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Articles 211 - 240 of 282
Full-Text Articles in Astrophysics and Astronomy
Asteroseismology Of The Pg 1159 Star Pg 0122+200, Jianning Fu, Matt A. Wood
Asteroseismology Of The Pg 1159 Star Pg 0122+200, Jianning Fu, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
Context. The variable pre-white dwarf PG 1159 stars (GW Vir) are g-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the opportunity to better understand the instability mechanism and to validate the physics of the neutrino production in dense plasma. Aims. To achieve such a goal requires determining precisely its fundamental parameters. This is the goal of this paper. Methods. We present new multi-site photometric observations obtained in 2001 and …
Spectropolarimetric Survey Of Hydrogen-Rich White Dwarf Stars, Adéla Kawka, Stéphane Vennes, Gary D. Schmidt, Dayal T. Wickramasinghe, Rolf Koch
Spectropolarimetric Survey Of Hydrogen-Rich White Dwarf Stars, Adéla Kawka, Stéphane Vennes, Gary D. Schmidt, Dayal T. Wickramasinghe, Rolf Koch
Aerospace, Physics, and Space Science Faculty Publications
We have conducted a survey of 61 southern white dwarfs searching for magnetic fields using Zeeman spectropolarimetry. Our objective is to obtain a magnetic field distribution for these objects and, in particular, to find white dwarfs with weak fields. We found one possible candidate (WD 0310-688) that may have a weak magnetic field of -6.1 ±2.2 kG. Next, we determine the fraction and distribution of magnetic white dwarfs in the solar neighborhood and investigate the probability of finding more of these objects based on the current incidence of magnetism in white dwarfs within 20 pc of the Sun. We have …
Iron In Hot Da White Dwarfs, Stéphane Vennes, Pierre Chayer, Jean François Dupuis, Thierry M. Lanz
Iron In Hot Da White Dwarfs, Stéphane Vennes, Pierre Chayer, Jean François Dupuis, Thierry M. Lanz
Aerospace, Physics, and Space Science Faculty Publications
We present a study of the iron abundance pattern in hot, hydrogen-rich (DA) white dwarfs. The study is based on new and archival far-ultraviolet spectroscopy of a sample of white dwarfs in the temperature range 30,000 K ≲ Teff ≲ 64,000 K. The spectra obtained with the Far Ultraviolet Spectroscopic Explorer, along with spectra obtained with the Hubble Space Telescope Imaging Spectrograph and the International Ultraviolet Explorer, sample Fe III-Fe VI absorption lines, enabling a detailed iron abundance analysis over a wider range of effective temperatures than previously afforded. The measurements reveal abundance variations in excess of 2 orders of …
Further Evidence For Variable Synchrotron Emission In Xte J1118+480 In Outburst, Robert I. Hynes, Edward L. Robinson, Kevin J. Pearson, Dawn M. Gelino, Wei Cui, Yongquan Xue, Matt A. Wood, Todd K. Watson, Don Earl Winget, Isaac M. Silver
Further Evidence For Variable Synchrotron Emission In Xte J1118+480 In Outburst, Robert I. Hynes, Edward L. Robinson, Kevin J. Pearson, Dawn M. Gelino, Wei Cui, Yongquan Xue, Matt A. Wood, Todd K. Watson, Don Earl Winget, Isaac M. Silver
Aerospace, Physics, and Space Science Faculty Publications
We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE Jill 8+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ∼10 s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHKS photometry, as in the previous outburst, exhibits especially large-amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power law of slope α = -0.78 ± 0.07, where Fᵧ …
Heavy-Ion Elemental Abundances In Large Solar Energetic Particle Events And Their Implications For The Seed Population, Mihir I. Desai, Glenn M. Mason, Robert E. Gold, Stamatios M. Krimigis, Christina M.S. Cohen, Richard A. Mewaldt, Joseph E. Mazur, Joseph R. Dwyer
