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Articles 211 - 240 of 317
Full-Text Articles in Astrophysics and Astronomy
Multi-Site Photometry Of The Pulsating Herbig Ae Star V346 Ori, S Bernabei, T D. Oswalt
Multi-Site Photometry Of The Pulsating Herbig Ae Star V346 Ori, S Bernabei, T D. Oswalt
Aerospace, Physics, and Space Science Faculty Publications
Context. The study of pulsation in pre-main-sequence intermediate-mass stars represents an important tool for deriving information about fundamental stellar parameters and internal structure, as well as testing theoretical models. Interest in this class of variable stars has increased significantly during the last decade and about 30 members are presently known in the literature. Aims. After constructing the frequency spectrum of oscillations in V346 Ori, we apply asteroseismic tools to these data to estimate the intrinsic parameters (mass, luminosity, effective temperature) of V346 Ori and obtain information about its internal structure. Methods. CCD time-series photometry in the Johnson V filter was …
Preliminary Xcov26 Results For Ec14012-1446, Judith L. Provençal, Matt A. Wood, Stéphane Vennes
Preliminary Xcov26 Results For Ec14012-1446, Judith L. Provençal, Matt A. Wood, Stéphane Vennes
Aerospace, Physics, and Space Science Faculty Publications
EC14012-1446 is a hydrogen atmosphere (DA) white dwarf pulsator. Its rich pulsation spectrum displays a range of excited modes with complex multiplet structure, in addition to numerous combination frequencies. In April 2008, EC14012-1446 was the primary target of XCOV26. We obtained over 300 hrs of nearly continuous high speed photometry with the goal of using the nonlinear pulse shapes to empirically determine the parameters of the convection zone. The Fourier transform (FT) of the light curve contains power between 1000 to 4000 μHz, with the dominant peak at 1234 μHz. We find 13 independent frequencies distributed in 8 modes, as …
Fuse Observations Of Intermediate Temperature Da: Atmospheric Parameters And Metal Abundances, Jean François Dupuis, Vincent Hénault-Brunet, Perre Chayer, Stéphane Vennes, Jeffrey W. Kruk
Fuse Observations Of Intermediate Temperature Da: Atmospheric Parameters And Metal Abundances, Jean François Dupuis, Vincent Hénault-Brunet, Perre Chayer, Stéphane Vennes, Jeffrey W. Kruk
Aerospace, Physics, and Space Science Faculty Publications
We present results from our analysis of a sample of DA white dwarfs having effective temperature below 25,000 K observed with the FUSE satellite with the goals of better understanding the origin of metals detected in the atmosphere of these stars. When possible, we combine the FUSE spectra with the IUE spectra and determine atmospheric parameters by fitting the Lyman line profiles. In general we find a good agreement with published values based on fits of the Balmer series. We observe that the continuum in the blue wing of the Lyman α line profile is generally lower in comparison with …
A Multizone Model For Simulating The High-Energy Variability Of Tev Blazars, Philip B. Graff, Markos Georganopoulos, Eric S. Perlman, Demosthenes Kazanas
A Multizone Model For Simulating The High-Energy Variability Of Tev Blazars, Philip B. Graff, Markos Georganopoulos, Eric S. Perlman, Demosthenes Kazanas
Aerospace, Physics, and Space Science Faculty Publications
We present a time-dependent multizone code for simulating the variability of synchrotron self-Compton (SSC) sources. The code adopts a multizone pipe geometry for the emission region, appropriate for simulating emission from a standing or propagating shock in a collimated jet. Variations in the injection of relativistic electrons in the inlet propagate along the length of the pipe, cooling radiatively. Our code for the first time takes into account the nonlocal, time-retarded nature of SSC losses that are thought to be dominant in TeV blazars. The observed synchrotron and SSC emission is followed self-consistently, taking into account light-travel time delays. At …
