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1997

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Articles 1 - 30 of 117

Full-Text Articles in Physical Sciences and Mathematics

A Detailed Comparison Of Hubble Space Telescopefaint Object Spectrograph Andiueultraviolet Spectra Of Selected Seyfert Nuclei, Anuradha Koratkar, Ian Evans, Sharon Pesto, Cynthia Taylor Dec 1997

A Detailed Comparison Of Hubble Space Telescopefaint Object Spectrograph Andiueultraviolet Spectra Of Selected Seyfert Nuclei, Anuradha Koratkar, Ian Evans, Sharon Pesto, Cynthia Taylor

Dartmouth Scholarship

Despite the contributions of the Hubble Space Telescope Faint Object Spectrograph (FOS) to the archive of UV observations of active galactic nuclei, the vast majority of UV reference data were obtained using the International Ultraviolet Explorer (IUE) satellite. These data remain important since they provide historical information about the intensities of the UV continua and emission lines that is needed to constrain models of the active nucleus. A detailed comparison of the FOS and IUE data is critical to understanding how the measurable quantities depend on the individual instrumental calibrations, and how any conclusions derived from modeling the …

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A New Approach To Probing Large-Scale Power With Peculiar Velocities, Hume A. Feldman, Richard Watkins Dec 1997

A New Approach To Probing Large-Scale Power With Peculiar Velocities, Hume A. Feldman, Richard Watkins

Dartmouth Scholarship

We propose a new strategy for probing the power spectrum on large scales using galaxy peculiar velocities. We explore the properties of surveys that cover only two small fields in opposing directions on the sky. Surveys of this type have several advantages over those that attempt to cover the entire sky; in particular, by concentrating on galaxies in narrow cones, these surveys are able to achieve the density needed to measure several moments of the velocity field with only a modest number of objects, even for surveys designed to probe scales >∼100h−1Mpc. We construct mock surveys with this …

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The Century Survey: A Deeper Slice Of The Universe, Margaret J. Geller, Michael J. Kurtz, Gary Wegner, John R. Thorstensen Dec 1997

The Century Survey: A Deeper Slice Of The Universe, Margaret J. Geller, Michael J. Kurtz, Gary Wegner, John R. Thorstensen

Dartmouth Scholarship

The "Century Survey" (CS hereafter) is a complete redshift survey of a 1° wide strip. It covers 0.03 steradians to a limiting mR = 16.13. The survey is 98.4% complete and contains 1762 galaxies. Large-scale features in the survey are qualitatively similar to those in other surveys: there are large voids surrounded or nearly surrounded by thin dense regions which are sections of structures like (and including) the Great Wall. The survey crosses the classical Corona Borealis supercluster. The galaxy density enhancement associated with this system extends for <˜100h-1 Mpc-1 (the Hubble constant is H0 = 100h …

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Chromospherically Active Stars. Xvi. The Double-Lined Binary 42 Capricorni, Francis C. Fekel Dec 1997

Chromospherically Active Stars. Xvi. The Double-Lined Binary 42 Capricorni, Francis C. Fekel

Information Systems and Engineering Management Research Publications

New spectroscopic observations of the chromospherically active binary, 42 Capricorni, have resulted in the detection of lines of the secondary, improved orbital elements, and the determination of fundamental properties of the components. 42 Cap has an orbital period of 13.174004 d, an eccentricity of 0.176, and a mass ratio A/B of 1.375. No evidence for a variation of the center-of-mass velocity, suggested by earlier investigators, has been found. Spectral types of the primary and secondary are G1 IV and G2 V, respectively. The V mag difference of 1.94 and HIPPARCOS parallax result in MV = 2.79 mag for A and …

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Displacement Of The Earth's Bow Shock And Magnetopause Due To An Impinging Interplanetary Shock Wave, William A. Olson Dec 1997

Displacement Of The Earth's Bow Shock And Magnetopause Due To An Impinging Interplanetary Shock Wave, William A. Olson

