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 6571 - 6600 of 8865

Full-Text Articles in Astrophysics and Astronomy

Search For Gravitational Waves From Binary Inspirals In S3 And S4 Ligo Data, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales Mar 2008

Search For Gravitational Waves From Binary Inspirals In S3 And S4 Ligo Data, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales

Faculty Publications

We report on a search for gravitational waves from the coalescence of compact binaries during the third and fourth LIGO science runs. The search focused on gravitational waves generated during the inspiral phase of the binary evolution. In our analysis, we considered three categories of compact binary systems, ordered by mass: (i) primordial black hole binaries with masses in the range 0.35M

Go to article

Five Planets Orbiting 55 Cancri, Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler, Steve S. Vogt, Gregory Laughlin, Gregory W. Henry, David Abouav, Kathryn M. G. Peek, Jason T. Wright, John A. Johnson, Chris Mccarthy, Howard Isaacson Mar 2008

Five Planets Orbiting 55 Cancri, Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler, Steve S. Vogt, Gregory Laughlin, Gregory W. Henry, David Abouav, Kathryn M. G. Peek, Jason T. Wright, John A. Johnson, Chris Mccarthy, Howard Isaacson

Information Systems and Engineering Management Research Publications

We report 18 years of Doppler shift measurements of a nearby star, 55 Cancri, that exhibits strong evidence for five orbiting planets. The four previously reported planets are strongly confirmed here. A fifth planet is presented, with an apparent orbital period of 260 days, placing it 0.78 AU from the star in the large empty zone between two other planets. The velocity wobble amplitude of 4.9 m s−1 implies a minimum planet mass Msin i = 45.7 M⊕. The orbital eccentricity is consistent with a circular orbit, but modest eccentricity solutions give similar χ2ν fits. All five planets reside in …

Go to article

On The Enhanced Cosmic-Ray Ionization Rate In The Diffuse Cloud Toward Ζ Persei, Gargi Shaw, Gary J. Ferland, R. Srianand, N. P. Abel, P. A. M. Van Hoof, P. C. Stancil Mar 2008

On The Enhanced Cosmic-Ray Ionization Rate In The Diffuse Cloud Toward Ζ Persei, Gargi Shaw, Gary J. Ferland, R. Srianand, N. P. Abel, P. A. M. Van Hoof, P. C. Stancil

Physics and Astronomy Faculty Publications

The spatial distribution of the cosmic-ray flux is important in understanding the interstellar medium (ISM) of the Galaxy. This distribution can be analyzed by studying different molecular species along different sight lines whose abundances are sensitive to the cosmic-ray ionization rate. Recently several groups have reported an enhanced cosmic-ray ionization rate (ζ=χCRζstandard) in diffuse clouds compared to the standard value, ζstandard (=2.5×10-17 s-1), measured toward dense molecular clouds. In an earlier work we reported an enhancement χCR=20 toward HD 185418. McCall et al. have reported χCR=48 toward ζ …

Go to article

The Central Component Of Gravitational Lens Q0957+561, Deborah B. Haarsma, Joshua N. Winn, Irwin Shapiro, Joseph Lehár Mar 2008

The Central Component Of Gravitational Lens Q0957+561, Deborah B. Haarsma, Joshua N. Winn, Irwin Shapiro, Joseph Lehár

University Faculty Publications and Creative Works

In 1981, a faint radio source (G′) was detected near the center of the lensing galaxy of the famous "twin quasar" Q0957+561. It is still unknown whether this central radio source is a third quasar image or an active nucleus of the lensing galaxy, or a combination of both. In an attempt to resolve this ambiguity, we observed Q0957+561 at radio wavelengths of 13 cm, 18 cm, and 21 cm, using the Very Long Baseline Array in combination with the phased Very Large Array and the Green Bank Telescope. We measured the spectrum of G′ for the first time and …

Go to article

The Robotic Super-Lotis Telescope: Results & Future Plans, G. G. Williams, P. A. Milne, H. S. Park, S. D. Barthelmy, Dieter H. Hartmann, A. Updike, K. Hurley Feb 2008

The Robotic Super-Lotis Telescope: Results & Future Plans, G. G. Williams, P. A. Milne, H. S. Park, S. D. Barthelmy, Dieter H. Hartmann, A. Updike, K. Hurley

