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2010

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Articles 211 - 240 of 276

Full-Text Articles in Astrophysics and Astronomy

The Acs Survey Of Galactic Globular Clusters. Viii. Effects Of Environment On Globular Cluster Global Mass Functions, Nathaniel E. Q. Paust, I. Neill Reid, Giampaolo Piotto, Antonio Aparicio, Jay Anderson, Ata Sarajedini, Luigi R. Bedin, Brian Chaboyer Jan 2010

The Acs Survey Of Galactic Globular Clusters. Viii. Effects Of Environment On Globular Cluster Global Mass Functions, Nathaniel E. Q. Paust, I. Neill Reid, Giampaolo Piotto, Antonio Aparicio, Jay Anderson, Ata Sarajedini, Luigi R. Bedin, Brian Chaboyer

Dartmouth Scholarship

We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models to extrapolate from our observations to the global cluster behavior. The global present-day mass functions for these clusters are well matched by power laws from the turnoff, ≈0.8 M ☉, to 0.2-0.3 M ☉ on the lower main sequence. The slopes of those power-law fits, α, have been correlated with an extensive set of intrinsic and extrinsic cluster properties to investigate which parameters may influence the form …

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The Determination Of Reddening From Intrinsic Vr Colors Of Rr Lyrae Stars, Andrea Kunder, Brian Chaboyer, Andrew Layden Jan 2010

The Determination Of Reddening From Intrinsic Vr Colors Of Rr Lyrae Stars, Andrea Kunder, Brian Chaboyer, Andrew Layden

Dartmouth Scholarship

New R-band observations of 21 local field RR Lyrae variable stars are used to explore the reliability of minimum light (V – R) colors as a tool for measuring interstellar reddening. For each star, R-band intensity mean magnitudes and light amplitudes are presented. Corresponding V-band light curves from the literature are supplemented with the new photometry, and (V – R) colors at minimum light are determined for a subset of these stars as well as for other stars in the literature. Two different definitions of minimum light color are examined, one which uses …

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A Hybrid Particle-Continuum Method For Hydrodynamics Of Complex Fluids, Alejandro Garcia, A. Donev, J. B. Bell, B. Alder Jan 2010

A Hybrid Particle-Continuum Method For Hydrodynamics Of Complex Fluids, Alejandro Garcia, A. Donev, J. B. Bell, B. Alder

Faculty Publications

A previously developed hybrid particle-continuum method [J. B. Bell, A. Garcia, and S. A. Williams, Multiscale Model. Simul., 6 (2008), pp. 1256–1280] is generalized to dense fluids and two- and three-dimensional flows. The scheme couples an explicit fluctuating compressible Navier–Stokes solver with the isotropic direct simulation Monte Carlo (DSMC) particle method [A. Donev, A. L. Garcia, and B. J. Alder, J. Stat. Mech. Theory Exp., 2009 (2009), article P11008]. To achieve bidirectional dynamic coupling between the particle (microscale) and continuum (macroscale) regions, the continuum solver provides state-based boundary conditions to the particle subdomain, while the particle solver provides flux-based boundary …

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The Globular Cluster System Of Ngc 1399. V. Dynamics Of The Cluster System Out To 80 Kpc, Y. Schuberth, T. Richtler, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky, L. Infante Jan 2010

The Globular Cluster System Of Ngc 1399. V. Dynamics Of The Cluster System Out To 80 Kpc, Y. Schuberth, T. Richtler, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky, L. Infante

Faculty Publications

Globular clusters (GCs) are tracers of the gravitational potential of their host galaxies. Moreover, their kinematic properties may provide clues for understanding the formation of GC systems and their host galaxies. We use the largest set of GC velocities obtained so far of any elliptical galaxy to revise and extend the previous investigations (Richtler et al. 2004) of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax cluster of galaxies. The GC velocities are used to study the kinematics, their relation with population properties, and the dark matter halo of NGC 1399. We have obtained 477 …

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Central Dark Matter Content Of Early-Type Galaxies: Scaling Relations And Connections With Star Formation Histories, N. R. Napolitano, Aaron J. Romanowsky, A. J. Tortora Jan 2010

