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Articles 271 - 300 of 317
Full-Text Articles in Astrophysics and Astronomy
Nonlinear Parallel And Perpendicular Diffusion Of Charged Cosmic Rays In Weak Turbulence, Andreas Schalchi, John William Bieber, William H. Matthaeus, Gang Qin
Nonlinear Parallel And Perpendicular Diffusion Of Charged Cosmic Rays In Weak Turbulence, Andreas Schalchi, John William Bieber, William H. Matthaeus, Gang Qin
Aerospace, Physics, and Space Science Faculty Publications
The problem of particle transport perpendicular to a magnetic background field is well known in cosmic-ray astrophysics. Whereas it is widely accepted that quasi-linear theory (QLT) of particle transport does not provide the correct results for perpendicular diffusion, it was assumed for a long time that QLT is the correct theory for parallel diffusion. In the current paper we demonstrate that QLT is in general also incorrect for parallel particle transport if we consider composite turbulence geometry. Motivated through the recent success of the so-called nonlinear guiding center theory of perpendicular diffusion, we present a new theory for parallel and …
Spectral Properties Of Heavy Ions Associated With The Passage Of Interplanetary Shocks At 1 Au, Mihir I. Desai, Joseph R. Dwyer
Spectral Properties Of Heavy Ions Associated With The Passage Of Interplanetary Shocks At 1 Au, Mihir I. Desai, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
We have surveyed the energy spectra of ∼0.1-100 MeV nucleonˉ¹ C, O, and Fe nuclei associated with the passage of 72 interplanetary (IP) shocks observed on board the ACE spacecraft during the period 1997 October-2002 October. Our main results are as follows: (1) The spectral fit parameters are independent of the local shock properties. (2) About 7% of the events exhibit increasing Fe/O ratios with energy; the remaining events have Fe/O ratios that either remain constant or decrease with energy. (3) The Fe/O ratio in the shock-associated particles is typically ∼30% lower than in the ambient population. (4) The fractionation …
Interplanetary Transport Mechanisms Of Solar Energetic Particles, Gang Qin, Ming Zhang, Joseph R. Dwyer, Hamid K. Rassoul
Interplanetary Transport Mechanisms Of Solar Energetic Particles, Gang Qin, Ming Zhang, Joseph R. Dwyer, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
Numerical simulations of charged particle trajectories in a Parker field with model turbulence are used to study the transport mechanisms of solar energetic particles (SEPs): magnetic focusing, pitch-angle diffusive transport due to magnetic fluctuations, and adiabatic cooling. The results of the simulations are compared with analytical formulae for the transport effects. We find that adiabatic cooling is significant for SEPs traveling from the Sun to 1 AU. The simulation results agree much better with the anisotropic adiabatic cooling effect theory than with the isotropic one. Also, we show that the simulation results agree well with the theory of magnetic focusing …
Spectroscopic And Photometric Analysis Of Hs 1136+6646: A Hot Young Dao+K7 V Post-Common-Envelope, Pre-Cataclysmic Variable Binary, David K. Sing, Terry D. Oswalt, Mark J. Rudkin, K Johnston, S Rafferty
Spectroscopic And Photometric Analysis Of Hs 1136+6646: A Hot Young Dao+K7 V Post-Common-Envelope, Pre-Cataclysmic Variable Binary, David K. Sing, Terry D. Oswalt, Mark J. Rudkin, K Johnston, S Rafferty
Aerospace, Physics, and Space Science Faculty Publications
Extensive photometric and spectroscopic observations have been obtained for HS 1136+6646. The observations reveal a newly formed post–common-envelope binary system containing a hot ~DAO.5 primary and a highly irradiated secondary. HS 1136+6646 is the most extreme example yet of a class of short-period hot H-rich white dwarfs with K–M companion systems such as V471 Tau and Feige 24. HS 1136+6646 is a double-line spectroscopic binary showing emission lines of H I, He II, C II, Ca II, and Mg II, due in part to irradiation of the K7 V secondary by the hot white dwarf. Echelle spectra reveal the hydrogen …
Abundances Of Heavy And Ultraheavy Ions In ³He-Rich Solar Flares, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer, Jack Randy Jokipii, Robert E. Gold, Stamatios M. Krimigis
Abundances Of Heavy And Ultraheavy Ions In ³He-Rich Solar Flares, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer, Jack Randy Jokipii, Robert E. Gold, Stamatios M. Krimigis
Aerospace, Physics, and Space Science Faculty Publications
We have surveyed ³He-rich solar energetic particle (SEP) events over the period 1997 September-2003 April in order to characterize abundances of heavy ions near 400 keV nucleonˉ¹. The first part of the study focuses on 20 distinct SEP events that show the previously observed pattern in which, relative to O, heavy ions through Fe are enriched, with the enrichment increasing with mass. We find that these enrichments are well correlated such that ³He-rich SEP events with high Fe/C also show larger enrichments in other heavy ions. Ultraheavy (UH; taken as 78-220 amu) ions are routinely seen in these events with …
