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

Astrophysics and Astronomy Commons™

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

Publications

Discipline
Institution
Keyword
Publication Year
File Type

Articles 331 - 360 of 533

Full-Text Articles in Astrophysics and Astronomy

Dual Gamma-Ray Mission, S. Boggs, C. Wunderer, P. Von Ballmoos, T. Takahashi, N. Gehrels, J. Tueller, M. Baring, J. Beacom, R. Diehl, J Greiner, E Grove, Dieter H. Hartmann Jan 2010

Dual Gamma-Ray Mission, S. Boggs, C. Wunderer, P. Von Ballmoos, T. Takahashi, N. Gehrels, J. Tueller, M. Baring, J. Beacom, R. Diehl, J Greiner, E Grove, Dieter H. Hartmann

Publications

Gamma-rays at MeV energies provide a unique window on the high energy Universe, especially so for nuclear astrophysics. The potential for significant contributions, e.g., to the understanding of SNe Ia as well as the large potential for new discoveries has long been recognized, but technical progress in this challenging energy band has been slow. The groundbreaking discoveries of CGRO’s COMPTEL, however, have inspired and driven the development of powerful new instrumentation over the past decade. Novel detector technologies developed in the US and Japan enable compact Compton telescopes, greatly improving the efficiency and field-of-view achievable with this technique successfully employed …

Go to article

The Dynamic X-Ray Sky Of The Local Universe, S. Boggs, C. Wunderer, P. Von Ballmoos, T. Takahashi, N. Gehrels, J. Tueller, M. Baring, J. Beacom, R. Diehl, Dieter H. Hartmann Jan 2010

The Dynamic X-Ray Sky Of The Local Universe, S. Boggs, C. Wunderer, P. Von Ballmoos, T. Takahashi, N. Gehrels, J. Tueller, M. Baring, J. Beacom, R. Diehl, Dieter H. Hartmann

Publications

Over the next decade, we can expect time domain astronomy to flourish at optical and radio wavelengths. In parallel with these efforts, a dedicated transient "machine" operating at higher energies (X-ray band through soft gamma-rays) is required to reveal the unique subset of events with variable emission predominantly visible above 100 eV. Here we focus on the transient phase space never yet sampled due to the lack of a sensitive, wide-field and triggering facility dedicated exclusively to catching high energy transients and enabling rapid coordinated multi-wavelength follow-up. We first describe the advancements in our understanding of known X-ray transients that …

Go to article

On The Origin Of The Highest Redshift Gamma-Ray Bursts, Krzysztof Belczynski, Daniel E. Holz, Chris L. Fryer, Edo Berger, Dieter H. Hartmann, Brain O'Shea Jan 2010

On The Origin Of The Highest Redshift Gamma-Ray Bursts, Krzysztof Belczynski, Daniel E. Holz, Chris L. Fryer, Edo Berger, Dieter H. Hartmann, Brain O'Shea

Publications

GRB 080913 and GRB 090423 are the most distant gamma-ray bursts (GRBs) known to date, with spectroscop-ically determined redshifts of z = 6.7 and z = 8.1, respectively. The detection of bursts at this early epoch of the universe significantly constrains the nature of GRBs and their progenitors. We perform population synthesis studies of the formation and evolution of early stars, and calculate the resulting formation rates of short- and long-duration GRBs at high redshift. The peak of the GRB rate from Population II stars occurs at z ∼ 7for a model with efficient/fast mixing of metals, while it is …

Go to article

The White Dwarfs Within 20 Parsecs Of The Sun: Kinematics And Statistics, Edward M. Sion, J. B. Holberg, Terry D. Oswalt, George P. Mccook, Richard Wasatonic Oct 2009

The White Dwarfs Within 20 Parsecs Of The Sun: Kinematics And Statistics, Edward M. Sion, J. B. Holberg, Terry D. Oswalt, George P. Mccook, Richard Wasatonic

