Astrophysics and Astronomy Commons^™

The Properties Of The Stellar Nuclei With The Host Galaxy Morphology In The Acsvcs, Hyun-Chul Lee

Physics & Astronomy Faculty Publications

We have revisited the ACS Virgo Cluster Survey (ACSVCS), a Hubble Space Telescope program to obtain ACS/WFC g and z bands imaging for a sample of 100 early-type galaxies in the Virgo Cluster. In this study, we examine 51 nucleated early-type galaxies in the ACSVCS in order to look into the relationship between the photometric and structural properties of stellar nuclei and their host galaxies. We morphologically dissect galaxies into five classes. We note that (1) the stellar nuclei of dwarf early-type galaxies (dS0, dE, and dE,N) are generally fainter and bluer with g > 18.95 and (g-z) < 1.40 compared to some brighter and redder counterparts of the ellipticals (E) and lenticular galaxies (S0), (2) the g-band half-light radii of stellar nuclei of all dwarf early-type galaxies (dS0, dE, and dE,N) are smaller than 20 pc and their average is about 4 pc, and (3) the colors of red stellar nuclei with (g - z) > 1.40 in bright …

A Study Of The Orbits Of The Logarithmic Potential For Galaxies, Sree Ram Valluri, Paul Wiegert, John Drozd, Matt Dasilva

Physics and Astronomy Publications

The logarithmic potential is of great interest and relevance in the study of the dynamics of galaxies. Some small corrections to the work of Contopoulos & Seimenis (1990) who used the method of Prendergast (1982) to find periodic orbits and bifurca- tions within such a potential are presented. The solution of the orbital radial equation for the purely radial logarithmic potential is then considered using the p-ellipse (pre- cessing ellipse) method pioneered by Struck (2006). This differential orbital equation is a special case of the generalized Burgers equation. The apsidal angle is also deter- mined, both numerically as well as …

Lunar Occultation Observer: A Nuclear Astrophysics All-Sky Survey Mission Concept, Riley Freelove

Von Braun Symposium Student Posters

No abstract provided.

Fabrication And Application Of Vertically Aligned Carbon Nanotube Templated Silicon Nanomaterials, Jun Song

Theses and Dissertations

A process, called carbon nanotube templated microfabrication (CNT-M) makes high aspect ratio microstructures out of a wide variety of materials by growing patterned vertically aligned carbon nanotubes (VACNTs) as a framework and then infiltrating various materials into the frameworks by chemical vapor deposition (CVD). By using the CNT-M procedure, a partial Si infiltration of carbon nanotube frameworks results in porous three dimensional microscale shapes consisting of silicon-carbon nanotube composites. The addition of thin silicon shells to the vertically aligned CNTs (VACNTs) enables the fabrication of robust silicon nanostructures with edibility to design a wide range of geometries. Nanoscale dimensions are …

Hubble Space Telescope Imaging Of Post-Starburst Quasars, S. Cales, M. Brotherton, Zhaohui Shang, Vardha Bennert, Gabriela Canalizo, R. Stoll, R. Ganguly, D. Berk, Cassandra Paul, A. Diamond-Stanic

Faculty Publications

We present images of 29 post-starburst quasars (PSQs) from a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel Snapshot program. These broadlined active galactic nuclei (AGNs) possess the spectral signatures of massive (Mburst ∼ 1010 M⊙), moderate-aged stellar populations (hundreds of Myr). Thus, their composite nature provides insight into the AGN–starburst connection. We measure quasar-to-host galaxy light contributions via semi-automated two-dimensional light profile fits of point-spread-function-subtracted images. We examine the host morphologies and model the separate bulge and disk components. The HST/ACS-F606W images reveal an equal number of spiral (13/29) and early-type (13/29) hosts, with the …

Critical Differences And Clues In Eta Car's 2009 Event, Andrea Mehner, Kris Davidson, John C. Martin, Roberta M. Humphreys, Kazunori Ishibashi, Gary J. Ferland

Physics and Astronomy Faculty Publications

We monitored Eta Carinae with the Hubble Space Telescope WFPC2 and Gemini GMOS throughout the 2009 spectroscopic event, which was expected to differ from its predecessor in 2003. Here we report major observed differences between events and their implications. Some of these results were quite unexpected. (1) The UV brightness minimum was much deeper in 2009. This suggests that physical conditions in the early stages of an event depend on different parameters than the "normal" inter-event wind. Extra mass ejection from the primary star is one possible cause. (2) The expected He II λ4687 brightness maximum was followed several weeks …