Publications

We provide an overview of the robotic Super-LOTIS (Livermore Optical Transient Imaging System) telescope and present results from gamma-ray burst (GRB) afterglow observations using Super-LOTIS and other Steward Observatory telescopes. The 0.6-m Super-LOTIS telescope is a fully robotic system dedicated to the measurement of prompt and early time optical emission from GRBs. The system began routine operations from its Steward Observatory site atop Kitt Peak in April 2000 and currently operates every clear night. The telescope is instrumented with an optical CCD camera and a four position filter wheel. It is capable of observing Swift Burst Alert Telescope (BAT) error …

Go to article

Clouds Search For Variability In Brown Dwarf Atmospheres: Infrared Spectroscopic Time Series Of L/T Transition Brown Dwarfs, D. Stephens, B. Goldman, M. C. Cushing, M. S. Marley, E. Artigau, K. S. Baliyan, V. J. S. Bejar, J. A. Caballero, N. Chanover, M. Connelley, R. Doyon, T. Forveille, S. Ganesh, C. R. Gelino, H. B. Hammel, J. Holtzman, S. Joshi, U. C. Joshi, S. K. Leggett, M. C. Liu Feb 2008

Clouds Search For Variability In Brown Dwarf Atmospheres: Infrared Spectroscopic Time Series Of L/T Transition Brown Dwarfs, D. Stephens, B. Goldman, M. C. Cushing, M. S. Marley, E. Artigau, K. S. Baliyan, V. J. S. Bejar, J. A. Caballero, N. Chanover, M. Connelley, R. Doyon, T. Forveille, S. Ganesh, C. R. Gelino, H. B. Hammel, J. Holtzman, S. Joshi, U. C. Joshi, S. K. Leggett, M. C. Liu

Faculty Publications

L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres that could host weather-like phenomena. The detection of photometric or spectral variability would provide insight into unresolved atmospheric heterogeneities, such as holes in a global cloud deck. Indeed, a number of ultra-cool dwarfs have been reported to vary. Additional time-resolved spectral observations of brown dwarfs offer the opportunity for further constraining and characterising atmospheric variability. Aims. It has been proposed that growth of heterogeneities in the global cloud deck may account for the L- to T-type transition when brown dwarf photospheres evolve from cloudy to clear conditions. Such a mechanism is …

Go to article

Relativistic Particle-In-Cell Simulation Of Prompt And Early Afterglows From Grbs, K.-I. Nishikawa, P. Hardee, Y. Mizuno, M. Medvedev, B. Zhang, Dieter H. Hartmann, G. J. Fishman Feb 2008

Relativistic Particle-In-Cell Simulation Of Prompt And Early Afterglows From Grbs, K.-I. Nishikawa, P. Hardee, Y. Mizuno, M. Medvedev, B. Zhang, Dieter H. Hartmann, G. J. Fishman

Publications

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and microquasars commonly exibit power-law emission spectra. Recent PIC simulations of relativistic electro-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless, relativistic shocks, particle (electron, positron, and ion) acceleration is due to plasma waves and their associated instabilities (e.g., the Weibel (filamentation) instability) created in shock region. The simulations show that the Weibel instability in responsible for generating and amplifying highly non-uniform, small-scale magnetic fields. These fields contribute to the …

Go to article

A Precise Measurement Of The Muon Neutrino–Nucleon Inclusive Charged Current Cross Section Off An Isoscalar Target In The Energy Range 2.5 < EV < 40 Gev By Nomad, Nomad Collaboration, Q. Wu, S. R. Mishra, A. Godley, Roberto Petti, S. Alekhin, P. Astier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, M. Banner, G. Bassompierre, K. Benslama, N. Besson, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Boyd, A. Bueno, Et. Al. Feb 2008

A Precise Measurement Of The Muon Neutrino–Nucleon Inclusive Charged Current Cross Section Off An Isoscalar Target In The Energy Range 2.5 < EV < 40 Gev By Nomad, Nomad Collaboration, Q. Wu, S. R. Mishra, A. Godley, Roberto Petti, S. Alekhin, P. Astier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, M. Banner, G. Bassompierre, K. Benslama, N. Besson, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Boyd, A. Bueno, Et. Al.

