Bulletin of the American Physical Society
Joint Fall 2012 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 57, Number 10
Thursday–Saturday, October 25–27, 2012; Lubbock, Texas
Session L2: Cosmology, General Relativity, Astrophysics: 2012 Graduate Robert S. Hyer Award Recipient & Contributed Papers |
Hide Abstracts |
Chair: Malik Rakhmanov, University of Texas at Brownsville Room: Holiday Inn Towers Heritage |
Saturday, October 27, 2012 10:15AM - 10:45AM |
L2.00001: The variations of geomagnetic energy and solar irradiance and their impacts on Earth's upper atmosphere Invited Speaker: Yanshi Huang It is important to understand and estimate the energy inputs to the upper atmosphere, in order to provide accurate calculation and prediction of the thermospheric neutral density, which is important for satellite orbital determination. The primary energy sources of Earth's upper atmosphere are the solar irradiance and geomagnetic energy including Joule heating and particle precipitation. Various data (OMNI2, CHAMP, DMSP) and models (SOLAR2000, FISM, Weimer05, AMIE, NCAR TIE-GCM) are utilized to investigate the variations of energy inputs and their influences on the coupled thermosphere-ionosphere system, with focus on the wavelength dependence of solar irradiance enhancement during are events, the geomagnetic energy associated with high-speed solar wind streams, the altitudinal distribution of Joule heating in different solar conditions, and the variation of solar irradiance and geomagnetic energy inputs during last solar cycle. [Preview Abstract] |
Saturday, October 27, 2012 10:45AM - 10:57AM |
L2.00002: Cosmology in One-dimension: Evolution of correlation and Fractal Void Geometry Bruce Miller, Jean-Louis Rouet Concentrations of matter in the universe, such as galaxies and galactic clusters, originated as very small density fluctuations in the early universe. The existence of galaxy clusters and super-clusters suggests that a natural scale for the matter distribution may not exist. A point of controversy is whether the distribution is fractal and, if so, over what range of scales. Even with recent astronomical surveys and simulations, it is difficult to extract information concerning fractal properties with confidence. With one-dimensional models we can overcome these limitations by carrying out simulations with on the order of a quarter of a million particles. They clearly demonstrate that the important dynamics for cluster formation occurs in the position-velocity plane. Here we present the recent results of our on-going study of the fractal geometry of one dimensional models of the expanding universe. The evolution of the power spectra and correlation function will be followed and their relation to the correlation dimension will be explored. An improved approach for determining the fractal dimensions of low density regions (voids) will be presented. [Preview Abstract] |
Saturday, October 27, 2012 10:57AM - 11:09AM |
L2.00003: Growth of Structure in the Szekeres Inhomogeneous Cosmological Models and the Matter-Dominated Era Austin Peel, Mustapha Ishak Observations reveal that the universe is not truly homogeneous--large voids and galaxy superclusters can occupy significant fractions of the observable universe. Light that reaches us travels through and is influenced by these inhomogeneous structures. As cosmological data become ever more precise, it is important to explore frameworks that relax the usual assumptions of perfect homogeneity and isotropy to determine how inhomogeneities might affect our interpretation of observations. As a step toward this, we study large-scale structure growth in the Szekeres inhomogeneous cosmological models. The Szekeres metric is an exact solution of Einstein's field equations with an irrotational dust source that in general has no symmetries. We use the Goode and Wainwright formulation of the models, which can be considered as exact perturbations of some associated Friedmann-Lema\^itre-Robertson-Walker (FLRW) background, and identify a density contrast that we evolve through the matter-dominated era. The equation for the density contrast turns out to contain the usual linearly perturbed FLRW terms plus two nonlinear terms. We find that the Szekeres growth rate is stronger than the linearly perturbed FLRW approach by up to a factor of five, reflecting the exact Szekeres nonlinear effects. [Preview Abstract] |
Saturday, October 27, 2012 11:09AM - 11:21AM |
