A Detailed Model Atmosphere Analysis Of Cool White Dwarfs In The Sloan Digital Sky Survey,
2010
Smithsonian Astrophysical Observatory
A Detailed Model Atmosphere Analysis Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool WD candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool WDs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope data sets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30 km s–1. Our near-infrared observations reveal eight …
Monster In The Dark: The Ultraluminous Grb 080607 And Its Dusty Environment,
2010
Department of Physics and Astronomy, Clemson University
Monster In The Dark: The Ultraluminous Grb 080607 And Its Dusty Environment, Dieter H. Hartmann, D. A. Perley, A. N. Morgan, A. Updike, F. Yuan, C. W. Awkerlof, A. A. Miller, J. S. Bloom, S. B. Cenko, W. Li
Publications
We present early-time optical through infrared photometry of the bright gamma-ray burst GRB 080607, starting only 6 s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric dataset allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information on the ultraviolet continuum absorption properties of any sightline outside our Local Group to date. The extinction properties are not adequately modeled by any ordinary extinction template (including the average Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud curves), partially because the 2175 A …
Simulations Of A Monolithic Lanthanum Bromide Gamma-Ray Detector,
2010
University of New Hampshire - Main Campus
Simulations Of A Monolithic Lanthanum Bromide Gamma-Ray Detector, Camden Ertley, Chris Bancroft, Peter F. Bloser, Taylor Connor, Jason S. Legere, Mark L. Mcconnell, James M. Ryan
Space Science Center
We have been working on the development of a detector design for a large area coded aperture imaging system operating in the 10-600 keV energy range. The detector design is based on an array of Lanthanum Bromide (LaBr3) scintillators, each directly coupled to a Hamamatsu 64-channel multi-anode photomultiplier tube (MAPMT). This paper focuses on the development of the GEANT4-based simulations as an aid in the optimization of the detector design. The simulations have been validated by comparisons with various laboratory data sets. We will summarize the current status and latest findings from this study.
On The Transit Potential Of The Planet Orbiting Iota Draconis,
2010
California Institute of Technology
On The Transit Potential Of The Planet Orbiting Iota Draconis, Stephen R. Kane, Sabine Reffert, Gregory W. Henry, Debra A. Fischer, Christian Schwab, Kelsey I. Clubb, Christoph Bergmann
Information Systems and Engineering Management Research Publications
Most of the known transiting exoplanets are in short-period orbits, largely due to the bias inherent in detecting planets through the transit technique. However, the eccentricity distribution of the known radial velocity planets results in many of those planets having a non-negligible transit probability. One such case is the massive planet orbiting the giant star iota Draconis, a situation where both the orientation of the planet's eccentric orbit and the size of the host star inflate the transit probability to a much higher value than for a typical hot Jupiter. Here we present a revised fit of the radial velocity …
Modeling Broadband X-Ray Absorption Of Massive Star Winds,
2010
Swarthmore College
Modeling Broadband X-Ray Absorption Of Massive Star Winds, M. A. Leutenegger, David H. Cohen, J. Zsargó, Erin Marie Martell , '09, James Paton Macarthur , '11, S. P. Owocki, M. Gagné, D. J. Hillier
Physics & Astronomy Faculty Works
We present a method for computing the net transmission of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming that the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes that all observed X-rays are emitted without …
On The Disappearance Of The Broad-Line Region In Low-Luminosity Active Galactic Nuclei,
2010
University of Kentucky
On The Disappearance Of The Broad-Line Region In Low-Luminosity Active Galactic Nuclei, Moshe Elitzur, Luis C. Ho
Physics and Astronomy Faculty Publications
The disk-wind scenario for the broad-line region (BLR) and toroidal obscuration in active galactic nuclei (AGNs) predicts the disappearance of the BLR at low luminosities. In accordance with the model predictions, data from a nearly complete sample of nearby AGNs show that the BLR disappears at luminosities lower than 5 × 1039(M/107 M⊙)2/3 erg s-1, where M is the black hole mass. The radiative efficiency of accretion onto the black hole is ≲10-3 for these sources, indicating that their accretion is advection-dominated.