Faculty Publications

We present a measurement of the muon neutrino–nucleon inclusive charged current cross section, off an isoscalar target, in the neutrino energy range 2.5⩽Ev ⩽ 40GeV. The significance of this measurement is its precision, ±4% in 2.5⩽Ev ⩽ 10GeV, and ± 2.6% in 10⩽Ev ⩽ 40GeV regions, where significant uncertainties in previous experiments still exist, and its importance to the current and proposed long baseline neutrino oscillation experiments.

Go to article

A New, Bright, Short-Period, Emission Line Binary In Ophiuchus, M. A. Stark, Richard A. Wade, John R. Thorstensen, Christopher S. Peters Feb 2008

A New, Bright, Short-Period, Emission Line Binary In Ophiuchus, M. A. Stark, Richard A. Wade, John R. Thorstensen, Christopher S. Peters

Dartmouth Scholarship

The 11th magnitude star LS IV-08°3 has been classified previously as an OB star in the Luminous Stars survey, or alternatively as a hot subdwarf. It is actually a binary star. We present spectroscopy, spectroscopic orbital elements, and time-series photometry from observations made at the Kitt Peak National Observatory 2.1 m, Steward Observatory 2.3 m, MDM Observatory 1.3 m and 2.4 m, Hobby-Eberly 9.2 m, and Michigan State University 0.6 m telescopes. The star exhibits emission of varying strength in the cores of H and He I absorption lines. Emission is also present at 4686 Å (He II) and near …

Go to article

Arecibo H I Absorption Measurements Of Pulsars And The Electron Density At Intermediate Longitudes In The First Galactic Quadrant, J. M. Weisberg, S. Stanimirović, K. Xilouris, A. Hedden, A. De La Fuente, S. B. Anderson, F. A. Jenet Feb 2008

Arecibo H I Absorption Measurements Of Pulsars And The Electron Density At Intermediate Longitudes In The First Galactic Quadrant, J. M. Weisberg, S. Stanimirović, K. Xilouris, A. Hedden, A. De La Fuente, S. B. Anderson, F. A. Jenet

Physics & Astronomy Faculty Publications

We have used the Arecibo telescope to measure the H I absorption spectra of eight pulsars. We show how kinematic distance measurements depend on the values of the Galactic constants R0 and Θ0, and we select our preferred current values from the literature. We then derive kinematic distances for the low-latitude pulsars in our sample and electron densities along their lines of sight. We combine these measurements with all others in the inner Galactic plane visible from Arecibo to study the electron density in this region. The electron density in the interarm range 48° < l < 70° is 0.017-0.007+0.012(68% c.1.) cm-3. This is 0.75-0.22+0.49(68% c.1.) of the value calculated by the Galactic electron density model of Cordes & Lazio. The model agrees more closely with electron density measurements toward Arecibo pulsars lying closer to the Galactic center, at 30° < l < 48°. Our analysis leads to the best current estimate of the distance of the relativistic binary pulsar B1913+16: d = 9.0 ± 3 kpc We use the high-latitude pulsars to search for small-scale structure in the interstellar hydrogen observed in absorption over multiple epochs. PSR B0301+19 exhibited significant changes in its absorption spectrum over 22 yr, indicating H I structure on a ∼500 AU scale. © 2008. The American Astronomical Society. All rights reserved.

Go to article

De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen Feb 2008

De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen

Dartmouth Scholarship

Close white dwarf - red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf - red dwarf binary with a relatively short (~8.7 hours) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters which we discuss in the frame work of common-envelope evolution. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of …

Go to article

Implications Of Cosmological Gamma-Ray Absorption. Ii. Modifications Of Gamma-Ray Spectra, Dieter H. Hartmann, T. M. Kneiske, T. Bretz, K. Mannheim Feb 2008

Implications Of Cosmological Gamma-Ray Absorption. Ii. Modifications Of Gamma-Ray Spectra, Dieter H. Hartmann, T. M. Kneiske, T. Bretz, K. Mannheim

Publications

Bearing on the model for the time-dependent metagalactic radiation field developed in the first paper of this series, we compute the gamma-ray attenuation due to pair production in photon-photon scattering. Emphasis is on the effects of varying the star formation rate and the fraction of UV radiation assumed to escape from the star forming regions, the latter being important mainly for high-redshift sources. Conversely, we investigate how the metagalactic radiation field can be measured from the gamma-ray pair creation cutoff as a function of redshift, the Fazio-Stecker relation. For three observed TeV-blazars (Mkn501, Mkn421, H1426+428) we study the effects of …