Heavy-Ion Elemental Abundances In Large Solar Energetic Particle Events And Their Implications For The Seed Population, Mihir I. Desai, Glenn M. Mason, Robert E. Gold, Stamatios M. Krimigis, Christina M.S. Cohen, Richard A. Mewaldt, Joseph E. Mazur, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
We have surveyed the ∼0.1-10 MeV nucleonˉ¹ abundances of heavy ions from ³He through Fe in 64 large solar energetic particle (LSEP) events observed on board the Advanced Composition Explorer from 1997 November through 2005 January. Our main results are (1) the 0.5-2.0 MeV nucleonˉ¹ ³He/⁴He ratio is enhanced between factors of ∼2-150 over the solar wind value in 29 (∼46%) events. (2) The Fe/O ratio in most LSEP events decreases with increasing energy up to ∼60 MeV nucleonˉ¹. (3) The Fe/O ratio is independent of CME speed, flare longitude, event size, the ³He/⁴He ratio, the pre-event Fe/O ratio, and …
The Role Of Interplanetary Scattering In Western Hemisphere Large Solar Energetic Particle Events, Glenn M. Mason, Mihir I. Desai, Christina M.S. Cohen, Richard A. Mewaldt, Edward C. Stone, Joseph R. Dwyer
The Role Of Interplanetary Scattering In Western Hemisphere Large Solar Energetic Particle Events, Glenn M. Mason, Mihir I. Desai, Christina M.S. Cohen, Richard A. Mewaldt, Edward C. Stone, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
Using high-sensitivity instruments on the ACE spacecraft, we have examined the intensities of O and Fe in 14 large solar energetic particleevents whose parent activity was in the solar western hemisphere. Sampling the intensities at low (∼273 keV nucleonˉ¹) and high (∼12 MeV nucleonˉ¹) energies, we find that at the same kinetic energy per nucleon, the Fe/O ratio decreases with time, as has been reported previously. This behavior is seen in more than 70% of the cases during the rise to maximum intensity and continues in most cases into the decay phase. We find that for most events if we …
Whole Earth Telescope Observations Of The Pulsating Subdwarf B Star Pg 0014+067, Maja Vučković, Matt A. Wood, V. Wilkat
Whole Earth Telescope Observations Of The Pulsating Subdwarf B Star Pg 0014+067, Maja Vučković, Matt A. Wood, V. Wilkat
Aerospace, Physics, and Space Science Faculty Publications
PG 0014+067 is one of the most promising pulsating subdwarf B stars for seismic analysis, as it has a rich pulsation spectrum. The richness of its pulsations, however, poses a fundamental challenge to understanding the pulsations of these stars, as the mode density is too complex to be explained only with radial and nonradial low-degree (l < 3) p-modes without rotational splittings. One proposed solution, suggested by Brassard et al. in 2001 for the case of PG 0014+067 in particular, assigns some modes with high degree (l - 3). On the other hand, theoretical models of sdB stars suggest that they may retain rapidly rotating cores, and so the high mode density may result from the presence of a few rotationally split triplet (l = 1) and quintuplet (l = 2) modes, along with radial (l = 0)p-modes. To examine alternative theoretical models for these stars, we need better frequency resolution and denser longitude coverage. Therefore, we observed this star with the Whole Earth Telescope for two weeks in 2004 October. In this paper we report the results of Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG 0014+067 do not appear to fit any theoretical model currently available; however, we find a simple empirical relation that is able to match all of the well-determined frequencies in this star.
