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Articles 7591 - 7620 of 8870

Full-Text Articles in Astrophysics and Astronomy

Acceleration Of ³He Nuclei At Interplanetary Shocks, Mihir I. Desai, Glenn M. Mason, Joseph R. Dwyer, Joseph E. Mazur, Charles W. Smith, Ruth M. Skoug May 2001

Acceleration Of ³He Nuclei At Interplanetary Shocks, Mihir I. Desai, Glenn M. Mason, Joseph R. Dwyer, Joseph E. Mazur, Charles W. Smith, Ruth M. Skoug

Aerospace, Physics, and Space Science Faculty Publications

We have surveyed the 0.5-2.0 MeV nucleonˉ¹ ion composition of 56 interplanetary (IP) shocks observed with the Ultra - Low-Energy Isotope Spectrometer on board the Advanced Composition Explorer from 1997 October 1 through 2000 November 30. Our results show the first ever measurement (25 cases) of ³He ions being accelerated at IP shocks. The ³He/⁴He ratio at the 25 shocks exhibited a wide range of values between 0.0014 and 0.24; the ratios were enhanced between factors of ∼3 and 600 over the solar wind value. During the survey period, the occurrence probability of ³He-rich shocks increased with rising solar activity …

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Formation Of Rydberg Atoms In An Expanding Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, M. J. Lim, S. Kulin, R. Dumke, S. L. Rolston Apr 2001

Formation Of Rydberg Atoms In An Expanding Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, M. J. Lim, S. Kulin, R. Dumke, S. L. Rolston

Faculty Publications

We study the formation of Rydberg atoms in expanding plasmas at temperatures of 1–1000 K and densities from 10^5–10^10 cm^-3. Up to 20% of the initially free charges recombine in about 100 us, and the binding energy of the Rydberg atoms approximately equals the increase in the kinetic energy of the remaining free electrons. Three-body recombination is expected to dominate in this regime, yet most of our results are inconsistent with this mechanism.

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What Determines The Emission Peak Energy Of The Blue Luminescence In Highly Mg-Doped P-Gan?, John S. Colton, P. Y. Yu Apr 2001

What Determines The Emission Peak Energy Of The Blue Luminescence In Highly Mg-Doped P-Gan?, John S. Colton, P. Y. Yu

Faculty Publications

We report a study of the 2.8 eV blue luminescence (BL) in heaviliy Mg-doped p-GaN via resonant excitation with a tunable blue dye laser. The dependence of the BL on the excitation photon energy (Eex) is unlike that of the yellow luminescence found in n-type GaN. An Urbach-type band tail, with Urbach parameter of 33 meV is observed in the vicinity of the BL energy. We propose that the peak energy of the BL marks the transition from localized states to delocalized states within this band tail.

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Helium Emission From Classical T Tauri Stars: Dual Origin In Magnetospheric Infall And Hot Wind, Georgina Beristain, Suzan Edwards, John Kwan Apr 2001

Helium Emission From Classical T Tauri Stars: Dual Origin In Magnetospheric Infall And Hot Wind, Georgina Beristain, Suzan Edwards, John Kwan

Astronomy: Faculty Publications

High-resolution emission-line profiles of He I and He II in 31 classical T Tauri stars are analyzed with the aim of probing the environs of the star-disk interface in accreting low-mass young stars. The diagnostic power of the helium lines lies in their high-excitation potentials, which restrict their formation to a region either of high temperature or close proximity to a source of ionizing radiation. The He I profiles are decomposed into kinematic components that support the paradigm of magnetically controlled accretion from the disk onto the stellar surface but also require a significant contribution from a hot wind. A …

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Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos Apr 2001

Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos

Dartmouth Scholarship

The zero-temperature effective equation of motion is derived for a scalar field interacting with other fields. For a broad range of cases, involving interaction with as few as one or two fields, dissipative regimes are found for the scalar field system. The zero-temperature limit constitutes a baseline effect that will be prevalent in any general statistical state. Thus, the results found here provide strong evidence that dissipation is the norm not the exception for an interacting scalar field system. For application to inflationary cosmology, this provides convincing evidence that warm inflation could be a natural dynamics once proper treatment of …

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Mass Density Profiles Of Low Surface Brightness Galaxies, Stacy S. Mcgaugh Apr 2001

Mass Density Profiles Of Low Surface Brightness Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We derive the mass density profiles of dark matter halos that are implied by high spatial resolution rotation curves of low surface brightness galaxies. We find that, at small radii, the mass density distribution is dominated by a nearly constant density core with a core radius of a few kiloparsecs. For ρ(r) ∼ rα, the distribution of inner slopes α is strongly peaked around α = -0.2. This is significantly shallower than the cuspy α ≤ -1 halos found in cold dark matter simulations. While the observed distribution of α does have a tail toward such extreme values, the derived …