Central Dark Matter Content Of Early-Type Galaxies: Scaling Relations And Connections With Star Formation Histories, N. R. Napolitano, Aaron J. Romanowsky, A. J. Tortora

Faculty Publications

We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of 〈ρDM〉∝R−2eff provides the first clear indication of cuspy DM haloes in these galaxies – akin to standard Λ cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as …

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A Long-Period Planet Orbiting A Nearby Sun-Like Star, Hugh R. A. Jones, R. Paul Butler, Chris Tinney, Simon O'Toole, Rob Wittenmyer, Gregory W. Henry, Stefano Meschiari, Steve Vogt, Eugenio Rivera, Greg Laughlin, Brad D. Carter, Jeremy Bailey, James S. Jenkins Jan 2010

A Long-Period Planet Orbiting A Nearby Sun-Like Star, Hugh R. A. Jones, R. Paul Butler, Chris Tinney, Simon O'Toole, Rob Wittenmyer, Gregory W. Henry, Stefano Meschiari, Steve Vogt, Eugenio Rivera, Greg Laughlin, Brad D. Carter, Jeremy Bailey, James S. Jenkins

Information Systems and Engineering Management Research Publications

The Doppler wobble induced by the extra-solar planet HD 134987b was first detected by data from the Keck Telescope nearly a decade ago, and was subsequently confirmed by data from the Anglo-Australian Telescope (AAT). However, as more data have been acquired for this star over the years since, the quality of a single Keplerian fit to that data has been getting steadily worse. The best-fitting single Keplerian to the 138 Keck and AAT observations now in hand has an root-mean-square (rms) scatter of 6.6 m s−1. This is significantly in excess of both the instrumental precision achieved by both the …

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Observations Of Ozone Production In A Dissipating Tropical Convective Cell During Tc4, Gary A. Morris, A. M. Thompson, K. E. Pickering, S. Chen, E. J. Bucsela, P. A. Kucera Jan 2010

Observations Of Ozone Production In A Dissipating Tropical Convective Cell During Tc4, Gary A. Morris, A. M. Thompson, K. E. Pickering, S. Chen, E. J. Bucsela, P. A. Kucera

Physics and Astronomy Faculty Publications

From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times …

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A Model For Predicting Extragalactic Jet Lifetimes, Daniel S. Spicer, Robert Bingham, Stephen O'Sullivan Jan 2010

A Model For Predicting Extragalactic Jet Lifetimes, Daniel S. Spicer, Robert Bingham, Stephen O'Sullivan

Articles

Abstract. In this letter, we propose a model to explain the disintegration of ex- tragalactic jets and to predict the associated timescale. The model assumes that a jet is current and charge neutral as well as collimated at its source; however, the forward electron current gradually decays producing a magnetic field transverse to the direction of jet propagation. This growing transverse magnetic field eventually causes the jet to disintegrate.

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A Two-Dimensional, Linear–Elastic Model To Explain Radial Extensional Fractures, Pantheon Fossae, Caloris Basin, Mercury, Brianne Mcdonough Jan 2010

A Two-Dimensional, Linear–Elastic Model To Explain Radial Extensional Fractures, Pantheon Fossae, Caloris Basin, Mercury, Brianne Mcdonough

Undergraduate Review

In this study, two-dimensional linear elasticity theory is used to model the lithospheric stress field that produces radial extensional fractures observed at Pantheon Fossae in the Caloris Basin of Mercury. These fractures were imaged by the MESSENGER mission flyby of Mercury on January 14, 2008 and show radial fractures extending outward from a 40-kilometer impact crater named Apollodorus. Recent studies have proposed several different mechanisms to explain these fractures, including magmatic processes, central basin uplift, and stresses produced by the formation of the impact crater itself.