Holographic Renormalization Of Asymptotically Lifshitz Spacetimes, Robert A. Mcnees Iv, Robert Mann

Physics: Faculty Publications and Other Works

A variational formulation is given for a theory of gravity coupled to a massive vector in four dimensions, with Asymptotically Lifshitz boundary conditions on the fields. For theories with critical exponent z=2 we obtain a well-defined variational principle by explicitly constructing two actions with local boundary counterterms. As part of our analysis we obtain solutions of these theories on a neighborhood of spatial infinity, study the asymptotic symmetries, and consider different definitions of the boundary stress tensor and associated charges. A constraint on the boundary data for the fields figures prominently in one of our formulations, and in that case …

A Model Of So-Called "Zebra" Emissions In Solar Flare Radio Burst Continua, R. A. Treumann, R. Nakamura, W. Baumjohann

Dartmouth Scholarship

A simple mechanism for the generation of elec- tromagnetic “Zebra” pattern emissions is proposed. “Zebra” bursts are regularly spaced narrow-band radio emissions on the otherwise broadband radio continuum emitted by the ac- tive solar corona. The mechanism is based on the generation of an ion-ring distribution in a magnetic mirror geometry in the presence of a properly directed field-aligned electric po- tential field. Such ion-rings or ion-conics are well known from magnetospheric observations. Under coronal condi- tions they may become weakly relativistic. In this case the ion-cyclotron maser generates a number of electromagnetic ion-cyclotron harmonics which modulate the electron maser …

Sparse Spectral-Tau Method For The Three-Dimensional Helically Reduced Wave Equation On Two-Center Domains, Stephen R. Lau, Richard H. Price

Physics & Astronomy Faculty Publications

We describe a multidomain spectral-tau method for solving the three-dimensional helically reduced wave equation on the type of two-center domain that arises when modeling compact binary objects in astrophysical applications. A global two-center domain may arise as the union of Cartesian blocks, cylindrical shells, and inner and outer spherical shells. For each such subdomain, our key objective is to realize certain (differential and multiplication) physical-space operators as matrices acting on the corresponding set of modal coefficients. We then achieve sparse realizations through the integration “preconditioning” of Coutsias, Hagstrom, Hesthaven, and Torres. Since ours is the first three-dimensional multidomain implementation of …

The Initial Mass Function And Disk Frequency Of The Ρ Ophiuchi Cloud: An Extinction-Limited Sample, Kristen Erickson, Bruce Wilking, Michael Meyer, John Robinson, Lauren Stephenson

Physics Faculty Works

We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of candidate young stars covering 1.3 deg2 of the ρ Ophiuchi star-forming region. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys are biased toward particular stages of stellar evolution and are not optimal for studies of the disk frequency and initial mass function. We have obtained over 300 optical spectra to help identify 135 association members based on the presence of Hα in emission, lithium absorption, X-ray emission, a mid-infrared excess, a common proper motion, reflection nebulosity, and/or …

Ferromagnetic Resonance On Ni Nanowire Arrays, Mircea Chipara, Ralph Skomski, Roger D. Kirby, David J. Sellmyer

Physics & Astronomy Faculty Publications

Ferromagnetic resonance investigations on Ni nanowires are reported. The angular dependence of the resonance line position is analyzed within a thermodynamic approach that includes shape anisotropy (ellipsoids of revolution), magnetocrystalline anisotropies (cubic and uniaxial), and dipole–dipole interactions. The results are supported by hysteresis loops, obtained on the same sample.