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First Results From The Anglo-Australian Planet Search: A Brown Dwarf Candidate And A 51 Peg-Like Planet, Chris G. Tinney, R. Paul Butler, Geoffrey W. Marcy, Hugh R. A. Jones, Alan J. Penny, Steve S. Vogt, Kevin Apps, Gregory W. Henry Apr 2001

First Results From The Anglo-Australian Planet Search: A Brown Dwarf Candidate And A 51 Peg-Like Planet, Chris G. Tinney, R. Paul Butler, Geoffrey W. Marcy, Hugh R. A. Jones, Alan J. Penny, Steve S. Vogt, Kevin Apps, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We report results from the Anglo-Australian Planet Search, a survey for planets around 200 solar-type stars in the southern hemisphere that is being carried out on the 3.9 m Anglo-Australian Telescope. Limiting Doppler precisions of 3 m s-1 have been demonstrated from the first 2.5 years of operation, making this the highest-precision planet search in the southern hemisphere. From these data we report results for two new substellar detections. The first is a 51 Peg-like planet around the star HD 179949 with M sin i = 0.84 MJUP. Photometric study reveals this is not a transiting system. The second is …

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A Search For Previously Unrecognized Metal-Poor Subdwarfs In The Hipparcos Astrometric Catalogue, I. N. Reid, F. Van Wyk, F. Marang, G. Roberts, D. Kilkenny, S. Mahoney Apr 2001

A Search For Previously Unrecognized Metal-Poor Subdwarfs In The Hipparcos Astrometric Catalogue, I. N. Reid, F. Van Wyk, F. Marang, G. Roberts, D. Kilkenny, S. Mahoney

Dartmouth Scholarship

We have identified 317 stars included in the Hipparcos astrometric catalogue that have parallaxes measured to a precision of better than 15 per cent, and the location of which in the (MV,(B−V)T) diagram implies a metallicity comparable to or less than that of the intermediate‐abundance globular cluster M5. We have undertaken an extensive literature search to locate Strömgren, Johnson/Cousins and Walraven photometry for over 120 stars. In addition, we present new UBV(RI)C photometry of 201 of these candidate halo stars, together with similar data for a further 14 known metal‐poor subdwarfs. These …

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Infrared Spectroscopy Of Symbiotic Stars. Iii. First Orbits For Three S-Type Systems, Francis C. Fekel, Kenneth H. Hinkle, Richard Joyce, Michael F. Skrutskie Apr 2001

Infrared Spectroscopy Of Symbiotic Stars. Iii. First Orbits For Three S-Type Systems, Francis C. Fekel, Kenneth H. Hinkle, Richard Joyce, Michael F. Skrutskie

Information Systems and Engineering Management Research Publications

Infrared radial velocities have been used to derive the first well-determined orbital elements for the cool giants of three symbiotic systems, BF Cyg, V1329 Cyg, and V343 Ser=AS 289. Periods found for BF Cyg and V1329 Cyg from the radial velocity data are in good agreement with periods previously determined for their light variations, and the orbits are circular. Masses for the components of BF Cyg and V1329 Cyg were determined by combining our orbital elements for the cool giants with elements for their hot stars. BF Cyg and V1329 Cyg are shown to be detached binary systems. The third …

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Geocoronal H-A [Alpha] Intensity Measurements Using The Wisconsin H-A [Alpha] Mapper Fabry-Perot Facility, S. Nossal, F. L. Roesler, J. Bishop, R. J. Reynolds, M. Haffner, S. Tufte, J. Percival, E. J. Mierkiewicz Apr 2001

Geocoronal H-A [Alpha] Intensity Measurements Using The Wisconsin H-A [Alpha] Mapper Fabry-Perot Facility, S. Nossal, F. L. Roesler, J. Bishop, R. J. Reynolds, M. Haffner, S. Tufte, J. Percival, E. J. Mierkiewicz

Physical Sciences - Daytona Beach

"The Wisconsin H-a [alpha] Mapper (WHAM), a remotely operable, semi-automated Fabry-Perot located at Kitt Peak Observatory, has been making an all-sky survey of interstellar hydrogen Balmer a [alpha] (H-a [alpha]) emissions since 1997. Using the annular summing spectroscopy technique, WHAM has acquired ~[approx.] 37,000 spectra to date, spanning almost 100 nights of observations. Since all of the galactic emission spectral data contain the terrestrial H-a [alpha] (6562.7 Å) emission line, these measurements constitute a rich source of geocoronal data for investigating natural variability in the upper atmosphere. The WHAM observations also serve as a benchmark for comparison with future …

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First-Principles Elastic Constants And Electronic Structure Of Α-Pt2si And Ptsi, Gus L. W. Hart, O. Beckstein, J. E. Klepeis, O. Pankratov Mar 2001

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 …

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Fractal Quasar Clouds, Mark Bottorff, Gary J. Ferland Mar 2001

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 …

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0920+3517_Nir_Spex, Maria Teresa Ruiz Mar 2001

0920+3517_Nir_Spex, Maria Teresa Ruiz

Publications and Research

No abstract provided.