Solar Cycle Variations In The Composition Of The Suprathermal Heavy-Ion Population Near 1 Au, Mihir I. Desai, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer
Solar Cycle Variations In The Composition Of The Suprathermal Heavy-Ion Population Near 1 Au, Mihir I. Desai, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
We have measured the annual variation in the quiet-time composition of interplanetary suprathermal ions between 0.04 and 1 MeV nucleon-1 from 1994 November 20 through 2006 January 1. Our results show the following: (1) The C/O and Fe/O ratios are similar to the corresponding values measured in the solar wind and corotating interaction regions (CIRs) during solar minimum conditions of 1994-1997 and 2005. (2) During periods of increased solar activity between 1998 and 2002, the C/O ratio is similar to that measured in solar energetic particle (SEP) events, while the Fe/O ratio lies between the values measured in coronal mass …
Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adéla Kawka, Stéphane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri
Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adéla Kawka, Stéphane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri
Aerospace, Physics, and Space Science Faculty Publications
We report the identification of LP 400-22 (WD 2234+222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080 ± 140 K and a surface gravity of log g = 6.32 ± 0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 M⊙. The tangential velocity of this white dwarf is 414 ± 43 km s-1, making it one of the fastest moving white dwarfs known. We discuss probable evolutionary scenarios for this …
Spectroscopic Identification Of Cool White Dwarfs In The Solar Neighborhood, Adela Kawka, Stéphane Vennes
Spectroscopic Identification Of Cool White Dwarfs In The Solar Neighborhood, Adela Kawka, Stéphane Vennes
Aerospace, Physics, and Space Science Faculty Publications
The New Luyten Two-Tenths catalog contains a large number of high proper motion white dwarf candidates that remain to be spectroscopically confirmed. We present new spectroscopic observations, as well as SDSS archival spectra of 49 white dwarf candidates selected from the revised NLTT catalog of Salim & Gould. Of these, 34 are cool DA white dwarfs with temperatures ranging from approximately 5000 up to 11,690 K, and 11 are DC white dwarfs with temperatures ranging from 4300 K (NLTT 18555) up to 11,000 K. Three of the DA white dwarfs also display abundances of heavy elements (NLTT 3915, NLTT 44986, …
A Far-Ultraviolet Study Of The Hot White Dwarf In The Dwarf Nova Ww Ceti, Patrick Godon, Laura Seward, Edward M. Sion, Paula Szkody
A Far-Ultraviolet Study Of The Hot White Dwarf In The Dwarf Nova Ww Ceti, Patrick Godon, Laura Seward, Edward M. Sion, Paula Szkody
Aerospace, Physics, and Space Science Faculty Publications
We present a synthetic spectral analysis of IUE archival and FUSE (Far Ultraviolet Spectroscopic Explorer) far-UV spectra of the peculiar dwarf nova WW Cet. During the quiescence of WW Cet, a white dwarf with T wd ∼ 26,000 ± 1000 K can account for the far-UV flux and yields the proper distance. However, the best agreement with the observations is provided by a two-temperature white dwarf model with a cooler white dwarf at T wd = 25,000 K providing 75% of the far-UV flux and a hotter region (accretion belt or optically thick disk ring) with T = 40,000 K …
The Solar Flare Of The 14th Of July 2000 (L3+C Detector Results), Pablo Achard, Gyöngyi Baksay, László A. Baksay, K Dehmelt, Marcus Hohlmann, D Rembeczki, Z Szillasi, I Vodopianov, The L3 Collaboration
The Solar Flare Of The 14th Of July 2000 (L3+C Detector Results), Pablo Achard, Gyöngyi Baksay, László A. Baksay, K Dehmelt, Marcus Hohlmann, D Rembeczki, Z Szillasi, I Vodopianov, The L3 Collaboration
Aerospace, Physics, and Space Science Faculty Publications
Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods.The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary …
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Aerospace, Physics, and Space Science Faculty Publications
We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the presence of (at least) 15 periodicities in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557, Paper I). Based on high-S/N, medium-resolution spectra obtained at the Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT Telescope, new NLTE spectroscopic derivations of the atmospheric parameters of PG 1325+101 are presented. The mean values of T eff = 35 050 ± 220 K, log …
