Astrophysics and Astronomy Commons^™

Simulation Of Relativistic Jets And Associated Self-Consistent Radiation, K.-I. Nishikawa, E. J. Choi, K. Min, P. Hardee, Y. Mizuno, C. Zhang, J. Niemiec, M. Medvedev, A. Norlund, J Frederiksen, M Pohl, H Sol, Dieter H. Hartmann, G J. Fishman

Publications

Plasma instabilities excited in collisionless shocks are responsible for particle acceleration. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a par-tially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection behind the shock. Our initial …

Carina Ob Stars: X-Ray Signatures Of Wind Shocks And Magnetic Fields, M. Gagné, G. Fehon, M. R. Savoy, David H. Cohen, L. K. Townsley, P. S. Broos, M. S. Povich, M. F. Corcoran, N. R. Walborn, N. R. Evans, A. F.J. Moffat, Y. Nazé, L. M. Oskinova

Physics & Astronomy Faculty Works

The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L-X/L-bol relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with …

Abundances Of Stars With Planets: Trends With Condensation Temperature, Simon C. Schuler, Davin Flateau, Katia Cunha, Jeremy R. King, Luan Ghezzi, Verne V. Smith

Publications

Precise abundances of 18 elements have been derived for 10 stars known to host giant planets from high signal-to-noise ratio, high-resolution echelle spectroscopy. Internal uncertainties in the derived abundances are typically 0.05 dex. The stars in our sample have all been previously shown to have abundances that correlate with the condensation temperature (Tc) of the elements in the sense of increasing abundances with increasing Tc; these trends have been interpreted as evidence that the stars may have accreted H-depleted planetary material. Our newly derived abundances also correlate positively with Tc, although slopes of linear least-square fits to the [m/H]–Tc relations …

Measurements Of Mass Accretion Rates In Herbig Ae/Be Stars, Brian Donehew

All Dissertations

Herbig Ae/Be stars(HAeBes) are young stellar objects of spectral class F2 through B0, with the central star often surrounded by a circumstellar disk of gas and dust. They are the higher mass analogs to T Tauri stars. The interaction between the star and the disk is not well understood, nor is the disk structure. The central star will often accrete mass from the disk, and the mass accretion rate is an important parameter for modeling the disk structure and evolution. The methods for measuring mass accretion rates of T Tauri stars are generally not applicable to HAeBe stars. As such, …

Modeling Gamma-Ray Bursts, Amanda Maxham

UNLV Theses, Dissertations, Professional Papers, and Capstones

Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies(from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general …

A Multi-Wavelength Study On Gamma-Ray Bursts And Their Afterglows, Binbin Zhang

UNLV Theses, Dissertations, Professional Papers, and Capstones

During the prompt emission and afterglow phases, GRBs(Gamma-Ray Bursts) release their huge amount of energy not limited in gamma-ray, but in a wide range of muti-wavelengths, from radio band to GeV gamma-rays. Thanks to the recent missions of Swift and Fermi, I was able to use their multi-wavelength observation data of GRBs and study their physical natures. I have processed all the Swift BAT/XRT and Fermi GBM/LAT GRB observation data. Based on the Swift data, I have studied the following comprehensive topics: (1) high-latitude "curvature effect" of early X-ray tails of GRBs Swift XRT afterglow (2) diverse physical origins of …

A Study Of Carbon Features In Type Ia Supernova Spectra, Jerod T. Parrent, R. C. Thomas, Robert A. Fesen, G. H. Marion

Dartmouth Scholarship

One of the major differences between various explosion scenarios of Type Ia supernovae (SNe Ia) is the remaining amount of unburned (C+O) material and its velocity distribution within the expanding ejecta. While oxygen absorption features are not uncommon in the spectra of SNe Ia before maximum light, the presence of strong carbon absorption has been reported only in a minority of objects, typically during the pre-maximum phase. The reported low frequency of carbon detections may be due to low signal-to-noise data, low abundance of unburned material, line blending between C II 6580 and Si II 6355, ejecta temperature differences, asymmetrical …

