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Articles 121 - 150 of 282
Full-Text Articles in Astrophysics and Astronomy
Observational Constraints On The Degenerate Mass-Radius Relation, Jay B. Holberg, Terry D. Oswalt, M A. Barstow
Observational Constraints On The Degenerate Mass-Radius Relation, Jay B. Holberg, Terry D. Oswalt, M A. Barstow
Aerospace, Physics, and Space Science Faculty Publications
The white dwarf mass-radius relationship is fundamental to modern astrophysics. It is central to routine estimation of DA white dwarf masses derived from spectroscopic temperatures and gravities. It is also the basis for observational determinations of the white dwarf initial-final-mass relation. Nevertheless, definitive and detailed observational confirmations of the mass-radius relation (MRR) remain elusive owing to a lack of sufficiently accurate white dwarf masses and radii. Current best estimates of masses and radii allow only broad conclusions about the expected inverse relation between masses and radii in degenerate stars. In this paper, we examine a restricted set of 12 DA …
The Initial-Final Mass Relation Among White Dwarfs In Wide Binaries, Jingkun Zhao, T. D. Oswalt, Lee Anne Wilson, Qian Wang, Gang Zhao
The Initial-Final Mass Relation Among White Dwarfs In Wide Binaries, Jingkun Zhao, T. D. Oswalt, Lee Anne Wilson, Qian Wang, Gang Zhao
Aerospace, Physics, and Space Science Faculty Publications
We present the initial–final mass relation derived from 10 white dwarfs in wide binaries that consist of a main-sequence star and a white dwarf. The temperature and gravity of each white dwarf were measured by fitting theoretical model atmospheres to the observed spectrum using a χ2 fitting algorithm. The cooling time and mass were obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main-sequence component to an uncertainty of about 0.17 dex in log t. The difference between the total age and white dwarf cooling time is taken as the …
The 2010 Very High Energy Y-Ray Flare And 10 Years Of Multi-Wavelength Observations Of M 87, A. Abramowski, Mihai Cara, Eric S. Perlman, The H.E.S.S. Collaboration, The Magic Collaboration
The 2010 Very High Energy Y-Ray Flare And 10 Years Of Multi-Wavelength Observations Of M 87, A. Abramowski, Mihai Cara, Eric S. Perlman, The H.E.S.S. Collaboration, The Magic Collaboration
Aerospace, Physics, and Space Science Faculty Publications
The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3 – 6) × 109 M ☉) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE γ-ray emitter since 2006. The VHE γ-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in …
Fragile Binary Candidates In The Sdss Dr8 Spectroscopic Archive, J K. Zhao, Terry D. Oswalt, G Zhao
Fragile Binary Candidates In The Sdss Dr8 Spectroscopic Archive, J K. Zhao, Terry D. Oswalt, G Zhao
Aerospace, Physics, and Space Science Faculty Publications
We present a catalog of 80 very wide fragile binary candidates (projected separations >10,000 AU) from the Sloan Digital Sky Survey Data Release Eight spectral archive. The pairs were selected based on proper motion, radial velocity, metallicity, and photometric parallax criteria. The angular separations of these pairs range from 3" to 250 ". The peak in the metallicity distribution of these pairs is about −0.5 dex of solar metallicity. Space motions and reduced proper motion diagrams indicate that all these pairs are members of the disk. The chromospheric activity index SHK of each component in 38 binary candidates having spectra …
The Agile Monitoring Of Cygnus X-3: Transient Gamma-Ray Emission And Spectral Constraints, Giovanni Piano, Diana Carina Hannikainen
The Agile Monitoring Of Cygnus X-3: Transient Gamma-Ray Emission And Spectral Constraints, Giovanni Piano, Diana Carina Hannikainen
Aerospace, Physics, and Space Science Faculty Publications
We present the AGILE-GRID (Astro-rivelatore Gamma a Immagini LEggero – Gamma-Ray Imaging Detector) monitoring of Cygnus X-3, during the period between November 2007 and July 2009. We report here the whole AGILE-GRID monitoring of Cygnus X-3 in the AGILE “pointing” mode data-taking, to confirm that the γ-ray activity coincides with the same repetitive pattern of multiwavelength emission and analyze in depth the overall γ-ray spectrum by assuming both leptonic and hadronic scenarios. Seven intense γ-ray events were detected in this period, with a typical event lasting one or two days. These durations are longer than the likely cooling times of …
The Evolution Of Ultracompact X-Ray Binaries, Lennart M. Van Haaften, Gijs A. Nelemans, Rasmus Voss, Matt A. Wood, Jan Kuijpers
