Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Institution
-
- University of Texas Rio Grande Valley (708)
- University of Kentucky (579)
- Selected Works (543)
- Dartmouth College (436)
- Embry-Riddle Aeronautical University (428)
-
- Tennessee State University (403)
- Brigham Young University (363)
- San Jose State University (320)
- Florida Institute of Technology (290)
- University of New Mexico (264)
- University of Massachusetts Amherst (215)
- University of Nevada, Las Vegas (215)
- University of New Hampshire (208)
- University of Louisville (207)
- Swarthmore College (205)
- University of Alabama in Huntsville (173)
- Clemson University (169)
- Andrews University (150)
- Old Dominion University (135)
- Western University (128)
- Smith College (122)
- University of Nebraska - Lincoln (119)
- Utah State University (114)
- University of South Carolina (107)
- California Polytechnic State University, San Luis Obispo (94)
- Munster Technological University (94)
- University of Arkansas, Fayetteville (92)
- Chapman University (89)
- SelectedWorks (84)
- City University of New York (CUNY) (82)
- Keyword
-
- Astrophysics (290)
- Astronomy (258)
- Galaxies (246)
- Galaxies: evolution (243)
- Stars (205)
-
- Planetary systems (142)
- White dwarfs (132)
- Refereed Publications (130)
- Gravitational waves (129)
- Accretion (128)
- Galaxies: structure (128)
- Physics (116)
- Cosmology (115)
- Galaxies: spiral (111)
- Galaxies: formation (104)
- X-rays (100)
- Galaxies: high-redshift (90)
- Surveys (90)
- 1.3 PHYSICAL SCIENCES (89)
- Galaxies: ISM (84)
- Quasars (83)
- Binaries (81)
- Cosmology and astronomy (79)
- Stellar activity (75)
- Galaxies: fundamental parameters (74)
- Spectroscopic binaries (74)
- Galaxies: stellar content (69)
- Physics and Astronomy (69)
- Mars (68)
- Galaxy evolution (67)
- Publication Year
- Publication
-
- Physics and Astronomy Faculty Publications and Presentations (695)
- Faculty Publications (637)
- Physics and Astronomy Faculty Publications (615)
- Publications (508)
- Dartmouth Scholarship (430)
-
- Information Systems and Engineering Management Research Publications (401)
- Aerospace, Physics, and Space Science Faculty Publications (266)
- Theses and Dissertations (210)
- Physics & Astronomy ETDs (206)
- Physics & Astronomy Faculty Works (204)
- Faculty and Staff Scholarship (195)
- Space Science Center (159)
- Physics Faculty Publications (144)
- Physics & Astronomy Faculty Research (140)
- Astronomy: Faculty Publications (120)
- Space Journal (102)
- Benne Holwerda (101)
- Richard Ignace (87)
- Physical Sciences Publications (84)
- Mauro Giavalisco (82)
- Ted von Hippel (79)
- Mathematics, Physics, and Computer Science Faculty Articles and Research (77)
- Macalester Journal of Physics and Astronomy (76)
- Honors Theses (68)
- Aaron J. Romanowsky (67)
- Physics and Astronomy Faculty Research Publications (67)
- Physics & Astronomy (64)
- Electronic Thesis and Dissertation Repository (63)
- Faculty and Student Publications (63)
- Department of Physics and Astronomy: Syllabi (62)
- Publication Type
Articles 7891 - 7920 of 9206
Full-Text Articles in Physical Sciences and Mathematics
First-Principles Elastic Constants And Electronic Structure Of Α-Pt2si And Ptsi, Gus L. W. Hart, O. Beckstein, J. E. Klepeis, O. Pankratov
First-Principles Elastic Constants And Electronic Structure Of Α-Pt2si And Ptsi, Gus L. W. Hart, O. Beckstein, J. E. Klepeis, O. Pankratov
Faculty Publications
We have carried out a first-principles study of the elastic properties and electronic structure for two room-temperature stable Pt silicide phases, tetragonal α-Pt2Si, and orthorhomic PtSi. We have calculated all of the equilibrium structural parameters for both phases; the a and c lattice constants for α-Pt2Si and the a, b, and c lattice constants and four internal structural parameters for PtSi. These results agree closely with experimental data. We have also calculated the zero-pressure elastic constants, confirming prior results for pure Pt and Si and predicting values for the six (nine) independent, nonzero elastic constants of α-Pt2Si (PtSi). These calculations …