Gamma-Ray Burst Populations, Francisco J. Virgili

UNLV Theses, Dissertations, Professional Papers, and Capstones

Over the last fifty years the field of gamma-ray bursts has shown incredible growth, but the amassing of data has also left observers and theorists alike wondering about some of the basic questions surrounding these phenomena. Additionally, these events show remarkable individuality and extrema, ranging in redshift throughout the observable universe and over ten orders of magnitude in energy. This work focuses on analyzing groups of bursts that are different from the general trend and trying to understand whether these bursts are from different intrinsic populations and if so, what can be said about their progenitors. This is achieved through …

3-D Mesoscale Mhd Simulations Of A Cusp-Like Magnetic Configuration: Method And First Results, E. Adamson, A. Otto, K. Nykyri

Publications

We present a local mesoscale model of the magnetospheric cusp region with high resolution (up to 300 km). We discuss the construction and implementation of the initial configuration and give a detailed description of the numerical simulation. An overview of simulation results for the case of strongly northward interplanetary magnetic field (IMF) is then presented and compared with data from Cluster 2 spacecraft from 14 February 2003. Results show a cusp diamagnetic cavity (CDC) with depth normal to the magnetospheric boundary on the order of 1–2Re and a much larger extent of ~5–9Re tangential to the boundary, bounded by a …

Numerical Simulations Of Accretion Disks And Extrasolar Planets, Stefan Luketic

UNLV Theses, Dissertations, Professional Papers, and Capstones

We study mass outflows from astrophysical objects. Using numerical hydrodynamical simulations, we investigate outflows from accretion disks and exoplanets. In the first part of this dissertation, we present the results of Zeus 2D hydrodynamical simulations of the disk photosphere irradiated by strong X–rays that are produced in the innermost part of the disk of an accreting black hole. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results to the well– studied X–ray transient source GRO J1655–40, we utilized the observed mass of its black hole and the observed properties of its X–ray radiation …

Arecibo Palfa Survey And Einstein@Home: Binary Pulsar Discovery By Volunteer Computing, B. Knispel, P. Lazarus, B. Allen, D. Anderson, C. Aulbert, N. D.R. Bhat, O. Bock, S. Bogdanov, A. Brazier, Fredrick A. Jenet

Physics & Astronomy Faculty Publications

We report the discovery of the 20.7ms binary pulsar J1952+2630, made using the distributed computing project Einstein@Home in Pulsar ALFA survey observations with the Arecibo telescope. Follow-up observations with the Arecibo telescope confirm the binary nature of the system. We obtain a circular orbital solution with an orbital period of 9.4hr, a projected orbital radius of 2.8lt-s, and a mass function of f = 0.15 M ⊙ by analysis of spin period measurements. No evidence of orbital eccentricity is apparent; we set a 2σ upper limit e ≲ 1.7 × 10 -3 . The orbital parameters suggest a massive white …

Improved Orbital Parameters And Transit Monitoring For Hd 156846b, Stephen R. Kane, Andrew W. Howard, Genady Pilyavsky, Suvrath Mahadevan, Gregory W. Henry, Kaspar Von Braun, David R. Ciardi, Diana Dragomir, Debra A. Fischer, Eric L. N. Jensen, Gregory Laughlin, Solange V. Ramirez, Jason T. Wright

Information Systems and Engineering Management Research Publications

HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a period of 359.55 days. The pericenter passage at a distance of 0.16 AU is nearly aligned to our line of sight, offering an enhanced transit probability of 5.4% and a potentially rich probe of the dynamics of a cool planetary atmosphere impulsively heated during close approach to a bright star (V = 6.5). We present new radial velocity (RV) and photometric measurements of this star as part of the Transit Ephemeris Refinement and Monitoring Survey. The RV measurements from the Keck–High Resolution Echelle Spectrometer …

Bachelor’S Thesis In Physics: A Chernoff Analysis Of An Invisible Quantum Tripwire With Photon Loss, Daniel Lum

Honors Capstones

No abstract provided.