Observations Of The Pulsating White Dwarf G 185-32, Bárbara Garcia Castanheira, Matt A. Wood
Observations Of The Pulsating White Dwarf G 185-32, Bárbara Garcia Castanheira, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
We observed the pulsating hydrogen atmosphere white dwarf G 185-32 with the Whole Earth Telescope in 1992. We report on a weighted Fourier transform of the data detecting 18 periodicities in its light curve. Using the Hubble Space Telescope Faint Object Spectrograph time resolved spectroscopy, and the wavelength dependence of the relative amplitudes, we identify the spherical harmonic degree (ℓ) for 14 pulsation signals. We also compare the determinations of effective temperature and surface gravity using the excited modes and atmospheric methods, obtaining Teff = 11960 ± 80 K, log g = 8.02 ± 0.04 and M = 0.617 ± …
Perpendicular Transport Of Solar Energetic Particles In Heliospheric Magnetic Fields, Ming Zhang, Jack Randy Jokipii, Robert Bruce Mckibben
Perpendicular Transport Of Solar Energetic Particles In Heliospheric Magnetic Fields, Ming Zhang, Jack Randy Jokipii, Robert Bruce Mckibben
Aerospace, Physics, and Space Science Faculty Publications
This paper presents direct observational evidence for large perpendicular diffusive flows of solar energetic particles in heliospheric magnetic fields. Using anisotropy measurements of 40-92 MeV protons obtained by the High-Energy Telescope of the COSPIN consortium on Ulysses at high heliographic latitudes, we find that during several gradual solar particle events, for periods of many hours, the observed particle flow is directed at significant angles to the measured local magnetic field direction, which can only be explained by cross-field diffusion. The variation of the particle flow direction with the magnetic field direction seen in the 2000 July 14 solar energetic particle …
Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, Matt A. Wood, Nicole M. Silvestri
Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, Matt A. Wood, Nicole M. Silvestri
Aerospace, Physics, and Space Science Faculty Publications
We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213. 13 s observed in ZZ Ceti drifts at a rate dP/dt ≤ (5.5 ± 1.9) × 10ˉ¹⁵ s sˉ¹, after correcting for proper motion. Our results are consistent with previous Ṗ values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is | Ṗ / |≥ 1.2 …
Elemental Fractionation In Small Solar Energetic Particle Events, Penny L. Slocum, Joseph R. Dwyer
Elemental Fractionation In Small Solar Energetic Particle Events, Penny L. Slocum, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
Using the Solar Isotope Spectrometer on the Advanced Composition Explorer (ACE), we have measured the 11.0-21.8 MeV nucleon-1 heavy (Z ≥ 6) element abundances of 39 small solar energetic particle (SEP) events that occurred between 1998 April 3 and 2002 February 26. Using He isotope data from the UltraLow-Energy Isotope Spectrometer on ACE, we have classified the events according to their 0.5-2.0 MeV nucleonˉ¹ ³He/⁴He ratios. We find that their average heavy-element composition is similar to that of either large gradual events or ³He-rich events, depending on their ³He/⁴He ratio. As seen in recent studies of small SEP events, we …
Pks 0736+017: A Striking Optical Flare And Intriguing Microvariability, Sandra D. Clements, A Jenks, Y Torres
Pks 0736+017: A Striking Optical Flare And Intriguing Microvariability, Sandra D. Clements, A Jenks, Y Torres
Aerospace, Physics, and Space Science Faculty Publications
The compact, flat-spectrum radio quasar PKS 0736+017 was monitored for microvariability on 10 nights in early 2002 using the 0.9 m SARA telescope on Kitt Peak in Arizona. On January 14, PKS 0736+017 flared dramatically, brightening by 1.3 R mag in 2 hours. Prior to the flare, PKS 0736+017 exhibited quasi-periodic variations. During and after the flare, more complex oscillations occurred. Impressive variability was displayed on two additional nights in January, while observations during the following 3 months found PKS 0736+017 to be fairly quiescent. PKS 0736+017 was somewhat redder while brighter and fading than when dimmer but flaring. During …
Nonlinear Collisionless Perpendicular Diffusion Of Charged Particles, William H. Matthaeus, Gang Qin, John William Bieber, Gary Paul Zank
Nonlinear Collisionless Perpendicular Diffusion Of Charged Particles, William H. Matthaeus, Gang Qin, John William Bieber, Gary Paul Zank
Aerospace, Physics, and Space Science Faculty Publications
A nonlinear theory of the perpendicular diffusion of charged particles is presented, including the influence of parallel scattering and dynamical turbulence. The theory shows encouraging agreement with numerical simulations.