The Evolution Of Ultracompact X-Ray Binaries, Lennart M. Van Haaften, Gijs A. Nelemans, Rasmus Voss, Matt A. Wood, Jan Kuijpers
Aerospace, Physics, and Space Science Faculty Publications
Context. Ultracompact X-ray binaries (UCXBs) typically consist of a white dwarf donor and a neutron star or black hole accretor. The evolution of UCXBs and very low mass ratio binaries in general is poorly understood. In particular, the dynamical behavior of an accretion disk extending to a large radius (relative to the orbit) is unclear. Aims. We investigate the evolution of UCXBs in order to learn for which mass ratios and accretor types these systems can exist, and if they do, what are their orbital and neutron star spin periods, mass transfer rates and evolutionary timescales. Methods. We compute tracks …
A Deep Search For The Host Galaxies Of Gamma-Ray Bursts With No Detected Optical Afterglow, Andrea Rossi, E E. Gonsalves
A Deep Search For The Host Galaxies Of Gamma-Ray Bursts With No Detected Optical Afterglow, Andrea Rossi, E E. Gonsalves
Aerospace, Physics, and Space Science Faculty Publications
Context. Gamma-ray bursts (GRBs) can provide information about star formation at high redshifts. Even in the absence of a bright optical/near-infrared/radio afterglow, the high detection rate of X-ray afterglows by Swift/XRT and its localization precision of 2–3 arcsec facilitates the identification and the study of GRB host galaxies. Aims. We focus on the search for the host galaxies of 17 bursts with arcsec-sized XRT error circles but no detected long-wavelength afterglow, in spite of their deep and rapid follow-up observations. Three of these events can also be classified as truly dark bursts, i.e., the observed upper limit on the optical …
Agile Detection Of Cygnus X-3 Γ-Ray Active States During The Period Mid-2009/Mid-2010, A Bulgarelli, Diana C. Hannikainen
Agile Detection Of Cygnus X-3 Γ-Ray Active States During The Period Mid-2009/Mid-2010, A Bulgarelli, Diana C. Hannikainen
Aerospace, Physics, and Space Science Faculty Publications
Context. Cygnus X-3 (Cyg X-3) is a well-known microquasar producing variable emission at all wavelengths. Cyg X-3 is a prominent X-ray binary producing relativistic jets, and studying its high energy emission is crucial for the understanding of the fundamental acceleration processes in accreting compact objects. Aims. Our goal is to study extreme particle acceleration and γ-ray production above 100 MeV during special spectral states of Cyg X-3 usually characterized by a low hard X-ray flux and enhanced soft X-ray states. Methods. We observed Cyg X-3 with the AGILE satellite in extended time intervals from 2009 Jun.–Jul., and 2009 Nov.–2010 Jul. …
International Observational Campaigns Of The Last Two Eclipses In Ee Cephei: 2003 And 2008/9, Cezary Galan, Peter Németh
International Observational Campaigns Of The Last Two Eclipses In Ee Cephei: 2003 And 2008/9, Cezary Galan, Peter Németh
Aerospace, Physics, and Space Science Faculty Publications
Context. EE Cep is an unusual long-period (5.6 yr) eclipsing binary discovered during the mid-twentieth century. It undergoes almost-grey eclipses that vary in terms of both depth and duration at different epochs. The system consists of a Be type star and a dark dusty disk around an invisible companion. EE Cep together with the widely studied ε Aur are the only two known cases of long-period eclipsing binaries with a dark, dusty disk component responsible for periodic obscurations. Aims. Two observational campaigns were carried out during the eclipses of EE Cep in 2003 and 2008/9 to verify whether the eclipsing …
Deviation From Quark Number Scaling Of The Anisotropy Parameter V₂ Of Pions, Kaons, And Protons In Au+Au Collisions At √S Nn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, Phenix Collaboration
Deviation From Quark Number Scaling Of The Anisotropy Parameter V₂ Of Pions, Kaons, And Protons In Au+Au Collisions At √S Nn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
Measurements of the anisotropy parameter v₂ of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum pT, and transverse kinetic energy KET at midrapidity (|η|<0.35) in Au+Au collisions at √sNN=200 GeV are presented. Pions and protons are identified up to pT= 6 GeV/c, and kaons up to pT= 4 GeV/c, by combining information from time-of-flight and aerogel Čerenkov detectors in the PHENIX Experiment. The scaling of v₂ with the number of valence quarks (nq) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/nq in noncentral Au+Au collisions (20-60%), but this scaling remains valid in central collisions (0-10%).