Physical Conditions In Barnard's Loop, Components Of The Orion-Eridanus Bubble, And Implications For The Warm Ionized Medium Component Of The Interstellar Medium, C. R. O'Dell, Gary J. Ferland, R. L. Porter, P. A. M. Vanhoof

Physics and Astronomy Faculty Publications

We have supplemented existing spectra of Barnard's Loop with high accuracy spectrophotometry of one new position. Cloudy photoionization models were calculated for a variety of ionization parameters and stellar temperatures and compared with the observations. After testing the procedure with recent observations of M43, we establish that Barnard's Loop is photoionized by four candidate ionizing stars, but agreement between the models and observations is only possible if Barnard's Loop is enhanced in heavy elements by about a factor of 1.4. Barnard's Loop is very similar in properties to the brightest components of the Orion-Eridanus Bubble and the warm ionized medium …

Emission From Hot Dust In The Infrared Spectra Of Gamma-Ray Bright Blazars, Michael P. Malmrose, Alan P. Marscher, Svetlana G. Jorstad, Robert Nikutta, Moshe Elitzur

Physics and Astronomy Faculty Publications

A possible source of γ-ray photons observed from the jets of blazars is inverse Compton scattering by relativistic electrons of infrared seed photons from a hot, dusty torus in the nucleus. We use observations from the Spitzer Space Telescope to search for signatures of such dust in the infrared spectra of four γ-ray bright blazars, the quasars 4C 21.35, CTA102, and PKS 1510-089, and the BL Lacertae object ON231. The spectral energy distribution (SED) of 4C 21.35 contains a prominent infrared excess indicative of dust emission. After subtracting a non-thermal component with a power-law spectrum, we fit a …

The Double Galaxy Cluster Abell 2465 - I. Basic Properties: Optical Imaging And Spectroscopy, Gary A. Wegner

Dartmouth Scholarship

Optical imaging and spectroscopic observations of the z= 0.245 double galaxy cluster Abell 2465 are described. This object appears to be undergoing a major merger. It is a double X-ray source and is detected in the radio at 1.4 GHz. The purpose of this paper is to investigate signatures of the interaction of the two components. Redshifts were measured to determine velocity dispersions and virial radii of each component. The technique of fuzzy clustering was used to assign membership weights to the galaxies in each clump. Using redshifts of 93 cluster members within 1.4 Mpc of the subcluster centres, …

Stereoscopic Visualization As A Tool For Learning Astronomy Concepts, Norman M. Joseph

Department of Computer Graphics Technology Degree Theses

Three-dimensional (3D) visualization is becoming an extensively used educational tool. 3D visualization tends to be most useful when demonstrating concepts involving the very large – such as astronomy, or the very small – such as nanotechnology. Stereo visualization allows students to familiarize and immerse themselves in worlds which are difficult or impossible to experience in real life. This study will evaluate the educational benefit of teaching lessons involving a highly spatially-oriented topic (astronomy) using stereoscopic visualization technology.

We have used a stereoscopic visualization system, installed in a classroom, to deploy 3D simulation packages for use in classroom instruction. This educational …

Dust And The Type Ii-Plateau Supernova 2004dj, W. P. S. Meikle, R. Kotak, D. Farrah, S. Mattila, S. D. Van Dyk, A. C. Andersen, R. Fesen

Dartmouth Scholarship

We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106-1393 days after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 days and 165 days, reaching a mass of 0.3 × 10^–5 M _☉. Throughout the observations, much of the longer wavelength (>10 μm) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess …

A Mip-Based Energy Calibration Of The Star Endcap Electromagnetic Calorimeter For 2009, Zachary Nault

Symposium on Research and Creative Expression (SORCE)

The Endcap Electromagnetic Calorimeter (EEMC) is an integral part of the STAR detector at RHIC. The EEMC is used in detecting forward particles from polarized proton interactions, which aid in understanding the spin structure of the proton. In order to properly use the data collected, the energy and position measurements in the EEMC need to be well known. To accomplish this, a calibration of the EEMC was done using minimum ionizing particles (MIPs) for the 2009 run.