A Novel Method For Measuring The Extragalactic Background Light: Fermi Application To The Lobes Of Fornax A, Markos Georganopoulos, Rita M. Sambruna, Demosthenes Kazanas, Analia N. Cillis, Chi C. Cheung, Eric S. Perlman, Katherine M. Blundell, David S. Davis
A Novel Method For Measuring The Extragalactic Background Light: Fermi Application To The Lobes Of Fornax A, Markos Georganopoulos, Rita M. Sambruna, Demosthenes Kazanas, Analia N. Cillis, Chi C. Cheung, Eric S. Perlman, Katherine M. Blundell, David S. Davis
Aerospace, Physics, and Space Science Faculty Publications
We describe a new method for measuring the extragalactic background light (EBL) through the detection of γ-ray inverse Compton (IC) emission due to scattering of the EBL photons off relativistic electrons in the lobes of radio galaxies. Our method has no free physical parameters and is a powerful tool when the lobes are characterized by a high-energy sharp break or cutoff in their electron energy distribution (EED). We show that such a feature will produce a high-energy IC “imprint” of the EBL spectrum in which the radio lobes are embedded and show how this imprint can be used to derive …
Sph Simulations Of Direct Impact Accretion In The Ultracompact Am Cvn Binaries, Joshua Dolence, Matt A. Wood, Isaac Silver
Sph Simulations Of Direct Impact Accretion In The Ultracompact Am Cvn Binaries, Joshua Dolence, Matt A. Wood, Isaac Silver
Aerospace, Physics, and Space Science Faculty Publications
The ultracompact binary systems V407 Vul (RX J1914.4+2456) and HM Cnc (RX J0806.3+1527), a two-member subclass of the AM CVn stars, continue to generate interest because they defy unambiguous classification. Three proposed models remain viable at this time, but none of the three are significantly more compelling than the remaining two, and all three can satisfy the observational constraints if parameters in the models are tuned. One of the three proposed models is the direct impact model of Marsh & Steeghs, in which the accretion stream impacts the surface of a rapidly rotating primary white dwarf directly, but at a …
Cosmic Ray Transport And Production In The Galaxy: A Stochastic Propagation Simulation Approach, Ashraf Farahat, Ming Zhang, Hamid Rassoul, James J. Connell
Cosmic Ray Transport And Production In The Galaxy: A Stochastic Propagation Simulation Approach, Ashraf Farahat, Ming Zhang, Hamid Rassoul, James J. Connell
Aerospace, Physics, and Space Science Faculty Publications
Galactic cosmic-ray composition reflects the effects of nuclear interactions during propagation through the interstellar medium. In order to use measurements to determine the source of cosmic rays, one needs a model to deconvolute the propagation effect. This paper presents a new numerical method to solve cosmic-ray diffusive transport equations with a complete network of nuclear interactions. The new method uses the time backward Markov stochastic processes to solve the transport equation by tracing the particles’ trajectories starting from the solar system back to their sources in the Galaxy. To make the calculation efficient for large arrays of equations for many …
Abundances And Energy Spectra Of Corotating Interaction Region Heavy Ions Observed During Solar Cycle 23, Glenn M. Mason, Richard A. Leske, Mihir I. Desai, Christina M.S. Cohen, Joseph R. Dwyer, Joseph E. Mazur, Richard A. Mewaldt, Robert E. Gold, Stamatios M. Krimigis
Abundances And Energy Spectra Of Corotating Interaction Region Heavy Ions Observed During Solar Cycle 23, Glenn M. Mason, Richard A. Leske, Mihir I. Desai, Christina M.S. Cohen, Joseph R. Dwyer, Joseph E. Mazur, Richard A. Mewaldt, Robert E. Gold, Stamatios M. Krimigis
Aerospace, Physics, and Space Science Faculty Publications
Using instruments on the ACE spacecraft, we surveyed the heavy-ion spectra and composition over the range He– Fe for 41 corotating interaction regions (CIRs) during 1998–2007. Below~ 1 MeV nucleon^-1 the spectra are power laws in kinetic energy nucleon^-1 with an average spectral index of 2:51 ± 0:10, rolling over above ~ 1 MeV nucleon^-1 to power-law spectra with an average index of 4:47 ± 0:17. The spectral shapes for different species are similar, leading to relative abundances that are constant over our energy range, even though the intensities cover up to 8 orders of magnitude. Relative to oxygen, the …