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Sensitivity Of Planetary Boundary Layer To Varying Volumetric Soil Moisture: A Mesoscale Models Comparision, Asrid Suarez Gonzalez Jan 2010

Sensitivity Of Planetary Boundary Layer To Varying Volumetric Soil Moisture: A Mesoscale Models Comparision, Asrid Suarez Gonzalez

Mahurin Honors College Capstone Experience/Thesis Projects

A comparison between two Mesoscale models, Colorado State University Regional Atmospheric Model System (RAMS) version 4.4 coupled with the Land‐Ecosystem– Atmosphere Feedback Model (LEAF2) and Penn State/NCAR’s Mesoscale Model (MM5) coupled with NOAH Land Surface Model, was conducted in order to assess the sensitivity of forecasted boundary layer variables to anomalous volumetric soil moistures. The study elaborates on the findings of Quintanar et al. (2008) using the study’s experimental design as a template for our numerical model comparison. The experiments were conducted using the same synoptic events examined by Quintanar et al. (2008): June 11, June 17 and June 22, …

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Solar Observations During A Solar Minimum Using A Small Radio Telescope, Gary Forrester Jan 2010

Solar Observations During A Solar Minimum Using A Small Radio Telescope, Gary Forrester

Undergraduate Review

The Sun is currently in a quiescent phase called solar minimum. We used Bridgewater State College’s (B.S.C.’s) Small Radio Telescope (SRT) to observe solar radio emission during this quiet phase and correlated our data to solar X-ray data readily available through the National Oceanic and Atmospheric Administration (NOAA). Previous observations made during a period of high solar activity (solar maximum) using one of M.I.T.’s SRTs showed that some solar radio and X-ray events were correlated, while others were not. We made observations during solar minimum and found one event where there was a correlation between radio and X-ray emission.

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The Horizontal Electric Field Induced By A Lightning Return Stroke, S L. Meredith, S K. Earles, Niescja E. Turner Jan 2010

The Horizontal Electric Field Induced By A Lightning Return Stroke, S L. Meredith, S K. Earles, Niescja E. Turner

Physics and Astronomy Faculty Research

Problem statement: Develop a new formula which describes the horizontal electric field induced by a lightning return stroke in contact with an imperfect conductive surface. Approach: A new method for describing the horizontal electric field induced by a lightning return stroke will be presented. The method presented here had utilized an approach which purposely downplayed the physics of how image theory was employed in the presence of an imperfect conductive surface. It did so by adopting a technique which had focused on the geometry that existed between the lightning channel and surface ground. In doing so, new expressions …

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A New Method To Describe Image Theory For An Imperfect Conductor, S L. Meredith, S K. Earles, Niescja E. Turner Jan 2010

A New Method To Describe Image Theory For An Imperfect Conductor, S L. Meredith, S K. Earles, Niescja E. Turner

Physics and Astronomy Faculty Research

Problem statement: Modify the equations associated with image theory in order to account for perfect and imperfect conductors. Approach: A novel approach for describing the application of image theory for an imperfect conductive surface was presented. The method presented here purposely downplays the physics of how image theory was employed to account for a charge which is in the presence of an imperfect conductive surface. In turn, it adopted an approach which focused on the geometry that existed between the charged particle and surface ground. In doing so, the proposed method formulated a solution that had minimized the …

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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 …

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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 …

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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 …

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Aztec Half Square Degree Survey Of The Shades Fields - I. Maps, Catalogues And Source Counts, J. E. Austermann, J. S. Dunlop, T. A. Perera, K. S. Scott, G. W. Wilson, I. Aretxaga, D. H. Hughes, O. Almaini, E. L. Chapin, S. C. Chapman, M. Cirasuolo, D. L. Clements, K. E.K. Coppin, L. Dunne, S. Dye, S. A. Eales, E. Egami, D. Farrah, D. Ferrusca, S. Flynn, D. Haig, M. Halpern, E. Ibar, R. J. Ivison, E. Van Kampen, Y. Kang, S. Kim, C. Lacey, James D. Lowenthal, P. D. Mauskopf, R. J. Mclure, A. M.J. Mortier Jan 2010

Aztec Half Square Degree Survey Of The Shades Fields - I. Maps, Catalogues And Source Counts, J. E. Austermann, J. S. Dunlop, T. A. Perera, K. S. Scott, G. W. Wilson, I. Aretxaga, D. H. Hughes, O. Almaini, E. L. Chapin, S. C. Chapman, M. Cirasuolo, D. L. Clements, K. E.K. Coppin, L. Dunne, S. Dye, S. A. Eales, E. Egami, D. Farrah, D. Ferrusca, S. Flynn, D. Haig, M. Halpern, E. Ibar, R. J. Ivison, E. Van Kampen, Y. Kang, S. Kim, C. Lacey, James D. Lowenthal, P. D. Mauskopf, R. J. Mclure, A. M.J. Mortier