The Effect Of Strong Electrostatic And Magnetostatic Fields On The Activity Of Radioactive Nuclides, Sam Schaub

Symposium on Research and Creative Expression (SORCE)

This experiment seeks to measure the effect of strong electrostatic and magnetostatic fields on the decay constant of short-lived radioactive isotopes. Though it is assumed in modern radioactivity theory that such fields should not have any measurable effect, conclusive evidence utilizing modern equipment is absent from published literature. Samples have been monitored that exhibit beta-minus, beta-plus, electron capture, and internal conversion modes of radioactive decay. Radioactive nuclides chosen for this study include I-128, Cs-134, and Cu-64. The half-lives in this collection of radioactive nuclides range from 25 minutes to 12.7 hours. Sodium Iodide detectors are used to monitor the samples …

The Study Of Variability In Oxygen-Rich Proto-Planetary Nebulae, Kristie Shaw

Symposium on Research and Creative Expression (SORCE)

In this project, I am studying and analyzing the light and color variations for two proto-planetary nebulae (PPNe). PPNe is a stage in a star’s life where the star is in the process of losing its outer layers and exposing its core. I observed at the Valparaiso University Observatory, using the 0.4 meter telescope and an electronic camera to take digital images. I reduced these data using an image processing program to get the numerical data results. I plotted these results as a light curve showing the variation in brightness of the star versus time. By observing in three different …

Measurement Of Neutron Reflectivity From A Silicon Crystal: Preparation For An Nmdm Measurement, Benjamin Barber

Symposium on Research and Creative Expression (SORCE)

Physicists from Argonne National Laboratories, Valparaiso University, the University of Hawaii, and the National Institute for Standards and Technology have designed an experiment to use the known neutron magnetic dipole moment (nMDM) to measure Schwinger scattering in silicon (Si), a process whereby the orientation of the magnetic dipole polarization is altered by interactions with the atomic electric fields in a Si crystal. This measurement is intended to be a precursor to a search for a neutron electric dipole moment (nEDM) employing a similar spin rotation via a different interaction. Both measurements depend on neutron Bragg reflections down a slotted Si …

An Observational Study Of Variable Stars, Joel Rogers, Wesley Cheek

Symposium on Research and Creative Expression (SORCE)

This past summer, we carried out an observational study of light variability in approximately 20 stars.  Our goal was to document their changes in brightness, determine a period of the variability, and investigate whether their brightness changes were correlated with changes in color (and thus temperature). These stars are part of a special class of stars that have evolved beyond the red giant phase but have not yet become white dwarfs.  Little is known about their variability during this phase.  We observed them on almost every clear night during the summer of 2010.  We then compared the data for this …

Nonadiabatic Generation Of A Pure Spin Current In A One-Dimensional Quantum Ring With Spin-Orbit Interaction, Marian Nita, D C. Marinescu, Andrei Manolescu, Vidar Gudmundsson

Publications

We demonstrate the theoretical possibility of obtaining a pure spin current in a 1D ring with spin-orbit interaction by irradiation with a nonadiabatic, two-component terahertz laser pulse, whose spatial asymmetry is reflected by an internal phase difference φ. The solutions of the equation of motion for the density operator are obtained for a spin-orbit coupling linear in the electron momentum (Rashba) and they are used to calculate the time-dependent charge and spin currents. We find that there are critical values of φ at which the charge current disappears, while the spin current reaches a maximum or a minimum value.