Evidence For A Suprathermal Seed Population Of Heavy Ions Accelerated By Interplanetary Shocks Near 1 Au, Mihir I. Desai, Glenn M. Mason, Joseph R. Dwyer, Joseph E. Mazur, Robert E. Gold, Stamatios M. Krimigis, Charles W. Smith, Ruth M. Skoug
Evidence For A Suprathermal Seed Population Of Heavy Ions Accelerated By Interplanetary Shocks Near 1 Au, Mihir I. Desai, Glenn M. Mason, Joseph R. Dwyer, Joseph E. Mazur, Robert E. Gold, Stamatios M. Krimigis, Charles W. Smith, Ruth M. Skoug
Aerospace, Physics, and Space Science Faculty Publications
We have surveyed the 0.1-10 MeV nucleonˉ¹ elemental abundances at 72 interplanetary (IP) shocks observed by the Ultra-Low-Energy Isotope Spectrometer on board the Advanced Composition Explorer from 1997 October through 2002 September. We find the following: (1) The C/O ratios in IP shocks were substantially depleted (by more than ∼40%) relative to solar wind values. (2) The IP shock abundances were poorly correlated with those measured in the slow and fast solar wind. (3) Energetic ions above ∼0.1 MeV nucleonˉ¹ from impulsive and gradual solar energetic particle events (SEPs) were present upstream of all the IP shocks in our survey. …
Delay In Solar Energetic Particle Onsets At High Heliographic Latitudes, Silvia C. Dalla, Ming Zhang
Delay In Solar Energetic Particle Onsets At High Heliographic Latitudes, Silvia C. Dalla, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
Ulysses observations have shown that solar energetic particles (SEPs) can easily reach high heliographic latitudes. To obtain information on the release and propagation of SEPs prior to their arrival at Ulysses, we analyse the onsets of nine large high-latitude particle events. We measure the onset times in several energy channels, and plot them versus inverse particle speed. This allows us to derive an experimental path length and time of release from the solar atmosphere. We repeat the procedure for near-Earth observations by Wind and SOHO. We find that the derived path lengths at Ulysses are 1.06 to 2.45 times the …
2mass J0516288+260738: Discovery Of The First Eclipsing Late K + Brown Dwarf Binary System?, Sonja L. Schüh, Matt A. Wood
2mass J0516288+260738: Discovery Of The First Eclipsing Late K + Brown Dwarf Binary System?, Sonja L. Schüh, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
We report the discovery of a new eclipsing system less than one arcminute south of the pulsating DB white dwarf KUV 05134+2605 . The object could be identified with the point source 2MASS J0516288+260738 published by the Two Micron All Sky Survey. We present and discuss the first light curves as well as some additional colour and spectral information. The eclipse period of the system is 1.29 d, and, assuming this to be identical to the orbital period, the best light curve solution yields a mass ratio of m₂/m₁=0.11, a radius ratio of r₂/r₁ ≈ 1 and an inclination of …
The Everchanging Pulsating White Dwarf Gd358, Souza Oliveira Kepler, Matt A. Wood, Nicole M. Silvestri, Thomas J. Ahrens
The Everchanging Pulsating White Dwarf Gd358, Souza Oliveira Kepler, Matt A. Wood, Nicole M. Silvestri, Thomas J. Ahrens
Aerospace, Physics, and Space Science Faculty Publications
We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired more than 232 000 independent measurements. We also report on 48 hours of time-series photometric observations in Aug 1996. We detected the non-radial g-modes consistent with degree ℓ = 1 and radial order 8 to 20 and their linear combinations up to 6th order. We also detect, for the first time, a high amplitude ℓ = 2 mode, with a period of 796 s. In the 2000 …
