Third Component Search And Abundances Of The Very Dusty Short-Period Binary Bd +20°307,
2012
Tennessee State University
Third Component Search And Abundances Of The Very Dusty Short-Period Binary Bd +20°307, Francis C. Fekel, Maria J. Cordero, Raphael Galicher, Benjamin Zuckerman, Carl Melis, Alycia J. Weinberger
Information Systems and Engineering Management Research Publications
We have obtained near-infrared adaptive optics imaging and collected additional radial velocity observations to search for a third component in the extremely dusty short-period binary system BD +20°307. Our image shows no evidence for a third component at separations greater than 19 AU. Our four seasons of radial velocities have a constant center-of-mass velocity and are consistent with the systemic velocities determined at two earlier epochs. Thus, the radial velocities also provide no support for a third component. Unfortunately, the separation domains covered by our imaging and radial velocity results do not overlap. Thus, we examined the parameters for possible …
Non-Equilibrium Landauer Transport Model For Hawking Radiation From A Black Hole,
2012
University of Michigan
Non-Equilibrium Landauer Transport Model For Hawking Radiation From A Black Hole, P. D. Nation, M. P. Blencowe, Franco Nori
Dartmouth Scholarship
We propose that the Hawking radiation energy and entropy flow rates from a black hole can be viewed as a one-dimensional (1D), non-equilibrium Landauer transport process. Support for this viewpoint comes from previous calculations invoking conformal symmetry in the near-horizon region, which give radiation rates that are identical to those of a single 1D quantum channel connected to a thermal reservoir at the Hawking temperature. The Landauer approach shows in a direct way the particle statistics independence of the energy and entropy fluxes of a black hole radiating into vacuum, as well as one near thermal equilibrium with its environment. …
The Kepler Light Curves Of V1504 Cygni And V344 Lyrae: A Study Of The Outburst Properties,
2012
University of Maryland - Baltimore County
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 …
High-Resolution X-Ray Spectroscopy Reveals The Special Nature Of The Wolf-Rayet Star Winds.,
2012
University Potsdam
High-Resolution X-Ray Spectroscopy Reveals The Special Nature Of The Wolf-Rayet Star Winds., L. Oskinova, K. Gayley, W.-R. Hamann, D. Huenemoerder, Richard Ignace, A. Pollock
ETSU Faculty Works
We present the first high-resolution X-ray spectrum of a putatively single Wolf–Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, “cool” stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at …
Ionized Reflection Spectra From Accretion Disks Illuminated By X-Ray Pulsars,
2012
Georgia Institute of Technology
Ionized Reflection Spectra From Accretion Disks Illuminated By X-Ray Pulsars, D. R. Ballantyne, J. D. Purvis, R. G. Strausbaugh, R. C. Hickox
Dartmouth Scholarship
X-ray reflection signatures are observed around multiple classes of accreting compact objects. Modelling these features yield important constraints on the physics of accretion disks, motivating the development of X-ray reflection models appropriate for a variety of systems and illumination conditions. Here, constant density ionized X-ray reflection models are presented for a disk irradiated with a very hard power-law X-ray spectrum (\Gamma < 1) and a variable high-energy cutoff. These models are then applied to the Suzaku data of the accreting X-ray pulsar LMC X-4, where very good fits are obtained with a highly ionized reflector responsible for both the broad Fe K line and the soft excess. The ionized reflector shows strong evidence for significant Doppler broadening and is redshifted by ~10^4 km/s. These features indicate that the reflecting material is associated with the complex dynamics occurring at the inner region of the magnetically-truncated accretion disk. Thus, reflection studies of X-ray pulsar spectra may give important insights into the accretion physics at the magnetospheric radius.