Publications

We present the kinematical properties, distribution of spectroscopic subtypes, and stellar population subcomponents of the white dwarfs within 20 pc of the Sun.We find no convincing evidence of halo white dwarfs in the total 20 pc sample of 129 white dwarfs nor is there convincing evidence of genuine thick disk subcomponent members within 20 parsecs. Virtually, the entire 20 pc sample likely belongs to the thin disk. The total DA to non-DA ratio of the 20 pc sample is 1.6, a manifestation of deepening envelope convection which transforms DA stars with sufficiently thin H surface layers into non-DAs. The addition …

Go to article

Book Review: Finding The Big Bang, T. D. Oswalt Oct 2009

Book Review: Finding The Big Bang, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Finding the Big Bang edited by P. James E. Peebles, Lyman A. Page Jr., and R. Bruce Partridge Cambridge, 2009 571p, 9780521519823 $80.00

Go to article

Using Population Synthesis Of Massive Stars To Study The Interstellar Medium Near Ob Associations, R. Voss, R. Diehl, Dieter H. Hartmann, M. Cerviño, J. S. Vink, G. Meynet, M. Limongi, A. Chieffi Sep 2009

Using Population Synthesis Of Massive Stars To Study The Interstellar Medium Near Ob Associations, R. Voss, R. Diehl, Dieter H. Hartmann, M. Cerviño, J. S. Vink, G. Meynet, M. Limongi, A. Chieffi

Publications

Aims. We study the massive stars in OB associations and their surrounding interstellar medium environment, using a population synthesis code. Methods. We developed a new population synthesis code for groups of massive stars, where we model the emission of different forms of energy and matter from the stars of the association. In particular, the ejection of the two radioactive isotopes 26Al and 60Fe is followed, as well as the emission of hydrogen ionizing photons, and the kinetic energy of the stellar winds and supernova explosions. We investigate various alternative astrophysical inputs and the resulting output sensitivities, especially effects due to …

Go to article

Weibel Instability And Associated Strong Fields In A Fully 3d Simulation Of A Relativistic Shock, K.-I. Nishikawa, J. Niemiec, P. E. Hardee, M. Medvedev, H. Sol, Y. Mizuno, B. Zhang, M. Pohl, M. Oka, Dieter H. Hartmann Aug 2009

Weibel Instability And Associated Strong Fields In A Fully 3d Simulation Of A Relativistic Shock, K.-I. Nishikawa, J. Niemiec, P. E. Hardee, M. Medvedev, H. Sol, Y. Mizuno, B. Zhang, M. Pohl, M. Oka, Dieter H. Hartmann

Publications

Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) excited in collision-less shocks are responsible for particle (electron, positron, and ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. The simulation has been performed using a long simulation system in order to study the nonlinear stages of the Weibel instability, the particle acceleration mechanism, and the shock structure. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic …

Go to article

Tracing The Inner Edge Of The Disk Around Hd 100546 With Rovibrational Co Emission Lines, Sean D. Brittain, Joan R. Najita, John S. Carr Aug 2009

Tracing The Inner Edge Of The Disk Around Hd 100546 With Rovibrational Co Emission Lines, Sean D. Brittain, Joan R. Najita, John S. Carr

Publications

In this paper we present high-resolution 4.7 μm spectra of the isolated Herbig Be star HD 100546. HD 100546 has been the subject of intense scrutiny because it is a young nearby star with a transitional disk. We observe the Δv = 1 rovibrational CO transitions in order to clarify the distribution of warm gas in the inner disk. Modeling of the CO spectrum indicates that the gas is vibrationally excited by collisions and UV fluorescence. The observed emission extends from 13 to 100 AU. The inner edge of the molecular gas emission is consistent with the inner edge of …

Go to article

Revealing The Structure Of A Pre-Transitional Disk: The Case Of The Herbig F Star Sao 206462 (Hd 135344b), C A. Grady, G Schneider, M L. Sitko, G M. Williger, K Hamaguchi, Sean D. Brittain, K Ablordeppey, D Apai, L Beerman, W J. Carpenter Jul 2009

Revealing The Structure Of A Pre-Transitional Disk: The Case Of The Herbig F Star Sao 206462 (Hd 135344b), C A. Grady, G Schneider, M L. Sitko, G M. Williger, K Hamaguchi, Sean D. Brittain, K Ablordeppey, D Apai, L Beerman, W J. Carpenter

