Et. Al. Sep 2011

Veritas Observations Of The Tev Binary Ls I+61 Degrees 303 During 2008-2010, P. T. Reynolds, Et. Al.

Physical Sciences Publications

We present the results of observations of the TeV binary LS I +61° 303 with the VERITAS telescope array between 2008 and 2010, at energies above 300 GeV. In the past, both ground-based gamma-ray telescopes VERITAS and MAGIC have reported detections of TeV emission near the apastron phases of the binary orbit. The observations presented here show no strong evidence for TeV emission during these orbital phases; however, during observations taken in late 2010, significant emission was detected from the source close to the phase of superior conjunction (much closer to periastron passage) at a 5.6 standard deviation (5.6σ) post-trials …

Go to article

Tev And Multi-Wavelength Observations Of Mrk 421 In 2006-2008, P. T. Reynolds, Et. Al. Sep 2011

Tev And Multi-Wavelength Observations Of Mrk 421 In 2006-2008, P. T. Reynolds, Et. Al.

Physical Sciences Publications

We report on TeV γ-ray observations of the blazar Mrk 421 (redshift of 0.031) with the VERITAS observatory and the Whipple 10 m Cherenkov telescope. The excellent sensitivity of VERITAS allowed us to sample the TeV γ-ray fluxes and energy spectra with unprecedented accuracy where Mrk 421 was detected in each of the pointings. A total of 47.3 hr of VERITAS and 96 hr of Whipple 10 m data were acquired between 2006 January and 2008 June. We present the results of a study of the TeV γ-ray energy spectra as a function of time and for different flux levels. …

Go to article

Nicmos Polarimetry Of "Polar-Scattered" Seyfert 1 Galaxies, Daniel P. Batcheldor, Andrew Edward Robinson, David J. Axon, Stuart Young, S Quinn, James E. Smith, James H. Hough, David M. Alexander Sep 2011

Nicmos Polarimetry Of "Polar-Scattered" Seyfert 1 Galaxies, Daniel P. Batcheldor, Andrew Edward Robinson, David J. Axon, Stuart Young, S Quinn, James E. Smith, James H. Hough, David M. Alexander

Aerospace, Physics, and Space Science Faculty Publications

The nuclei of Seyfert 1 galaxies exhibit a range of optical polarization characteristics that can be understood in terms of two scattering regions producing orthogonal polarizations: an extended polar scattering region (PSR) and a compact equatorial scattering region (ESR), located within the circum-nuclear torus. Here we present NICMOS 2.0 μm imaging polarimetry of six "polar-scattered" Seyfert 1 (S1) galaxies, in which the PSR dominates the optical polarization. The unresolved nucleus (<058) is significantly polarized in only three objects, but five of the six exhibit polarization in a 058-15 circum-nuclear annulus. In Fairall 51 and ESO 323-G077, the polarization position angle at 2 μm (θ2 μm) is consistent with the average for the optical spectrum(θv), implying that the nuclear polarization is dominated by polar scattering at both wavelengths. The same is probably true for NGC3227. In both NGC 4593 and Mrk 766, there is a large difference between θ2 μm and θv off-nucleus, where polar scattering is expected to dominate. This may be due to contamination by interstellar polarization in NGC4593, but there is no clear explanation in the case of the strongly polarized Mrk766. Lastly, in Mrk1239, a large change (60°) in θ2 μm between the nucleus and the annulus indicates that the unresolved nucleus and its immediate surroundings have different polarization states at 2μm, which we attribute to the ESR and PSR, respectively. A further implication is that the source of the scattered 2 μm emission in the unresolved nucleus is the accretion disk, rather than torus hot dust emission.

Go to article

An Effect Of Perpendicular Diffusion On The Anisotropy Of Solar Energetic Particles From Unconnected Sources, Gang Qin, H. Q. He, Ming Zhang Sep 2011

An Effect Of Perpendicular Diffusion On The Anisotropy Of Solar Energetic Particles From Unconnected Sources, Gang Qin, H. Q. He, Ming Zhang

Aerospace, Physics, and Space Science Faculty Publications

Recently, Tan and coworkers studied the 2001 September 24 solar energetic particle (SEP) event observed by the Wind spacecraft at 1AU and found that there is a counter-streaming particle beam with a deep depression of flux at 90° pitch angle during the beginning of the event. They suggested that it is a result of a reflecting boundary at some distance outside of 1AU. While this scenario could be true under some specific configuration of an interplanetary magnetic field, in this paper we offer another possible explanation. We simulated the SEP event by solving the five-dimensional focused transport equation numerically for …

Go to article

Ferromagnetic Resonance On Ni Nanowire Arrays, Mircea Chipara, Ralph Skomski, Roger D. Kirby, David J. Sellmyer Sep 2011

Ferromagnetic Resonance On Ni Nanowire Arrays, Mircea Chipara, Ralph Skomski, Roger D. Kirby, David J. Sellmyer

Physics & Astronomy Faculty Publications

Ferromagnetic resonance investigations on Ni nanowires are reported. The angular dependence of the resonance line position is analyzed within a thermodynamic approach that includes shape anisotropy (ellipsoids of revolution), magnetocrystalline anisotropies (cubic and uniaxial), and dipole–dipole interactions. The results are supported by hysteresis loops, obtained on the same sample.