Long-Lived Time-Dependent Remnants During Cosmological Symmetry Breaking: From Inflation To The Electroweak Scale,
2010
Dartmouth College
Long-Lived Time-Dependent Remnants During Cosmological Symmetry Breaking: From Inflation To The Electroweak Scale, Marcelo Gleiser, Noah Graham, Nikitas Stamatopoulos
Dartmouth Scholarship
Through a detailed numerical investigation in three spatial dimensions, we demonstrate that long-lived time-dependent field configurations emerge dynamically during symmetry breaking in an expanding de Sitter spacetime. We investigate two situations: a single scalar field with a double-well potential and an SU(2) non-Abelian Higgs model. For the single scalar, we show that large-amplitude oscillon configurations emerge spontaneously and persist to contribute about 1.2% of the energy density of the Universe. We also show that for a range of parameters, oscillon lifetimes are enhanced by the expansion and that this effect is a result of parametric resonance. For the SU(2) case, …
Acoustical Analysis Of A Horn-Loaded Compression Drivers Using Numerical Analysis,
2010
Brigham Young University - Provo
Acoustical Analysis Of A Horn-Loaded Compression Drivers Using Numerical Analysis, Daniel Ross Tengelsen
Theses and Dissertations
Two numerical techniques, the boundary-element method (BEM) and the finite-difference method (FDM), are used for simulating the radiation from horn-loaded compression drivers and from an infinitely-baffled, finite-length pipe. While computations of the horn-loaded compression driver are in steady state, transient analysis of the finite-length pipe is studied as a precursor to transient analysis within the horn-loaded compression driver. BEM numerical simulations show promise for the development of new designs. Numerical simulations serve as a good tool for time and cost-effective prototyping as poor designs are detected before they are built.
Perpendicular Ion Heating By Low-Frequency Alfvén-Wave Turbulence In The Solar Wind,
2010
University of New Hampshire, Durham
Perpendicular Ion Heating By Low-Frequency Alfvén-Wave Turbulence In The Solar Wind, Benjamin D. G. Chandran, Bo Li, Barrett N. Rogers, Eliot Quataert, Kai Germaschewski
Dartmouth Scholarship
We consider ion heating by turbulent Alfvén waves (AWs) and kinetic Alfvén waves (KAWs) with wavelengths (measured perpendicular to the magnetic field) that are comparable to the ion gyroradius and frequencies ω smaller than the ion cyclotron frequency Ω. We focus on plasmas in which β < 1, where β is the ratio of plasma pressure to magnetic pressure. As in previous studies, we find that when the turbulence amplitude exceeds a certain threshold, an ion's orbit becomes chaotic. The ion then interacts stochastically with the time-varying electrostatic potential, and the ion's energy undergoes a random walk. Using phenomenological arguments, we derive an analytic expression for the rates at which different ion species are heated, which we test by simulating test particles interacting with a spectrum of randomly phased AWs and KAWs. We find that the stochastic heating rate depends sensitively on the quantity ε = δv ρ/v ⊥, where v ⊥ (v ∥) is the component of the ion velocity perpendicular (parallel) to the background magnetic field B 0, and δv ρ (δB ρ) is the rms amplitude of the velocity (magnetic-field) fluctuations at the gyroradius scale. In the case …
Temperature And Variability Of Three Ionian Volcanoes,
2010
Brigham Young University - Provo
Temperature And Variability Of Three Ionian Volcanoes, Daniel R. Allen
Theses and Dissertations
Cassini spacecraft images of Io obtained during its flyby of Jupiter in late 2000 and early 2001 were used to determine the lava composition and eruption style of three faint hotspots, Pillan, Wayland, and Loki. We found a maximum color temperature of 1130+/-289 K for Pillan and maximum color temperatures of 1297+/-289 K and 1387+/-287 K for Wayland and Loki, respectively. These temperatures are suggestive of basaltic lava. The temperatures with the best signal-to-noise ratios also suggested basaltic lava and were found to be 780+/-189 K, 1116+/-250 K, and 1017+/-177 K for Pillan, Wayland, and Loki, respectively. Pillan showed increased …
Potassium Chlorate Decomposition Under High Pressure,