Optical Polarization And Spectral Variability In The M87 Jet, Eric S. Perlman, Mihai Cara, Matthew Bourque, Raymond C. Simons
Optical Polarization And Spectral Variability In The M87 Jet, Eric S. Perlman, Mihai Cara, Matthew Bourque, Raymond C. Simons
Aerospace, Physics, and Space Science Faculty Publications
During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability has also been seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST-1 shows a highly significant correlation between flux and polarization, with P increasing from 20% at minimum to >40% at maximum, while the orientation of its electric vector stayed constant. HST-1's optical-UV spectrum is very hard (αUV-O 0.5, F ν ∞ ν-α), and …
V344 Lyrae: A Touchstone Su Uma Cataclysmic Variable In The Kepler Field, Matt A. Wood, Martin D. Still, Steve B. Howell, John K. Cannizzo, Alan P. Smale
V344 Lyrae: A Touchstone Su Uma Cataclysmic Variable In The Kepler Field, Matt A. Wood, Martin D. Still, Steve B. Howell, John K. Cannizzo, Alan P. Smale
Aerospace, Physics, and Space Science Faculty Publications
We report on the analysis of the Kepler short-cadence (SC) light curve of V344 Lyr obtained during 2009 June 20 through 2010 March 19 (Q2-Q4). The system is an SU UMa star showing dwarf nova (DN) outbursts and superoutbursts, and promises to be a touchstone for CV studies for the foreseeable future. The system displays both positive and negative superhumps with periods of 2.20 and 2.06 hr, respectively, and we identify an orbital period of 2.11 hr. The positive superhumps have a maximum amplitude of ~0.25 mag, the negative superhumps have a maximum amplitude of ~0.8 mag, and the orbital …
Deep Multiwaveband Observations Of The Jets Of 0208-512 And 1202-262, Eric S. Perlman
Deep Multiwaveband Observations Of The Jets Of 0208-512 And 1202-262, Eric S. Perlman
Aerospace, Physics, and Space Science Faculty Publications
We present deep Hubble Space Telescope, Chandra, Very Large Array, and Australia Telescope Compact Array images of the jets of PKS 0208-512 and PKS 1202-262, which were found in a Chandra survey of a flux-limited sample of flat-spectrum radio quasars with jets. We discuss in detail their X-ray morphologies and spectra. We find optical emission from one knot in the jet of PKS 1202-262 and two regions in the jet of PKS 0208-512. The X-ray emission of both jets is most consistent with external Comptonization of cosmic microwave background photons by particles within the jet, while the optical emission is …
Energy Spectrum Of Energetic Particles Accelerated By Shock Waves: From Focused Transport To Diffusive Acceleration, Pingbing Zuo, Ming Zhang, Konstantin V. Gamayunov, Hamid K. Rassoul, Xi Luo
Energy Spectrum Of Energetic Particles Accelerated By Shock Waves: From Focused Transport To Diffusive Acceleration, Pingbing Zuo, Ming Zhang, Konstantin V. Gamayunov, Hamid K. Rassoul, Xi Luo
Aerospace, Physics, and Space Science Faculty Publications
The focused transport equation (FTE) includes all the necessary physics for modeling the shock acceleration of energetic particles with a unified description of first-order Fermi acceleration, shock drift acceleration, and shock surfing acceleration. It can treat the acceleration and transport of particles with an anisotropic distribution. In this study, the energy spectrum of pickup ions accelerated at shocks of various obliquities is investigated based on the FTE. We solve the FTE by using a stochastic approach. The shock acceleration leads to a two-component energy spectrum. The low-energy component of the spectrum is made up of particles that interact with shock …
Nicmos Polarimetry Of "Polar-Scattered" Seyfert 1 Galaxies, Daniel P. Batcheldor, Andrew Edward Robinson, David J. Axon, Stuart Young, S Quinn, James E. Smith, James H. Hough, David M. Alexander
Nicmos Polarimetry Of "Polar-Scattered" Seyfert 1 Galaxies, Daniel P. Batcheldor, Andrew Edward Robinson, David J. Axon, Stuart Young, S Quinn, James E. Smith, James H. Hough, David M. Alexander
Aerospace, Physics, and Space Science Faculty Publications