Theses and Dissertations

Interplanetary shock waves (ISWs) propagating through the solar wind can collide with the earth's bow shock, resulting in a series of new shocks, contact discontinuities, and rarefaction waves which interact to effectively move the bow shock and magnetopause toward the earth. A one dimensional MacCormack predictor corrector algorithm with Flux Corrected Transport (FCT) was developed to model the ISW bow shock and magnetopause interactions, and to numerically predict their propagation speeds after collision. Analytic relationships for the Mach numbers and propagation speeds of the generated shock waves and contact discontinuities were used to validate the model and to compare numerical …

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Unfolding Of The Period-Two Bifurcation In A Fiber Laser Pumped With Two Modulation Tones, Scott Glasgow, T. C. Newell, A. Gavrielides, V. Kovanis, D. Sukow, T. Erneux Dec 1997

Unfolding Of The Period-Two Bifurcation In A Fiber Laser Pumped With Two Modulation Tones, Scott Glasgow, T. C. Newell, A. Gavrielides, V. Kovanis, D. Sukow, T. Erneux

Faculty Publications

The effect of a small second frequency component on a pump modulated neodymium fiber laser is investigated experimentally and theoretically. This term, whose frequency is exactly half the primary driver, incites an unfolding of the attractor. It breaks the period two pitchfork bifurcation and splits the period one orbit. The modification of the bifurcation diagram is studied analytically by employing a map derived from the class B laser rate equations. We determine specific conditions and scaling laws for this phenomenon. Our analytical predictions are in good agreement with recorded experimental data.

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Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox Nov 1997

Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox

Physics Faculty Publications

Escape of ions is potentially important for the evolution of volatiles on Mars, but the mechanisms and rates of ion escape processes are not fully understood. Instruments on the Russian Phobos 2 orbiter have, however, measured fluxes of heavy ions apparently of ionospheric origin in the optical shadow of Mars. These ions are assumed to arise from escape processes induced by the interaction of the solar wind with the ionosphere. We determine here upper limits to the ion loss rates by imposing upward flux boundary conditions on models of the low and high solar activity Mars ionosphere. The maximum fluxes …

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Prototype For Sontrac: A Scintillating Plastic Fiber Detector For Solar Neutron Spectroscopy, James M. Ryan, Janis Baltgalvis, D Holslin, John R. Macri, Mark L. Mcconnell, Cornelia B. Wunderer, Aaron R. Polichar Oct 1997

Prototype For Sontrac: A Scintillating Plastic Fiber Detector For Solar Neutron Spectroscopy, James M. Ryan, Janis Baltgalvis, D Holslin, John R. Macri, Mark L. Mcconnell, Cornelia B. Wunderer, Aaron R. Polichar

Space Science Center

We report the scientific motivation for and performance measurements of a prototype detector system for SONTRAC, a solar neutron tracking experiment designed to study high- energy solar flare processes. The full SONTRAC instrument will measure the energy and direction of 20 to 200 MeV neutrons by imaging the ionization tracks of the recoil protons in a densely packed bundle of scintillating plastic fibers. The prototype detector consists of a 12.7 mm square bundle of 250 micrometer scintillating plastic fibers, 10 cm long. A photomultiplier detects scintillation light from one end of the fiber bundle and provides a detection trigger to …

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The I Band Tully-Fisher Relation For Cluster Galaxies: Data Presentation., Riccardo Giovanelli, Martha P. Haynes, Terry Herter, Nicole P. Vogt, Gary Wegner, John J. Salzer, Luiz N. Da Costa, Wolfram Freudling Oct 1997

The I Band Tully-Fisher Relation For Cluster Galaxies: Data Presentation., Riccardo Giovanelli, Martha P. Haynes, Terry Herter, Nicole P. Vogt, Gary Wegner, John J. Salzer, Luiz N. Da Costa, Wolfram Freudling

Dartmouth Scholarship

Observational parameters which can be used for redshift-independent distance determination using the Tully-Fisher (TF) technique are given for 782 spiral galaxies in the fields of 24 clusters or groups. I band photometry for the full sample was either obtained by us or compiled from published literature. Rotational velocities are derived either from 21 cm spectra or optical emission line long--slit spectra, and converted to a homogeneous scale. In addition to presenting the data, a discussion of the various sources of error on TF parameters is introduced, and the criteria for the assignment of membership to each cluster are given.