A New Look At The Local White Dwarf Population, Jay B. Holberg, Edward M. Sion, Terry D. Oswalt, George P. Mccook, S Foran, John P. Subasavage
A New Look At The Local White Dwarf Population, Jay B. Holberg, Edward M. Sion, Terry D. Oswalt, George P. Mccook, S Foran, John P. Subasavage
Aerospace, Physics, and Space Science Faculty Publications
We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20 pc sample is currently …
Orbital Parameters And Chemical Composition Of Four White Dwarfs In Post-Common-Envelope Binaries, Adéla Kawka, Stéphane Vennes, Jean François Dupuis, Pierre Chayer, Thierry M. Lanz
Orbital Parameters And Chemical Composition Of Four White Dwarfs In Post-Common-Envelope Binaries, Adéla Kawka, Stéphane Vennes, Jean François Dupuis, Pierre Chayer, Thierry M. Lanz
Aerospace, Physics, and Space Science Faculty Publications
We present FUSE observations of the hot white dwarfs in the post-common-envelope binaries Feige 24, EUVE J0720-317, BPM 6502, and EUVE J2013+400. The spectra show numerous photospheric absorption lines, which trace the white dwarf orbital motion. We report the detection of C III, O VI, P V, and Si IV in the spectra of Feige 24, EUVE J0720-317, and EUVE J2013+400 and the detection of C III, N II, Si III, Si IV, and Fe III in the spectra of BPM 6502. Abundance measurements support the possibility that white dwarfs in post-common-envelope binaries accrete material from the secondary star wind. …
Cold Nuclear Matter Effects On J/Ψ Production As Constrained By Deuteron-Gold Measurements At Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Cold Nuclear Matter Effects On J/Ψ Production As Constrained By Deuteron-Gold Measurements At Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
We present a new analysis of J/ψ production yields in deuteron-gold collisions at √sNN=200 GeV using data taken from the PHENIX experiment in 2003 and previously published in S. S. Adler et al. [Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/ψ data taken in 2005 are used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors (RdAu). A suppression of J/ψ in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial-state low-ₓ gluons in the gold nucleus. The …
Constraining Convection Parameters From The Light Curve Shapes Of Pulsating White Dwarf Stars: The Cases Of Ec 14012-1446 And Wd 1524-0030, Gerald Handler, Judith L. Provençal, Michael H. Montgomery, Encarni Romero-Colmenero, Kaushar Sanchawala, Monika A. Lendl, Matt A. Wood, Isaac M. Silver, Paul G. Beck, Wenping Chen
Constraining Convection Parameters From The Light Curve Shapes Of Pulsating White Dwarf Stars: The Cases Of Ec 14012-1446 And Wd 1524-0030, Gerald Handler, Judith L. Provençal, Michael H. Montgomery, Encarni Romero-Colmenero, Kaushar Sanchawala, Monika A. Lendl, Matt A. Wood, Isaac M. Silver, Paul G. Beck, Wenping Chen
Aerospace, Physics, and Space Science Faculty Publications
Montgomery [1] developed a method to probe convection in pulsating white dwarf stars which allows the recovery of the thermal response time of the convection zone by fitting observed non sinusoidal light curves. He applied this method to two objects; the Whole Earth Telescope (WET) observed the pulsating DB white dwarf GD 358 for just this purpose. Given this WET run's success, it is time to extend Montgomery's method to pulsating DA white dwarf (ZZ Ceti) stars. We present observations of two ZZ Ceti stars, WD 1524 - 0030 and EC 14012 - 1446, both observed from multiple sites. EC …
The Pulsation Modes Of The Pre-White Dwarf Pg 1159-035, Jörge E.S. Costa, Matt A. Wood, Thomas J. Ahrens
The Pulsation Modes Of The Pre-White Dwarf Pg 1159-035, Jörge E.S. Costa, Matt A. Wood, Thomas J. Ahrens
Aerospace, Physics, and Space Science Faculty Publications