Fractal Quasar Clouds, Mark Bottorff, Gary J. Ferland
Fractal Quasar Clouds, Mark Bottorff, Gary J. Ferland
Physics and Astronomy Faculty Publications
This paper examines whether a fractal cloud geometry can reproduce the emission-line spectra of active galactic nuclei (AGNs). The nature of the emitting clouds is unknown, but many current models invoke various types of magnetohydrodynamic confinement. Recent studies have argued that a fractal distribution of clouds, in which subsets of clouds occur in self-similar hierarchies, is a consequence of such confinement. Whatever the confinement mechanism, fractal cloud geometries are found in nature and may be present in AGNs too. We first outline how a fractal geometry can apply at the center of a luminous quasar. Scaling laws are derived that …
0920+3517_Nir_Spex, Maria Teresa Ruiz
An Optical Survey Of Outlying Ejecta In Cassiopeia A: Evidence For A Turbulent, Asymmetric Explosion, Robert A. Fesen
An Optical Survey Of Outlying Ejecta In Cassiopeia A: Evidence For A Turbulent, Asymmetric Explosion, Robert A. Fesen
Dartmouth Scholarship
A deep optical survey of the Cassiopeia A supernova remnant has revealed dozens of new emissionline ejecta knots out beyond the remnantÏs bright nebular shell. Most of the newly detected knots exhibit a 4500È 7500 A. spectrum dominated by [N II ] jj 6548,6583 line emissions. After accounting for possible decelerations, the estimated space velocities for about four dozen of these [N II ] knots suggest a nearly isotropic ^ 10,000 km s~1 ejection velocity. However, a small group along the southwestern limb show signi‹cantly higher velocities of up to 12,000 km s~1 . Over 20 outlying O] S emission …
Hubble Space Telescope Images Of The Ultraluminous Supernova Remnant Complex In Ngc 6946, William P. Blair, Robert A. Fesen, Eric M. Schlegel
Hubble Space Telescope Images Of The Ultraluminous Supernova Remnant Complex In Ngc 6946, William P. Blair, Robert A. Fesen, Eric M. Schlegel
Dartmouth Scholarship
We present Hubble Space Telescope (HST) narrow-passband Hα and [S II] images and broadband continuum images of the region around an extremely luminous optical and X-ray supernova remnant complex in the spiral galaxy NGC 6946. These images, obtained with the PC1 CCD of the Wide Field Planetary Camera 2, show a circular, limb-brightened shell of diameter 035 [9 d/(5.1 Mpc) pc] superposed on the edge of a larger, lower surface brightness elliptical shell (14 × 08, or 34 pc × 20 pc). The HST images allow us to see that the [S II] : Hα ratio remains …
Theoretical Profile Shapes For Optically Thin X-Ray Emission Lines From Spherical Stellar Winds., R. Ignace
Theoretical Profile Shapes For Optically Thin X-Ray Emission Lines From Spherical Stellar Winds., R. Ignace
Richard Ignace
One of the major outstanding problems in hot star wind theory is an understanding of the observed X-ray emissions from the early-type B, O, and Wolf-Rayet (WR) stars. The latest X-ray satellites Chandra and XMM-Newton are providing key new observations of resolved emission profiles to advance that understanding. This study presents a derivation of the expected emission-line profiles, assuming optically thin line emission and spherical symmetry, with a proper treatment of the attenuation of X-rays by the dense cool wind component. Examples of line profile variability for a narrow outflowing shell are presented. Then the case of embedded hot gas …
Near-Infrared Spectroscopy Of The Cassiopeia A And Kepler Supernova Remnants, Christopher L. Gerardy, Robert A. Fesen
Near-Infrared Spectroscopy Of The Cassiopeia A And Kepler Supernova Remnants, Christopher L. Gerardy, Robert A. Fesen
Dartmouth Scholarship
Near-infrared spectra (0.95 – 2.4 μm) of the Cassiopeia A and Kepler supernova remnants (SNRs) are presented. Low-dispersion (R ≈ 700) spectra were obtained for five bright fast-moving ejecta knots (FMKs) at two locations on the main shell and for three bright circumstellar knots (QSFs) near the southwest rim of Cas A. The main shell FMKs in Cas A exhibit a sparse near- infrared spectrum dominated by [S II] 1.03 μm emission with a handful of other, fainter emission lines. Among these are two high-ionization silicon lines, [Si VI] 1.96 μm and [Si X] 1.43 μm, which have been detected …