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Automated Classification Of Stellar Spectra. Ii: Two-Dimensional Classification With Neural Networks And Principal Components Analysis, Ted Von Hippel, Coryn A.L. Bailer-Jones, Mike Irwin Oct 1997

Automated Classification Of Stellar Spectra. Ii: Two-Dimensional Classification With Neural Networks And Principal Components Analysis, Ted Von Hippel, Coryn A.L. Bailer-Jones, Mike Irwin

Publications

We investigate the application of neural networks to the automation of MK spec- tral classification. The data set for this project consists of a set of over 5000 optical (3800–5200°A) spectra obtained from objective prism plates from the Michigan Spec- tral Survey. These spectra, along with their two-dimensional MK classifications listed in the Michigan Henry Draper Catalogue, were used to develop supervised neural network classifiers. We show that neural networks can give accurate spectral type classifications (68 = 0.82 subtypes, rms= 1.09 subtypes) across the full range of spectral types present in the data set (B2–M7). We show also that …

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A Prototype For Sontrac, A Scintillating Plastic Fiber Tracking Detector For Neutron Imaging And Spectroscopy, James M. Ryan, John R. Macri, Mark L. Mcconnell, C B. Wunderer, D Holslin, Aaron R. Polichar, Janis Baltgalvis Oct 1997

A Prototype For Sontrac, A Scintillating Plastic Fiber Tracking Detector For Neutron Imaging And Spectroscopy, James M. Ryan, John R. Macri, Mark L. Mcconnell, C B. Wunderer, D Holslin, Aaron R. Polichar, Janis Baltgalvis

Space Science Center

We report on tests of a prototype detector system designed to perform imaging and spectroscopy on 20 to 250 MeV neutrons. Although developed for the study of high-energy solar flare processes, the detection techniques employed for SONTRAC, the SOlar Neutron TRACking experiment, can be applied to measurements in a variety of disciplines including atmospheric physics, radiation therapy and nuclear materials monitoring. The SONTRAC instrument measures the energy and direction ofneutrons by detecting double neutron-proton scatters and recording images of the ionization tracks of the recoil protons in a densely packed bundle of scintillating plastic fibers stacked in orthogonal layers. By …

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System For Electron Paramagnetic Resonance Measurements At High Pressure And Low Temperature, Ke Huang, Daniel L. Decker, H. Mark Nelson, J. Dean Barnett Oct 1997

System For Electron Paramagnetic Resonance Measurements At High Pressure And Low Temperature, Ke Huang, Daniel L. Decker, H. Mark Nelson, J. Dean Barnett

Faculty Publications

Major improvements have been made on the sensitive high pressure electron paramagnetic resonance (EPR) system developed previously in 1978 at this laboratory. These changes allow low temperature measurements and provide a more stable signal. The high pressure EPR cell is placed inside a vacuum chamber to provide thermal isolation, so that the system may be cooled by a closed cycle refrigerator to temperatures between 45 and 60 K, depending on the energy input to the modulation coil. The combination of high pressure and low temperature greatly expands the thermodynamic range over which EPR measurements can be made. An improved and …

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Do The Broad Emission Line Clouds See The Same Continuum That We See?, Kirk Korista, Gary J. Ferland, Jack Baldwin Oct 1997

Do The Broad Emission Line Clouds See The Same Continuum That We See?, Kirk Korista, Gary J. Ferland, Jack Baldwin