Context. PG 1159-035 , a pre-white dwarf with Teff ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. …
Study Of The Solar Anisotropy Of Cosmic Ray Primaries Of About 200 Gev Energy With The L3+C Muon Detector, G Baksay, L Baksay, K Dehmelt, M Hohlmann, Z Szillasi, I Vodopianov, The L3 Collaboration
Study Of The Solar Anisotropy Of Cosmic Ray Primaries Of About 200 Gev Energy With The L3+C Muon Detector, G Baksay, L Baksay, K Dehmelt, M Hohlmann, Z Szillasi, I Vodopianov, The L3 Collaboration
Aerospace, Physics, and Space Science Faculty Publications
Context. Primary cosmic rays experience multiple deflections in the non-uniform galactic and heliospheric magnetic fields which may generate anisotropies. Aims. A study of anisotropies in the energy range between 100 and 500 GeV is performed. This energy range is not yet well explored. Methods. The L3 detector at the CERN electron-positron collider, LEP, is used for a study of the angular distribution of atmospheric muons with energies above 20 GeV. This distribution is used to investigate the isotropy of the time-dependent intensity of the primary cosmic-ray flux with a Fourier analysis. Results. A small deviation from isotropy at energies around …
Quantitative Constraints On The Transport Properties Of Hot Partonic Matter From Semi-Inclusive Single High Transverse Momentum Pion Suppression In Au+Au Collisions At √Snn = 200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Quantitative Constraints On The Transport Properties Of Hot Partonic Matter From Semi-Inclusive Single High Transverse Momentum Pion Suppression In Au+Au Collisions At √Snn = 200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
The PHENIX experiment has measured the suppression of semi-inclusive single high-transverse-momentum π0's in Au+Au collisions at √sNN = 200 GeV. The present understanding of this suppression is in terms of energy loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dNg/dy, the medium transport coefficient q, or the …
Transverse Momentum And Centrality Dependence Of Dihadron Correlations In Au+Au Collisions At Snn=200 Gev: Jet Quenching And The Response Of Partonic Matter, Andrew Marshall Adare, Gyöngyi Baksay, László Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Transverse Momentum And Centrality Dependence Of Dihadron Correlations In Au+Au Collisions At Snn=200 Gev: Jet Quenching And The Response Of Partonic Matter, Andrew Marshall Adare, Gyöngyi Baksay, László Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
Azimuthal angle (Δ) correlations are presented for charged hadrons from dijets for 0.4
Dihadron Azimuthal Correlations In Au+Au Collisions At √Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Dihadron Azimuthal Correlations In Au+Au Collisions At √Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
Azimuthal angle (Δϕ) correlations are presented for a broad range of transverse momentum (0.4
Charged Hadron Multiplicity Fluctuations In Au+Au And Cu+Cu Collisions From √Snn=22.5 To 200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Charged Hadron Multiplicity Fluctuations In Au+Au And Cu+Cu Collisions From √Snn=22.5 To 200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at √sNN=62.4 and 200 GeV, and Cu+Cu collisions at √sNN=22.5,62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for nondynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions …
High-Energy Electron Beams Launched Into Space By Thunderstorms, Joseph R. Dwyer, Brian W. Grefenstette, David M. Smith
High-Energy Electron Beams Launched Into Space By Thunderstorms, Joseph R. Dwyer, Brian W. Grefenstette, David M. Smith
Aerospace, Physics, and Space Science Faculty Publications