2010
Citrus College
Potassium Chlorate Decomposition Under High Pressure, Harrison Ruiz, Michael G. Pravica, Martin Galley
Undergraduate Research Opportunities Program (UROP)
High pressure physics involves placing various substances under high pressure and observing changes in that substance. In this experiment this high amount of pressure is induced using a diamond anvil cell. A diamond anvil cell uses a metal gasket to hold the sample between two diamonds, which will press on the sample to reach high pressures. High pressures are reached with a moderate amount of force by exerting that force over a small area. Diamonds are used for the compression because of their hardness and ability to resist compression. The pressure being exerted on the sample using a diamond anvil …
Properties Of Z≥6 Galaxies In Cosmological Sph Simulations,
2010
University of Nevada, Las Vegas
Properties Of Z≥6 Galaxies In Cosmological Sph Simulations, Jason Jaacks
Undergraduate Research Opportunities Program (UROP)
Recent upgrades to the Hubble Space Telescope have given observers their deepest look into our Universe yet, seeing nearly 13 billion years into the past. This new observational data has presented those of us that use simulations to study the early Universe a benchmark opportunity to evaluate the ability of these codes to reproduce the photometric properties being observed. Establishing this agreement allows us to probe deeper into the physical properties such as mass, star formation histories and star formation rates of these early galaxies. This research lays the ground work for examining the contribution of primordial galaxies to the …
Mutation Size Optimizes Speciation In An Evolutionary Model,
2010
University of Missouri
Mutation Size Optimizes Speciation In An Evolutionary Model, Nathan Dees, Sonya Bahar
Physics Faculty Works
The role of mutation rate in optimizing key features of evolutionary dynamics has recently been investigated in various computational models. Here, we address the related question of how maximum mutation size affects the formation of species in a simple computational evolutionary model. We find that the number of species is maximized for intermediate values of a mutation size parameter μ; the result is observed for evolving organisms on a randomly changing landscape as well as in a version of the model where negative feedback exists between the local population size and the fitness provided by the landscape. The same result …
How Lightning Tortuosity Affects The Electromagnetic Fields By Augmenting Their Effective Distance,
2010
Trinity University
How Lightning Tortuosity Affects The Electromagnetic Fields By Augmenting Their Effective Distance, S L. Meredith, S K. Earles, I N. Kostanic, Niescja E. Turner, C E. Otero
Physics and Astronomy Faculty Research
A novel approach for developing the electromagnetic fields from a lightning return stroke which follows a tortuous path will be presented. The proposed model is unique in that it recognizes that the symmetrical tortuosity of lightning directly impacts the observable distance r, which in turn, alters the resulting electromagnetic fields. In the literature, lightning return stroke models typically employ the assumption that the cloud-to-ground path is straight. Although this assumption yields fairly consistent results across an array of varying approaches, it does not account for lightning's natural physical appearance. Furthermore, straight-line models only account for the cloud-to-ground discharges and do …
Spectroscopic Abundances And Membership In The Wolf 630 Moving Group,
2010
University of Rochester
Spectroscopic Abundances And Membership In The Wolf 630 Moving Group, Eric J. Bubar, Jeremy R. King
Publications
The concept of kinematic assemblages evolving from dispersed stellar clusters has remained contentious since Eggen’s initial formulation of moving groups in the 1960s. With high-quality parallaxes from the Hipparcos space astrometry mission, distance measurements for thousands of nearby, seemingly isolated stars are currently available. With these distances, a high-resolution spectroscopic abundance analysis can be brought to bear on the alleged members of these moving groups. If a structure is a relic of an open cluster, the members can be expected to be monolithic in age and abundance in as much as homogeneity is observed in young open clusters. In this …
