Astrophysics and Astronomy Commons^™

The Variable Quiescent X-Ray Emission Of The Neutron Star Transient Xte J1701-462, Joel K. Fridriksson, Jeroen Homan, Rudy Wijnands, Edward M. Cackett, Diego Altamirano, Nathalie Degenaar, Edward F. Brown, Mariano Méndez, Tomaso M. Belloni

Physics and Astronomy Faculty Research Publications

We present the results of continued monitoring of the quiescent neutron star low-mass X-ray binary XTE J1701-462 with Chandra and Swift. A new Chandra observation from 2010 October extends our tracking of the neutron star surface temperature from ≃ 800 days to ≃ 1160 days since the end of an exceptionally luminous 19 month outburst. This observation indicates that the neutron star crust may still be slowly cooling toward thermal equilibrium with the core; another observation further into quiescence is needed to verify this. The shape of the overall cooling curve is consistent with that of a broken power law, …

Supernova Remnants And Cosmic Ray Acceleration Mechanisms, Ariel L. Simons, Yasunobu Uchiyama

STAR Program Research Presentations

Supernova remnants (SNRs) are considered to be the primary energy source of galactic-origin cosmic rays. Within this prediction exist two models, leptonic and hadronic, to explain the acceleration of charged particles up to a PeV in energy. Using data from the Fermi Gamma-ray Space Telescope (FGST) each model is expected to produce a distinct spectral energy distribution (SED) over a photon energy range of 100MeV to 100GeV. This analysis is focused on the methods for generating SEDs for the SNR Cassiopeia A and how they can be used to constrain the likelihood of either acceleration model.

Mass Loss History Of Evolved Stars, Kathleen M. Geise

Electronic Theses and Dissertations

We provide high-resolution maps of the circumstellar dust shells of several dozen Asymptotic Giant Branch (AGB) stars using data from the Spitzer space telescope Multiband Imaging Photometer (MIPS) imaged at 70µm. AGB stars are the major contributors of chemical elements such as carbon, oxygen and silicon, which are essential to the existence of life in the universe, through mass loss processes that take place at the surface of the star. We probe the spatial distribution of cold (~40 K) dust grains in order to trace the history of mass loss from the observed radial density variation in these shells. Our …

X-Ray Monitoring Of Classical Novae In The Central Region Of M 31 Iii. Autumn And Winter 2007/2008 And 2008/2009, M. Henze, W. Pietsch, F. Haberl, M. Hernanz, G. Sala, D. Hartzidimitriou, M. Della Velle, A. Rau, Dieter H. Hartmann, V. Burwitz

Publications

Context. Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of the galaxy M 31. Aims. We performed a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra between Nov. 2007 and Feb. 2008 and between Nov. 2008 and Feb. 2009, respectively, to find SSS counterparts of CNe, determine the duration of their SSS phase, and derive physical outburst parameters. Methods. We systematically searched our data for X-ray counterparts of CNe, determined their X-ray light curves and characterised their spectra using blackbody fits and white dwarf (WD) atmosphere models. Additionally, …

Chandra X-Ray Spectroscopy Of The Very Early O Supergiant Hd 93129a: Constraints On Wind Shocks And The Mass-Loss Rate, David H. Cohen, M. Gagné, M. A. Leutenegger, James Paton Macarthur , '11, Emma Edwina Wollman , '09, J. O. Sundqvist, A. W. Fullerton, S. P. Owocki

Physics & Astronomy Faculty Works

We present an analysis of both the resolved X-ray emission-line profiles and the broad-band X-ray spectrum of the O-2 If* star HD 93129A, measured with the Chandra High Energy Transmission Grating Spectrometer ( HETGS). This star is among the earliest and most massive stars in the Galaxy, and provides a test of the embedded wind-shock scenario in a very dense and powerful wind. A major new result is that continuum absorption by the dense wind is the primary cause of the hardness of the observed X-ray spectrum, while intrinsically hard emission from colliding wind shocks contributes less than 10 per …

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.

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.

