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Series

Astrophysics and Astronomy

2012

Aerospace, Physics, and Space Science Faculty Publications

Articles 1 - 22 of 22

Full-Text Articles in Physical Sciences and Mathematics

Breaks In Thin And Thick Disks Of Edge-On Galaxies Imaged In The Spitzer Survey Of Stellar Structure In Galaxies (S4g), Sébastien Comerón, Trisha Mizusawa Nov 2012

Breaks In Thin And Thick Disks Of Edge-On Galaxies Imaged In The Spitzer Survey Of Stellar Structure In Galaxies (S4g), Sébastien Comerón, Trisha Mizusawa

Aerospace, Physics, and Space Science Faculty Publications

Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms—one of dynamical origin affecting both disks simultaneously and …

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Exploring The Effects Of Stellar Rotation And Wind Clearing: Debris Disks Around F Stars, Trisha F. Mizusawa, Luisa M. Rebull, John R. Stauffer, Geoffrey Bryden, Michael Meyer, Inseok Song Nov 2012

Exploring The Effects Of Stellar Rotation And Wind Clearing: Debris Disks Around F Stars, Trisha F. Mizusawa, Luisa M. Rebull, John R. Stauffer, Geoffrey Bryden, Michael Meyer, Inseok Song

Aerospace, Physics, and Space Science Faculty Publications

We have conducted a study of debris disks around F stars in order to explore correlations between rotation, stellar winds, and circumstellar disks. We obtained new 24 {mu}m photometry from the Multiband Imaging Photometer for Spitzer (MIPS) camera for a sample of 188 relatively nearby F dwarfs with various rotation rates and optical colors, and combined it with archival MIPS data for 66 more F stars, as well as Wide-field Infrared Survey Explorer data for the entire sample, plus 9 more F stars. Based on the objects' K{sub s} - [24] and [3.4] - [22] colors, we identify 22 stars …

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Periodic Structure In The Megaparsec-Scale Jet Of Pks 0637-752, L. E.H. Godfrey, E. S. Perlman Oct 2012

Periodic Structure In The Megaparsec-Scale Jet Of Pks 0637-752, L. E.H. Godfrey, E. S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

We present 18 GHz Australia Telescope Compact Array imaging of the megaparsec-scale quasar jet PKS 0637–752 with angular resolution ~0farcs58. We draw attention to a spectacular train of quasi-periodic knots along the inner 11'' of the jet, with average separation ~1.1 arcsec (7.6 kpc projected). We consider two classes of model to explain the periodic knots: those that involve a static pattern through which the jet plasma travels (e.g., stationary shocks) and those that involve modulation of the jet engine. Interpreting the knots as re-confinement shocks implies the jet kinetic power Q jet ~ 1046 erg s–1, but the constant …

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A Method For Localizing Energy Dissipation In Blazars Using Fermi Variability, Amanda Dotson, Markos Georganopoulos, Demosthenes Kazanas, Eric S. Perlman Oct 2012

A Method For Localizing Energy Dissipation In Blazars Using Fermi Variability, Amanda Dotson, Markos Georganopoulos, Demosthenes Kazanas, Eric S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

The distance of a Fermi-detected blazar γ-ray emission site from a supermassive black hole is a matter of active debate. Here we present a method for testing if the GeV emission of powerful blazars is produced within the subparsec-scale broad-line region (BLR) or farther out in the parsec-scale molecular torus (MT) environment If the GeV emission takes place within the BLR, the inverse Compton (IC) scattering of the BLR ultraviolet (UV) seed photons that produces the γ-rays takes place at the onset of the Klein–Nishina regime. This causes the electron cooling time to become practically energy-independent and the variation of …

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Self-Consistent Model Of The Interstellar Pickup Protons, Alfvenic Turbulence, And Core Solar Wind In The Outer Heliosphere, Konstantin V. Gamayunov, Ming Zhang, Nikolai V. Pogorelov, Jacob Heerikhuisen, Hamid K. Rassoul Sep 2012

Self-Consistent Model Of The Interstellar Pickup Protons, Alfvenic Turbulence, And Core Solar Wind In The Outer Heliosphere, Konstantin V. Gamayunov, Ming Zhang, Nikolai V. Pogorelov, Jacob Heerikhuisen, Hamid K. Rassoul