Observed And Modeled Solar Cycle Variation In Geocoronal Hydrogen Using Nrlmsise-00 Thermosphere Conditions And The Bishop Analytic Exosphere Model,
2012
University of Wisconsin - Madison
Observed And Modeled Solar Cycle Variation In Geocoronal Hydrogen Using Nrlmsise-00 Thermosphere Conditions And The Bishop Analytic Exosphere Model, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler
Publications
High precision observations during Solar Cycle 23 using the Wisconsin H‐alpha Mapper (WHAM) Fabry‐Perot quantify a factor of 1.5 ± 0.15 higher Balmer α column emission intensity during near‐solar‐maximum than during solar minimum conditions. An unresolved question is how does the observed solar cycle variation in the hydrogen column emission compare with that calculated from the hydrogen distribution in atmospheric models? We have compared WHAM solar minimum and near‐solar‐maximum column intensity observations with calculations using the thermospheric hydrogen density profile and background thermospheric conditions from the Mass Spectrometer Incoherent Scatter (NRLMSISE‐00) empirical model extended to exospheric altitudes using the analytic …
Energetic Feedback And 26al From Massive Stars And Their Supernovae In The Carina Region,
2012
Department of Astrophysics/IMAPP, Radboud University Nijmegen
Energetic Feedback And 26al From Massive Stars And Their Supernovae In The Carina Region, R. Voss, P. Martin, R. Diehl, J. S. Vink, Dieter H. Hartmann, T. Preibisch
Publications
We study the populations of massive stars in the Carina region and their energetic feedback and ejection of 26Al. Methods. We did a census of the stellar populations in young stellar clusters within a few degrees of the Carina nebula. For each star we estimated the mass, based on the spectral type and the host cluster age. We used population synthesis to calculate the energetic feedback and ejection of 26Al from the winds of the massive stars and their supernova explosions. We used 7 years of INTEGRAL observations to measure the 26Al signal from the region. Results. The INTEGRAL 26Al …
Ion-By-Ion Cooling Efficiencies,
2012
California Institute of Technology
Ion-By-Ion Cooling Efficiencies, Orly Gnat, Gary J. Ferland
Physics and Astronomy Faculty Publications
We present ion-by-ion cooling efficiencies for low-density gas. We use Cloudy (version 10.00) to estimate the cooling efficiencies for each ion of the first 30 elements (H-Zn) individually. We present results for gas temperatures between 104 and 108 K, assuming low densities and optically thin conditions. When nonequilibrium ionization plays a significant role the ionization states deviate from those that obtain in collisional ionization equilibrium (CIE), and the local cooling efficiency at any given temperature depends on specific nonequilibrium ion fractions. The results presented here allow for an efficient estimate of the total cooling efficiency for any ionic …
Observational Constraints On The Degenerate Mass-Radius Relation,
2012
University of Arizona
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 …
Electron Microscopy Characterization Of Vanadium Dioxide Thin Films And Nanoparticles,
2012
Brigham Young University - Provo
Electron Microscopy Characterization Of Vanadium Dioxide Thin Films And Nanoparticles, Felipe Rivera
Theses and Dissertations
Vanadium dioxide (VO_2) is a material of particular interest due to its exhibited metal to insulator phase transition at 68°C that is accompanied by an abrupt and significant change in its electronic and optical properties. Since this material can exhibit a reversible drop in resistivity of up to five orders of magnitude and a reversible drop in infrared optical transmission of up to 80%, this material holds promise in several technological applications. Solid phase crystallization of VO_2 thin films was obtained by a post-deposition annealing process of a VO_{x,x approx 2} amorphous film sputtered on an amorphous silicon dioxide (SiO_2) …
Comparative Studies Of The Spectroscopic Properties Of Nd3+: Yag Nanocrystals Transparent Ceramic And Single Crystal,
2012
The University of Texas Rio Grande Valley
Comparative Studies Of The Spectroscopic Properties Of Nd3+: Yag Nanocrystals Transparent Ceramic And Single Crystal, M. Pokhrel, N. Ray, G. A. Kumar, D. K. Sardar
Physics & Astronomy Faculty Publications
Detailed comparative spectroscopic studies of Nd3+ doped YAG nanocrystals, transparent ceramic and single crystal have been performed. Although most of the radiative spectral properties of Nd3+ are almost in good agreement between the three hosts, the non-radiative losses are significantly high in nanocrystals, which are attributed due to the presence of large amount of hydroxyl groups on the nanocrystals surface which deteriorates the quality of the material for laser applications. In addition, wavelength dependent scattering loss for the Nd3+ doped YAG nanocrystals is found significantly high compared to those of Nd3+ doped single crystal and ceramic. © 2012 Optical Society …
A Note On The Weibel Instability And Thermal Fluctuations,
2012
Dartmouth College
A Note On The Weibel Instability And Thermal Fluctuations, R. A. Treumann, W. Baumjohann
Dartmouth Scholarship
The thermal fluctuation level of the Weibel in- stability is recalculated. It is shown that the divergence of the fluctuations at long wavelengths, i.e. the Weibel infrared catastrophe, never occurs. At large wavelengths the thermal fluctuation level is terminated by the presence of even the smallest available stable thermal anisotropy. Weibel fields penetrate only one skin depth into the plasma. When excited inside, they cause layers of antiparallel fields of skin depth width and vortices which may be subject to reconnection.