Astronomy: Faculty Publications

We present the first results from the largest deep extragalactic mm-wavelength survey undertaken to date. These results are derived from maps covering over 0.7 deg , made at λ = 1.1 mm, using the AzTEC continuum camera mounted on the James Clerk Maxwell Telescope. The maps were made in the two fields originally targeted at λ = 850 μm with the Submillimetre Common-User Bolometer Array (SCUBA) in the SCUBA Half-Degree Extragalactic Survey (SHADES) project, namely the Lockman Hole East (mapped to a depth of 0.9-1.3 mJy rms) and the Subaru/XMM-Newton Deep Field (mapped to a depth of 1.0-1.7 mJy rms). …

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Unidirectional Nonlinear Pt-Symmetric Optical Structures, Hamidreza Ramezani, Tsampikos Kottos Jan 2010

Unidirectional Nonlinear Pt-Symmetric Optical Structures, Hamidreza Ramezani, Tsampikos Kottos

Physics & Astronomy Faculty Publications

We show that nonlinear optical structures involving a balanced gain-loss profile can act as unidirectional optical valves. This is made possible by exploiting the interplay between the fundamental symmetries of parity (P) and time (T), with optical nonlinear effects. This unidirectional dynamics is specifically demonstrated for the case of an integrable PT-symmetric nonlinear system.

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Evidence For Supernova-Synthesized Dust From The Rising Afterglow Of Grb071025 At Z ∼ 5, Daniel A. Perley, J. S. Bloom, C. R. Klein, S. Covino, T. Minezaki, P. Wo´Zniak, W. T. Vestrand, G. G. Williams, P. Milne, N. R. Butler, Adria Updike, T. Kr¨Uhler, P. Afonso, A. Antonelli, L. Cowie, P. Ferrero, J. Greiner, D. H. Hartmann, Y. Kakazu, A. K¨Upc¨U Yoldas¸, A. N. Morgan, P. A. Price, J. X. Prochaska, Y. Yoshii Jan 2010

Evidence For Supernova-Synthesized Dust From The Rising Afterglow Of Grb071025 At Z ∼ 5, Daniel A. Perley, J. S. Bloom, C. R. Klein, S. Covino, T. Minezaki, P. Wo´Zniak, W. T. Vestrand, G. G. Williams, P. Milne, N. R. Butler, Adria Updike, T. Kr¨Uhler, P. Afonso, A. Antonelli, L. Cowie, P. Ferrero, J. Greiner, D. H. Hartmann, Y. Kakazu, A. K¨Upc¨U Yoldas¸, A. N. Morgan, P. A. Price, J. X. Prochaska, Y. Yoshii

Arts & Sciences Faculty Publications

No abstract provided.

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A Very Metal-Poor Damped Lyman-Α System Revealed Through The Most Energetic Grb 090926a, A. Rau, S. Savaglio, T. Kr¨ Uhler, P. Afonso, J. Greiner, S. Klose, P. Schady, S. Mcbreen, R. Filgas, F. Olivares E., A. Rossi, Adria Updike Jan 2010

A Very Metal-Poor Damped Lyman-Α System Revealed Through The Most Energetic Grb 090926a, A. Rau, S. Savaglio, T. Kr¨ Uhler, P. Afonso, J. Greiner, S. Klose, P. Schady, S. Mcbreen, R. Filgas, F. Olivares E., A. Rossi, Adria Updike

Arts & Sciences Faculty Publications

No abstract provided.