Publications

SAO 206462 (HD 135344B) has previously been identified as a Herbig F star with a circumstellar disk with a dip in its infrared excess near 10 mum. In combination with a low accretion rate estimated from Br gamma, it may represent a gapped, but otherwise primordial or "pre-transitional" disk. We test this hypothesis with Hubble Space Telescope coronagraphic imagery, FUV spectroscopy and imagery and archival X-ray data, and spectral energy distribution (SED) modeling constrained by the observed system inclination, disk outer radius, and outer disk radial surface brightness (SB) profile using the Whitney Monte Carlo Radiative Transfer Code. The essentially …

Go to article

A Near-Infrared Spectroscopic Survey Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Piotr M. Kowalski, Ted Von Hippel Jul 2009

A Near-Infrared Spectroscopic Survey Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Piotr M. Kowalski, Ted Von Hippel

Publications

We present near-infrared photometric observations of 15 and spectroscopic observations of 38 cool white dwarfs (WDs). This is the largest near-infrared spectroscopic survey of cool WDs to date. Combining the Sloan Digital Sky Survey photometry and our near-infrared data, we perform a detailed model atmosphere analysis. The spectral energy distributions of our objects are explained fairly well by model atmospheres with temperatures ranging from 6300 K down to 4200 K. Two WDs show significant absorption in the infrared, and are best explained with mixed H/He atmosphere models. Based on the up-to-date model atmosphere calculations by Kowalski & Saumon, we find …

Go to article

The First Two Transient Supersoft X-Ray Sources In M31 Globular Clusters And The Connection To Classical Novae, M. Henze, W. Pietsch, F. Haberl, G. Sala, R. Quimby, M. Hernanz, M. Della Valle, P. Milne, G. G. Williams, V Burwitz, J Greiner, H Stiele, Dieter H. Hartmann, A.K.H. Dong, K Hornoch Jun 2009

The First Two Transient Supersoft X-Ray Sources In M31 Globular Clusters And The Connection To Classical Novae, M. Henze, W. Pietsch, F. Haberl, G. Sala, R. Quimby, M. Hernanz, M. Della Valle, P. Milne, G. G. Williams, V Burwitz, J Greiner, H Stiele, Dieter H. Hartmann, A.K.H. Dong, K Hornoch

Publications

Context. Classical novae (CNe) have been found to represent the major class of supersoft X-ray sources (SSSs) in our neighbour galaxy M 31. Aims. We determine the properties and evolution of the two first SSSs ever discovered in the M 31 globular cluster (GC) system. Methods. We have used XMM-Newton, Chandra and Swift observations of the centre region of M 31 to discover both SSSs and to determine their X-ray light curves and spectra. We performed detailed analysis of XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and NLTE white dwarf (WD) atmosphere models. For …

Go to article

Spitzer Observations Of The Oldest White Dwarfs In The Solar Neighborhood, Mukremin Kilic, Ted Von Hippel, Et Al. May 2009

Spitzer Observations Of The Oldest White Dwarfs In The Solar Neighborhood, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We present Spitzer 5-15 μm spectroscopy of one cool white dwarf and 3.6-8 μm photometry of 51 cool white dwarfs with T eff < 6000 K. The majority of our targets have accurate BVRIJHKphotometry and trigonometric parallax measurements available, which enables us to perform a detailed model atmosphere analysis using their optical, near- and mid-infrared photometry with state-of-the-art model atmospheres. We demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models. Our best-fit models are consistent with the observations within 5% in all filters except the IRAC 8 μm band, which has the lowest signal-to-noise ratio photometry. Excluding …

Go to article

The Very Short Supersoft X-Ray State Of The Classical Nova M31n 2007-11a, M. Henze, W. Pietsch, G. Sala, M. Della Valle, M. Hernanz, J. Greiner, V. Burwitz, M. J. Freyberg, F. Haberl, Dieter H. Hartmann, P Milne, G G. Williams May 2009