The Ghosts Survey. I. Hubble Space Telescope Advanced Camera For Surveys Data., D. J. Radburn-Smith, R. S. De Jong, A. C. Seth, J. Bailin, E. F. Bell, T. M. Brown, J. S. Bullock, S. Courteau, J. J. Dalcanton, H. C. Ferguson, P. Goudfrooij, S. Holfeltz, Benne W. Holwerda, C. Purcell, J. Sick, D. Streich, M. Vlajic, D. B. Zucker

Faculty and Staff Scholarship

We present an overview of the GHOSTS survey, the largest study to date of the resolved stellar populations in the outskirts of disk galaxies. The sample consists of 14 disk galaxies within 17 Mpc, whose outer disks and halos are imaged with the Hubble Space Telescope Advanced Camera for Surveys (ACS). In the first paper of this series, we describe the sample, explore the benefits of using resolved stellar populations, and discuss our ACS F606W and F814W photometry. We use artificial star tests to assess completeness and use overlapping regions to estimate photometric uncertainties. The median depth of the survey …

Star Messangers, Paul Zimet, Ellen Maddow

Kahn Institute Projects

Star Messengers is a musical theater work about two scientists, Galileo Galilei and Johannes Kepler, who changed our view of the universe. Writer Paul Zimet and composer Ellen Maddow have created a carnival of genres—opera, Com- media dell’Arte, Strindbergian Dream Play, and contemporary dance/theater—to produce a theatrical language that conveys the wonder of Galileo’s and Kepler’s discoveries.

While some aspects of Galileo’s life and discoveries are well known, hardly anything is popularly known of his scientific contemporaries. Johannes Kepler’s realization that the planets moved not in perfect circles, but in elliptical paths, was a leap of mind as extraordinary as …

Helical Antiferromagnetic Ordering In The Lowest Landau Level Of A Semiconductor Superlattice, Liqiu Zheng, D C. Marinescu

Publications

When subjected to a tilted magnetic field, the ground state of a semiconductor superlattice (SL) with two identical quantum wells per unit cell is shown to exhibit different magnetic configurations that are dependent on the strength and direction of the field and the SL characteristics. Intra- and interunit cell tunneling between the wells, assumed to be infinitely attractive, generate an energy miniband structure of the lowest Landau level that, in cooperation with the Zeeman splitting, creates, at certain points in the momentum space, an energy difference between opposite-spin single-particle states that can be overcome by the Coulomb interaction. Within the …

From The Big Bang To Table Mountain: The Cosmic Biography Of Atoms, Shane L. Larson

Public Talks

No abstract provided.

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. Vii. 47 Andromedae, 38 Cassiopeiae, And Hr 8467, Francis C. Fekel, Jocelyn Tomkin, Michael H. Williamson, Dimitri Pourbaix

Information Systems and Engineering Management Research Publications

Improved orbital elements for three double-lined spectroscopic binaries, 47 And, 38 Cas, and HR 8467, have been determined with extensive new radial velocities. For 38 Cas lines of the secondary have been detected for the first time. Given the orbital periods for these systems of 35.3682, 134.130, and 42.3813 days, respectively, it is not surprising that all three have either moderate or relatively high eccentricities. The orbital dimensions (a1sin i and a2sin i) and minimum masses (m1sin 3i and m2sin 3i) have accuracies of 0.5% or better. An astrometric orbit for 38 Cas, which was recomputed with Hipparcos astrometry and …

Investigating Students' Mental Models And Knowledge Construction Of Microscopic Friction. I. Implications For Curriculum Design And Development, Edgar D. Corpuz, N. Sanjay Rebello

Physics & Astronomy Faculty Publications

In this paper, we discuss the first phase of a multiphase study aimed at investigating the dynamics of students' knowledge construction in the context of unfamiliar physical phenomenon-microscopic friction. The first phase of this study involved the investigation of the variations in students' mental models of microscopic friction. Clinical interviews were conducted with 11 students enrolled in conceptual modern physics to elicit their ideas and generate themes of explanations. A phenomenographic approach of data analysis was employed to establish the variations in students' explanations. Results show that students' mental models of friction at the atomic level are dominated by their …

Ejecta Knot Flickering, Mass Ablation, And Fragmentation In Cassiopeia A, Robert A. Fesen, Jordan A. Zastrow, Molly C. Hammell, J. Michael Shull, Devin W. Silvia

Dartmouth Scholarship

Ejecta knot flickering, ablation tails, and fragmentation are expected signatures associated with the gradual dissolution of high-velocity supernova (SN) ejecta caused by their passage through an inhomogeneous circumstellar medium or interstellar medium (ISM). Such phenomena mark the initial stages of the gradual merger of SN ejecta with and the enrichment of the surrounding ISM. Here we report on an investigation of this process through changes in the optical flux and morphology of several high-velocity ejecta knots located in the outskirts of the young core-collapse SN remnant Cassiopeia A using Hubble Space Telescope images. Examination of WFPC2 F675W and combined ACS …