Go to article

The Unusual Vertical Mass Distribution Of Ngc 4013 Seen Through The Spitzer Survey Of Stellar Structure In Galaxies (S4g)., Sebastien Comeron, Bruce G. Elmegreen, Johan H. Knapen, Kartik Sheth, Joannah L. Hinz, Michael W. Regan, Armando Gil De Paz, Juan Carlos Munoz-Mateos, Karin Menendez-Delmestre, Mark Seibert, Taehyun Kim, Trisha Mizusawa, Eija Laurikainen, Heikki Salo, Jarkko Laine, E. Athanassoula, Albert Bosma, Ronald J. Buta, Dimitri A. Gadotti, Luis C. Ho, Benne W. Holwerda, Eva Schinnerer, Dennis Zaritsky Sep 2011

The Unusual Vertical Mass Distribution Of Ngc 4013 Seen Through The Spitzer Survey Of Stellar Structure In Galaxies (S4g)., Sebastien Comeron, Bruce G. Elmegreen, Johan H. Knapen, Kartik Sheth, Joannah L. Hinz, Michael W. Regan, Armando Gil De Paz, Juan Carlos Munoz-Mateos, Karin Menendez-Delmestre, Mark Seibert, Taehyun Kim, Trisha Mizusawa, Eija Laurikainen, Heikki Salo, Jarkko Laine, E. Athanassoula, Albert Bosma, Ronald J. Buta, Dimitri A. Gadotti, Luis C. Ho, Benne W. Holwerda, Eva Schinnerer, Dennis Zaritsky

Faculty and Staff Scholarship

NGC 4013 is a nearby Sb edge-on galaxy known for its “prodigious” H i warp and its “giant” tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6μm images from the Spitzer Survey of Stellar Structure in Galaxies. We find evidence for NGC …

Go to article

The 25 Parsec Local White Dwarf Population, Jerry B. Holberg, Terry D. Oswalt, Edward M. Sion, George P. Mccook Sep 2011

The 25 Parsec Local White Dwarf Population, Jerry B. Holberg, Terry D. Oswalt, Edward M. Sion, George P. Mccook

Publications

We have extended our detailed survey of the local white dwarf population from 20 pc to 25 pc, effectively doubling the sample volume, which now includes 232 stars. In the process new stars within 20 pc have been added, a more uniform set of distance estimates as well as improved spectral and binary classifications are available. The present 25 pc sample is estimated to be about 68% complete (the corresponding 20 pc sample is now 86% complete). The space density of white dwarfs is unchanged at 4.8 ± 0.5 x 10-3 pc-3. This new study includes a white dwarf mass …

Go to article

Compact Binaries In Star Clusters - Ii. Escapers And Detection Rates, J. M.B. Downing, M. J. Benacquista, M. Giersz, R. Spurzem Sep 2011

Compact Binaries In Star Clusters - Ii. Escapers And Detection Rates, J. M.B. Downing, M. J. Benacquista, M. Giersz, R. Spurzem

Physics & Astronomy Faculty Publications

We use a self-consistent Monte Carlo treatment of stellar dynamics to investigate black hole binaries that are dynamically ejected from globular clusters in order to determine if they will be gravitational wave sources. We find that many of the ejected binaries initially have short periods and will merge within a Hubble time due to gravitational wave radiation. Thus they are potential sources for ground-based gravitational wave detectors. We estimate the yearly detection rate for current and advanced ground-based detectors and find an enhancement over the rate predicted for binaries produced by pure stellar evolution in galactic fields. We conclude that, …

Go to article

Whispers From The Cosmos: The Dawn Of Gravitational Wave Astronomy, Shane L. Larson Aug 2011

Whispers From The Cosmos: The Dawn Of Gravitational Wave Astronomy, Shane L. Larson

Public Talks

No abstract provided.

Go to article

Galaxies: Island Universes In The Cosmos, Shane L. Larson Aug 2011

Galaxies: Island Universes In The Cosmos, Shane L. Larson

Public Talks

No abstract provided.