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Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Deosthenes Kazanas Jan 2010

Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Deosthenes Kazanas

Aerospace, Physics, and Space Science Faculty Publications

We present new Chandra observations of the radio galaxy 3C 445, centered on its southern radio hot spot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hot spot. Attempting to reproduce both the observed spectral energy distribution and the displacement excludes all one-zone models. Modeling of the radio-optical hot spot spectrum suggests that the electron distribution has a low-energy cutoff or break approximately at the proton rest mass energy. The X-rays could be due to external Compton scattering of the cosmic microwave background coming from the fast (Lorentz factor Γ ≈ 4) part of …

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A Multi-Wavelength Spectral And Polarimetric Study Of The Jet Of 3c 264, Eric S. Perlman Jan 2010

A Multi-Wavelength Spectral And Polarimetric Study Of The Jet Of 3c 264, Eric S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

We present a comprehensive multi-band spectral and polarimetric study of the jet of 3C 264 (NGC 3862). Included in this study are three Hubble Space Telescope (HST) optical and ultraviolet polarimetry data sets, along with new and archival Very Large Array radio imaging and polarimetry, a re-analysis of numerous HST broadband data sets from the near infrared to the far ultraviolet, and a Chandra ACIS-S observation. We investigate similarities and differences between optical and radio polarimetry, in both degree of polarization and projected magnetic field direction. We also examine the broadband spectral energy distribution of both the nucleus and jet …

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Magnetic Cloud Boundary Layer Of 9 November 2004 And Its Associated Space Weather Effects, Pingbing Zuo, Fengsi Wei, Xueshang Feng, Xiaojun Xu, Wenbin Song Jan 2010

Magnetic Cloud Boundary Layer Of 9 November 2004 And Its Associated Space Weather Effects, Pingbing Zuo, Fengsi Wei, Xueshang Feng, Xiaojun Xu, Wenbin Song

Aerospace, Physics, and Space Science Faculty Publications

On 9 November 2004, the WIND spacecraft detected a magnetic cloud boundary layer (MCBL) during the interval from 19:07 UT to 20:30 UT. Within the MCBL, there is intense southward magnetic field and the dynamic pressure is rather high, which makes it much geoeffective. Twenty-three minutes later, the MCBL arrived on the magnetopause. An intense geomagnetic storm main phase was driven by the sustaining strong southward magnetic field within the MCBL. During the passage of the MCBL, a typical magnetospheric substorm was triggered. The substorm onset was synthetically identified by the aurora breakup, magnetic dipolarization, dispersionless particle injection, Pi2 pulsation, …

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The Heavily Polluted Atmosphere Of The Daz White Dwarf Galex J193156.8+011745, Stephane Vennes, Adéla Kawka, Péter Németh Jan 2010

The Heavily Polluted Atmosphere Of The Daz White Dwarf Galex J193156.8+011745, Stephane Vennes, Adéla Kawka, Péter Németh

Aerospace, Physics, and Space Science Faculty Publications

We report on the discovery of a new heavily polluted white dwarf. The DAZ white dwarf GALEX J193156.8+011745 was identified in a joint Galaxy Evolution Explorer (GALEX)/GSC survey of ultraviolet-excess objects. Optical spectra obtained at ESO New Technology Telescope show strong absorption lines of magnesium and silicon, and a detailed abundance analysis based on Very Large Telescope-Kueyen UVES spectra reveal super-solar abundances of silicon and magnesium and near-solar abundances of oxygen, calcium and iron. The overall abundance pattern bears the signature of on-going accretion on to the white dwarf atmosphere. The infrared spectral energy distribution shows an excess in the …

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Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Demosthenes Kazanas Jan 2010

Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Demosthenes Kazanas

Aerospace, Physics, and Space Science Faculty Publications

We present new Chandra observations of the radio galaxy 3C 445, centered on its southern radio hot spot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hot spot. Attempting to reproduce both the observed spectral energy distribution and the displacement excludes all one-zone models. Modeling of the radio-optical hot spot spectrum suggests that the electron distribution has a low-energy cutoff or break approximately at the proton rest mass energy. The X-rays could be due to external Compton scattering of the cosmic microwave background coming from the fast (Lorentz factor Γ ≈ 4) part of …

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Thunderstorm Characteristics Associated With Rhessi Identified Terrestrial Gamma Ray Flashes, Michael E. Splitt, Steven M. Lazarus, Diana H. Barnes, Joseph R. Dwyer, Hamid K. Rassoul, David M. Smith, Bryna J. Hazelton, Brian W. Grefenstette Jan 2010

Thunderstorm Characteristics Associated With Rhessi Identified Terrestrial Gamma Ray Flashes, Michael E. Splitt, Steven M. Lazarus, Diana H. Barnes, Joseph R. Dwyer, Hamid K. Rassoul, David M. Smith, Bryna J. Hazelton, Brian W. Grefenstette