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 …

Dynamical Masses Of Early-Type Galaxies: A Comparison To Lensing Results And Implications For The Stellar Initial Mass Function And The Distribution Of Dark Matter, J. Thomas, R. P. Saglia, R. Bender, D. Thomas, K. Gebhardt, J. Magorrian, E. M. Corsini, G. Wegner, S. Seitz

Dartmouth Scholarship

This work aims to study the distribution of the luminous and dark matter in Coma early-type galaxies. Dynamical masses obtained under the assumption that mass follows light do not match with the masses of strong gravitational lens systems of similar velocity dispersions. Instead, dynamical fits with dark matter haloes are in good agreement with lensing results. We derive mass-to-light ratios of the stellar populations from Lick absorption line indices, reproducing well the observed galaxy colours. Even in dynamical models with dark matter haloes the amount of mass that follows the light increases more rapidly with the galaxy velocity dispersion than …

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 Young Exoplanet Transit Initiative (Yeti), R. Neuhäuser, R. Errmann, A. Berndt, G. Maciejewski, H. Takahashi, W. P. Chen, D. P. Dimitrov, T. Pribulla, E. H. Nikogossian, Eric L.N. Jensen, L. Marschall, Z.-Y. Wu, A. Kellerer, F. M. Walter, C. Briceño, R. Chini, M. Fernández, S. Raetz, G. Torres, D. W. Latham, S. N. Quinn, A. Niedzielski, L. Bukowiecki, G. Nowak, T. Tomov, K. Tachihara, S. C.-L. Hu, L. W. Hung, D. P. Kjurkchieva, V. S. Radeva, B. M. Mihov, L. Slavcheva-Mihova, I. N. Bozhinova, J. Budaj, M. Vanko, E. Kundra, L. Hambalek, V. Krushevska, T. Movsessian, H. Harutyunyan, J. J. Downes, J. Hernandez, V. H. Hoffmeister, David H. Cohen, Imoleayo Samson Abel , '14, Rebecca Ruby Ahmad , '14, Seth Walker Chapman , '14, Sierra Clare Eckert , '14, Jackson Goodman , '13, Adrien Charles Guerard , '14, H. M. Kim, Andrew Evan Koontharana , '11, Joshua Daniel Sokol , '11, Jennifer Trinh , '11, Yuwen Wang , '14, X. Zhou, R. Redmer, U. Kramm, N. Nettelmann, M. Mugrauer, J. Schmidt, M. Moualla, C. Ginski, C. Marka, C. Adam, M. Seeliger, S. Baar, T. Roell, T. O.B. Schmidt, L. Trepl, T. Eisenbeiss, S. Fiedler, N. Tetzlaff, E. Schmidt, M. M. Hohle, M. Kitze, N. Chakrova, C. Grafe, K. Schreyer, V. V. Hambaryan, C. H. Broeg, J. Koppenhoefer, A. K. Pandey

Physics & Astronomy Faculty Works

We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6-m telescopes around the world to monitor continuously young (<= 100 Myr), nearby (<= 1 kpc) stellar clusters mainly to detect young transiting planets (and to study other variability phenomena on time-scales from minutes to years). The telescope network enables us to observe the targets continuously for several days in order not to miss any transit. The runs are typically one to two weeks long, about three runs per year per cluster in two or three subsequent years for about ten clusters. There are thousands of stars detectable in each field with several hundred known cluster members, e. g. in the first cluster observed, Tr-37, a typical cluster for the YETI survey, there are at least 469 known young stars detected in YETI data down to R = 16.5 mag with sufficient precision of 50 millimag rms (5 mmag rms down to R = 14.5 mag) to detect transits, so that we can expect at least about one young transiting object in this cluster. If we observe similar to 10 similar clusters, we can expect to detect similar to 10 young transiting planets with radius determinations. The precision given above is for a typical telescope of the YETI network, namely the 60/90-cm Jena telescope (similar brightness limit, namely within +/-1 mag, for the others) so that planetary transits can be detected. For targets with a periodic transit-like light curve, we obtain spectroscopy to ensure that the star is young and that the transiting object can be sub-stellar; then, we obtain Adaptive Optics infrared images and spectra, to exclude other bright eclipsing stars in the (larger) optical PSF; we carry out other observations as needed to rule out other false positive scenarios; finally, we also perform spectroscopy to determine the mass of the transiting companion. For planets with mass and radius determinations, we can calculate the mean density and probe the internal structure. We aim to constrain planet formation models and their time-scales by discovering planets younger than similar to 100 Myr and determining not only their orbital parameters, but also measuring their true masses and radii, which is possible so far only by the transit method. Here, we present an overview and first results. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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 …

Stellar Fossils: Globular Clusters As Probes Of The Galaxy, Shane L. Larson

Public Talks

No abstract provided.