The nuclei of Seyfert 1 galaxies exhibit a range of optical polarization characteristics that can be understood in terms of two scattering regions producing orthogonal polarizations: an extended polar scattering region (PSR) and a compact equatorial scattering region (ESR), located within the circum-nuclear torus. Here we present NICMOS 2.0 μm imaging polarimetry of six "polar-scattered" Seyfert 1 (S1) galaxies, in which the PSR dominates the optical polarization. The unresolved nucleus (<058) is significantly polarized in only three objects, but five of the six exhibit polarization in a 058-15 circum-nuclear annulus. In Fairall 51 and ESO 323-G077, the polarization position angle at 2 μm (θ2 μm) is consistent with the average for the optical spectrum(θv), implying that the nuclear polarization is dominated by polar scattering at both wavelengths. The same is probably true for NGC3227. In both NGC 4593 and Mrk 766, there is a large difference between θ2 μm and θv off-nucleus, where polar scattering is expected to dominate. This may be due to contamination by interstellar polarization in NGC4593, but there is no clear explanation in the case of the strongly polarized Mrk766. Lastly, in Mrk1239, a large change (60°) in θ2 μm between the nucleus and the annulus indicates that the unresolved nucleus and its immediate surroundings have different polarization states at 2μm, which we attribute to the ESR and PSR, respectively. A further implication is that the source of the scattered 2 μm emission in the unresolved nucleus is the accretion disk, rather than torus hot dust emission.
An Effect Of Perpendicular Diffusion On The Anisotropy Of Solar Energetic Particles From Unconnected Sources, Gang Qin, H. Q. He, Ming Zhang
An Effect Of Perpendicular Diffusion On The Anisotropy Of Solar Energetic Particles From Unconnected Sources, Gang Qin, H. Q. He, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
Recently, Tan and coworkers studied the 2001 September 24 solar energetic particle (SEP) event observed by the Wind spacecraft at 1AU and found that there is a counter-streaming particle beam with a deep depression of flux at 90° pitch angle during the beginning of the event. They suggested that it is a result of a reflecting boundary at some distance outside of 1AU. While this scenario could be true under some specific configuration of an interplanetary magnetic field, in this paper we offer another possible explanation. We simulated the SEP event by solving the five-dimensional focused transport equation numerically for …
Propagation Of Solar Energetic Particles In Three-Dimensional Interplanetary Magnetic Fields: In View Of Characteristics Of Sources, H. Q. He, Gang Qin, Ming Zhang
Propagation Of Solar Energetic Particles In Three-Dimensional Interplanetary Magnetic Fields: In View Of Characteristics Of Sources, H. Q. He, Gang Qin, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
In this paper, a model of solar energetic particle (SEP) propagation in the three-dimensional Parker interplanetary magnetic field is calculated numerically. We study the effects of the different aspects of particle sources on the solar surface, which include the source location, coverage of latitude and longitude, and spatial distribution of source particle intensity, on propagation of SEPs with both parallel and perpendicular diffusion. We compute the particle flux and anisotropy profiles at different observation locations in the heliosphere. From our calculations, we find that the observation location relative to the latitudinal and longitudinal coverage of particle source has the strongest …
Broad Lyα Emission From Three Nearby Bl Lacertae Objects, John T. Stocke, Charles W. Danforth, Eric S. Perlman
Broad Lyα Emission From Three Nearby Bl Lacertae Objects, John T. Stocke, Charles W. Danforth, Eric S. Perlman
Aerospace, Physics, and Space Science Faculty Publications
We present far-UV HST/COS spectra of four nearby BLLac objects. BLLac spectra are dominated by a smooth, power-law continuum which arises in a relativistic jet. However, the spectra are not necessarily featureless; weak, broad- and/or narrow-line emission is sometimes seen in high-quality optical spectra. We present detections of Lyα emission in HST/COS spectra of Mrk421 (z = 0.030) and PKS2005-489 (z = 0.071) as well as an archival HST/GHRS observation of Mrk501 (z = 0.0337). Archival HST/STIS observations of PKS2155-304 (z = 0.116) show no Lyα emission to a very low upper limit. Using the assumption that the broad-line region …