Locating The Accretion Footprint On A Herbig Ae Star: Mwc 480,
2010
Eureka Scientific
Locating The Accretion Footprint On A Herbig Ae Star: Mwc 480, C A. Grady, K Hamaguchi, G Schneider, B Stecklum, B E. Woodgate, J E. Mccleary, G M. Williger, M L. Sitko, F Menard, Th. Henning, Sean D. Brittain
Publications
Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star–disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-chromatic data for the Herbig Ae star MWC 480 to address whether similar processes occur in intermediatemass stars. MWC 480 has X-ray emission typical of actively accreting Herbig Ae stars, but with ∼10× more photoelectric absorption than expected from optical and FUV data. We consider three sources …
Swift Monitoring Of Cygnus X-2: Investigating The Near-Ultraviolet-X-Ray Connection,
2010
University of California at Santa Barbara
Swift Monitoring Of Cygnus X-2: Investigating The Near-Ultraviolet-X-Ray Connection, E. S. Rykoff, E. M. Cackett, J. M. Miller
Physics and Astronomy Faculty Research Publications
The neutron star X-ray binary (NSXRB) Cyg X-2 was observed by the Swift satellite 51 times over a 4 month period in 2008 with the X-ray Telescope (XRT), UV/optical telescope, and Burst Alert Telescope (BAT) instruments. During this campaign, we observed Cyg X-2 in all three branches of the Z track (horizontal, normal, and flaring branches). We find that the NUV emission is uncorrelated with the soft X-ray flux detected with the XRT and is anticorrelated with the BAT X-ray flux and the hard X-ray color. The observed anticorrelation is inconsistent with simple models of reprocessing as the source of …
On Using The Color-Magnitude Diagram Morphology Of M67 To Test Solar Abundances,
2010
Max Planck Institute for Astrophysics
On Using The Color-Magnitude Diagram Morphology Of M67 To Test Solar Abundances, Z. Magic, A. Serenelli, A. Weiss, B. Chaboyer
Dartmouth Scholarship
The open cluster M67 has solar metallicity and an age of about 4 Gyr. The turnoff (TO) mass is close to the minimum mass for which solar metallicity stars develop a convective core during main sequence evolution as a result of the development of hydrogen burning through the CNO cycle. The morphology of the color-magnitude diagram (CMD) of M67 around the TO shows a clear hook-like feature, a direct sign that stars close to the TO have convective cores. VandenBerg et al. investigated the possibility of using the morphology of the M67 TO to put constraints on the solar metallicity, …
Internal Transitions In Nuclei And Applications To Astrophysics And Cosmochemistry,
2010
Clemson University
Internal Transitions In Nuclei And Applications To Astrophysics And Cosmochemistry, Joseph Johnson
All Dissertations
In this dissertation I analyze internal transitions in nuclei and their potential effects on s-process branching and on accelerated β-decay in cosmochemical samples. To accomplish my analysis, I have constructed a number of computational tools, which I have publicly released or make available through this thesis. I apply my analysis to the question of s-process branching at 186Re and study the implications for the osmium isotopes in mainstream presolar SiC grains. My essential conclusion is that the problem of the large neutron flux inferred from the SiC osmium isotopic abundances cannot be solved by branching through an out-of-equilibrium isomer of …
Observing Co In Circumstellar Disks,
2010
Clemson University
Observing Co In Circumstellar Disks, Matthew Troutman
All Dissertations
This dissertation includes high-resolution, near-infrared spectroscopy to study CO in circumstellar disks around Herbig Ae/Be stars. The velocity-resolved spectra was used to measure the distribution of gas in the circumstellar disk and thus determine the evolutionary state of the system. Near-infrared spectra were obtained on over 30 young circumstellar disks around Herbig Ae/Be stars to study the physical processes in the disk. The radial location of the CO emitting gas bears directly on the evolutionary state of the transition objects in the sample. This study included a detailed study of the debris disk star β Pictoris where the disk mass …