Physics and Astronomy Faculty Publications

Recent observations of quasars, Mrk 335 and the HST quasar composite spectrum, have indicated that many quasars have remarkably soft ionizing continua (f ∝ ~ ν-2, 13.6-100 eV). We point out that the number of photons with hν > 54.4 eV is insufficient to create the observed strengths of the He II emission lines. While the numbers of photons which energize C IV λ1549 and O VI λ1034 are sufficient, even the most efficiently emitting clouds for these two lines must each cover at least 20%-40% of the source. If the typical quasar ionizing continuum is indeed this …

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Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland Sep 1997

Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

The narrow emission line spectra of active galactic nuclei are not accurately described by simple photoionization models of single clouds. Recent Hubble Space Telescope images of Seyfert 2 galaxies show that these objects are rich with ionization cones, knots, filaments, and strands of ionized gas. Here we extend to the narrow-line region the ``locally optimally emitting cloud'' (LOC) model, in which the observed spectra are predominantly determined by powerful selection effects. We present a large grid of photoionization models covering a wide range of physical conditions and show the optimal conditions for producing many of the strongest emission lines. We …

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Inclination Effects In Spiral Galaxy Gravitational Lensing, Ariyeh Maller, Ricardo Flores, Joel Primack Sep 1997

Inclination Effects In Spiral Galaxy Gravitational Lensing, Ariyeh Maller, Ricardo Flores, Joel Primack

Physics Faculty Works

Spheroidal components of spiral galaxies have been considered to be the only dynamically important component in gravitational lensing studies to date. Here we point out that including the disk component can have a significant effect, which depends on the disk inclination, on a variety of lensing properties that are relevant to present studies and future surveys. As an example, we look at the multiple image system B1600+434, which was recently identified as being lensed by a spiral galaxy. We find that by including the disk component, one can understand the fairly large image separation as being caused by the inclination …

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Faint Sources In The Euve Survey: Identification Of White Dwarfs, Active Late‐Type Stars, And Galactic Nuclei, Elisha Polomski, Stephane Vennes, John R. Thorstensen, Mihalis Mathioudakis, Emilio E. Falco Sep 1997

Faint Sources In The Euve Survey: Identification Of White Dwarfs, Active Late‐Type Stars, And Galactic Nuclei, Elisha Polomski, Stephane Vennes, John R. Thorstensen, Mihalis Mathioudakis, Emilio E. Falco

Dartmouth Scholarship

We report the classification of 21 new extreme-ultraviolet sources from the recent catalog of Lampton et al. The optical spectra presented identify the objects as 14 active late-type stars (including two double active stars and a possible T Tauri star), three white dwarfs, and six active galactic nuclei (a Seyfert galaxy, the BL Lac object 1ES 1028+511 [=EUVE J1031+508], and four quasi-stellar objects). We have detected Ca II absorption lines in the BL Lac object and measured its redshift. Two of the white dwarfs are unusually massive (M > 1.1 M☉). Our sample of late-type stars includes five …

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Optically Identified Supernova Remnants In The Nearby Spiral Galaxies Ngc 5204, Ngc 5585, Ngc 6946, M81, And M101, David M. Matonick, Robert A. Fesen Sep 1997

Optically Identified Supernova Remnants In The Nearby Spiral Galaxies Ngc 5204, Ngc 5585, Ngc 6946, M81, And M101, David M. Matonick, Robert A. Fesen

Dartmouth Scholarship

We present the results of an optical search for supernova remnants (SNRs) in the spiral galaxies NGC 5204, NGC 5585, NGC 6946, M81, and M101. Using the criterion that emission nebulae with [S II]/Hα ≥ 0.45 are identified as SNRs, we found three SNRs in NGC 5204, five in NGC 5585, 27 in NGC 6946, 41 in M81, and 93 in M101. Including the 35 SNRs recently detected in NGC 2403 by Matonick et al., we have doubled the current number of galaxies that have been well searched for SNRs and increased the number of known extragalactic SNRs by about …

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Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle Sep 1997

Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle

Physics Faculty Publications

We have constructed a new model of the ionosphere of Titan that includes 67 species and 626 reactions. Although N2+ is the major ion produced over most of the ionosphere, the ionization flows to ions whose parent neutrals have lower ionization potentials and to ions formed from species with large proton affinities. In contrast to other models, which have predicted that HCNH+ should be the major ion, our calculations suggest that the major ions at and below the ion peak are hydrocarbon ions, and H, C, and N-containing ions. Our predicted peak electron density for a solar …

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Stellar Populations And The White Dwarf Mass Function: Connections To Supernova Ia Luminosities, Ted Von Hippel, G. D. Bothum, R. A. Schommer Sep 1997

Stellar Populations And The White Dwarf Mass Function: Connections To Supernova Ia Luminosities, Ted Von Hippel, G. D. Bothum, R. A. Schommer

Publications

We discuss the luminosity function of SNe Ia under the assumption that recent evidence for dispersion in this standard candle is related to variations in the white dwarf mass function (WDMF) in the host galaxies. We develop a simple parameterization of the WDMF as a function of age of a stellar population and apply this to galaxies of different morphological types. We show that this simplified model is consistent with the observed WDMF of Bergeron et al. (1992) for the solar neighborhood. Our simple models predict that WDMF variations can produce a range of more than 1.8 mag in MB(SN …

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The Hanle Effect As A Diagnostic Of Magnetic Fields In Stellar Envelopes I. Theoretical Results For Integrated Line Profiles., R. Ignace, K. H. Nordsieck, J. P. Cassinelli Aug 1997

The Hanle Effect As A Diagnostic Of Magnetic Fields In Stellar Envelopes I. Theoretical Results For Integrated Line Profiles., R. Ignace, K. H. Nordsieck, J. P. Cassinelli

Richard Ignace

The Hanle effect concerns the modification of polarized resonance-line scattering by magnetic fields; thus, it can be used as a diagnostic of stellar magnetic fields. The Hanle effect has been used to determine the field strength and distribution of magnetic structures present in prominences of the Sun. To investigate its potential use in stellar astronomy, the simplified case of an optically thin axisymmetric ring illuminated by a stellar point source is considered. The results are then used to derive the polarization from polar plumes, equatorial disks, and spherical shells. The integrated line polarization is calculated for axisymmetric rings with a …

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Inference Of Steady Stellar Wind V(R) Laws From Optically Thin Emission Lines I. Idealised Analysis For The Profile Of A Single Line., J. C. Brown, L. L. Richardson, J. P. Cassinelli, R. Ignace Aug 1997

Inference Of Steady Stellar Wind V(R) Laws From Optically Thin Emission Lines I. Idealised Analysis For The Profile Of A Single Line., J. C. Brown, L. L. Richardson, J. P. Cassinelli, R. Ignace

Richard Ignace

Abstract The form of the profile Flambda_0__({DELTA}λ) of an emission line from a steady spherical wind of velocity profile v(r) is derived for the case when optical depths are small, when stellar occultation of the wind is neglected, and when v(r) is highly supersonic. It is shown how the resulting integral equation for v(r), given Flambda_0__ ({DELTA}λ), can be inverted to yield v(r) if the line emissivity function j(r) is known. Solutions are demonstrated for simulated data in the case of a recombination line (j{prop.to}n^2^) for various trial forms of v(r). The solution is unique provided dv/dr does not change …

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Co J = 3-2 Emission In The Radio Galaxy 53w002 At Z = 2.394, N Z. Scoville, Min S. Yun, R A. Windhorst, W C. Keel, L Armus Aug 1997

Co J = 3-2 Emission In The Radio Galaxy 53w002 At Z = 2.394, N Z. Scoville, Min S. Yun, R A. Windhorst, W C. Keel, L Armus