A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion
A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion
Publications
The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based distance moduli that place them at a distance within 20 pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such well-known systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is largely complete …
Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer
Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer
Dartmouth Scholarship
We present long-slit spectroscopy, B - and R -bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters, which are known to be either in a star-forming phase or to have had star formation that recently terminated. From the long-slit spectra, obtained with the Blanco 4 m telescope, we ‹nd that emission lines in the star-forming cluster galaxies are signi‹cantly more centrally concentrated than in a sample of ‹eld galaxies. The broadband imaging reveals that two currently starforming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has …
The Hanle Effect As A Diagnostic Of Magnetic Fields In Stellar Envelopes Iii. Including The Finite Star Depolarization Effect., R. Ignace
Richard Ignace
The Hanle effect is a relatively new magnetic diagnostic in stellar astrophysics. Although a substantial literature exists for applications of the Hanle effect in solar studies, the Hanle effect is only a fledgling subject in stellar astrophysics, with previous work focusing on simplistic cases to isolate the magnetic effects on polarized resonance scattering line profiles. In particular, applications to stars have treated the star as a point source of illumination. This paper carries the work forward by considering the consequences of finite stellar size for the line polarization. An approach based on intensity moments is derived. For optically thin line …
Comptel Observations Of The Blazars 3c 454.3 And Cta 102, S Zhang, W Collmar, V Schonfelder, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Comptel Observations Of The Blazars 3c 454.3 And Cta 102, S Zhang, W Collmar, V Schonfelder, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Space Science Center
We have analyzed the two blazars of 3C 454.3 and CTA 102 using all available COMPTEL data from 1991 to 1999. In the 10–30 MeV band, emission from the general direction of the sources is found at the 4σ-level, being consistent with contributions from both sources. Below 10 MeV only 3C 454.3 is significantly detected, with the strongest evidence (5.6 σ) in the 3–10 MeV band. Significant flux variability is not observed for both sources, while a low emission is seen most of the years in the 3–10 MeV light curve for 3C 454.3. Its time-averaged MeV spectrum suggests a …
Comptel Gamma-Ray Observations Of The C4 Solar Flare On 20 January 2000, C A. Young, M B. Arndt, K Bennett, A Connors, H Debrunner, R Diehl, Mark L. Mcconnell, R S. Miller, G Rank, James M. Ryan, V Schonfelder, C Winkler
Comptel Gamma-Ray Observations Of The C4 Solar Flare On 20 January 2000, C A. Young, M B. Arndt, K Bennett, A Connors, H Debrunner, R Diehl, Mark L. Mcconnell, R S. Miller, G Rank, James M. Ryan, V Schonfelder, C Winkler
Space Science Center
The “Pre-SMM” (Vestrand and Miller 1998) picture of gamma-ray line (GRL) flares was that they are relatively rare events. This picture was quickly put in question with the launch of the Solar Maximum Mission (SMM). Over 100 GRL flares were seen with sizes ranging from very large GOES class events (X12) down to moderately small events (M2). It was argued by some (Bai 1986) that this was still consistent with the idea that GRL events are rare. Others, however, argued the opposite (Vestrand 1988; Cliver, Crosby and Dennis 1994), stating that the lower end of this distribution was just a …