The Chromospheric Activity, Age, Metallicity, And Space Motions Of 36 Wide Binaries, Jingkun Zhao, Terry D. Oswalt, Mark J. Rudkin, Gang Zhao, Yuqin Chen
The Chromospheric Activity, Age, Metallicity, And Space Motions Of 36 Wide Binaries, Jingkun Zhao, Terry D. Oswalt, Mark J. Rudkin, Gang Zhao, Yuqin Chen
Aerospace, Physics, and Space Science Faculty Publications
We present the chromospheric activity (CA) levels, metallicities, and full space motions for 41 F, G, K, and M dwarf stars in 36 wide binary systems. Thirty-one of the binaries contain a white dwarf (WD) component. In such binaries, the total age can be estimated by adding the cooling age of the WD to an estimate of the progenitor's main-sequence lifetime. To better understand how CA correlates to stellar age, 14 cluster member stars were also observed. Our observations demonstrate for the first time that, in general, CA decays with age from 50 Myr to at least 8 Gyr for …
Cosmic-Ray Modulation By The Global Merged Interaction Region In The Heliosheath, Xi Luo, Ming Zhang, Hamid K. Rassoul, Nikolai V. Pogorelov
Cosmic-Ray Modulation By The Global Merged Interaction Region In The Heliosheath, Xi Luo, Ming Zhang, Hamid K. Rassoul, Nikolai V. Pogorelov
Aerospace, Physics, and Space Science Faculty Publications
It was found by Voyager 1 and Voyager 2 that the Global Merged Interaction Region (GMIR) still has effects on cosmic-ray transport in the heliosheath. The GMIR produced by the intense solar activities of 2005 September propagated into the heliosheath in 2006, causing several decreases in the cosmic-ray flux at Voyager 1. Motivated by these observations, we investigate cosmic-ray modulation by the GMIR in the heliosheath using a three-dimensional Galactic cosmic-ray modulation code that includes the drift effect, termination shock, and a propagating GMIR. The simulation reproduces all major modulation features found by previous cosmic-ray observations in the supersonic solar …
An X-Ray Imaging Survey Of Quasar Jets: Testing The Inverse Compton Model, Herman L. Marshall, Jonathan M. Gelbord, Daniel A. Schwartz, David W. Murphey, James E.J. Lovell, Diana M. Worrall, Mark Birkinshaw, Eric S. Perlman, Leith E.H. Godfrey, David L. Jauncey
An X-Ray Imaging Survey Of Quasar Jets: Testing The Inverse Compton Model, Herman L. Marshall, Jonathan M. Gelbord, Daniel A. Schwartz, David W. Murphey, James E.J. Lovell, Diana M. Worrall, Mark Birkinshaw, Eric S. Perlman, Leith E.H. Godfrey, David L. Jauncey
Aerospace, Physics, and Space Science Faculty Publications
We present results from continued Chandra X-ray imaging and spectroscopy of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like extended structure. X-rays are detected from 24 of the 39 jets observed so far. We compute the distribution of αrx, the spectral index between the X-ray and radio bands, showing that it is broad, extending at least from 0.8 to 1.2. While there is a general trend that the radio brightest jets are detected most often, it is clear that predicting the X-ray flux from the radio knot flux densities is risky, so a shallow X-ray survey is the …
A Selection Of Hot Subluminous Stars In The Galex Survey – I. Correlation With The Guide Star Catalog, S. Vennes, A. Kawka, P. Nemeth
A Selection Of Hot Subluminous Stars In The Galex Survey – I. Correlation With The Guide Star Catalog, S. Vennes, A. Kawka, P. Nemeth
Aerospace, Physics, and Space Science Faculty Publications
We assembled a catalogue of bright, hot subdwarf and white dwarf stars extracted from a joint ultraviolet, optical and infrared source list. The selection is secured using colour criteria that correlate well with effective temperatures Teff≳ 12 000 K. We built a NUV− V versus V − J diagram for ≳60 000 bright sources using the Galaxy Evolution Explorer (GALEX) NUV magnitude (NUV < 14), the associated Guide Star Catalog (GSC2.3.2) photographic quick-V magnitude and the Two-Micron All-Sky Survey J and H magnitudes. This distillation process delivered a catalogue of ≈700 sources with NUV− V < 0.5 comprising ∼160 known hot subdwarf stars and another ∼60 known white dwarf stars. A reduced proper-motion diagram built using the proper-motion measurements extracted from the Naval Observatory Merged Astrometric Dataset allowed us to identify an additional ∼120 new hot subdwarf candidates and ∼10 hot white dwarf candidates. We present a spectroscopic study of a subset of 52 subdwarfs, 48 of them analysed here for the first time, and with nine objects brighter than V ∼ 12. …