Using CGRO/BATSE data, a possible new source of high-energy electrons and positrons in the earth's inner magnetosphere is presented. These particles are generated within the upper atmosphere by Compton scattering and pair-production of gamma-rays originating from near the tropopause as Terrestrial Gamma-ray Flashes (TGFs). Once created, these energetic electrons and positrons follow the geomagnetic field into the inner magnetosphere where they can be detected in low-earth orbit, either near the TGF magnetic foot point or at the conjugate point several thousand kilometers away. Approximately 17% of CGRO/BATSE events previously identified as terrestrial gamma-ray flashes are, in fact, such electrons and …
Hubble Space Telescope Near-Infrared Snapshot Survey Of 3cr Radio Source Counterparts. Ii. An Atlas And Inventory Of The Host Galaxies, Mergers, And Companions, David J. E. Floyd, Eric Perlman
Hubble Space Telescope Near-Infrared Snapshot Survey Of 3cr Radio Source Counterparts. Ii. An Atlas And Inventory Of The Host Galaxies, Mergers, And Companions, David J. E. Floyd, Eric Perlman
Aerospace, Physics, and Space Science Faculty Publications
We present the second part of an H-band (1.6 μm) "atlas" of z < 0.3 3CR radio galaxies, using the Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (HST NICMOS2). We present new imaging for 21 recently acquired sources and host galaxy modeling for the full sample of 101 (including 11 archival) - an 87% completion rate. Two different modeling techniques are applied, following those adopted by the galaxy morphology and the quasar host galaxy communities. Results are compared and found to be in excellent agreement, although the former breaks down in the case of sources with strong active galactic nuclei (AGNs). Companion sources are tabulated, and the presence of mergers, tidal features, dust disks, and jets are cataloged. The tables form a catalog for those interested in the structural and morphological dust-free host galaxy properties of the 3CR sample, and for comparison with morphological studies of quiescent galaxies and quasar host galaxies. Host galaxy masses are estimated and found to typically lie at around 2 × 1011 M⊙. In general, the population is found to be consistent with the local population of quiescent elliptical galaxies, but with a longer tail to low Sérsic index, mainly consisting of low-redshift (z < 0.1) and low-radio-power (FR I) sources. A few unusually disky FR II host galaxies are picked out for further discussion. Nearby external sources are identified in the majority of our images, many of which we argue are likely to be companion galaxies or merger remnants. The reduced NICMOS data are now publicly available from our Web site.
The Extreme Outburst Of Ex Lup In 2008: Optical Spectra And Light Curve, Ágnes Kóspál, P. Németh, Péter Ábrahám, Mária Kun, Arne A. Henden, Albert F. Jones
The Extreme Outburst Of Ex Lup In 2008: Optical Spectra And Light Curve, Ágnes Kóspál, P. Németh, Péter Ábrahám, Mária Kun, Arne A. Henden, Albert F. Jones
Aerospace, Physics, and Space Science Faculty Publications
EX Lup is the prototype of EXors, a class of pre-main sequence eruptive variables, exhibiting unpredictable brightenings lasting some months (Herbig, 1977; Herbig et al., 2001; Herbig, 2007). According to the current picture, eruptions of pre-main sequence stars are caused by enhanced accretion (Hartmann & Kenyon, 1996). In quiescent phase, EX Lup has typically V 13 mag, while in outburst, it may brighten by 1{4 mag. The last known are-up happened in 2002 (Herbig, 2007). As was announced by Jones (2008), EX Lup has been in outburst again since at least 2008 January 15. Based on visual estimates, the star …
The Warps Survey. Vii. The Warps-Ii Cluster Catalog, Donald J. Horner, Eric S. Perlman, Harald Ebeling, Laurence R. Jones, Caleb A. Scharf, Gary Wegner, Matthew Malkan, Ben Maughan
The Warps Survey. Vii. The Warps-Ii Cluster Catalog, Donald J. Horner, Eric S. Perlman, Harald Ebeling, Laurence R. Jones, Caleb A. Scharf, Gary Wegner, Matthew Malkan, Ben Maughan
Aerospace, Physics, and Space Science Faculty Publications