Go to article

Star Formation In Self-Gravitating Disks In Active Galactic Nuclei. I. Metallicity Gradients In Broad-Line Regions, Jian-Min Wang, Jun-Qiang Ge, Chen Hu, Jack A. Baldwin, Yan-Rong Li, Gary J. Ferland, Fei Xiang, Chang-Shuo Yan, Shu Zhang Aug 2011

Star Formation In Self-Gravitating Disks In Active Galactic Nuclei. I. Metallicity Gradients In Broad-Line Regions, Jian-Min Wang, Jun-Qiang Ge, Chen Hu, Jack A. Baldwin, Yan-Rong Li, Gary J. Ferland, Fei Xiang, Chang-Shuo Yan, Shu Zhang

Physics and Astronomy Faculty Publications

It has been suggested that the high metallicity generally observed in active galactic nuclei (AGNs) and quasars originates from ongoing star formation in the self-gravitating part of accretion disks around supermassive black holes (SMBHs). We designate this region as the star-forming (SF) disk, in which metals are produced from supernova explosions (SNexp) while at the same time inflows are driven by SNexp-excited turbulent viscosity to accrete onto the SMBHs. In this paper, an equation of metallicity governed by SNexp and radial advection is established to describe the metal distribution and evolution in the SF disk. We find that the metal …

Go to article

Veritas Observations Of The Unusual Extragalactic Transient Swift J164449.3+573451, P. T. Reynolds, Et Al Aug 2011

Veritas Observations Of The Unusual Extragalactic Transient Swift J164449.3+573451, P. T. Reynolds, Et Al

Physical Sciences Publications

We report on very high energy (>100 GeV) gamma-ray observations of Swift J164449.3+573451, an unusual transient object first detected by the Swift Observatory and later detected by multiple radio, optical, and X-ray observatories. A total exposure of 28 hr was obtained on Swift J164449.3+573451 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) during 2011 March 28-April 15. We do not detect the source and place a differential upper limit on the emission at 500 GeV during these observations of 1.4 × 10–12 erg cm–2 s–1 (99% confidence level). We also present time-resolved upper limits and use a …

Go to article

Detailed Abundances Of The Solar Twins 16 Cygni And B Cygni: Constraining Planet Formation Models, Simon C. Schuler, Katia Cunha, Verne V. Smith, Luan Ghezzi, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard Aug 2011

Detailed Abundances Of The Solar Twins 16 Cygni And B Cygni: Constraining Planet Formation Models, Simon C. Schuler, Katia Cunha, Verne V. Smith, Luan Ghezzi, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard

Publications

Results of a detailed abundance analysis of the solar twins 16 Cyg A and 16 Cyg B based on high-resolution, high signal-to-noise ratio echelle spectroscopy are presented. 16 Cyg B is known to host a giant planet while no planets have yet been detected around 16 Cyg A. Stellar parameters are derived directly from our high-quality spectra, and the stars are found to be physically similar, with ΔTeff = +43 K, Δ log g =−0.02 dex, and Δξ = +0.10 km s−1 (in the sense of A − B), consistent with previous findings. Abundances of 15 elements are derived and …

Go to article

Beating The Spin-Down Limit On Gravitational Wave Emission From The Vela Pulsar, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya D. Mohanty, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano Aug 2011

Beating The Spin-Down Limit On Gravitational Wave Emission From The Vela Pulsar, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya D. Mohanty, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We present direct upper limits on continuous gravitational wave emission from the Vela pulsar using data from the Virgo detector's second science run. These upper limits have been obtained using three independent methods that assume the gravitational wave emission follows the radio timing. Two of the methods produce frequentist upper limits for an assumed known orientation of the star's spin axis and value of the wave polarization angle of, respectively, 1.9 × 10-24 and 2.2 × 10-24, with 95% confidence. The third method, under the same hypothesis, produces a Bayesian upper limit of 2.1 × 10-24, with 95% degree of …

Go to article

Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo Aug 2011

Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo

Faculty Publications

Magnesium alloys are among the lightest structural materials known and are of considerable technological interest. To develop superior magnesium alloys, experimentalists must have a thorough understanding of the concentration-dependent precipitates that form in a given system, and hence, the thermodynamic stability of crystal phases must be determined. This information is often lacking but can be supplied by first-principles methods. Within the high-throughput framework, AFLOW, T = 0 K ground-state predictions are made by scanning a large set of known candidate structures for thermodynamic (formation energy) minima. The following 34 systems are investigated: AlMg, AuMg, CaMg, CdMg, CuMg, FeMg , GeMg, …

Go to article

Galaxy Formation In Heavily Overdense Regions At Z ~ 10: The Prevalence Of Disks In Massive Halos, Emilio Romano-Díaz, Jun-Hwan Choi, Isaac Shlosman, Michele Trenti Aug 2011

Galaxy Formation In Heavily Overdense Regions At Z ~ 10: The Prevalence Of Disks In Massive Halos, Emilio Romano-Díaz, Jun-Hwan Choi, Isaac Shlosman, Michele Trenti