Nova M31n 2007-12b: Supersoft X-Rays Reveal An Intermediate Polar?, W. Pietsch, M. Henze, F. Haberl, M. Hernanz, G. Sala, Dieter H. Hartmann, M. Della Valle

Publications

Context. In the central part of M 31, a high number of optical novae can be targeted within the field of view of the XMM-Newton EPIC and Chandra HRC-I X-ray detectors. A special monitoring program of the area has allowed us to investigate supersoft emission of individual novae in detail and perform a statistical analysis of the sample. Aims. For the He/N nova M31N 2007-12b, we aimed to constrain the time of appearance of a supersoft source (SSS) and the duration of the SSS state as well as determine the spectral and time variability while the source was bright. Methods. …

Quiescent X-Ray Variability From The Neutron Star Transient Aql X-1, E. M. Cackett, J. K. Fridriksson, J. Homan, J. M. Miller, R. Wijnands

Physics and Astronomy Faculty Research Publications

A number of studies have revealed variability from neutron star low-mass X-ray binaries during quiescence. Such variability is not well characterized, or understood, but may be a common property that has been missed due to lack of multiple observations. One such source where variability has been observed is Aql X-1. Here, we analyse 14 Chandra and XMM-Newton observations of Aql X-1 in quiescence, covering a period of approximately 2 yr. There is clear variability between the epochs, with the most striking feature being a flare-like increase in the flux by a factor of 5. Spectral fitting is inconclusive as to …

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 …

A Volume-Limited Photometric Survey Of 114 Γ Doradus Candidates, Gregory W. Henry, Francis C. Fekel, Stephen M. Henry

Information Systems and Engineering Management Research Publications

We have carried out a photometric survey of a complete, volume-limited sample of γ Doradus candidates. The sample was extracted from the Hipparcos catalog and consists of 114 stars with colors and absolute magnitudes within the range of known γ Doradus stars and that also lie within a specified volume of 266,600 pc3. We devoted one year of observing time with our T12 0.8 m automatic photometric telescope to acquire nightly observations of the complete sample of stars. From these survey observations, we identify 37 stars with intrinsic variability of 0.002 mag or more. Of these 37 variables, 8 have …

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 …

Near-Field Radiative Heat Transfer Between Macroscopic Planar Surfaces, R. S. Ottens, Volker Quetschke, Stacy Wise, A. A. Alemi, R. Lundock, G. Mueller, D. H. Reitze, D. B. Tanner, B. F. Whiting

Physics & Astronomy Faculty Publications

Near-field radiation allows heat to propagate across a small vacuum gap at rates several orders of magnitude above that of far-field, blackbody radiation. Although heat transfer via near-field effects has been discussed for many years, experimental verification of this theory has been very limited. We have measured the heat transfer between two macroscopic sapphire plates, finding an increase in agreement with expectations from theory. These experiments, conducted near 300K, have measured the heat transfer as a function of separation over mm to μm and as a function of temperature differences between 2.5 and 30K. The experiments demonstrate that evanescence can …

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.

Revised Orbit And Transit Exclusion For Hd 114762b, Stephen R. Kane, Gregory W. Henry, Diana Dragomir, Debra A. Fischer, Andrew W. Howard, Xuesong Wang, Jason T. Wright

Information Systems and Engineering Management Research Publications

Transiting planets around bright stars have allowed the detailed follow-up and characterization of exoplanets, such as the study of exoplanetary atmospheres. The Transit Ephemeris Refinement and Monitoring Survey is refining the orbits of the known exoplanets to confirm or rule out both transit signatures and the presence of additional companions. Here we present results for the companion orbiting HD 114762 in an eccentric 84 day orbit. Radial velocity analysis performed on 19 years of Lick Observatory data constrain the uncertainty in the predicted time of mid-transit to ∼5 hr, which is less than the predicted one-half day transit duration. We …