We present the galaxy cluster catalog from the second, larger phase of the Wide Angle ROSAT Pointed Survey (WARPS), an X-ray selected survey for high-redshift galaxy clusters. WARPS is among the largest deep X-ray cluster surveys and is being used to study the properties and evolution of galaxy clusters. The WARPS-II sample contains 125 clusters serendipitously detected in a survey of 301 ROSAT PSPC pointed observations and covers a sky area of 56.7 deg2. Of these 125 clusters, 53 have not been previously reported in the literature. We have nearly complete spectroscopic follow-up of the clusters, which range in redshift …
The Webt Campaign On The Blazar 3c 279 In 2006, Markus Böttcher, Jeff W. Robertson, Stéphane Vennes
The Webt Campaign On The Blazar 3c 279 In 2006, Markus Böttcher, Jeff W. Robertson, Stéphane Vennes
Aerospace, Physics, and Space Science Faculty Publications
The quasar 3C 279 was the target of an extensive multiwavelength monitoring campaign from 2006 January through April. An optical-IR-radio monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration was organized around target-of-opportunity X-ray and soft γ-ray observations with Chandra and INTEGRAL in 2006 mid-January, with additional X-ray coverage by RXTE and Swift XRT. In this paper we focus on the results of the WEBT campaign. The source exhibited substantial variability of optical flux and spectral shape, with a characteristic timescale of a few days. The variability patterns throughout the optical BVRI bands were very closely correlated with each …
A New Phenomenon In Impulsive-Flare-Associated Energetic Particles, Eileen E. Chollet, Joe Giacalone, Joseph E. Mazur, M Al Dayeh
A New Phenomenon In Impulsive-Flare-Associated Energetic Particles, Eileen E. Chollet, Joe Giacalone, Joseph E. Mazur, M Al Dayeh
Aerospace, Physics, and Space Science Faculty Publications
We present ACE/ULEIS and Wind/STEP observations of a new and unusual feature of energetic ions between 0.02 and 3 MeV nucleon ˉ¹ associated with impulsive solar flares. In addition to the usual velocity dispersion associated with the transit in the heliospheric magnetic field of energetic particles from a small localized source on the Sun, these events also show intermittent behavior that may be related to the magnetic flux tube structure of the solar wind. These are anomalous bursts of low-energy particles, which we call "tassels." Tassels are enhancements of ions extending to much lower energies than those associated with the …
Cpd -20 1123 (Albus 1) Is A Bright He-B Subdwarf, Stéphane Vennes, Adéla Kawka, Jonathan Allyn Smith
Cpd -20 1123 (Albus 1) Is A Bright He-B Subdwarf, Stéphane Vennes, Adéla Kawka, Jonathan Allyn Smith
Aerospace, Physics, and Space Science Faculty Publications
Based on photometric and astrometric data it has been proposed that Albus 1 (also known as CPD -20 1123) might be a hot white dwarf similar to G191-B2B or, alternatively, a hot subdwarf. We obtained a series of optical spectra showing that CPD -20 1123 is a bright He-B subdwarf. We analyzed the H i Balmer and He i line spectra and measured Tcff = 19,800 ± 400 K, and. Thislogg p 4.55 ± 0.10 and log N(He)/N(H) p 0.15 ± 0.15 This peculiar object belongs to a family of evolved helium-rich stars that may be the products of double-degenerate …
Spitzer Transit And Secondary Eclipse Photometry Of Gj 436b, Drake Deming, Joseph Patrick Harrington, Gregory P. Laughlin, Sara Seager, Sarah B. Navarro, William C. Bowman, Karen Horning
Spitzer Transit And Secondary Eclipse Photometry Of Gj 436b, Drake Deming, Joseph Patrick Harrington, Gregory P. Laughlin, Sara Seager, Sarah B. Navarro, William C. Bowman, Karen Horning
Aerospace, Physics, and Space Science Faculty Publications
We report the results of infrared (8 μm) transit and secondary eclipse photometry of the hot Neptune exoplanet, GJ 436b using Spitzer. The nearly photon-limited precision of these data allows us to measure an improved radius for the planet and to detect the secondary eclipse. The transit (centered at HJD p 2454280.78149 ± 0.00016) shows the flat-bottomed shape typical of infrared transits, and it precisely defines the planet-to-star radius ratio (±), independent of the stellar properties. However, we obtain the planetary radius, as well as the stellar mass and radius, by fitting to the transit curve simultaneously with an empirical …