The Very Short Supersoft X-Ray State Of The Classical Nova M31n 2007-11a, M. Henze, W. Pietsch, G. Sala, M. Della Valle, M. Hernanz, J. Greiner, V. Burwitz, M. J. Freyberg, F. Haberl, Dieter H. Hartmann, P Milne, G G. Williams

Publications

Context. Short supersoft X-ray source (SSS) states (durations ≤100 days) of classical novae (CNe) indicate massive white dwarfs that are candidate progenitors of supernovae type Ia. Aims. We carry out a dedicated optical and X-ray monitoring program of CNe in the bulge of M 31. Methods. We discovered M31N 2007-11a and determined its optical and X-ray light curve. We used the robotic Super-LOTIS tele-scope to obtain the optical data and XMM-Newton and Chandra observations to discover an X-ray counterpart to that nova. Results. Nova M31N 2007-11a is a very fast CN, exhibiting a very short SSS state with an appearance …

Go to article

Book Review: Clocks In The Sky: The Story Of Pulsars, T. D. Oswalt May 2009

Book Review: Clocks In The Sky: The Story Of Pulsars, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Clocks in the Sky: The Story of Pulsars by Geoff McNamara, Springer/Praxis, 2008 190p, 9780387765600 $29.95.

Go to article

Inverting Color–Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades, Steven Degennaro, Ted Von Hippel, Et Al. May 2009

Inverting Color–Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades, Steven Degennaro, Ted Von Hippel, Et Al.

Publications

We have extended our Bayesian modeling of stellar clusters—which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres—to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 ± 45 …

Go to article

Multisite Photometry Of The Pulsating Herbig Ae Star V346 Ori, S. Bernabei, Terry D. Oswalt, V. Ripepi, A. Ruoppo, Et Al. Apr 2009

Multisite Photometry Of The Pulsating Herbig Ae Star V346 Ori, S. Bernabei, Terry D. Oswalt, V. Ripepi, A. Ruoppo, Et Al.

Publications

The study of pulsation in Pre--Main--Sequence intermediate-mass stars represents an important tool for deriving information on fundamental stellar parameters and internal structure, as well as for testing current theoretical models. Interest in this class of variable stars has significantly increased during the last decade and about 30 members are presently known in the literature. AIMS: We have constructed the frequency spectrum of the oscillations in V346 Ori. We apply asteroseismic tools to these data to estimate the intrinsic parameters (mass, luminosity, effective temperature) of V346 Ori and to obtain information on its internal structure. METHODS: CCD time series photometry in …

Go to article

Photometric Calibrations For 21st Century Science, Stephen M. Kent, Terry D. Oswalt, Mary Elizabeth Kaiser, Et Al. Mar 2009

Photometric Calibrations For 21st Century Science, Stephen M. Kent, Terry D. Oswalt, Mary Elizabeth Kaiser, Et Al.

Publications

The answers to fundamental science questions in astrophysics, ranging from the history of the expansion of the universe to the sizes of nearby stars, hinge on our ability to make precise measurements of diverse astronomical objects. As our knowledge of the underlying physics of objects improves along with advances in detectors and instrumentation, the limits on our capability to extract science from measurements is set, not by our lack of understanding of the nature of these objects, but rather by the most mundane of all issues: the precision with which we can calibrate observations in physical units. We stress the …

Go to article

Grb 080913 At Redshift 6.7, J. Greiner, T. Krühler, J. P. U. Fynbo, A. Rossi, R. Schwarz, S. Klose, S. Savaglio, N. R. Tanvir, S. Mcbreen, T Totani, B B. Zhang, X F. Wu, D Watson, S D. Barthelmy, A P. Beardmore, P Ferrero, N Gehrels, D A. Kann, N Kawai, A Küpcü Yoldaş, P Mészáros, B Milvang-Jensen, S R. Oates, D Pierini, P Schady, K Toma, P M. Vreeswijk, A Yoldas, B Zhang, P Afonso, K Aoki, D N. Burrows, C Clemens, R Filgas, Z Haiman, Dieter H. Hartmann Mar 2009