Star Formation In Self-Gravitating Disks In Active Galactic Nuclei. I. Metallicity Gradients In Broad-Line Regions, Jian-Min Wang, Jun-Qiang Ge, Chen Hu, Jack A. Baldwin, Yan-Rong Li, Gary J. Ferland, Fei Xiang, Chang-Shuo Yan, Shu Zhang

Physics and Astronomy Faculty Publications

It has been suggested that the high metallicity generally observed in active galactic nuclei (AGNs) and quasars originates from ongoing star formation in the self-gravitating part of accretion disks around supermassive black holes (SMBHs). We designate this region as the star-forming (SF) disk, in which metals are produced from supernova explosions (SNexp) while at the same time inflows are driven by SNexp-excited turbulent viscosity to accrete onto the SMBHs. In this paper, an equation of metallicity governed by SNexp and radial advection is established to describe the metal distribution and evolution in the SF disk. We find that the metal …

Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo

Faculty Publications

Magnesium alloys are among the lightest structural materials known and are of considerable technological interest. To develop superior magnesium alloys, experimentalists must have a thorough understanding of the concentration-dependent precipitates that form in a given system, and hence, the thermodynamic stability of crystal phases must be determined. This information is often lacking but can be supplied by first-principles methods. Within the high-throughput framework, AFLOW, T = 0 K ground-state predictions are made by scanning a large set of known candidate structures for thermodynamic (formation energy) minima. The following 34 systems are investigated: AlMg, AuMg, CaMg, CdMg, CuMg, FeMg , GeMg, …

Galaxy Formation In Heavily Overdense Regions At Z ~ 10: The Prevalence Of Disks In Massive Halos, Emilio Romano-Díaz, Jun-Hwan Choi, Isaac Shlosman, Michele Trenti

Physics and Astronomy Faculty Publications

Using a high-resolution cosmological numerical simulation, we have analyzed the evolution of galaxies at z ~ 10 in a highly overdense region of the universe. These objects could represent the high-redshift galaxies recently observed by the Hubble's Wide Field Camera 3 and could as well be possible precursors of QSOs at z ~ 6-7. To overcome the sampling and resolution problems in cosmological simulations of these rare regions, we have used the constrained realizations method. Our main result for z ~ 10 shows the high-resolution central region of 3.5 h^–1 Mpc radius in comoving coordinates being completely dominated by …

Structure And Feedback In 30 Doradus. Ii. Structure And Chemical Abundances, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

We use our new optical-imaging and spectrophotometric survey of key diagnostic emission lines in 30 Doradus, together with CLOUDY photoionization models, to study the physical conditions and ionization mechanisms along over 4000 individual lines of sight at points spread across the face of the extended nebula, out to a projected radius 75 pc from R136 at the center of the ionizing cluster NGC 2070. We focus on the physical conditions, geometry, and importance of radiation pressure on a point-by-point basis, with the aim of setting observational constraints on important feedback processes. We find that the dynamics and large-scale structure of …

On The Measurement Of Angular Dependent Sound Transmission Through Airborne Supercritical Plates, Matthew D. Shaw

Theses and Dissertations

A method of measuring angular dependence of acoustic transmission through supercritical plates in air is discussed. The coincidence effect occurs in a supercritical plate when the component of the acoustic wave number parallel to the plate matches the bending wave number in the plate. The transmission of sound is a maximum at the angle where this trace wave number matching occurs. The theory of the coincidence effect is well-defined for unbounded thin plates using plane-wave excitation. However, experimental results for finite plates are known to diverge from theory, especially near grazing angles. An experimental setup has been developed in order …

Scaling Carbon Nanotube Localization By Floating Potential Dielectrophoresis: An Enabling Geometry, Brian S. Davis

Theses and Dissertations

Dielectrophoresis has been used as a technique for the parallel localization and alignment of both semiconducting and metallic carbon nanotubes (CNTs) at junctions between electrodes. A variation of this technique known as Floating Potential Dielectrophoresis (FPD) allows for a self-limiting number of CNTs to be localized at each junction, on a massively parallel scale. However, the smallest FPD geometries to date are restricted to conductive substrates and have a lower limit on floating electrode size. We present a geometry which eliminates this lower limit and enables FPD to be performed on non-conducting substrates. We also discuss experiments clarifying the self-limiting …

N Ii Λλ5668−5712: A New Class Of Spectral Features In Eta Carinae, Andrea Mehner, Kris Davidson, Gary J. Ferland

Physics and Astronomy Faculty Publications

We report on the N II λλ5668-5712 emission and absorption lines in the spectrum of η Carinae. Spectral lines of the stellar wind regions can be classified into four physically distinct categories: (1) low-excitation emission such as H I and Fe II, (2) higher-excitation He I features, (3) the N II lines discussed in this paper, and (4) He II emission. These categories have different combinations of radial velocity behavior, excitation processes, and dependences on the secondary star. The N II lines are the only known features that originate in "normal" undisturbed zones of the primary wind but depend primarily …