Aerospace, Physics, and Space Science Faculty Publications

A self-consistent model of the interstellar pickup protons, the slab component of the Alfvenic turbulence, and core solar wind (SW) protons is presented for r {>=} 1 along with the initial results of and comparison with the Voyager 2 (V2) observations. Two kinetic equations are used for the pickup proton distribution and Alfvenic power spectral density, and a third equation governs SW temperature including source due to the Alfven wave energy dissipation. A fraction of the pickup proton free energy, f{sub D} , which is actually released in the waveform during isotropization, is taken from the quasi-linear consideration without …

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Self-Consistent Model Of The Interstellar Pickup Protons, Alfvenic Turbulence, And Core Solar Wind In The Outer Heliosphere, Konstantin V. Gamayunov, Ming Zhang, Hamid K. Rassoul, Nikolai V. Pogorelov, Jacob Heerikhuisen Sep 2012

Self-Consistent Model Of The Interstellar Pickup Protons, Alfvenic Turbulence, And Core Solar Wind In The Outer Heliosphere, Konstantin V. Gamayunov, Ming Zhang, Hamid K. Rassoul, Nikolai V. Pogorelov, Jacob Heerikhuisen

Aerospace, Physics, and Space Science Faculty Publications

A self-consistent model of the interstellar pickup protons, the slab component of the Alfvenic turbulence, and core solar wind (SW) protons is presented for r {>=} 1 along with the initial results of and comparison with the Voyager 2 (V2) observations. Two kinetic equations are used for the pickup proton distribution and Alfvenic power spectral density, and a third equation governs SW temperature including source due to the Alfven wave energy dissipation. A fraction of the pickup proton free energy, f{sub D} , which is actually released in the waveform during isotropization, is taken from the quasi-linear consideration without …

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A Theory Of Bimodal Acceleration Of Pickup Ions By Compressive Solar Wind Turbulence Under Pressure Balance, Ming Zhang, Reinhard Schlickeiser Sep 2012

A Theory Of Bimodal Acceleration Of Pickup Ions By Compressive Solar Wind Turbulence Under Pressure Balance, Ming Zhang, Reinhard Schlickeiser

Aerospace, Physics, and Space Science Faculty Publications

Recently, it was demonstrated that stochastic acceleration of particles going through a series of compressive plasma waves can be efficient and fast. It could be too fast so that the pressure built up by the accelerated particles may in turn modify the amplitude of waves to prevent the particles from having an exploding pressure. We call this condition pressure balance. In this paper, we take into account the fact that active acceleration of particles only occupies a limited volume of space due to a possible intermittent nature of plasma waves or turbulence. We develop a bimodal acceleration theory that treats …

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A Multi-Wavelength Study Of The Jet, Lobes, And Core Of The Quasar Pks 2101-490, Leith E.H. Godfrey, Eric S. Perlman Aug 2012

A Multi-Wavelength Study Of The Jet, Lobes, And Core Of The Quasar Pks 2101-490, Leith E.H. Godfrey, Eric S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

We present a detailed study of the x-ray, optical, and radio emission from the jet, lobes, and core of the quasar PKS 2101−490 as revealed by new Chandra, Hubble Space Telescope (HST), and ATCA images. We extract the radio to x-ray spectral energy distributions from seven regions of the 13'' jet, and model the jet x-ray emission in terms of Doppler beamed inverse Compton scattering of the cosmic microwave background (IC/CMB) for a jet in a state of equipartition between particle and magnetic field energy densities. This model implies that the jet remains highly relativistic hundreds of kiloparsecs from the …

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Simulated Lsst Survey Of Rr Lyrae Stars Throughout The Local Group, Hakeem M. Oluseyi, Christopher Culliton, Muhammad Furqan, Keri L. Hoadley, Paul Regencia, Akeem J. Wells Jul 2012

Simulated Lsst Survey Of Rr Lyrae Stars Throughout The Local Group, Hakeem M. Oluseyi, Christopher Culliton, Muhammad Furqan, Keri L. Hoadley, Paul Regencia, Akeem J. Wells

Aerospace, Physics, and Space Science Faculty Publications

We report on a study to determine the efficiency of the Large Synoptic Survey Telescope (LSST) to recover the periods, brightnesses, and shapes of RR Lyrae stars’ light curves in the volume extending to heliocentric distances of 1.5 Mpc. We place the smoothed light curves of 30 type ab and 10 type c RR Lyrae stars in 1007 fields across the sky, each of which represents a different realization of the LSST sampling cadences, and that sample five particular observing modes. A light curve simulation tool was used to sample the idealized RR Lyrae stars’ light curves, returning each as …