Grb 080913 At Redshift 6.7, J. Greiner, T. Krühler, J. P. U. Fynbo, A. Rossi, R. Schwarz, S. Klose, S. Savaglio, N. R. Tanvir, S. Mcbreen, T Totani, B B. Zhang, X F. Wu, D Watson, S D. Barthelmy, A P. Beardmore, P Ferrero, N Gehrels, D A. Kann, N Kawai, A Küpcü Yoldaş, P Mészáros, B Milvang-Jensen, S R. Oates, D Pierini, P Schady, K Toma, P M. Vreeswijk, A Yoldas, B Zhang, P Afonso, K Aoki, D N. Burrows, C Clemens, R Filgas, Z Haiman, Dieter H. Hartmann

Publications

We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i and z bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to λ = 9400 Å, and zero flux for 7500 Å<λ< 9400 Å, which we interpret as the onset of a Gunn–Peterson trough at z = 6.695± 0.025 (95.5% confidence level), making GRB 080913 the highest-redshift gamma-ray burst (GRB) to date, and more distant than the highest-redshift QSO. We note that many redshift indicators that are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2 m class telescopes can identify most high-redshift GRBs.

Go to article

Book Review: Electronic Imaging In Astronomy: Detectors And Instrumentation 2nd Ed., T. D. Oswalt Mar 2009

Book Review: Electronic Imaging In Astronomy: Detectors And Instrumentation 2nd Ed., T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Electronic imaging in astronomy : detectors and instrumentation 2nd ed. by Ian S. McLean, Springer/Praxis, 2008 552p, 9783540765820 $99.00

Go to article

The Dust Cloud Around The White Dwarf G 29-38. Ii. Spectrum From 5 To 40 Μm And Mid-Infrared Photometric Variability, William T. Reach, Ted Von Hippel, Et Al. Mar 2009

The Dust Cloud Around The White Dwarf G 29-38. Ii. Spectrum From 5 To 40 Μm And Mid-Infrared Photometric Variability, William T. Reach, Ted Von Hippel, Et Al.

Publications

We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1 to 35 μm. The spectral model for G29-38 dust combines a wide range of materials based on spectral studies of comets and debris disks. In order of their contribution to the mid-infrared emission, the most abundant minerals around G29-38 are amorphous carbon (λ < 8 μm), amorphous and crystalline silicates (5-40 μm), water ice (10-15 and 23-35 μm), and metal sulfides (18-28 μm). The amorphous C can be equivalently replaced by other materials (like metallic Fe) with featureless infrared spectra. The best-fitting crystalline silicate is Fe-rich pyroxene. In order to absorb enough starlight to power the observed emission, the disk must either be much thinner than the stellar radius (so that it can be heated from above and below) or it must have an opening angle wider than 2°. A "moderately optically thick" torus model fits well if the dust extends inward to 50 times the white dwarf radius, all grains hotter than 1100 K are vaporized, the optical depth from the star through the disk is τ∥ = 5, and the radial density profile ∝r –2.7; the total mass of this model disk is 2 × 1019 g. A physically thin (less than the white dwarf radius) and optically thick disk can contribute to the near-infrared continuum only; such a disk cannot …

Go to article

In Situ Probes Of The First Galaxies And Reionization: Gamma-Ray Bursts, Matthew Mcquinn, Joshua S. Bloom, Jonathan Grindlay, David Band, S. D. Barthemy, E. Berger, A. Corsi, S. Covino, G. J. Fishman, Steven R. Furlanetto, Neil Gehrels, Dieter H. Hartmann, Chryssa Kouveliotou, A S. Kutyrev, Abraham Loeb, S Harvard Moseley, Tsvi Piran, L Piro, J X. Prochaska, R Salvaterra, P Schady, A M. Soderberg, G Tagliaferri Feb 2009

In Situ Probes Of The First Galaxies And Reionization: Gamma-Ray Bursts, Matthew Mcquinn, Joshua S. Bloom, Jonathan Grindlay, David Band, S. D. Barthemy, E. Berger, A. Corsi, S. Covino, G. J. Fishman, Steven R. Furlanetto, Neil Gehrels, Dieter H. Hartmann, Chryssa Kouveliotou, A S. Kutyrev, Abraham Loeb, S Harvard Moseley, Tsvi Piran, L Piro, J X. Prochaska, R Salvaterra, P Schady, A M. Soderberg, G Tagliaferri

Publications

The first structures in the Universe formed at z > 7, at higher redshift than all currently known galaxies. Since GRBs are brighter than other cosmological sources at high redshift and exhibit simple power-law afterglow spectra that is ideal for absorption studies, they serve as powerful tools for studying the early universe. New facilities planned for the coming decade will be able to obtain a large sample of high-redshift GRBs. Such a sample would constrain the nature of the first stars, galaxies, and the reionization history of the Universe.