The Milagro Gamma-Ray Observatory, J E. Mcenery, R Atkins, W Benbow, D Berley, M L. Chen, D G. Coyne, B L. Dingus, D E. Dorfan, R W. Ellsworth, D Evans, A Falcone, L Fleysher, R Fleysher, G Gisler, J A. Goodman, T J. Haines, C M. Hoffman, S Hugenberger, L A. Kelley, I Leonor, Mark L. Mcconnell, J F. Mccullough, R S. Miller, A I. Mincer, M F. Morales, P Nemethy, James M. Ryan, B Shen, A Shoup, C Sinnis, A J. Smith, G W. Sullivan, O T. Tumer, K Wang, M O. Wascko, S Westerhoff, D A. Williams, G B. Yodh
The Milagro Gamma-Ray Observatory, J E. Mcenery, R Atkins, W Benbow, D Berley, M L. Chen, D G. Coyne, B L. Dingus, D E. Dorfan, R W. Ellsworth, D Evans, A Falcone, L Fleysher, R Fleysher, G Gisler, J A. Goodman, T J. Haines, C M. Hoffman, S Hugenberger, L A. Kelley, I Leonor, Mark L. Mcconnell, J F. Mccullough, R S. Miller, A I. Mincer, M F. Morales, P Nemethy, James M. Ryan, B Shen, A Shoup, C Sinnis, A J. Smith, G W. Sullivan, O T. Tumer, K Wang, M O. Wascko, S Westerhoff, D A. Williams, G B. Yodh
Space Science Center
The Milagro water Cherenkov detector began full operation in January 2000. This detector is capable of monitoring the Northern sky at energies above 500 GeV for sources of equivalent strength to the Crab Nebula over one year of integration. We report on the current performance and sensitivity of Milagro.
Building Blocks For Reliable Complex Nonlinear Numerical Simulations, Helen Yee
Building Blocks For Reliable Complex Nonlinear Numerical Simulations, Helen Yee
United States National Aeronautics and Space Administration: Publications
This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is …
Designing Adaptive Low-Dissipative High Order Schemes For Long-Time Integrations, Helen Yee, Bjorn Sjögreen
Designing Adaptive Low-Dissipative High Order Schemes For Long-Time Integrations, Helen Yee, Bjorn Sjögreen
United States National Aeronautics and Space Administration: Publications
A general framework for the design of adaptive low-dissipative high order schemes is presented. It encompasses a rather complete treatment of the numerical approach based on four integrated design criteria: (1) For stability considerations, condition the governing equations before the application of the appropriate numerical scheme whenever it is possible. (2) For consistency, compatible schemes that possess stability properties, including physical and numerical boundary condition treatments, similar to those of the discrete analogue of the continuum are preferred. (3) For the minimization of numerical dissipation contamination, efficient and adaptive numerical dissipation control to further improve nonlinear stability and accuracy should …
The Pomeron Intercept In Lambda Phi**Theory In 4 Minkowski + 1 Compact Dimensions, Kirill Tuchin
The Pomeron Intercept In Lambda Phi**Theory In 4 Minkowski + 1 Compact Dimensions, Kirill Tuchin
Kirill Tuchin
We calculate the total cross section for two scalar particles scattering at high energies in λφ3 theory in five dimensions, four of which are usual Minkowski ones and the fifth is compact. It is shown that the cross section is dominated by exchange of Pomeron whose intercept is larger than in usual four-dimensional case.
Multiband Microvariability Observations Of Bl Lacertae During The Outburst Of 1997, Sandra D. Clements, Michael T. Carini
Multiband Microvariability Observations Of Bl Lacertae During The Outburst Of 1997, Sandra D. Clements, Michael T. Carini
Aerospace, Physics, and Space Science Faculty Publications
BL Lac was observed in the V and R bands on 11 nights in 1997 July during a major optical outburst. It varied continuously, exhibiting nightly variations ranging from 0.1 to 0.6 mag. Over the course of the 11 nights, BL Lac was seen to vary by 1.8 R magnitudes. Color variations were also observed, with BL Lac becoming bluer as it brightened. The influence of variable seeing conditions on the observed variations was investigated. No correlation was found between the observed microvariability and the local seeing conditions.