Aerospace, Physics, and Space Science Faculty Publications

The characteristics of thunderstorms that produce terrestrial gamma-ray flashes (TGFs) observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are determined using climatological and meteorological data. RHESSI observed TGFs follow diurnal, seasonal, and geographic patterns that are very similar to those of thunderstorms confirming, in part, that these events are directly connected to thunderstorm activity. The TGF producing thunderstorms are shown to be closely associated with tall (ranging from 13.6 km to 17.3 km) tropical thunderstorm systems, a finding that is consistent with theoretical expectations from models of relativistic breakdown that relate the source region to the spectral …

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Acceleration Of Suprathermal Particles By Compressional Plasma Wave Trains In The Solar Wind, Ming Zhang Jan 2010

Acceleration Of Suprathermal Particles By Compressional Plasma Wave Trains In The Solar Wind, Ming Zhang

Aerospace, Physics, and Space Science Faculty Publications

This paper presents a calculation of particle acceleration by an idealized compressional plasma wave train. In this model, suprathermal particles, such as pickup ions, are continuously injected into a wave train consisting of a series of compression or rarefaction regions. The momentum distribution of particles will become broader and broader as they go through the wave train, which is very similar to diffusion in momentum space. The acceleration process is very fast: it does not take too many wave cycles even with a small compression amplitude to reach an asymptotic steady state momentum distribution. In the absence of large-scale adiabatic …

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Diffusion Of Relativistic Runaway Electrons And Implications For Lightning Initiation, Joseph R. Dwyer Jan 2010

Diffusion Of Relativistic Runaway Electrons And Implications For Lightning Initiation, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

Using detailed Monte Carlo simulations, the diffusion coefficients for relativistic runaway electron avalanches in air are found for the range of electric field strengths applicable to thunderclouds. Diffusion causes runaway electron avalanches to spread perpendicular to and parallel to the avalanche direction, resulting in much smaller peak conductivities than would be inferred otherwise. The idea that runaway electron avalanches seeded by extensive cosmic ray air showers may initiate lightning has gained considerable popularity in recent years. However, using the diffusion coefficients calculated in this paper along with the avalanche multiplication limit from X-ray and positron feedback, it is found that …

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Star Formation And Uv Colors Of The Brightest Cluster Galaxies In The Representative Xmm-Newton Cluster Structure Survey, Megan Donahue, Seth Bruch, Emily Wang, G. Mark Voit Jan 2010

Star Formation And Uv Colors Of The Brightest Cluster Galaxies In The Representative Xmm-Newton Cluster Structure Survey, Megan Donahue, Seth Bruch, Emily Wang, G. Mark Voit

University Faculty Publications and Creative Works

We present UV broadband photometry and optical emission-line measurements for a sample of 32 brightest cluster galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM-Newton Optical Monitor, supplemented by existing archival Galaxy Evolution Explorer photometry. We detected Hα and forbidden line emission in seven (22%) of these BCGs, in …

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High-Resolution Cavity-Enhanced Spectroscopy Of Molecular Ion Beams, Manori Perera, Andrew Mills, Brian Siller, Michael Porambo, Kyle Crabtree, Carrie Kauffman, Holger Kreckel, Benjamin Mccall Jan 2010

High-Resolution Cavity-Enhanced Spectroscopy Of Molecular Ion Beams, Manori Perera, Andrew Mills, Brian Siller, Michael Porambo, Kyle Crabtree, Carrie Kauffman, Holger Kreckel, Benjamin Mccall

Scholarship

Molecular ions play a pivotal role in the chemistry of the interstellar medium due to their high reactivity even at low temperature. To identify these ions in interstellar space, it is essential to obtain high resolution laboratory spectra of potential interstellar ions for comparison to observational data. At the University of Illinois, we are developing a Sensitive, Cooled, Resolved Ion BEam Spectrometer (SCRIBES) that will allow us to obtain high resolution infrared direct absorption spectra of rotationally cold molecular ions in the absence of neutral molecules. This instrument can overcome many of the problems that arise when using other spectroscopic …

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