Runaway Breakdown In The Jovian Atmospheres, Joseph R. Dwyer, Lee M. Coleman, Ramon E. Lopez, Ziad H. Saleh, D. Concha, Michael G. Brown, Hamid K. Rassoul
Runaway Breakdown In The Jovian Atmospheres, Joseph R. Dwyer, Lee M. Coleman, Ramon E. Lopez, Ziad H. Saleh, D. Concha, Michael G. Brown, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
Using detailed Monte Carlo calculations, the properties of runaway breakdown in the atmospheres of the four gas giant planets in our solar system are investigated, and the runaway avalanche lengths and average runaway electron kinetic energies are presented as a function of atmospheric electric field strengths. The runaway breakdown threshold field for the Jovian atmospheres is found to be 10 times smaller than the conventional breakdown field when hydrometeors are present, compared to 3 times smaller for Earth's atmosphere, indicating that runaway breakdown processes may be much more efficient in the gas giants than on Earth. In the Earth's atmosphere, …
A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt
A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt
Aerospace, Physics, and Space Science Faculty Publications
We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination …
Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri
Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri
Aerospace, Physics, and Space Science Faculty Publications
This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 μHz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after …
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Aerospace, Physics, and Space Science Faculty Publications
In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff - 35 000 K, log g = 5.8, log N(Hs)/N(H) = -1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies …
Galactic Cosmic-Ray Modulation Using A Solar Minimum Mhd Heliosphere: A Stochastic Particle Approach, Bryan M. Ball, Ming Zhang, Hamid K. Rassoul, Timur J. Linde
Galactic Cosmic-Ray Modulation Using A Solar Minimum Mhd Heliosphere: A Stochastic Particle Approach, Bryan M. Ball, Ming Zhang, Hamid K. Rassoul, Timur J. Linde
Aerospace, Physics, and Space Science Faculty Publications
An example of Galactic cosmic-ray modulation in a fully three-dimensional heliosphere is presented here. We use a stochastic particle method to solve for modulation without requiring symmetric boundaries or fields. We include all typical modulation terms, including full three-dimensional drift. We have applied this to an MHD heliosphere appropriate for solar minimum conditions. This field includes nonradial solar wind velocity components, as well as a built-in nonspherical termination shock. Parameters that are of interest in modulation can be analyzed in detail, particularly the momentum change of cosmic rays during their transport through the heliosphere. We show radial profiles of modulation …
Dq Herculis In Profile: Whole Earth Telescope Observations And Smoothed Particle Hydrodynamics Simulations Of An Edge-On Cataclysmic Variable System, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
The old nova DQ Herculis was the Whole Earth Telescope Northern Hemisphere target for the 1997 July campaign and was observed on four nights with the SARA 0.9 m telescope during 2003 June. We present updated ephemerides for the eclipse and 71 s timings. The Fourier transform displays power at the presumed white dwarf spin period of 71.0655 s, but no significant power at either 142 or 35.5 s. The mean pulsed light curve is obtained by folding on the orbital period modulus the mean ephemeris of the 71 s period, and from this we calculate an O - C …
Abundance Of Elements Beyond The Iron Group In Cool Do White Dwarfs, Pierre Chayer, Stéphane Vennes, Jean Jean François, Jeffrey W. Kruk
Abundance Of Elements Beyond The Iron Group In Cool Do White Dwarfs, Pierre Chayer, Stéphane Vennes, Jean Jean François, Jeffrey W. Kruk
Aerospace, Physics, and Space Science Faculty Publications
We report the presence of elements beyond the iron group in the atmospheres of the cool DO white dwarfs HD 149499 B and HZ 21. Photospheric lines of germanium (Z = 32), arsenic (33), selenium (34), tin (50), tellurium (52), iodine (53), and perhaps bromine (35) are observed in ultraviolet spectra of HD 149499 B obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Goddard High Resolution Spectrograph (GHRS), and the International Ultraviolet Explorer. Germanium, arsenic, and tellurium are also observed in FUSE and GHRS spectra of HZ 21. Light elements such as carbon, silicon, phosphorus, and sulfur are present …