The Role Of Llnl's Fast Calibration Facility In Diagnosing Nif Fusion Plasmas, Joshua G. Thompson, Carey Scott, Greg V. Brown

STAR Program Research Presentations

The Fusion and Astrophysics (FAST) Calibration and Diagnostic Facility uses the original Electron Beam Ion Trap (EBIT-I) to profile x-ray filters that are used in the Dante Soft X-Ray Diagnostic at the National Ignition Facility (NIF). FAST has an advantage over any other facility not only for its high accuracy, but also for its proximity to NIF in the Lawrence Livermore National Laboratory (LLNL). This makes for highly accurate and near-instantaneous filter calibration turnover.

EBIT-I was first constructed to create, trap, and observe static highly charged ions (HCIs) and conduct experimental astrophysics (creating an x-ray spectroscopy catalogue of ions). To …

Laboratory Astrophysics: Using Ebit Measurements To Interpret High Resolution Spectra From Celestial Sources, Carey Scott, Joshua Thompson, N. Hell, Greg V. Brown

STAR Program Research Presentations

Astrophysicists use radiation to investigate the physics controlling a variety of celestial sources, including stellar atmospheres, black holes, and binary systems. By measuring the spectrum of the emitted radiation, astrophysicists can determine a source’s temperature and composition. Accurate atomic data are needed for reliably interpreting these spectra. Here we present an overview of how LLNL’s EBIT facility is used to put the atomic data on sound footing for use by the high energy astrophysics community.

New Cross Sections For H On H2 Collisional Transitions, Qianxia Zou

UNLV Theses, Dissertations, Professional Papers, and Capstones

The cross section for H on H₂ collisions is important for astrophysics as well as our understanding of the simple chemical systems. This is the simplest atom-molecule cross section. With a new H₃ potential surface by Mielke et al., we have modified the ABC code by Skouteris, Castillo and Manolopoulos to calculate new cross sections. These cross sections are compared to previous cross section calculations.

Torus And Active Galactic Nucleus Properties Of Nearby Seyfert Galaxies: Results From Fitting Infrared Spectral Energy Distributions And Spectroscopy, Almudena Alonso-Herrero, Almeida Cristina Ramos, Rachel Mason, Ramos Andrés Asensio, Patrick F. Roche, Nancy A. Levenson, Moshe Elitzur, Christopher Packham, José Miguel Rodríguez Espinosa, Stuart Young, Tanio Díaz-Santos, Ana M. Pérez-García

Physics and Astronomy Faculty Publications

We used the CLUMPY torus models and a Bayesian approach to fit the infrared spectral energy distributions and ground-based high angular resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put tight constraints on torus model parameters such as the viewing angle i, the radial thickness of the torus Y, the angular size of the cloud distribution σ_torus, and the average number of clouds along radial equatorial rays N₀. We found that the viewing angle i is not the only parameter controlling the classification of a galaxy into type 1 or …

Photoemission By Large Electron Wave Packets Emitted Out The Side Of A Relativistic Laser Focus, Eric Flint Cunningham

Theses and Dissertations

There are at least two common models for calculating the photoemission of accelerated electrons. The 'extended-charge-distribution' method uses the quantum probability current (multiplied by the electron charge) as a source current for Maxwell's equations. The 'point-like-emitter' method treats the electron like a point particle instead of like a diffuse body of charge. Our goal is to differentiate between these two viewpoints empirically. To do this, we consider a large electron wave packet in a high-intensity laser field, in which case the two viewpoints predict measurable photoemission rates that differ by orders of magnitude. Under the treatment of the 'extended-charge-distribution' model, …

The Dark Side Of Qso Formation At High Redshifts, Emilio Romano-Díaz, Isaac Shlosman, Michele Trenti, Yehuda Hoffman