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Effects Of Perpendicular Diffusion On Energetic Particles Accelerated By The Interplanetary Coronal Mass Ejection Shock, Y Wang, Gang Qin, Ming Zhang Jun 2012

Effects Of Perpendicular Diffusion On Energetic Particles Accelerated By The Interplanetary Coronal Mass Ejection Shock, Y Wang, Gang Qin, Ming Zhang

Aerospace, Physics, and Space Science Faculty Publications

In this work, based on a numerical solution of the focused transport equation, we obtained the intensity and anisotropy time profiles of solar energetic particles (SEPs) accelerated by an interplanetary shock in the three-dimensional Parker magnetic field. The shock is treated as a moving source of energetic particles with an assumed particle distribution function. We computed the time profiles of particle flux and anisotropy as measured by an observer at 1 AU, equatorial plane, and various longitudes with respect to the shock propagation direction. With perpendicular diffusion, energetic particles can cross magnetic field lines. Particles may be detected before the …

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Empirical Determination Of Convection Parameters In White Dwarfs. I. Whole Earth Telescope Observations Of Ec14012-1446, Judith L. Provençal, Matt A. Wood, Stéphane Vennes, Péter Németh Jun 2012

Empirical Determination Of Convection Parameters In White Dwarfs. I. Whole Earth Telescope Observations Of Ec14012-1446, Judith L. Provençal, Matt A. Wood, Stéphane Vennes, Péter Németh

Aerospace, Physics, and Space Science Faculty Publications

We report on an analysis of 308.3 hr of high-speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope during the 2008 international observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897μHz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l = 1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004–2007 archival data, confirms …

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The Kepler Light Curves Of V1504 Cygni And V344 Lyrae: A Study Of The Outburst Properties, John K. Cannizzo, Alan P. Smale, Matt A. Wood, Martin D. Still, Steve B. Howell Mar 2012

The Kepler Light Curves Of V1504 Cygni And V344 Lyrae: A Study Of The Outburst Properties, John K. Cannizzo, Alan P. Smale, Matt A. Wood, Martin D. Still, Steve B. Howell

Aerospace, Physics, and Space Science Faculty Publications

We examine the Kepler light curves of V1504 Cyg and V344 Lyr, encompassing ~736 days at one-minute cadence. During this span each system exhibited ~64–65 outbursts, including 6 superoutbursts. We find that, in both systems, the normal outbursts lying between two superoutbursts increase in duration over time by a factor ~1.2–1.9, and then reset to a small value after the following superoutburst. In both systems the trend of quiescent intervals between normal outbursts is to increase to a local maximum about halfway through the supercycle—the interval from one superoutburst to the next—and then to decrease back to a small value …

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Observational Constraints On The Degenerate Mass-Radius Relation, Jay B. Holberg, Terry D. Oswalt, M A. Barstow Mar 2012

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 …

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The Initial-Final Mass Relation Among White Dwarfs In Wide Binaries, Jingkun Zhao, T. D. Oswalt, Lee Anne Wilson, Qian Wang, Gang Zhao Feb 2012

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 …

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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 Feb 2012

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 …

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Fragile Binary Candidates In The Sdss Dr8 Spectroscopic Archive, J K. Zhao, Terry D. Oswalt, G Zhao Feb 2012

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 …

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International Observational Campaigns Of The Last Two Eclipses In Ee Cephei: 2003 And 2008/9, Cezary Galan, Peter Németh Jan 2012

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 …

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The Agile Monitoring Of Cygnus X-3: Transient Gamma-Ray Emission And Spectral Constraints, Giovanni Piano, Diana Carina Hannikainen Jan 2012

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 …

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The Evolution Of Ultracompact X-Ray Binaries, Lennart M. Van Haaften, Gijs A. Nelemans, Rasmus Voss, Matt A. Wood, Jan Kuijpers Jan 2012

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 …

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A Deep Search For The Host Galaxies Of Gamma-Ray Bursts With No Detected Optical Afterglow, Andrea Rossi, E E. Gonsalves Jan 2012

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 …

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Agile Detection Of Cygnus X-3 Γ-Ray Active States During The Period Mid-2009/Mid-2010, A Bulgarelli, Diana C. Hannikainen Jan 2012

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. …

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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 Jan 2012

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%).

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