Diffusive Compression Acceleration Of Energetic Particles With An Application To Shock Acceleration Near Injection Energies, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
The behavior of energetic charged particles accelerated by a continuous plasma compression profile is explored in the framework of diffusion. At high enough energies, the accelerated particles have a power-law spectrum with a slope generally steeper than a shock spectrum with the same compression ratio. The spectral slope depends on the ratio of the diffusion coefficient to the product of the upstream plasma speed and the thickness of the compression region. In the limit of large diffusion, the spectrum becomes identical to that of diffusive shock acceleration, and when diffusion is small enough, it is consistent with adiabatic acceleration by …
The Mid-Infrared Emission Of M87, Eric S. Perlman, Rachel E. Mason, Christopher C. Packham, Nancy A. Levenson, Moshe Elitzur, Justin J. Schaefer, Masatoshi Imanishi, William B. Sparks, James T. Radomski
The Mid-Infrared Emission Of M87, Eric S. Perlman, Rachel E. Mason, Christopher C. Packham, Nancy A. Levenson, Moshe Elitzur, Justin J. Schaefer, Masatoshi Imanishi, William B. Sparks, James T. Radomski
Aerospace, Physics, and Space Science Faculty Publications
We discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87 in the mid-infrared (mid-IR) from 5 to 35 μm. These observations allow us to investigate mid-IR emission mechanisms in the core of M87 and to establish that the flaring, variable jet component HST-1 is not a major contributor to the mid-IR flux. The Spitzer data include a high signal-to-noise ratio 15-35 μm spectrum of the knot A/B complex in the jet, which is consistent with synchrotron emission. However, a synchrotron model cannot account for the observed nuclear spectrum, even when contributions from the jet, necessary due to the …
The Deep X-Ray Radio Blazar Survey. Iii. Radio Number Counts, Evolutionary Properties, And Luminosity Function Of Blazars, Paolo Padovani, Paolo Giommi, Hermine Landt, Eric S. Perlman
The Deep X-Ray Radio Blazar Survey. Iii. Radio Number Counts, Evolutionary Properties, And Luminosity Function Of Blazars, Paolo Padovani, Paolo Giommi, Hermine Landt, Eric S. Perlman
Aerospace, Physics, and Space Science Faculty Publications
Our knowledge of the blazar surface densities and luminosity functions, which are fundamental parameters, relies still on samples at relatively high flux limits. As a result, our understanding of this rare class of active galactic nuclei is mostly based on relatively bright and intrinsically luminous sources. We present the radio number counts, evolutionary properties, and luminosity functions of the faintest blazar sample with basically complete (∼95%) identifications. Based on the Deep X-Ray Radio Blazar Survey (DXRBS), it includes 129 flat-spectrum radio quasars ( FSRQs) and 24 BL Lac objects down to a 5 GHz flux and power ∼50 mJy and …
Lp 133-373: A New Chromospherically Active Eclipsing Dme Binary With A Distant, Cool White Dwarf Companion, Todd R. Vaccaro, Mark J. Rudkin, Adéla Kawka, Stéphane Vennes, T. D. Oswalt, Isaac M. Silver, Matt A. Wood, Jonathan Allyn Smith
Lp 133-373: A New Chromospherically Active Eclipsing Dme Binary With A Distant, Cool White Dwarf Companion, Todd R. Vaccaro, Mark J. Rudkin, Adéla Kawka, Stéphane Vennes, T. D. Oswalt, Isaac M. Silver, Matt A. Wood, Jonathan Allyn Smith
Aerospace, Physics, and Space Science Faculty Publications
We report the discovery of the partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically active dM4 stars in a circular 1.6 day orbit. Light and velocity curve modeling to our differential photometry and velocity data show that each star has a mass and radius of 0.340 ± 0.014 M⊙ and 0.33 ± 0.02 R⊙. The binary is itself part of a common proper motion pair with LP 133-374, a cool DC or possible DA white dwarf with a mass of 0.49-0.82 M⊙, which would make …