Oral Presentation: The Universe In A Box, Jason Jaacks

Festival of Communities: UG Symposium (Posters)

When and how galaxies formed throughout the history of the Universe is one of the most fundamental questions of astronomy and astrophysics. As technology improves, astronomers are able to push the frontier of galaxy observation to a period when the Universe was less than 1 billion years old. This is when the first galaxies are beginning to form. However, beyond the limits of observational technology lies data fundamental to our complete understanding of these processes. Using state-of-the-art cosmological hydrodynamic computer codes combined with access to the nation’s largest and fastest supercomputers, we are able to simulate the formation and evolution …

Serpentinite Weathering And Implications For Mars, Valerie Tu, Julie Baumeister, Rodney Metcalf, A. Olsen, Elisabeth Hausrath

Festival of Communities: UG Symposium (Posters)

In the search for life on Mars near-surface soil environments may be important habitats for life accessible to future missions. Serpentinite rocks have been documented on Mars, as well as other clay minerals including smectite and kaolinites. Previous studies of soils formed on serpentinites on Earth have documented the formation of extensive clays. Serpentinites are additionally of interest as habitats for life such as methanogens. Here we examine weathering of serpentinites from bedrock to soil surface, as a potential route for the formation of clay minerals on Mars from abundant ultramafic minerals. We additionally test for the presence of Fe-oxidizing …

Halo Occupation Of Lyman-Break Galaxies, Saju Varghese, Ken Nagamine, Jason Jaacks, Jun-Hwan Choi

Festival of Communities: UG Symposium (Posters)

Lyman-break galaxies (LBGs) are star-forming galaxies found at high redshift that provide large amounts of information on early star and galaxy formation. We use large-scale cosmological smoothed-particle hydrodynamical simulations to simulate the physical properties of LBGs, such as stellar mass, star-formation rate, and magnitude. In particular, we focus on the question of which dark matter (DM) halos host LBGs. Our simulation suggests that only 1.74% of all DM halos host LBGs, though among the massive DM halos with mass Mhalo >1011.5 Msun, the fraction is 51.93%. The occupation number of LBGs ranges from 1 to 17 per halo.

Detection Of Ch+ Emission From The Disc Around Hd 100546, W F. Thi, F Menard, G Meeus, C. Martin-Zaidi, P Woitke, E Tatulli, M Benisty, I Kamp, I Pascucci, C Pinte, C A. Grady, Sean D. Brittain, G J. White, C D. Howard, G Sandell, C Eiroa

Publications

Despite its importance in the thermal balance of the gas and in the determination of primeval planetary atmospheres, the chemistry in protoplanetary discs remains poorly constrained with only a handful of detected species. We observed the emission from the disc around the Herbig Be star HD 100546 with the PACS instrument in the spectroscopic mode on board the Herschel Space Telescope as part of the GAS in Protoplanetary Systems (GASPS) programme and used archival data from the DIGIT programme to search for the rotational emission of CH+. We detected in both datasets an emission line centred at 72.16 μm that …

Pulsar Timing Sensitivity To Very-Low-Frequency Gravitational Waves, Fredrick A. Jenet, J. W. Armstrong, Massimo Tinto

Physics & Astronomy Faculty Publications

We compute the sensitivity, constrained by instrumental, propagation, and other fundamental noises, of pulsar timing to very-low-frequency gravitational waves (GWs). Reaching predicted GW signal strengths will require suppression of time-of-arrival fluctuations caused by interstellar plasma turbulence and a reduction of white rms timing noise to ≲100  ns. Assuming negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles, the resulting single-pulsar signal-to-noise ratio=1 sensitivity is limited by terrestrial time standards at ℎrms∼2×10−16  [f/(1  cycle/year)]−1/2 for 𝑓<3×10−8  Hz, where f is the Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. Since this sensitivity is comparable to predicted GW signal levels, a reliable detection will require substantial signal-to-noise ratio improvement via pulsar timing array.

Efficient Decomposition Of Cosmic Microwave Background Polarization Maps Into Pure E, Pure B, And Ambiguous Components., Emory F. Bunn

Physics Faculty Publications

Separation of the B component of a cosmic microwave background (CMB) polarization map from the much larger E component is an essential step in CMB polarimetry. For a map with incomplete sky coverage, this separation is necessarily hampered by the presence of ambiguous modes which could be either E or B modes. I present an efficient pixel-space algorithm for removing the ambiguous modes and separating the map into pure E and B components. The method, which works for arbitrary geometries, does not involve generating a complete basis of such modes and scales the cube of the number of pixels on …