Go to article

Relativistic Iron Emission Lines In Neutron Star Low-Mass X-Ray Binaries As Probes Of Neutron Star Radii, Edward M. Cackett, Jon M. Miller, Sudip Bhattacharyya, Jonathan E. Grindlay, Jeroen Homan, Michiel Van Der Klis, M. Coleman Miller, Tod E. Strohmayer, Rudy Wijnands Feb 2008

Relativistic Iron Emission Lines In Neutron Star Low-Mass X-Ray Binaries As Probes Of Neutron Star Radii, Edward M. Cackett, Jon M. Miller, Sudip Bhattacharyya, Jonathan E. Grindlay, Jeroen Homan, Michiel Van Der Klis, M. Coleman Miller, Tod E. Strohmayer, Rudy Wijnands

Physics and Astronomy Faculty Research Publications

Using Suzaku observations of three neutron star low-mass X-ray binaries (Ser X-1, 4U 1820-30, and GX 349+2) we have found broad, asymmetric, relativistic Fe K emission lines in all three objects. These Fe K lines can be well fit by a model for lines from a relativistic accretion disk (``diskline''), allowing a measurement of the inner radius of the accretion disk and hence an upper limit on the neutron star radius. These upper limits correspond to 14.5-16.5 km for a 1.4 Msolar neutron star. The inner disk radii that we measure with Fe K lines are in good agreement …

Go to article

Exist's Gamma-Ray Burst Sensitivity, D. L. Band, J. E. Grindlay, A. Garson Iii, H. Krawczynski, Dieter H. Hartmann, S. Barthemy, N. Gehrels, G. Skinner Feb 2008

Exist's Gamma-Ray Burst Sensitivity, D. L. Band, J. E. Grindlay, A. Garson Iii, H. Krawczynski, Dieter H. Hartmann, S. Barthemy, N. Gehrels, G. Skinner

Publications

We use semianalytic techniques to evaluate the burst sensitivity of designs for the EXIST hard X-ray survey mis-sion. Applying these techniques to the mission design proposed for the Beyond Einstein program,we find that with its very large field of view and faint gamma-ray burst detection threshold, EXIST will detect and localize approximately two bursts per day, a large fraction of which may be at high redshift. We estimate that EXIST’s maximum sensitivity will be ~4 times greater than that of Swift’s Burst Alert Telescope. Bursts will be localized to better than 40" at thresh-old, with a burst position as good …

Go to article

Interacting Jets From Binary Protostars, Gareth Murphy, Thibaut Lery, Stephen O'Sullivan, Daniel S. Spicer, Francesca Bacciotti, Alex Rosen Feb 2008

Interacting Jets From Binary Protostars, Gareth Murphy, Thibaut Lery, Stephen O'Sullivan, Daniel S. Spicer, Francesca Bacciotti, Alex Rosen

Articles

Aims. We investigate potential models that could explain why multiple proto-stellar systems predominantly show single jets. During their formation, stars most frequently produce energetic outflows and jets. However, binary jets have only been observed in a very small number of systems. Methods. We model numerically 3D binary jets for various outflow parameters. We also model the propagation of jets from a specific source, namely L1551 IRS 5, known to have two jets, using recent observations as constraints for simulations with a new MHD code. We examine their morphology and dynamics, and produce synthetic emission maps. Results. We find that the …

Go to article

Optical Imaging And Spectroscopy Of The Galactic Supernova Remnant 3c 58 (G130.7+3.1), Robert Fesen, Gwen Rudie, Alan Hurford, Aljeandro Soto Feb 2008

Optical Imaging And Spectroscopy Of The Galactic Supernova Remnant 3c 58 (G130.7+3.1), Robert Fesen, Gwen Rudie, Alan Hurford, Aljeandro Soto

Dartmouth Scholarship

We present a comprehensive imaging and spectroscopic survey of optical emission knots associated with the young Galactic supernova remnant 3C 58. Hα images show hundreds of clumpy filaments and knots arranged in a complex structure covering a nearly circular area roughly 400'' in diameter. A quite different emission structure is seen in [O III], where the brightest features are less clumpy and largely confined to the remnant's northwest quadrant. Measured radial velocities of over 450 knots reveal two distinct kinematic populations; one with average and peak expansion velocities of 770 and 1100 km s−1, respectively, forming a thick …