Multisite Observations Of The Pms Δ Scuti Star V351 Ori, Vincenzo Ripepi, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Multisite Observations Of The Pms Δ Scuti Star V351 Ori, Vincenzo Ripepi, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Aerospace, Physics, and Space Science Faculty Publications
We present the results of multisite observations spanning two years on the pre-main-sequence (PMS) star V351 Ori. A total of around 180 hours of observations over 29 nights have been collected, allowing us to measure five different periodicities, most likely related to the δ Scuti variability of V351 Ori. Comparison with the predictions of linear nonadiabatic radial pulsation models put stringent constraints on the stellar parameters and indicate that the distance to V351 Ori is intermediate between the lower limit measured by Hipparcos (210 pc) and that of the Orion Nebula (450 pc). However, radial pulsation models are unable to …
Ulysses Cospin Observations Of Cosmic Rays And Solar Energetic Particles From The South Pole To The North Pole Of The Sun During Solar Maximum, Robert Bruce Mckibben, Ming Zhang
Ulysses Cospin Observations Of Cosmic Rays And Solar Energetic Particles From The South Pole To The North Pole Of The Sun During Solar Maximum, Robert Bruce Mckibben, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
In 2000–2001 Ulysses passed from the south to the north polar regions of the Sun in the inner heliosphere, providing a snapshot of the latitudinal structure of cosmic ray modulation and solar energetic particle populations during a period near solar maximum. Observations from the COSPIN suite of energetic charged particle telescopes show that latitude variations in the cosmic ray intensity in the inner heliosphere are nearly non-existent near solar maximum, whereas small but clear latitude gradients were observed during the similar phase of Ulysses’ orbit near the 1994–95 solar minimum. At proton energies above ∼10 MeV and extending up to …
Perpendicular Transport Of Charged Particles In Composite Model Turbulence: Recovery Of Diffusion, Gang Qin, William H. Matthaeus, John William Bieber
Perpendicular Transport Of Charged Particles In Composite Model Turbulence: Recovery Of Diffusion, Gang Qin, William H. Matthaeus, John William Bieber
Aerospace, Physics, and Space Science Faculty Publications
The computation of charged particle orbits in model turbulent magnetic fields is used to investigate the properties of particle transport in the directions perpendicular to the large-scale magnetic field. Recent results by Qin, Matthaeus, & Bieber demonstrate that parallel scattering suppresses perpendicular diffusion to a subdiffusive level when the turbulence lacks transverse structure. Here numerical computations are used to show that in turbulence in which there is substantial transverse structure, a second regime of diffusive transport can be established. In both the subdiffusion regime and this "second diffusion" regime, perpendicular transport is intrinsically nonlinear. The regime of second diffusion persists …
Wide Binary Systems And The Nature Of High-Velocity White Dwarfs, Nicole M. Silvestri, Terry D. Oswalt, Suzanne L. Hawley
Wide Binary Systems And The Nature Of High-Velocity White Dwarfs, Nicole M. Silvestri, Terry D. Oswalt, Suzanne L. Hawley
Aerospace, Physics, and Space Science Faculty Publications
We present measured radial velocities and complete space motions for 116 white dwarf stars with M dwarf companions. Thirteen pairs have " halo-like " velocities. According to a recent study by Oppenheimer et al., all these high-velocity white dwarfs should be considered part of the dark matter heavy halo of the Galaxy, based on their kinematics. Based on the near-solar abundance levels of the M dwarf companions, we conclude that 12 of our 13 high-velocity white dwarfs are actually part of the high-velocity tail of the thick disk, rather than the dark matter halo of the Galaxy, in agreement with …