Physics and Astronomy Faculty Publications

Observed high-redshift QSOs, at z ~ 6, may reside in massive dark matter (DM) halos of more than 10¹² M_☉ and are thus expected to be surrounded by overdense regions. In a series of 10 constrained simulations, we have tested the environment of such QSOs. The usage of constrained realizations has enabled us to address the issue of cosmic variance and to study the statistical properties of the QSO host halos. Comparing the computed overdensities with respect to the unconstrained simulations of regions empty of QSOs, assuming there is no bias between the DM and baryon distributions, and …

The Role Of Hole Localization In Sacrificial Hydrogen Production By Semiconductor-Metal Heterostructured Nanocrystals, Krishna P. Acharya, Rony S. Khnayzer, Timothy O’Connor, Geoffrey Diederich, Maria Kirsanova, Anna Klinkova, Daniel Roth, Erich Kinder, Martene Imboden, Mikhail Zamkov

Physics and Astronomy Faculty Publications

The effect of hole localization on photocatalytic activity of Pt-tipped semiconductor nanocrystals is investigated. By tuning the energy balance at the semiconductor-ligand interface, we demonstrate that hydrogen production on Pt sites is efficient only when electron-donating molecules are used for stabilizing semiconductor surfaces. These surfactants play an important role in enabling an efficient and stable reduction of water by heterostructured nanocrystals as they fill vacancies in the valence band of the semiconductor domain, preventing its degradation. In particular, we show that the energy of oxidizing holes can be efficiently transferred to a ligand moiety, leaving the semiconductor domain intact. This …

High Gravitational Waveform Accuracy At Null Infinity, Maria Babiuc-Hamilton

Physics Faculty Research

The aim of Cauchy-characteristic extraction is to provide a standardized waveform extraction tool for the numerical relativity community. The new extraction tool contains major improvements and corrections to previous versions and displays convergence. The error introduced by CCE satisfies the time domain criteria required for advanced LIGO data analysis. The importance of accurate waveforms to the gravitational wave astronomy has created an urgency for tools like CCE. The source code has been released to the public and is available as part of the Einstein Toolkit. We welcome applications to a variety of generic Cauchy codes implementing Einstein Equations of General …

Photoemission From A Laser-Driven Electron Wave Packet, John Purvis Corson

Theses and Dissertations

We use quantum electrodynamics (QED) to investigate the possibility of radiative interference from a single laser-driven electron wave packet. Intuition gleaned from classical electrodynamics suggests that radiation from a large electron wave packet might interfere destructively when different regions of the packet oscillate out of phase with each other. We show that when the incident light is represented with a multi-mode coherent state, the relative phases of the electron's constituent momenta have no influence of the amount of scattered light. Hence, the radiation does not depend on the amount of free-particle spreading experienced by the electron before the interaction. This …

The Role Of The Bow Shock In Solar Wind-Magnetosphere Coupling, R E. Lopez, V G. Merkin, J G. Lyon

Dartmouth Scholarship

No abstract provided.

Temporal And Spatial Aspects Of Gas Release During The 2010 Apparition Of Comet 103p/Hartley 2, M. Mumma, B. Bonev, G. Villanueva, L. Paganini, M. Disanti, E. Gibb, J. Keane, K. Meech, G. Blake, R. Ellis, M. Lippi, H. Boehnhardt, K. Magee-Sauer

Physics Faculty Works

We report measurements of eight primary volatiles (H2O, HCN, CH4, C2H6, CH3OH, C2H2, H2CO, and NH3) and two product species (OH and NH2) in comet 103P/Hartley 2 using high-dispersion infrared spectroscopy. We quantified the long- and short-term behavior of volatile release over a three-month interval that encompassed the comet's close approach to Earth, its perihelion passage, and flyby of the comet by the Deep Impact spacecraft during the EPOXI mission. We present production rates for individual species, their mixing ratios relative to water, and their spatial distributions in the coma on multiple dates. The production rates for water, ethane, HCN, …

A Layer Correlation Technique For Pion Energy Calibration At The 2004 Atlas Combined Beam Test, E. Abat, J M. Abdallah, T N. Addy, P Adragna, M Aharrouche, A Ahmad, T Pa Akesson, M Aleksa, C Alexa, K Anderson, A Andreazza, F Anghinolfi, A Antonaki, G Arabize, E Arik, T Atkinson, J Baines, O K. Baker, D Banfi, S Baron, Roberto Petti, Et. Al.

Faculty Publications

A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 …