Dynamics Of Stars And Globular Clusters In M87, Aaron J. Romanowsky, C. S. Kochanek
Dynamics Of Stars And Globular Clusters In M87, Aaron J. Romanowsky, C. S. Kochanek
Faculty Publications
We examine the dynamics of the stars and globular clusters in the nearby giant elliptical galaxy M87 and constrain the mass distribution, using all the available data over a large range of radii, including higher order moments of the stellar line-of-sight velocity distributions and the discrete velocities of over 200 globular clusters. We introduce an extension of spherical orbit modeling methods that makes full use of all the information in the data and provides very robust constraints on the mass models. We conclusively rule out a constant mass-to-light ratio model and infer that the radial density profile of the galaxy's …
Long‐Term Vri Photometry Of Small‐Amplitude Red Variables. I. Light Curves And Periods, John R. Percy, Joseph B. Wilson, Gregory W. Henry
Long‐Term Vri Photometry Of Small‐Amplitude Red Variables. I. Light Curves And Periods, John R. Percy, Joseph B. Wilson, Gregory W. Henry
Information Systems and Engineering Management Research Publications
We report up to 5000 days of VRI photometry, from a robotic photometric telescope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZ And, 4 Ori, RX Lep, UW Lyn, η Gem, μ Gem, ψ1 Aur, V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VY UMa, ST UMa, TU CVn, FS Com, SW Vir, 30 Her, α1 Her, V642 Her, R Lyr, V450 Aql, V1293 Aql, δ Sge, EU Del, V1070 Cyg, W Cyg, and μ Cep, as well as a few variable comparison stars. V …
10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul
10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul
Information Systems and Engineering Management Research Publications
We present high-resolution spectroscopy and precision photometry of five new γ Doradus and five new δ Scuti variables. The five new γ Doradus variables substantially increase the number of confirmed stars of this class. All 10 stars fall in the spectral class range F0–F2, but they are cleanly separated into two groups by their luminosity and photometric periods. However, the period gap between the γ Doradus and δ Scuti stars is becoming very narrow since we confirm that HD 155154 is a γ Doradus star with the shortest periods reported to date (the shortest of its four periods is ∼0.312 …
Bayesian Multiscale Deconvolution Applied To Gamma-Ray Spectroscopy, C A. Young, A Connors, E Kolaczyk, Mark L. Mcconnell, G Rank, James M. Ryan, V Schonfelder
Bayesian Multiscale Deconvolution Applied To Gamma-Ray Spectroscopy, C A. Young, A Connors, E Kolaczyk, Mark L. Mcconnell, G Rank, James M. Ryan, V Schonfelder
Space Science Center
A common task in gamma-ray astronomy is to extract spectral information, such as model constraints and incident photon spectrum estimates, given the measured energy deposited in a detector and the detector response. This is the classic problem of spectral “deconvolution” or spectral inversion. The methods of forward folding (i.e., parameter fitting) and maximum entropy “deconvolution” (i.e., estimating independent input photon rates for each individual energy bin) have been used successfully for gamma-ray solar flares (e.g., Rank, 1997; Share and Murphy, 1995). These methods have worked well under certain conditions but there are situations were they don’t apply. These are: 1) …
Comptel Observations Of The Virgo Blazars 3c 273 And 3c 279, W Collmar, V Schonfelder, S Zhang, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Comptel Observations Of The Virgo Blazars 3c 273 And 3c 279, W Collmar, V Schonfelder, S Zhang, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Space Science Center
We report the main MeV properties (detections, light curves, spectra) of the Virgo blazars 3C 273 and 3C 279 which were derived from a consistent analysis of all COMPTEL Virgo observations between 1991 and 1997.