Go to article

Masses, Luminosities, And Orbital Coplanarities Of The Μ Orionis Quadruple-Star System From Phases Differential Astrometry, Matthew W. Muterspaugh, Benjamin F. Lane, Francis C. Fekel, Maciej Konacki, Bernard F. Burke, Shrinivas R. Kulkarni, Mark M. Colavita, Michael Shao, Sloane J. Wiktorowicz Jan 2008

Masses, Luminosities, And Orbital Coplanarities Of The Μ Orionis Quadruple-Star System From Phases Differential Astrometry, Matthew W. Muterspaugh, Benjamin F. Lane, Francis C. Fekel, Maciej Konacki, Bernard F. Burke, Shrinivas R. Kulkarni, Mark M. Colavita, Michael Shao, Sloane J. Wiktorowicz

Information Systems and Engineering Management Research Publications

μ Orionis was identified by spectroscopic studies as a quadruple-star system. Seventeen high-precision differential astrometry measurements of μ Ori have been collected by the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES). These show both the motion of the long-period binary orbit and short-period perturbations superimposed on that caused by each of the components in the long-period system being themselves binaries. The new measurements enable the orientations of the long-period binary and short-period subsystems to be determined. Recent theoretical work predicts the distribution of relative inclinations between inner and outer orbits of hierarchical systems to peak near 40 and 140 …

Go to article

Lower Limit To The Scale Of An Effective Quantum Theory Of Gravitation, R. R. Caldwell, Daniel Grin Jan 2008

Lower Limit To The Scale Of An Effective Quantum Theory Of Gravitation, R. R. Caldwell, Daniel Grin

Dartmouth Scholarship

An effective quantum theory of gravitation in which gravity weakens at energies higher than ∼10−3  eV is one way to accommodate the apparent smallness of the cosmological constant. Such a theory predicts departures from the Newtonian inverse-square force law on distances below ∼0.05  mm. However, it is shown that this modification also leads to changes in the long-range behavior of gravity and is inconsistent with observed gravitational lenses.

Go to article

The Extinction Toward The Galactic Bulge From Rr Lyrae Stars, Andrea Kunder, Piotr Popowski, Kem H. Cook, Brian Chaboyer Jan 2008

The Extinction Toward The Galactic Bulge From Rr Lyrae Stars, Andrea Kunder, Piotr Popowski, Kem H. Cook, Brian Chaboyer

Dartmouth Scholarship

We present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, we derive the selective extinction coefficient RV,VR = AV/E(V − R) = 4.3 ± 0.2. This value is what is expected for a standard extinction law with R …

Go to article

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. Ii. Hr 2962, Hd 214686, And 16 Psc, Jocelyn Tomkin, Francis C. Fekel Jan 2008

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. Ii. Hr 2962, Hd 214686, And 16 Psc, Jocelyn Tomkin, Francis C. Fekel

Information Systems and Engineering Management Research Publications

Radial velocities from the 2.1 m telescope at McDonald Observatory and the coudé feed telescope at Kitt Peak National Observatory are used to determine new spectroscopic orbits for the double-lined spectroscopic binaries HR 2962 (F5V), HD 214686 (F8IV), and 16 Psc (F6Vb vw). The new orbital dimensions (a1sin i and a2sin i) and minimum masses (m1sin3i and m2sin3i) have accuracies of 0.1–1%. In the case of HD 214686, which has components of nearly the same mass (m1/m2 = 1.0080 ± 0.0013), we confirm that the component labeled as the primary in previous spectroscopic studies of this system is the slightly …

Go to article

Near Ultraviolet–Infrared Colours Of Red-Sequence Galaxies In Local Clusters, Timothy D. Rawle, Russell J. Smith, John R. Lucey, Michael J. Hudson, Gary A. Wegner Jan 2008

Near Ultraviolet–Infrared Colours Of Red-Sequence Galaxies In Local Clusters, Timothy D. Rawle, Russell J. Smith, John R. Lucey, Michael J. Hudson, Gary A. Wegner

Dartmouth Scholarship

We present GALEX near‐ultraviolet (NUV) and Two‐Micron All‐Sky Survey J‐band photometry for red‐sequence galaxies in local clusters. We define quiescent samples according to a strict emission threshold, removing galaxies with very recent star formation. We analyse the NUV–J colour–magnitude relation (CMR) and find that the intrinsic scatter is an order of magnitude larger than for the analogous optical CMR (∼0.35 rather than 0.05 mag), in agreement with previous studies. Comparing the NUV–J colours with spectroscopically derived stellar population parameters, we find a strong (>5.5σ) correlation with metallicity, only a marginal trend with …