Suppression Of Away-Side Jet Fragments With Respect To The Reaction Plane In Au + Au Collisions At √Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Szabolcs Rembeczki, Marcus Hohlmann
Suppression Of Away-Side Jet Fragments With Respect To The Reaction Plane In Au + Au Collisions At √Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Szabolcs Rembeczki, Marcus Hohlmann
Aerospace, Physics, and Space Science Faculty Publications
Pair correlations between large transverse momentum neutral pion triggers (pT=4 - 7 GeV/c) and charged hadron partners (pT=3 - 7 GeV/c) in central (0%-20%) and midcentral (20%-60%) Au+Au collisions at √sNN=200 GeV are presented as a function of trigger orientation with respect to the reaction plane. The particles are at larger momentum than where jet shape modifications have been observed, and the correlations are sensitive to the energy loss of partons traveling through hot dense matter. An out-of-plane trigger particle produces only 26±20% of the away-side pairs that are observed opposite of an in-plane trigger particle for midcentral (20%-60%) collisions. …
Suppression Of Away-Side Jet Fragments With Respect To The Reaction Plane In Au + Au Collisions At √Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Szabolcs Rembeczki, Marcus Hohlmann, Phenix Collaboration
Suppression Of Away-Side Jet Fragments With Respect To The Reaction Plane In Au + Au Collisions At √Snn=200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Szabolcs Rembeczki, Marcus Hohlmann, Phenix Collaboration
Aerospace, Physics, and Space Science Faculty Publications
Pair correlations between large transverse momentum neutral pion triggers (pT=4 - 7 GeV/c) and charged hadron partners (pT=3 - 7 GeV/c) in central (0%-20%) and midcentral (20%-60%) Au+Au collisions at √sNN=200 GeV are presented as a function of trigger orientation with respect to the reaction plane. The particles are at larger momentum than where jet shape modifications have been observed, and the correlations are sensitive to the energy loss of partons traveling through hot dense matter. An out-of-plane trigger particle produces only 26±20% of the away-side pairs that are observed opposite of an in-plane trigger particle for midcentral (20%-60%) collisions. …
The Structure Of X-Ray Emissions Fromtriggered Lightning Leadersmeasured By A Pinhole-Type X-Ray Camera, M. M. Schaal, J. R. Dwyer, S. Arabshahi, E. S. Cramer, R. J. Lucia, N. Y. Liu, H. K. Rassoul, D. M. Smith, J. W. Matten, A. G. Reid, J. D. Hill, D. M. Jordan, M. A. Uman
The Structure Of X-Ray Emissions Fromtriggered Lightning Leadersmeasured By A Pinhole-Type X-Ray Camera, M. M. Schaal, J. R. Dwyer, S. Arabshahi, E. S. Cramer, R. J. Lucia, N. Y. Liu, H. K. Rassoul, D. M. Smith, J. W. Matten, A. G. Reid, J. D. Hill, D. M. Jordan, M. A. Uman
Aerospace, Physics, and Space Science Faculty Publications
We investigate the structure of X-ray emissions from downward triggered lightning leaders using a pinhole-type X-ray camera (XCAM) located at the International Center for Lightning Research and Testing. This study builds on the work of Dwyer et al. (2011), which reported results from XCAM data from the 2010 summer lightning season. Additional details regarding the 2010 data are reported here. During the 2011 summer lightning season, the XCAM recorded 12 out of 17 leaders, 5 of which show downward leader propagation. Of those five leaders, one dart-stepped leader and two chaotic dart leaders are the focus of this paper. These …
Using Observations Of Distant Quasars To Constrain Quantum Gravity, Eric S. Perlman, Yeejack Ng, David J.E. Floyd, Wayne A. Christiansen
Using Observations Of Distant Quasars To Constrain Quantum Gravity, Eric S. Perlman, Yeejack Ng, David J.E. Floyd, Wayne A. Christiansen
Aerospace, Physics, and Space Science Faculty Publications