Physics and Astronomy Faculty Publications

Using a high-resolution cosmological numerical simulation, we have analyzed the evolution of galaxies at z ~ 10 in a highly overdense region of the universe. These objects could represent the high-redshift galaxies recently observed by the Hubble's Wide Field Camera 3 and could as well be possible precursors of QSOs at z ~ 6-7. To overcome the sampling and resolution problems in cosmological simulations of these rare regions, we have used the constrained realizations method. Our main result for z ~ 10 shows the high-resolution central region of 3.5 h–1 Mpc radius in comoving coordinates being completely dominated by …

Go to article

Structure And Feedback In 30 Doradus. Ii. Structure And Chemical Abundances, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland Aug 2011

Structure And Feedback In 30 Doradus. Ii. Structure And Chemical Abundances, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

We use our new optical-imaging and spectrophotometric survey of key diagnostic emission lines in 30 Doradus, together with CLOUDY photoionization models, to study the physical conditions and ionization mechanisms along over 4000 individual lines of sight at points spread across the face of the extended nebula, out to a projected radius 75 pc from R136 at the center of the ionizing cluster NGC 2070. We focus on the physical conditions, geometry, and importance of radiation pressure on a point-by-point basis, with the aim of setting observational constraints on important feedback processes. We find that the dynamics and large-scale structure of …

Go to article

Discovery Of A Bright, Extremely Low Mass White Dwarf In A Close Double Degenerate System, S. Vennes, J. R. Thorstensen, A. Kawka, P. Németh, J. N. Skinner Aug 2011

Discovery Of A Bright, Extremely Low Mass White Dwarf In A Close Double Degenerate System, S. Vennes, J. R. Thorstensen, A. Kawka, P. Németh, J. N. Skinner

Dartmouth Scholarship

We report the discovery of a bright (V ~ 13.7), extremely low-mass white dwarf in a close double degenerate system. We originally selected GALEX J171708.5+675712 for spectroscopic follow-up among a group of white dwarf candidates in an ultraviolet-optical reduced proper-motion diagram. The new white dwarf has a mass of 0.18 M_solar and is the primary component of a close double degenerate system (P=0.246137 d, K_1 = 288 km/s) comprising a fainter white dwarf secondary with M_2 ~ 0.9 M_solar. Light curves phased with the orbital ephemeris show evidence of relativistic beaming and weaker ellipsoidal variations. The light curves also reveal …

Go to article

On The Measurement Of Angular Dependent Sound Transmission Through Airborne Supercritical Plates, Matthew D. Shaw Aug 2011

On The Measurement Of Angular Dependent Sound Transmission Through Airborne Supercritical Plates, Matthew D. Shaw

Theses and Dissertations

A method of measuring angular dependence of acoustic transmission through supercritical plates in air is discussed. The coincidence effect occurs in a supercritical plate when the component of the acoustic wave number parallel to the plate matches the bending wave number in the plate. The transmission of sound is a maximum at the angle where this trace wave number matching occurs. The theory of the coincidence effect is well-defined for unbounded thin plates using plane-wave excitation. However, experimental results for finite plates are known to diverge from theory, especially near grazing angles. An experimental setup has been developed in order …

Go to article

Scaling Carbon Nanotube Localization By Floating Potential Dielectrophoresis: An Enabling Geometry, Brian S. Davis Aug 2011

Scaling Carbon Nanotube Localization By Floating Potential Dielectrophoresis: An Enabling Geometry, Brian S. Davis

Theses and Dissertations

Dielectrophoresis has been used as a technique for the parallel localization and alignment of both semiconducting and metallic carbon nanotubes (CNTs) at junctions between electrodes. A variation of this technique known as Floating Potential Dielectrophoresis (FPD) allows for a self-limiting number of CNTs to be localized at each junction, on a massively parallel scale. However, the smallest FPD geometries to date are restricted to conductive substrates and have a lower limit on floating electrode size. We present a geometry which eliminates this lower limit and enables FPD to be performed on non-conducting substrates. We also discuss experiments clarifying the self-limiting …

Go to article

N Ii Λλ5668−5712: A New Class Of Spectral Features In Eta Carinae, Andrea Mehner, Kris Davidson, Gary J. Ferland Aug 2011

N Ii Λλ5668−5712: A New Class Of Spectral Features In Eta Carinae, Andrea Mehner, Kris Davidson, Gary J. Ferland

Physics and Astronomy Faculty Publications

We report on the N II λλ5668-5712 emission and absorption lines in the spectrum of η Carinae. Spectral lines of the stellar wind regions can be classified into four physically distinct categories: (1) low-excitation emission such as H I and Fe II, (2) higher-excitation He I features, (3) the N II lines discussed in this paper, and (4) He II emission. These categories have different combinations of radial velocity behavior, excitation processes, and dependences on the secondary star. The N II lines are the only known features that originate in "normal" undisturbed zones of the primary wind but depend primarily …

Go to article

First Prev Next Last