Min S. Yun

We report a sensitive search for redshifted CO J = 3-2 emission from the weak radio galaxy 53W002 at z = 2.394. Maps at resolutions of 3'' and 235 km s-1 show a significant emission peak within 0farcs5 of the optical and radio continuum peaks. The measured narrowband flux is approximately 10 times the extrapolated centimeter-wavelength nonthermal radio continuum expected at 101.9 GHz and exhibits a spectral profile implying a 540 km s-1 width (FWHM) at a systemic redshift z = 2.394 ± 0.001 for CO (3-2). This emission has a total integrated flux of 1.51 ± 0.2 Jy km …

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Arcsecond Imaging Of Co Emission In The Nucleus Of Arp 220, N Z. Scoville, Min S. Yun, P M. Bryant Aug 1997

Arcsecond Imaging Of Co Emission In The Nucleus Of Arp 220, N Z. Scoville, Min S. Yun, P M. Bryant

Min S. Yun

We report high-resolution (1A) imaging of CO (2È1) and dust continuum emission in the ultraluminous galaxy Arp 220. The CO (1È0) line was also imaged at 2A resolution for comparison. Both data sets recover essentially all of the observed single-dish line emission. Our aperture synthesis maps reveal for the Ðrst time, multiple components in the dense gas: peaks corresponding to each of the double nuclei (separated by 0A.95 at P.A.\101¡) seen in the near infrared and radio continuum and a more extended disklike structure at P.A.\53¡, similar to the dust lane seen in optical images. Approximately two-thirds of the total …

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The Eclipsing Double-Lined Spectroscopic Binary System V505 Persei, Laurence A. Marschall, Robert P. Stefanik, Claud H. Lacy, Guillermo Torres, David B. Williams, Franz Agerer Aug 1997

The Eclipsing Double-Lined Spectroscopic Binary System V505 Persei, Laurence A. Marschall, Robert P. Stefanik, Claud H. Lacy, Guillermo Torres, David B. Williams, Franz Agerer

Physics and Astronomy Faculty Publications

The recently-discovered eclipsing double-lined spectroscopic binary V505 Persei (SAO 23229) consists of two nearly identical F5 main sequence stars in a 4.2 day orbit. We have obtained both spectroscopic and photometric observations of the binary that densely sample the complete cycle of radial velocity and light variations. These observations have been used to determine the elements of the orbit, to determine individual masses of the stars in the system to a precision of better than 1%, and to estimate an age for the system. The derived properties agree well with current stellar structure models and provide fundamental data for tests …

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White Dwarfs In Globular Clusters: Hubble Space Telescope Observations Of M4, Harvey B. Richer, Matt A. Wood Aug 1997

White Dwarfs In Globular Clusters: Hubble Space Telescope Observations Of M4, Harvey B. Richer, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

Using WFPC2 on the Hubble Space Telescope, we have isolated a sample of 258 white dwarfs (WDs) in the Galactic globular cluster M4. Fields at three radial distances from the cluster center were observed, and sizable WD populations were found in all three. The location of these WDs in the color-magnitude diagram, their mean mass of 0.51(±0.03) M⊙, and their luminosity function confirm basic tenets of stellar evolution theory and support the results from current WD cooling theory. The WDs are used to extend the cluster main-sequence mass function upward to stars that have already completed their nuclear evolution. The …

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Fluctuations In Finite N Equilibrium Stellar Systems, Martin D. Weinberg Jul 1997

Fluctuations In Finite N Equilibrium Stellar Systems, Martin D. Weinberg

Astronomy Department Faculty Publication Series

Gravitational amplification of Poisson noise in stellar systems is important on large scales. For example, it increases the dipole noise power by roughly a factor of six and the quadrupole noise by 50% for a King model profile. The dipole noise is amplified by a factor of fifteen for the core-free Hernquist model. The predictions are computed using the dressed-particle formalism of Rostoker & Rosenbluth (1960) and are demonstrated by n-body simulation. This result implies that a collisionless n-body simulation is impossible; The fluctuation noise which causes relaxation is an intrinic part of self gravity. In other words, eliminating two-body …

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Dynamics Of An Interacting Luminous Disk, Dark Halo, And Satellite Companion, Martin D. Weinberg Jul 1997