Aims. The small-scale nature of spacetime can be tested with observations of distant quasars. We comment on a recent paper by Tamburini et al. (2011, A&A, 533, A71) which claims that Hubble Space Telescope (HST) observations of the most distant quasars place severe constraints on models of foamy spacetime. Methods. If space is foamy on the Planck scale, photons emitted from distant objects will accumulate uncertainties in distance and propagation directions thus affecting the expected angular size of a compact object as a function of redshift. We discuss the geometry of foamy spacetime, and the appropriate distance measure for calculating …
The Increasing Rotation Period Of Comet 10p/Tempel 2, Matthew M. Knight, Tony L. Farnham, David G. Schleicher, Edward W. Schwieterman
The Increasing Rotation Period Of Comet 10p/Tempel 2, Matthew M. Knight, Tony L. Farnham, David G. Schleicher, Edward W. Schwieterman
Aerospace, Physics, and Space Science Faculty Publications
We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band light curves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked light curve and indicates a nucleus rotational period of 8.941 ± 0.002 hr with a peak-to-peak amplitude of ∼0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple-peaked solutions. This rotation period agrees with one of five possible solutions found in …
The Period And Amplitude Changes In The Coolest Gw Virginis Variable Star (Pg 1159-Type) Pg 0122+200, Gérard P. Vauclair, Jianning Fu, Jan Erik Solheim, Seunglee Kim, Noël Dolez, M Chevreton, Li Chen, Matt A. Wood, Isaac M. Silver, Zs Bognár, Margit Paparó, Alejandro H. Córsico
The Period And Amplitude Changes In The Coolest Gw Virginis Variable Star (Pg 1159-Type) Pg 0122+200, Gérard P. Vauclair, Jianning Fu, Jan Erik Solheim, Seunglee Kim, Noël Dolez, M Chevreton, Li Chen, Matt A. Wood, Isaac M. Silver, Zs Bognár, Margit Paparó, Alejandro H. Córsico
Aerospace, Physics, and Space Science Faculty Publications
Context: The PG 1159 pre-white dwarf stars experiment a rapidly cooling phase with a time scale of a few 106 years. Theoretical models predict that the neutrinos produced in their core should play a dominant role in the cooling, mainly at the cool end of the PG 1159 sequence. Measuring the evolutionary time scale of the coolest PG 1159 stars could offer a unique opportunity to empirically constrain the neutrino emission rate. Aims. A subgroup of the PG 1159 stars are nonradial pulsators, the GW Vir type of variable stars. They exhibit g-mode pulsations with periods of a few hundred …
Hydrogenation Of Magnesium Nanoblades: The Effect Of Concentration Dependent Hydrogen Diffusion, Bo Yang, Yuping He, Yiping Zhao
Hydrogenation Of Magnesium Nanoblades: The Effect Of Concentration Dependent Hydrogen Diffusion, Bo Yang, Yuping He, Yiping Zhao
Aerospace, Physics, and Space Science Faculty Publications
By assuming the H diffusion coefficient and H adsorption rate to be exponentially and linearly dependent on concentration, a physical model is developed to predict the hydrogenation process of Mg nanoblades. The predicted H uptake curves agree well with the experimental data from V-coated Mg nanoblades. The obtained H diffusion coefficients in MgHx between Mg and MgH2 have nearly three orders of magnitude variation. The characteristic time of H surface adsorption is longer than that of H diffusion in Mg but shorter than that in MgH2 for 100 nm thick nanoblades. A hydride shell is not formed during the hydrogenation.
Pitch Angle Scattering In The Outer Heliosheath And Formation Of The Interstellar Boundary Explorer Ribbon, Konstantin V. Gamayunov, Ming Zhang, Hamid K. Rassoul
Pitch Angle Scattering In The Outer Heliosheath And Formation Of The Interstellar Boundary Explorer Ribbon, Konstantin V. Gamayunov, Ming Zhang, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
The dominant and unexpected feature in the first Interstellar Boundary EXplorer (IBEX) maps is a ribbon of the enhanced energetic neutral atom (ENA) emissions. Presenting the first results from IBEX,McComas et al. identified six possible mechanisms of ribbon formation. One of the mechanisms, the so-called secondary ENA mechanism, was already quantitatively elaborated by Heerikhuisen et al., and they successfully reproduced the main features of the ribbon. We further study the "secondary ENA" mechanism by quantifying a previously omitted stage of the proton evolution between two consecutive acts of the charge-exchange in the outer heliosheath (OHS). The main findings can be …