Go to article

All-Sky Search For Periodic Gravitational Waves In Ligo S4 Data, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales Jan 2008

All-Sky Search For Periodic Gravitational Waves In Ligo S4 Data, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales

Faculty Publications

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50-1000 Hz and with the frequency's time derivative in the range -1×10-8Hzs-1 to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semicoherent methods of transforming and summing strain power from short Fourier transforms (SFTs) of the calibrated data have been used. The first, known as StackSlide, averages normalized power from each SFT. A "weighted Hough" scheme is also developed and used, which also allows for a multi-interferometer search. The third method, known as …

Go to article

The Dark Matter Halo Of Ngc 1399- Cdm Or Mond?, T. Richtler, Y. Schuberth, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky Jan 2008

The Dark Matter Halo Of Ngc 1399- Cdm Or Mond?, T. Richtler, Y. Schuberth, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky

Faculty Publications

Context. Central galaxies in galaxy clusters may be key discriminants in the competition between the cold dark matter (CDM) paradigm and modified Newtonian dynamics (MOND). Aims. We investigate the dark halo of NGC 1399, the central galaxy of the Fornax cluster, out to a galactocentric distance of 80 kpc. Methods.The data base consists of 656 radial velocities of globular clusters obtained with MXU/VLT and GMOS/Gemini, which is the largest sample so far for any galaxy. We performed a Jeans analysis for a non-rotating isotropic model. Results.An NFW halo with the parameters $r_{\rm s} = 50\,\rm {kpc}$ and $\varrho_{\rm s} = …

Go to article

A Magnetohydrodynamic Boost For Relativistic Jets, Yosuke Mizuno, Phillip Hardee, Dieter H. Hartmann, Ken-Ichi Nishikawa, Bing Zhang Jan 2008

A Magnetohydrodynamic Boost For Relativistic Jets, Yosuke Mizuno, Phillip Hardee, Dieter H. Hartmann, Ken-Ichi Nishikawa, Bing Zhang

Publications

We performed relativistic magnetohydrodynamic simulations of the hydrodynamic boosting mechanism for relativistic jets explored by Aloy & Rezzolla (2006) using the RAISHIN code. Simulation results show that the presence of a magnetic field changes the properties of the shock interface between the tenuous, overpressured jet (Vzj) flowing tangentially to a dense external medium. Magnetic fields can lead to more efficient acceleration of the jet, in comparison to the pure-hydrodynamic case. A "polodial" magnetic field (Bz), tangent to the interface and parallel to the jet flow, produces both a stronger outward moving shock and a stronger inward moving rarefaction wave. This …

Go to article

Constraints On First-Light Ionizing Sources From Optical Depth Of The Cosmic Microwave Background, J Shull, Aparna Venkatesan Jan 2008

Constraints On First-Light Ionizing Sources From Optical Depth Of The Cosmic Microwave Background, J Shull, Aparna Venkatesan

Physics and Astronomy

We examine the constraints on high-redshift star formation, ultraviolet and X-ray preionization, and the epoch of reionization at redshift zr, inferred from the recent WMAP-5 measurement, τe = 0.084 ± 0.016, of the electron- scattering optical depth of the cosmic microwave background (CMB). Half of this scattering can be accounted for by the optical depth, τe = 0.04-0.05, of a fully ionized intergalactic medium (IGM) at z ≤ zGP ≈ 6-7, consistent with Gunn-Peterson absorption in neutral hydrogen. The required additional optical depth, Δτe = 0.03 ± 0.02 atz > zGP, …

Go to article

Thermal Roots Of Correlation-Based Complexity, Philip Fraundorf Jan 2008

Thermal Roots Of Correlation-Based Complexity, Philip Fraundorf

Physics Faculty Works

Bayesian maxent lets one integrate thermal physics and information theory points of view in the quantitative study of complex systems. Since net surprisal (a free energy analog for measuring “departures from expected”) allows one to place second law constraints on mutual information (a multimoment measure of correlations), it makes a quantitative case for the role of reversible thermalization in the natural history of invention, and suggests multiscale strategies to monitor standing crop as well. It prompts one to track evolved complexity starting from live astrophysically observed processes, rather than only from evidence of past events. Various gradients and boundaries that …