Weak Localization In A Lateral Superlattice With Rashba And Dresselhaus Spin-Orbit Interaction,
2012
Clemson University
Weak Localization In A Lateral Superlattice With Rashba And Dresselhaus Spin-Orbit Interaction, D C. Marinescu, Andrei Manolescu
Publications
We calculate the weak localization (WL) correction to the conductivity of a lateral superlattice (LSL) with Rashba (R)-Dresselhaus (D) spin-orbit interaction (SOI). The superlattice is modeled as a sequence of parallel wires that support tunneling between adjacent sites, leading to the formation of extended Bloch states along its axis and a miniband in the energy spectrum. Our results, obtained by calculating the eigenvalues of the Cooperon operator in the diffusion approximation, indicate that the electron dephasing rate that determines the antilocalization correction is enhanced by a term proportional with the LSL potential and the bandwidth. Within the same formalism, the …
Hysteresis And Relaxation In Granular Permanent Magnets,
2012
The University of Texas Rio Grande Valley
Hysteresis And Relaxation In Granular Permanent Magnets, Ralph Skomski, B. Balamurugan, Tom A. George, Mircea Chipara, Xiao-Hui Wei, Jeff E. Shield, D. J. Sellmyer
Physics & Astronomy Faculty Publications
Some nontrivial aspects of the magnetic and structural characterization of hard-magnetic nanoparticles are investigated. Dilute ensembles are well-described by mean-field theory, although there is an asymmetry between exchange and magnetostatic interaction fields. Corrections to the mean-field approximation are caused by cooperative effects and have the character of Onsager reaction fields, which are much stronger in micromagnetism than in atomic-scale magnetism. The slow dynamics of zero-field-cooled (ZFC) magnetization curves is strongly affected by the particles0 magnetic anisotropy, which reduces the corresponding energy-barrier height from 25 to 19.1 kBT.
Asteroseismology Of The Nearby Sn-Ii Progenitor: Rigel. I. The Most High-Precision Photometry And Radial Velocity Monitoring,
2012
Zanjan Institute for Advanced Studies in Basic Sciences
Asteroseismology Of The Nearby Sn-Ii Progenitor: Rigel. I. The Most High-Precision Photometry And Radial Velocity Monitoring, Ehsan Moravveji, Edward F. Guinan, Matt Shultz, Michael H. Williamson, Andres Moya
Information Systems and Engineering Management Research Publications
Rigel (β Ori, B8 Ia) is a nearby blue supergiant displaying α Cyg type variability, and is one of the nearest Type II supernova progenitors. As such it is an excellent test bed to study the internal structure of pre-core-collapse stars. In this study, for the first time, we present 28 days of high-precision MOST photometry and over six years of spectroscopic monitoring. We report 19 significant pulsation modes of signal-to-noise ratio, S/N ≳ 4.6 from radial velocities, with variability timescales ranging from 1.21 to 74.7 days, which are associated with high-order low-degree gravity modes. While the radial velocity variations …
On The Unification Of Active Galactic Nuclei,
2012
University of Kentucky
On The Unification Of Active Galactic Nuclei, Moshe Elitzur
Physics and Astronomy Faculty Publications
The inevitable spread in properties of the toroidal obscuration of active galactic nuclei (AGNs) invalidates the widespread notion that type 1 and 2 AGNs are intrinsically the same objects, drawn randomly from the distribution of torus covering factors. Instead, AGNs are drawn preferentially from the distribution; type 2 are more likely drawn from the distribution higher end, type 1 from its lower end. Type 2 AGNs have a higher IR luminosity, lower narrow-line luminosity, and a higher fraction of Compton thick X-ray obscuration than type 1. Meaningful studies of unification statistics cannot be conducted without first determining the intrinsic distribution …
Veritas Observations Of Day-Scale Flaring Of M 87 In 2010 April,
2012
Cork Institute of Technology
Veritas Observations Of Day-Scale Flaring Of M 87 In 2010 April, P. T. Reynolds, Et. Al.
Physical Sciences Publications
VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 ± 0.16) × 10–11 cm–2 s–1 at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 ± 0.68) × 10–11 cm–2 s–1 for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation …
The Initial-Final Mass Relation Among White Dwarfs In Wide Binaries,
2012
Florida Institute of Technology
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,
2012
Universität Hamburg
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 …
Measurement Of Plasma Density In A Gas-Filled Ionizing Laser Focus,
2012
Brigham Young University - Provo
Measurement Of Plasma Density In A Gas-Filled Ionizing Laser Focus, Nathan Edward Heilmann
Theses and Dissertations
We use an interferometric method for measuring the plasma density in a laser-induced plasma as a function of time. Any changes in the density within 5 ns of generation is due plasma expansion and not recombination. The analytic solution for plasma expansion derived for ultracold Neutral Plasmas describes the expansion of our laser produced Neon plasma of densities up to approximately 40 Torr. A model for the utlracold neutral plasmas, in comparison with measurements of our plasmas, can be used to extract an electron temperature. Currently our plasmas have shown to have an electron temperature of approximately 44 eV.