Dynamics Of An Interacting Luminous Disk, Dark Halo, And Satellite Companion, Martin D. Weinberg

Astronomy Department Faculty Publication Series

This paper describes a method for determining the dynamical interaction between extended halo and spheroid components and an environmental disturbance. One finds that resonant interaction between a galaxy and passing interlopers or satellite companions can carry the disturbance inward, deep inside the halo, where it can perturb the disk. Applied to the Milky Way for example, the LMC and SMC appear to be sufficient to cause the observed Galactic warp and possibly seed other asymmetries. This is a multi-scale interaction in which the halo wake has a feature at roughly half the satellite orbital radius due to a 2:1 orbital …

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Sontrac-A Low Background, Large Area Solar Neutron Spectrometer, C B. Wunderer, D Holslin, John R. Macri, Mark L. Mcconnell, James M. Ryan Jul 1997

Sontrac-A Low Background, Large Area Solar Neutron Spectrometer, C B. Wunderer, D Holslin, John R. Macri, Mark L. Mcconnell, James M. Ryan

Space Science Center

SONTRAC will measure 20-250 MeV neutrons from solar flares using scintillator fibers viewed by CCD cameras to track neutron-proton scatters. SONTRAC can also be used to track gamma rays above 20 MeV. Veto shields are used to reject all charged particles. Gamma-ray and neutron events have very different track densities, allowing discrimination between the two. Double neutron-proton scatters allow unambiguous determination of the incident neutron energy and direction. Therefore, SONTRAC is capable of rejecting almost all background except neutrons from the solar direction. SONTRAC would have detected the June 15, 1991 flare with 42σ for 20-100 MeV neutrons, having an …

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Activation In The Comptel Double-Scattering Gamma-Ray Telescope, D Morris, Mark L. Mcconnell, James M. Ryan, R Diehl, U Oberlack, V Schonfelder, M Varendorff, G Weidenspointer, H Deboer, K Bennett Jul 1997

Activation In The Comptel Double-Scattering Gamma-Ray Telescope, D Morris, Mark L. Mcconnell, James M. Ryan, R Diehl, U Oberlack, V Schonfelder, M Varendorff, G Weidenspointer, H Deboer, K Bennett

Space Science Center

Abstract-The COMPTEL gamma-ray telescope has been operating in low Earth orbit for six years, since the launch of the Compton Gamma-Ray Observatory in April 1991. Comparisons of data for different orbits and epochs show evidence of activation on time scales from minutes (27Mg, q,2=9.5 min) to years C2Na, q&.58 yr). The activation is correlated with both the orbital altitude and solar cosmic-ray modulation. Because it requires coincident measurements in two different detectors, COMPTEL is most susceptible to instrumental background events in which two or more photons are produced simultaneously.

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Recurrent Geomagnetic Storms And Relativistic Electron Enhancements In The Outer Magnetosphere: Istp Coordinated Measurements, D N. Baker, X Li, Niescja E. Turner, J H. Allen, L F. Bargatze, J B. Blake, R B. Sheldon, H E. Spence, R D. Belian, G D. Reeves, S G. Kanekal, B Klecker, R P. Lepping, K Ogilvie, R A. Mewaldt, T Onsager, H J. Singer, G Rostoker Jul 1997

Recurrent Geomagnetic Storms And Relativistic Electron Enhancements In The Outer Magnetosphere: Istp Coordinated Measurements, D N. Baker, X Li, Niescja E. Turner, J H. Allen, L F. Bargatze, J B. Blake, R B. Sheldon, H E. Spence, R D. Belian, G D. Reeves, S G. Kanekal, B Klecker, R P. Lepping, K Ogilvie, R A. Mewaldt, T Onsager, H J. Singer, G Rostoker

Physics and Astronomy Faculty Research

New, coordinated measurements from the International Solar-Terrestrial Physics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earth's magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X-ray data are also used to identify the solar coronal holes that produce the high-speed solar wind streams which, in turn, cause the recurrent …

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