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Hubble Space Telescope Images Of The Ultraluminous Supernova Remnant Complex In Ngc 6946, William P. Blair, Robert A. Fesen, Eric M. Schlegel Mar 2001

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 …

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An Optical Survey Of Outlying Ejecta In Cassiopeia A: Evidence For A Turbulent, Asymmetric Explosion, Robert A. Fesen Mar 2001

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 …

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Near-Infrared Spectroscopy Of The Cassiopeia A And Kepler Supernova Remnants, Christopher L. Gerardy, Robert A. Fesen Feb 2001

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 …

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A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion Feb 2001

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 …

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Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer Feb 2001

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 …

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Gas Mass Fractions And The Evolution Of Low Surface Brightness Dwarf Galaxies, Stacy S. Mcgaugh Jan 2001

Gas Mass Fractions And The Evolution Of Low Surface Brightness Dwarf Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

The optical and H I properties are presented for a sample of low surface brightness (LSB) dwarf galaxies, cataloged from the Second Palomar Sky Survey. Gas mass fractions for LSB dwarfs reach the highest levels of any know galaxy type (fg = 95%), confirming that their low stellar densities are due to inefficient conversion of gas mass into stellar mass. Comparison with star formation models indicates that the blue optical colors of LSB dwarfs are not due to low metallicity or to recent star formation and can only be explained by a dominant stellar population less than 5 Gyr in …

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Long‐Term Vri Photometry Of Small‐Amplitude Red Variables. I. Light Curves And Periods, John R. Percy, Joseph B. Wilson, Gregory W. Henry Jan 2001

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 …

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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 Jan 2001

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 …

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Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull Jan 2001

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 …

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Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou Jan 2001

Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou

Faculty Publications

Molecular simulations of sound waves propagating in a dilute hard sphere gas have been performed using the direct simulation Monte Carlo method. A wide range of frequencies is investigated, including very high frequencies for which the period is much shorter than the mean collision time. The simulation results are compared to experimental data and approximate solutions of the Boltzmann equation. It is shown that free molecular flow is important at distances smaller than one mean free path from the excitation point.

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10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul Jan 2001

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 …

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Can Post T Tauri Stars Be Found? Yes!, Eric L.N. Jensen Jan 2001

Can Post T Tauri Stars Be Found? Yes!, Eric L.N. Jensen

Physics & Astronomy Faculty Works

I review the observational challenges of finding post T Tauri stars (PTTS), defined here as low-mass, pre-main-sequence stars with ages of 10(7)-10(8) yr. Such stars are difficult to find because they are less active than younger T Tauri stars, and they may not be associated with molecular gas. They are useful for studying the evolution of circumstellar disks and stellar activity between the 10(6)-yr ages of nearby star-forming regions and the main sequence. However, care must be taken in the search process so that the selection criteria used to locate such stars do not bias the sample used for subsequent …

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Disk Clearing In The Young Binary Ak Sco, Eric L.N. Jensen Jan 2001

Disk Clearing In The Young Binary Ak Sco, Eric L.N. Jensen

Physics & Astronomy Faculty Works

The pre-main-sequence spectroscopic binary AK Sco is surrounded by a circumbinary disk. Yet while this disk must be somewhat disturbed by the binary at its center, there is no evidence from current data that it has a cleared central hole like those seen in some young binaries, nor that accretion from the outer disk has been cut off. Indeed, most of its spectral and photometric diagnostics are indistinguishable from those of young single stars. Why doesn't this system show any evidence of disturbance of its disk? It may be that the center of the disk is indeed largely cleared, but …

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Disks In Young Binary Systems: Unresolved Millimeter-Wave Observations, Eric L.N. Jensen Jan 2001

Disks In Young Binary Systems: Unresolved Millimeter-Wave Observations, Eric L.N. Jensen

Physics & Astronomy Faculty Works

Observations at millimeter and submillimeter wavelengths are sensitive to the total mass of circumstellar and circumbinary dust in a multiple system, and in some cases single-dish observations can help constrain the location of disk material in spite of their lack of spatial resolution. Young binary stars show a great diversity of disk properties, with a large part of the variation accounted for by binary separation. Many of the closest binaries (those with separations a less than a few AU) harbor massive circumbinary disks. Binaries with a greater than or equal to 100 AU tend to have massive circumstellar disks. In …

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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 Jan 2001

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 …

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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 Jan 2001

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 …

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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 Jan 2001

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 …

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