L2.00004: Testing GR and Studying Dark Matter in the Aftermath of Galaxy Clusters Colliding Lindsay King, Helen Russell, Rebecca Canning, Douglas Clowe Astrophysical observations are consistent with most of the universe being dark: dark matter - predominantly cold - and dark energy. Unlike normal baryonic matter that we see directly, these dark components are studied via their impact on the dynamics and geometry of the universe, and on the growth of massive structures. Galaxy clusters are the most massive bound objects in the universe. Most of their normal matter is in the form of hot gas that emits X-rays. Seeing clusters after they have violently merged is very rare, but such systems are critical in testing gravity and general relativity on large scales, and in refining our understanding of dark matter. Dark matter and hot gas behave differently during a merger, with the hot gas becoming retarded and separated from the dominant dark matter. I discuss the importance of these systems, and outline how their strong and weak gravitational lensing signatures are used to map their mass - independent of it being luminous or dark. This map is compared with the distribution of the hot gas revealed by X-ray telescopes. Then I describe our current work on a unique galaxy cluster merger system. [Preview Abstract] |
Saturday, October 27, 2012 11:21AM - 11:33AM |
L2.00005: Self-Calibration Techniques for 3-point Intrinsic Alignment Correlations in Weak Gravitational Lensing Surveys Michael Troxel, Mustapha Ishak The weak lensing signal (cosmic shear) has been shown to be contaminated by correlations between the intrinsic alignment (IA) of galaxies, which poses a barrier to precision weak lensing measurements in planned surveys. We review recent work to extend the self-calibration approach to the cosmic shear bispectrum. The self-calibration techniques use the redshift separation dependencies of the IA bispectra and the non-linear galaxy bias in order to isolate and remove the impact of the IA correlations on the cosmic shear signal. We outline the proposed self-calibration techniques for the 3-point cosmic shear auto- and cross-correlations and summarize their performance. Using conservative estimates of photo-z accuracy, we find that planned surveys will be able to measure the IA redshift separation dependence over ranges of $|\Delta z^P|\le 0.2$ in the 3-point ellipticity auto-correlation. For the 3-point cross-correlations, we find that the self-calibration technique allows for reductions in the IA contamination by a factor of 10 or more over most scales and redshift bin choices and in all cases by a factor of 3-5 or more. The 3-point self-calibration techniques thus provide a means to greatly reduce the impact of IA on the cosmic shear signal. [Preview Abstract] |
Saturday, October 27, 2012 11:33AM - 11:45AM |
L2.00006: Big Bang Nucleosynthesis with a non-Maxwellian distribution John Fuqua, Carlos Bertulani, M.S. Hussein The cosmological big bang model is in agreement with many observations relevant for our understanding of the universe. However, comparison of calculations based on the model with observations is not straightforward because the data are subject to poorly known evolutionary effects and systematic errors. Nonetheless, the model is believed to be the only probe of physics in the early universe during the interval from 3-20 minutes, after which the temperature and density of the universe fell below that which is required for nuclear fusion and prevented elements heavier than beryllium from being formed. Here we consider primordial nucleosynthesis predictions with modified (Tsallis) statistics regarding the velocity or energy distribution of nucleons and nuclei. [Preview Abstract] |
Saturday, October 27, 2012 11:45AM - 11:57AM |
L2.00007: Variable Star Search Using ROTSE3 Data Farley Ferrante, Robert Kehoe I present results of a variable star search using data from the Robotic Optical Transient Search Experiment 3 (ROTSE3) telescopes. Variable stars fluctuate in magnitude as seen from Earth due either to changes in the star's luminosity or to changes in the amount of the star's light that reaches Earth. My research is focused on analysis of the time variation of optical light output as recorded in ROTSE 3 images. Specifically, I am attempting to identify short-period variable candidates such as delta Scuti stars, eclipsing binary stars, and contact binary stars. Amplitude variations for these classes of variables are on the order of one magnitude with periods on the order of two to five hours. The ROTSE3 telescope sensitivity holds the promise of significantly extending our reach to dimmer objects than previous searches and I will report on the confirmed discovery of a previously unidentified contact binary star in the constellation Sagittarius. This contact binary is now listed in the International Variable Star Index (VSX) maintained by the American Association of Variable Star Observers (AAVSO). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700