Go to article

Hd 100453: A Link Between Gas-Rich Protoplanetary Disks And Gas-Poor Debris Disks, K A. Collins, C A. Grady, K Hamaguchi, J P. Wisniewski, Sean D. Brittain, M Sitko, W J. Carpenter, J P. Williams, G S. Mathews, G M. Williger, R Van Boekel, A Carmona, Th. Henning, M E. Van Den Ancker, G Meeus, X P. Chen, R Petre, B E. Woodgate Feb 2009

Hd 100453: A Link Between Gas-Rich Protoplanetary Disks And Gas-Poor Debris Disks, K A. Collins, C A. Grady, K Hamaguchi, J P. Wisniewski, Sean D. Brittain, M Sitko, W J. Carpenter, J P. Williams, G S. Mathews, G M. Williger, R Van Boekel, A Carmona, Th. Henning, M E. Van Den Ancker, G Meeus, X P. Chen, R Petre, B E. Woodgate

Publications

HD 100453 has an IR spectral energy distribution (SED) which can be fit with a power law plus a blackbody. Previous analysis of the SED suggests that the system is a young Herbig Ae star with a gas-rich, flared disk. We reexamine the evolutionary state of the HD 100453 system by refining its age (based on a candidate low-mass companion) and by examining limits on the disk extent, mass accretion rate, and gas content of the disk environment. We confirm that HD 100453B is a common proper motion companion to HD 100453A, with a spectral type of M4.0V-M4.5V, and derive …

Go to article

Nuclear Resonances: The Quest For Large Column Densities And A New Tool, J. Greiner, S. Boggs, G. Dicocco, K. T. Freese, N. Gehrels, Dieter H. Hartmann, A. Iyudin, G. Kanbach, A. A. Zdziarski Jan 2009

Nuclear Resonances: The Quest For Large Column Densities And A New Tool, J. Greiner, S. Boggs, G. Dicocco, K. T. Freese, N. Gehrels, Dieter H. Hartmann, A. Iyudin, G. Kanbach, A. A. Zdziarski

Publications

Nuclear physics offers us a powerful tool: using nuclear resonance absorption lines to infer the physical conditions in astrophysical settings which are otherwise diffcult to deduce. Present-day technology provides an increase in sensitivity over previous gamma-ray missions large enough to utilize this tool for the first time. The most exciting promise is to measure gamma-ray bursts from the first star(s) at redshifts 20–60, but also active galactic nuclei are promising targets.

Go to article

Book Review: Escaping The Bonds Of Earth: The Fifties And The Sixties, T. D. Oswalt Jan 2009

Book Review: Escaping The Bonds Of Earth: The Fifties And The Sixties, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of by Ben Evans. Springer/Praxis, 2009 493p, 9780387790930 $39.95

Go to article

Book Review: Humans In Outer Space-Interdisciplinary Odysseys, Studies In Space Policy, 1, T. D. Oswalt Jan 2009

Book Review: Humans In Outer Space-Interdisciplinary Odysseys, Studies In Space Policy, 1, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Humans in Outer Space-Interdisciplinary Odysseys, Studies in Space Policy, 1. [ed.] by Luca Codignola and Kai-Uwe Schrogl with Agnieszka Lukaszczyk and Nicolas Peter SpringerWeinNewYork, 2009

Go to article

Statistical Analysis Of Stellar Evolution, David A. Van Dyk, Ted Von Hippel, Steven Degenarro, Nathan Stein, William Jefferys Jan 2009

Statistical Analysis Of Stellar Evolution, David A. Van Dyk, Ted Von Hippel, Steven Degenarro, Nathan Stein, William Jefferys