Spectral Properties Of He And Heavy Ions In ³He-Rich Solar Flares, Glenn M. Mason, Joseph R. Dwyer
Spectral Properties Of He And Heavy Ions In ³He-Rich Solar Flares, Glenn M. Mason, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
Using advanced instrumentation on the ACE spacecraft, we have conducted a survey of solar energetic particle spectra in ³He-rich events over a broad energy range ∼80 keV nucleon-1 to 15 MeV nucleonˉ¹ during the period 1997 September-2001 March. The spectra of ⁴He and heavy ions (C, N, O, Ne, Mg, Si, S, Ca, Fe) were generally similar over this range but often hardened below ∼1 MeV nucleonˉ¹. In most of the events there was even stronger hardening of the ³He spectrum below ∼1 MeV nucleonˉ¹, leading to an energy-dependent ³He: ⁴He ratio. These observations point to unique and distinct properties …
A Determination Of The Local Density Of White Dwarf Stars, Jay B. Holberg, Terry D. Oswalt, Edward M. Sión
A Determination Of The Local Density Of White Dwarf Stars, Jay B. Holberg, Terry D. Oswalt, Edward M. Sión
Aerospace, Physics, and Space Science Faculty 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 …
Tip Of The Red Giant Branch Distances To Ngc 4214, Ugc 685, And Ugc 5456, Jesús Maíz Apellániz, Lucas Cieza, John W. Mackenty
Tip Of The Red Giant Branch Distances To Ngc 4214, Ugc 685, And Ugc 5456, Jesús Maíz Apellániz, Lucas Cieza, John W. Mackenty
Aerospace, Physics, and Space Science Faculty Publications
We have used WFPC2 VRI observations to calculate the distances to three nearby galaxies, NGC 4214, UGC 685, and UGC 5456, using the tip of the red giant branch method. Our values for NGC 4214 (2.94 ± 0.18 Mpc) and UGC 685 (4.79 ± 0.30 Mpc) are the most precise measurements of the distances to these objects ever made. For UGC 5456 the data do not allow us to reach a decisive conclusion since there are two possible solutions, one leading toward a short distance around 3.8 Mpc and another one toward a long distance of 5.6 Mpc or more.
A New Heavy Ion Abundance Enrichment Pattern In ³He-Rich Solar Particle Events, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer
A New Heavy Ion Abundance Enrichment Pattern In ³He-Rich Solar Particle Events, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
We report the first examples of ³He-rich solar energetic particle (SEP) events with heavy ion enrichments that are not ordered generally by mass. A second new feature is the large enrichment of ¹⁴N, the first time large enrichments have been seen for heavy ions lighter than O or Ne. These SEP events were too small and at too low an energy (<500 keV nucleon-1) to have been observed previously. The best observed event, 2001 July 16, had abundance ratios C : N : O : Ne : Mg : Si : S : Ca : Fe of ∼0.8 : 1.0 : ≡ 1 : 0.5 : 0.5 : 2.0 : 2.4 : 0.2 : 0.9, corresponding, respectively, to enhancements over the slow solar wind of ∼1.2 :15 : ≡ 1 : 5. : 3.4 : 12 :49 : 19 : 7. This pattern is incompatible with a gravitational settling enrichment mechanism. The simultaneous large enhancements of ¹⁴N and ²⁸Si, which have identical charge-to-mass ratios for certain ionization states, suggest that selective plasma wave heating plays a key role, as has long been suspected. Enhancement of ¹⁴N implies relatively low temperatures (<1.5 × 10 6 K) since fully stripped ¹⁴N cannot be preferentially heated. Also, the presence of enhanced species such as ¹⁴N and ²⁸Si, along with others with small or no enhancements ( 16)O, ²⁰Ne), may indicate that the plasma waves must operate over a relatively narrow range of frequencies and that the material must be heated while the waves are present.