Cosmic Rays From Gamma-Ray Bursts In The Galaxy, Charles Dennison Dermer, Jeremy M. Holmes
Cosmic Rays From Gamma-Ray Bursts In The Galaxy, Charles Dennison Dermer, Jeremy M. Holmes
Aerospace, Physics, and Space Science Faculty Publications
The rate of terrestrial irradiation events by Galactic gamma-ray bursts (GRBs) is estimated using recent standard-energy results. We assume that GRBs accelerate high-energy cosmic rays, and we present results of three-dimensional simulations of cosmic rays moving in the Galactic magnetic field and diffusing through pitch-angle scattering. An on-axis GRB extinction event begins with a powerful prompt γ-ray and neutron pulse, followed by a longer lived phase from cosmic-ray protons and neutron-decay protons that diffuse toward Earth. Our results force a reinterpretation of reported ∼10¹⁸ eV cosmic-ray anisotropies and offer a rigorous test of the model in which high-energy cosmic rays …
The Model Dependence Of Solar Energetic Particle Mean Free Paths Under Weak Scattering, Gang Qin, Joseph R. Dwyer, Hamid K. Rassoul, Glenn M. Mason
The Model Dependence Of Solar Energetic Particle Mean Free Paths Under Weak Scattering, Gang Qin, Joseph R. Dwyer, Hamid K. Rassoul, Glenn M. Mason
Aerospace, Physics, and Space Science Faculty Publications
The mean free path is widely used to measure the level of solar energetic particles' diffusive transport. We model a solar energetic particle event observed by Wind STEP at 0.31-0.62 MeV nucleonˉ¹, by solving the focused transport equation using the Markov stochastic process theory. With different functions of the pitch angle diffusion coefficient D μμ, we obtain different parallel mean free paths for the same event. We show that the different values of the mean free path are due to the high anisotropy of the solar energetic particles. This makes it problematic to use just the mean free path to …
The Ccompton-Getting Effect Of Energetic Particles With An Anisotropic Pitch-Angle Distribution: An Application To Voyager 1 Results At ∼85 Au, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
This paper provides a theoretical simulation of anisotropy measurements by the Low-Energy Charged Particle (LECP) experiment on Voyager. The model starts with an anisotropic pitch-angle distribution function in the solar wind plasma reference frame. It includes the effects of both Compton-Getting anisotropy and a perpendicular diffusion anisotropy that possibly exists in the upstream region of the termination shock. The calculation is directly applied to the measurements during the late 2002 particle event seen by Voyager 1. It is shown that the data cannot rule out either the model with zero solar wind speed or the one with a finite speed …
The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvestri, Suzanne L. Hawley, Terry D. Oswalt
The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvestri, Suzanne L. Hawley, Terry D. Oswalt
Aerospace, Physics, and Space Science Faculty Publications
We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf component. The current limit for activity-age relations found for M dwarfs in open clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for the exploration of this relationship at ages older than 4 Gyr. The general trend of stars remaining active for a longer time at a later spectral type is confirmed. However, our larger sample and greater …
Where Are The Magnetic White Dwarfs With Detached, Nondegenerate Companions?, James Liebert, Terry D. Oswalt
Where Are The Magnetic White Dwarfs With Detached, Nondegenerate Companions?, James Liebert, Terry D. Oswalt
Aerospace, Physics, and Space Science Faculty Publications
The Sloan Digital Sky Survey has already more than doubled the sample of white dwarfs with spectral classi- fications, the subset with detached M dwarf companions, and the subset of magnetic white dwarfs. In the course of assessing these new discoveries, we have noticed a curious, unexpected property of the total lists of magnetic white dwarfs and of white dwarf plus main-sequence binaries: there appears to be virtually zero overlap between the two samples! No confirmed magnetic white dwarf has yet been found in such a pairing with a main-sequence star. The same statement can be made for the samples …
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 …