Publications

Color-Magnitude Diagrams (CMDs) are plots that compare the magnitudes (luminosities) of stars in different wavelengths of light (colors). High nonlinear correlations among the mass, color, and surface temperature of newly formed stars induce a long narrow curved point cloud in a CMD known as the main sequence. Aging stars form new CMD groups of red giants and white dwarfs. The physical processes that govern this evolution can be described with mathematical models and explored using complex computer models. These calculations are designed to predict the plotted magnitudes as a function of parameters of scientific interest, such as stellar age, mass, …

Go to article

Gravitational Wave Burst Source Direction Estimation Using Time And Amplitude Information, J. Markowitz, M. Zanolin, L. Cadonati, E. Katsavounidis Dec 2008

Gravitational Wave Burst Source Direction Estimation Using Time And Amplitude Information, J. Markowitz, M. Zanolin, L. Cadonati, E. Katsavounidis

Publications

In this article we study two problems that arise when using timing and amplitude estimates from a network of interferometers (IFOs) to evaluate the direction of an incident gravitational wave burst (GWB). First, we discuss an angular bias in the least squares timing-based approach that becomes increasingly relevant for moderate to low signal-to-noise ratios. We show how estimates of the arrival time uncertainties in each detector can be used to correct this bias. We also introduce a stand alone parameter estimation algorithm that can improve the arrival time estimation and provide root-sum-squared strain amplitude (h(rss)) values for each site. In …

Go to article

Magnetohydrodynamic Effects In Propagating Relativistic Jets: Reverse Shock And Magnetic Acceleration, Yosuke Mizuno, Bing Zhang, Bruno Giacomazzo, Ken-Ichi Nishikawa, Phillip E. Hardee, Shigehiro Nagataki, Dieter H. Hartmann Dec 2008

Magnetohydrodynamic Effects In Propagating Relativistic Jets: Reverse Shock And Magnetic Acceleration, Yosuke Mizuno, Bing Zhang, Bruno Giacomazzo, Ken-Ichi Nishikawa, Phillip E. Hardee, Shigehiro Nagataki, Dieter H. Hartmann

Publications

We solve the Riemann problem for the deceleration of an arbitrarily magne-tized relativistic flow injected into a static unmagnetized medium in one dimen-sion. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization σ (the Poynting-to-kinetic energy flux ratio), and the shock becomes a rarefaction wave when σ exceeds a critical value, σc, defined by the balance between the magnetic pressure in the flow and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly …

Go to article

A Three-Dimensional Pattern-Space Representation For Volumetric Arrays, William C. Barott, Paul G. Steffes Dec 2008

A Three-Dimensional Pattern-Space Representation For Volumetric Arrays, William C. Barott, Paul G. Steffes

Publications

A three-dimensional pattern-space representation is presented for volumetric arrays. In this representation, the radiation pattern of an array is formed by the evaluation of the three-dimensional pattern-space on a spherical surface. The scan angle of the array determines the position of this surface within the pattern-space. This pattern-space representation is used in conjunction with a genetic algorithm to minimize the sidelobe levels exhibited by a thinned volumetric array during scanning.

Go to article

Geocoronal Hydrogen Observations Spanning Three Solar Minima, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, L. M. Haffner, R. J. Reynolds, R. C. Woodward Nov 2008

Geocoronal Hydrogen Observations Spanning Three Solar Minima, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, L. M. Haffner, R. J. Reynolds, R. C. Woodward

Publications

The 11-year solar cycle is a dominant source of natural variability in the upper atmosphere, and its effect on atomic hydrogen distributions and emissions must be understood to investigate possible signs of longer-term climatic trends in this region. We present midlatitude geocoronal hydrogen Balmer α observations from solar cycle 23 (1997–2006) and three solar minimum periods, 1985, 1997, and 2006. The 1997 through 2006 observations were taken with the Wisconsin H-αMapper Fabry-Perot (WHAM), a ground-based CCD-annular summing instrument that began observations at the Kitt Peak Observatory in Arizona in 1997. The 1985 observations were made with a similarly …

Go to article

First Prev Next Last