The Temporal Spectrum Of The Sdb Pulsating Star Hs 2201+2610 At 2 Ms Resolution, R Silvotti, T D. Oswalt, Nicole M. Silvestri, Glenn Carlson
The Temporal Spectrum Of The Sdb Pulsating Star Hs 2201+2610 At 2 Ms Resolution, R Silvotti, T D. Oswalt, Nicole M. Silvestri, Glenn Carlson
Aerospace, Physics, and Space Science Faculty Publications
In this article we present the results of more than 180 hours of time-series photometry on the low gravity (log g = 5.4, Teff = 29 300 K, log He/H = -3.0 by number) sdB pulsating star HS 2201+2610, obtained between September 2000 and August 2001. The temporal spectrum is resolved and shows 5 close frequencies: three main signals at 2860.94, 2824.10 and 2880.69 μHz, with amplitudes of about 1%, 0.5% and 0.1% respectively, are detected from single run observations; two further peaks with very low amplitude (<0.07%) at 2738.01 and 2921.82 μHz are confirmed by phase analysis on several independent runs. Due to the small number of detected frequencies, it is not possible to obtain a univocal identification of the excited modes and perform a detailed seismological analysis of the star. No clear signatures of rotational splitting are seen. Nevertheless, the observed period spectrum is well inside the excited period window obtained from pulsation calculations with nonadiabatic models having effective temperature and surface gravity close to the spectroscopic estimates. Due to its relatively simple temporal spectrum, HS 2201+2610 is a very good candidate for trying to measure the secular variation of the pulsation periods in time. With this purpose a long-term monitoring of the star was started. The results of the first 11 months show amplitude variations up to ∼20% on time-scales of months, which are probably real, and allow us to measure the pulsation frequencies with an unprecedented 0.02 μHz resolution.
Asteroseismology Of Rxj 2117+3412, The Hottest Pulsating Pg 1159 Star, G Vauclair, Matt A. Wood
Asteroseismology Of Rxj 2117+3412, The Hottest Pulsating Pg 1159 Star, G Vauclair, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
The pulsating PG 1159 planetary nebula central star RXJ 2117+3412 has been observed over three successive seasons of a multisite photometric campaign. The asteroseismological analysis of the data, based on the 37 identified ℓ = 1 modes among the 48 independent pulsation frequencies detected in the power spectrum, leads to the derivation of the rotational splitting, the period spacing and the mode trapping cycle and amplitude, from which a number of fundamental parameters can be deduced. The average rotation period is 1.16 ± 0.05 days. The trend for the rotational splitting to decrease with increasing periods is incompatible with a …
Isotopic Composition Of Solar Energetic Particle Events Measured By Advanced Composition Explorer/Uleis, Joseph R. Dwyer, Glenn M. Mason, Joseph E. Mazur, Robert E. Gold, Stamatios M. Krimigis, Eberhard S. Möbius, Mark A. Popecki
Isotopic Composition Of Solar Energetic Particle Events Measured By Advanced Composition Explorer/Uleis, Joseph R. Dwyer, Glenn M. Mason, Joseph E. Mazur, Robert E. Gold, Stamatios M. Krimigis, Eberhard S. Möbius, Mark A. Popecki
Aerospace, Physics, and Space Science Faculty Publications
Since its 1997 August launch, the Ultra Low Energy Isotope Spectrometer (ULEIS) on board the Advanced Composition Explorer (ACE) has observed a large number of solar energetic particle (SEP) events in the 0.4-3 MeV nucleonˉ¹ range. These events show remarkable variability of both the elemental and isotopic compositions, with ²²Ne/²⁰Ne varying, from event to event, by up to a factor of 10, Fe/O by up to a factor of 100, and ³He/⁴He by up to a factor of 104. In this paper we present new measurements of the ²²Ne/²⁰Ne, ²⁶Mg/²⁴Mg, and ³He/⁴He ratios at ∼ 1 MeV nucleonˉ¹ and compare …
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
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 …
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, Jonathan Allyn Smith, Iain Neill Reid, Edward M. Sión
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, Jonathan Allyn Smith, Iain Neill Reid, Edward M. Sión
Aerospace, Physics, and Space Science Faculty Publications
We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 M⊙. This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average Teff ~ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf stars tend to …
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.
Asymptotic Analysis Of The Structure Of A Steady Planar Detonation: Review And Extension, William B. Bush, L. Krishnamurthy
Asymptotic Analysis Of The Structure Of A Steady Planar Detonation: Review And Extension, William B. Bush, L. Krishnamurthy
Aerospace, Physics, and Space Science Faculty Publications
The structure of a steady planar Chapman-Jouguet detonation, which is supported by a direct first-order one-step irreversible exothermic unimolecular reaction, subject to Arrhenius kinetics, is examined. Solutions are studied, by means of a limit-processexpansion analysis, valid for A, proportional to the ratio of the reaction rate to the flow rate, going to zero, and for β, proportional to the ratio of the activation temperature to the maximum flow temperature, going to infinity, with the product Aβ½ going to zero. The results, essentially in agreement with the Zeldovich-von Neumann-Dōring model, show that the detonation consists of (1) a three-region upstream shocklike …