Go to article

The Origin Of Molecular Hydrogen Emission In Cooling-Flow Filaments, Gary J. Ferland, A. C. Fabian, N. A. Hatch, R. M. Johnstone, R. L. Porter, P. A. M. Vanhoof, R. J. R. Williams Jan 2008

The Origin Of Molecular Hydrogen Emission In Cooling-Flow Filaments, Gary J. Ferland, A. C. Fabian, N. A. Hatch, R. M. Johnstone, R. L. Porter, P. A. M. Vanhoof, R. J. R. Williams

Physics and Astronomy Faculty Publications

The optical filaments found in many cooling flows in galaxy clusters consist of low-density (∼103 cm−3) cool (∼103 K) gas surrounded by significant amounts of cosmic-ray and magnetic field energy. Their spectra show anomalously strong low-ionization and molecular emission lines when compared with Galactic molecular clouds exposed to ionizing radiation such as the Orion complex. Previous studies have shown that the spectra cannot be produced by O-star photoionization. Here, we calculate the physical conditions in dusty gas that is well shielded from external sources of ionizing photons and is energized either by cosmic rays or dissipative …

Go to article

Poet: Polarimeters For Energetic Transients, J E. Hill, Mark L. Mcconnell, Peter F. Bloser, Jason S. Legere, John R. Macri, James M. Ryan, Scott Barthelmy, L Angelini, Takanori Sakamoto, J Kevin Black, H Hartmann, Philip Kaaret, Bing Zhang, Kunihito Ioka, Takashi Nakamura, Kenji Toma, Ryo Yamazaki, X Wu Jan 2008

Poet: Polarimeters For Energetic Transients, J E. Hill, Mark L. Mcconnell, Peter F. Bloser, Jason S. Legere, John R. Macri, James M. Ryan, Scott Barthelmy, L Angelini, Takanori Sakamoto, J Kevin Black, H Hartmann, Philip Kaaret, Bing Zhang, Kunihito Ioka, Takashi Nakamura, Kenji Toma, Ryo Yamazaki, X Wu

Space Science Center

POET (Polarimeters for Energetic Transients) is a Small Explorer mission concept proposed to NASA in January 2008. The principal scientific goal of POET is to measure GRB polarization between 2 and 500 keV. The payload consists of two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2–15 keV and a high energy polarimeter (Gamma‐Ray Polarimeter Experiment—GRAPE) that will measure polarization in the 60–500 keV energy range. Spectra will be measured from 2 keV up to 1 MeV. The POET spacecraft provides a zenith‐pointed platform for maximizing the exposure to deep space. …

Go to article

Taking Another Look: Light N-Capture Element Abundances In Metal-Poor Halo Stars, D. Burris, E. Jones, J. Lusk Jan 2008

Taking Another Look: Light N-Capture Element Abundances In Metal-Poor Halo Stars, D. Burris, E. Jones, J. Lusk

Journal of the Arkansas Academy of Science

Elements are produced in stars through a variety of processes; some are well known, others are still the object of active research. The elements Zirconium (Zr) and Yttrium (Y) are produced via neutron capture (ncapture). These elements reside in the mass range where there is uncertainty about the production mechanism at early time. The rapid n-capture process (r-process) was believed to be responsible for the production, but no study (Burris et al 2000, Gilroy et al 1988 and others) has been able to successfully use the r-process to reproduce the abundance signature for elements in this mass range for metal-poor …

Go to article

Equation Of State For A Van Der Waals Universe During Reissner–Nordstrom Expansion, Emil Prodanov, Rossen Ivanov, Vesselin Gueorguiev Jan 2008

Equation Of State For A Van Der Waals Universe During Reissner–Nordstrom Expansion, Emil Prodanov, Rossen Ivanov, Vesselin Gueorguiev

Articles

In a previous work [E.M. Prodanov, R.I. Ivanov and V.G. Gueorguiev, Reissner-Nordström expansion, Astropart. Phys. 27 (2007) 150], we proposed a classical model for the expansion of the Universe during the radiation-dominated epoch based on the gravitational repulsion of the Reissner-Nordström geometry — naked singularity description of particles that "grow" with the drop of the temperature. In this work we model the Universe during the Reissner-Nordström expansion as a van der Waals gas and determine the equation of state.

Go to article

First Prev Next Last