Gamma-Ray Spectral Variability Of Cygnus X-1, Mark L. Mcconnell, K Bennett, H Bloemen, W Collmar, W Hermsen, L Kuiper, W Paciesas, B F. Phlips, J Poutanen, James M. Ryan, V Schonfelder, H Steinle, A W. Strong, A A. Zdziarski
Gamma-Ray Spectral Variability Of Cygnus X-1, Mark L. Mcconnell, K Bennett, H Bloemen, W Collmar, W Hermsen, L Kuiper, W Paciesas, B F. Phlips, J Poutanen, James M. Ryan, V Schonfelder, H Steinle, A W. Strong, A A. Zdziarski
Space Science Center
We have used observations from CGRO to study the variation in the MeV emission of Cygnus X-1 between its low and high X-ray states. These data provide a measurement of the spectral variability above 1 MeV. The high state MeV spectrum is found to be much harder than that of the low state MeV spectrum. In particular, the power-law emission seen at hard X-ray energies in the high state spectrum (with a photon spectral index of 2.6) is found to extend out to at least 5 MeV, with no evidence for any cutoff. Here we present the data and describe …
Energetic Proton Spectra In The 11 June 1991 Solar Flare, C A. Young, K Bennett, A Connors, R Diehl, Mark L. Mcconnell, G Rank, James M. Ryan, R Suleiman, V Schonfelder, C Winkler
Energetic Proton Spectra In The 11 June 1991 Solar Flare, C A. Young, K Bennett, A Connors, R Diehl, Mark L. Mcconnell, G Rank, James M. Ryan, R Suleiman, V Schonfelder, C Winkler
Space Science Center
The June 11, 1991 gamma-ray flare seen by the Compton Gamma-ray Observatory (CGRO) displays several features that make it a dynamic and rich event. It is a member of a class of long duration gamma-ray events with both 2.223 MeV and greater than 8 MeV emission for hours after the impulsive phase. It also contains an inter-phase between the impulsive and extended phases that presents a challenge to the standard gamma-ray line (GRL) flare picture. This phase has strong 2.223 MeV emission and relatively weak 4.44 MeV emission indicative of a very hard parent proton spectrum. However, this would indicate …
Sontrac—A Scintillating Plastic Fiber Tracking Detector For Neutron And Proton Imaging Spectroscopy, James M. Ryan, John R. Macri, Mark L. Mcconnell, R S. Miller
Sontrac—A Scintillating Plastic Fiber Tracking Detector For Neutron And Proton Imaging Spectroscopy, James M. Ryan, John R. Macri, Mark L. Mcconnell, R S. Miller
Space Science Center
SONTRAC (SOlar Neutron TRACking imager and spectrometer) is a conceptual instrument intended to measure the energy and incident direction of 20–150 MeV neutrons produced in solar flares. The intense neutron background in a low-Earth orbit requires that imaging techniques be employed to maximize an instrument’s signal-to-noise ratio. The instrument is comprised of mutually perpendicular, alternating layers of parallel, scintillating, plastic fibers that are viewed by optoelectronic devices. Two stereoscopic views of recoil proton tracks are necessary to determine the incident neutron’s direction and energy. The instrument can also be used as a powerful energetic proton imager. Data from a fully …
X- And Gamma-Ray Observations Of The 15 November 1991 Solar Flare, M B. Arndt, A Connors, J Lockwood, Mark L. Mcconnell, R Suleiman, James M. Ryan, C A. Young, G Rank, V Schonfelder, H Debrunner, K Bennett, O R. Williams, C Winkler
X- And Gamma-Ray Observations Of The 15 November 1991 Solar Flare, M B. Arndt, A Connors, J Lockwood, Mark L. Mcconnell, R Suleiman, James M. Ryan, C A. Young, G Rank, V Schonfelder, H Debrunner, K Bennett, O R. Williams, C Winkler
Space Science Center
This work expands the current understanding of the 15 November 1991 Solar Flare. The flare was a well observed event in radio to gamma-rays and is the first flare to be extensively studied with the benefit of detailed soft and hard X-ray images. In this work, we add data from all four instruments on the Compton Gamma Ray Observatory. Using these data we determined that the accelerated electron spectrum above 170 keV is best fit with a power law with a spectral index of −4.6, while the accelerated proton spectrum above 0.6 MeV is fit with a power law of …
Study Of 5 And 10 Mm Thick Czt Strip Detectors, John R. Macri, Pierre C. Dufour, L A. Hamel, M Julien, Mark L. Mcconnell, M Mcclish, James M. Ryan, Mark Widholm
Study Of 5 And 10 Mm Thick Czt Strip Detectors, John R. Macri, Pierre C. Dufour, L A. Hamel, M Julien, Mark L. Mcconnell, M Mcclish, James M. Ryan, Mark Widholm
Space Science Center
We report progress in the study of 5 and 10 mm thick CZT strip detectors featuring orthogonal coplanar anode contacts. This novel anode geometry combines the advantages of pixel detectors with those of double-sided strip detectors. Like pixel detectors, these are electron-only devices that perform well as hard x-ray and y-ray spectrometers and imagers even in the thicker configurations required for reasonable detection efficiency at 1 MeV. Like double-sided strip detectors in an N x N configuration, these detectors require only 2N readout channels to form N2 “pixels”. Unlike doublesided strip detectors, all signal contacts for spectroscopy and 3- d …
Energy Content Of The Stormtime Ring Current, Niescja E. Turner, D N. Baker, T I. Pulkkinen, J L. Roeder, J F. Fennell, V K. Jordanova
Energy Content Of The Stormtime Ring Current, Niescja E. Turner, D N. Baker, T I. Pulkkinen, J L. Roeder, J F. Fennell, V K. Jordanova
Physics and Astronomy Faculty Research
Given the important role the ring current plays in magnetospheric energetics, it is essential to understand its strength and evolution in disturbed times. There are currently three main methods for deducing the strength of the ring current: measuring ground magnetic perturbations, measuring high-altitude magnetic perturbations, or directly measuring ring current particles. The use of ground magnetometers is the most convenient, and many use the ground magnetometer-derived Dst index as a proxy for the ring current. Recent work suggests, however, that a substantial portion of Dst may not be caused only by the ring current but also by local induction effects …
Ring Current Ion Composition During Solar Minimum And Rising Solar Activity: Polar/Cammice/Mics Results, T I. Pulkkinen, N Yu Ganushkina, D N. Baker, Niescja E. Turner, J F. Fennell, J L. Roeder, T A. Fritz, M Grande, B Kellett, G Kettmann
Ring Current Ion Composition During Solar Minimum And Rising Solar Activity: Polar/Cammice/Mics Results, T I. Pulkkinen, N Yu Ganushkina, D N. Baker, Niescja E. Turner, J F. Fennell, J L. Roeder, T A. Fritz, M Grande, B Kellett, G Kettmann
Physics and Astronomy Faculty Research
This paper shows statistical results of the ring current ion composition and its variability as a function of solar cycle and magnetospheric activity for 3 < L < 8. Spin-averaged energetic particle (1-200 keV) measurements from Polar are combined with geomagnetic indices as well as solar wind and interplanetary observations from the Wind spacecraft during a period from September 1996 to March 1999. The statistics are performed both for time-averaged values for all periods as well as for peak flux values during geomagnetic storms (defined as Dst < -50 nT) that occurred during this period. The average O+ energy density increases by about a factor of 5 during the rising phase of the solar cycle from the minimum values in 1996, while the average values of H+ and He show variability but no consistently increasing trend. The O+ flux is small (below 10%) compared with the hydrogen flux, and the average energy density ranges from a few percent at solar minimum to ∼10% at high solar activity time in …
Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull
Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull
Physics and Astronomy
Observational studies indicate that the intergalactic medium (IGM) is highly ionized up to redshifts just over 6. A number of models have been developed to describe the process of reionization and the effects of the ionizing photons from the first luminous objects. In this paper we study the impact of an X-ray background, such as high-energy photons from early quasars, on the temperature and ionization of the IGM prior to reionization, before the fully ionized bubbles associated with individual sources have overlapped. X-rays have large mean free paths relative to EUV photons, and their photoelectrons can have significant effects on …