Bulletin of the American Physical Society
11th Annual Meeting of the Northwest Section of APS
Volume 54, Number 6
Thursday–Saturday, May 14–16, 2009; Vancouver, BC, Canada
Session B1: Astrophysics, Cosmology and Gravity |
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Chair: Jo-Anne Brown, University of Calgary Room: Hennings 201 |
Friday, May 15, 2009 1:00PM - 1:36PM |
B1.00001: Searching for the Epoch of Reionization with the MWA Invited Speaker: Highly redshifted 21 cm emission from the Epoch of Reionization (EoR) is a unique cosmological probe, and upcoming EoR radio observations could revolutionize our understanding of structure formation and the emergence of the first luminous objects. However, 21 cm EoR observations are complicated by strong foreground contamination and stringent instrumental requirements. I will review the observational signatures of the Epoch of Reionization and how the faint 21 cm emission can be extracted from the foreground signals, and describe the Murchison Widefield Array my colleagues and I are constructing in Western Australia. [Preview Abstract] |
Friday, May 15, 2009 1:36PM - 1:48PM |
B1.00002: Cosmological tests of GR -- a look at the principals Levon Pogosian, Gong-Bo Zhao, Alessandra Silverstri, Joel Zylberberg Future cosmological surveys, through combination of galaxy counts and weak lensing measurements, will have the ability to map the evolution of matter perturbations and gravitational potentials from the matter dominated epoch until today. In addition to significantly tightening the existing bounds on allowed expansion histories, they will test the relationships between matter overdensities, local curvature, and the Newtonian potential. These relationships, given by Einstein's equations of General Relativity, can be modified in alternative gravity theories, or by the effects of massive neutrinos or exotic forms of Dark Energy. In this study, we introduce two arbitrary functions of time and scale which can account for any of the above departures from ``normal'' growth in the linear regime. We then use the Principal Component Analysis (PCA) to find the eigenmodes of these two functions which surveys like DES and LSST, in combination with CMB and SNe data, will constrain. The scale and time dependence of these eigenmodes can tell us which theoretical models will be better tested. The number of well-constrained modes is roughly equal to the number of additional growth parameters, beyond w(z), that one will be able to measure with future data. [Preview Abstract] |
Friday, May 15, 2009 1:48PM - 2:00PM |
B1.00003: Can we avoid dark energy? Jim Zibin The last decade has seen the consolidation of evidence that the expansion of the Universe is accelerating. The source for this acceleration is still a mystery, although most explanations employ some form of dark energy or modified gravity. An alternative approach, which has attracted considerable attention recently, is the idea that we live near the centre of a large, non-linear underdensity or {\em void.} I show that an appropriate void profile can fit both the latest cosmic microwave background and supernova data without dark energy. However, this requires either a fine-tuned primordial spectrum or a Hubble rate so low as to rule these models out. I also show that measurements of the radial baryon acoustic scale can provide very strong constraints, and discuss the ability of the matter power spectrum to constrain these models. These results have the more general application of testing the validity of the Cosmological Principle. [Preview Abstract] |
Friday, May 15, 2009 2:00PM - 2:12PM |
B1.00004: BLAST resolves origins of Cosmic Infrared Background Henry Ngo The cosmic infrared background (CIB), composed of starlight which is absorbed by dust and re-emitted at infrared wavelengths, has approximately the same intensity as the optical background. The CIB is most intense at around 200$\,\mu$m, where the atmosphere is very opaque, which makes observing it very difficult. The Balloon-borne Large-Aperture Submillimetre Telescope (BLAST) operates above 99.5\% of the atmosphere and has made the first direct observations at 250, 350 and 500$\,\mu$m. In December 2006, BLAST completed an 11-day flight over Antarctica. 220 hours of data were collected, 90 of which were spent in the Great Observatories Origins Deep Survey (GOODS) South Field. We calculate the covariance of the BLAST data with catalogs of 24$\,\mu$m sources. With this method, we measure the CIB brightness levels at BLAST wavelengths. This analysis resolves the CIB into contributions from 24$\,\mu$m identified galaxies. At 500$\,\mu$m, we find that over half of the light comes from sources with redshifts greater than 1.2. Furthermore, this analysis allows us to determine the characteristics of the galaxies which produce the CIB. [Preview Abstract] |
Friday, May 15, 2009 2:12PM - 2:24PM |
B1.00005: The Galactic Magnetic Field as Viewed from the VLA Cameron Van Eck, Jo-Anne Brown Interstellar magnetic fields play critical roles in many astrophysical processes. Yet despite their importance, our knowledge about magnetic fields in our Galaxy remains limited. For the field within the Milky Way much of what we do know comes from radio astronomy, through observations of polarization and Faraday rotation measures (RMs) of extragalactic sources and pulsars. A high angular density of RM measurements in several critical areas of the Galaxy is needed to clarify the Galactic magnetic field structure. Understanding the overall structure of the magnetic field will subsequently help us determine the origin and evolution of the field. In an effort to determine the overall structure of the field, Sun et al. (2008) produced 3 models of the Galactic magnetic field based on RM measurements available at the time. These models made distinct predictions for RMs in a region of the inner Galaxy at low Galactic latitude. Using observations made with the Very Large Array (VLA), we have determined RMs for sources in this critical region. In this talk we will present the results of our study and show how the RMs strongly support the ASS+RING model. [Preview Abstract] |
Friday, May 15, 2009 2:24PM - 2:36PM |
B1.00006: Protohalo Constraints to the Resonant Annihilation of Dark Matter Francis-Yan Cyr-Racine, Stefano Profumo, Kris Sigurdson It has recently been argued that the PAMELA, ATIC and PPB-BETS data showing a anomalous excess of high-energy cosmic ray positrons and electrons could be explained by annihilating dark matter in the galactic halo with an enhanced cross section relative to that in the early universe. We point out that having such a large annihilation cross section could trigger a burst of dark matter annihilation in the first protohalos that form at redshift $z\sim100-200$. We show that bounds from the diffuse gamma ray background and from the reonization of the intergalactic medium give rise to strong constraints on the zero temperature dark matter cross section which disfavor this interpretation of the PAMELA, ATIC and PPB-BETS results. [Preview Abstract] |
Friday, May 15, 2009 2:36PM - 2:50PM |
B1.00007: BREAK
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Friday, May 15, 2009 2:50PM - 3:02PM |
B1.00008: Black Body Detector Temperature from Gall and Planck Perspectives Clarence A. Gall The laws of Gall (http://sites.google.com/site/purefieldphysics) and Planck are generally defined with zero intensity at 0 K. However actual measurements involve detectors above absolute zero. These detectors must also be treated as approximate black body radiators. The zero intensity reference point is thus defined by the radiated intensity at the detector temperature. Planck's law thus becomes $\left( I_{P}=\frac{c_{1}}{\lambda ^{5}}\frac{1}{e^{\frac{c_{2}}{\lambda T}}\;-1}-\frac{c_{1}}{\lambda ^{5}}\frac{1}{e^{\frac{c_{2}}{\lambda T_{d}}}\;-1}\right) $ where $T_{d}$ is the detector temperature. Provided that $T>T_{d}\;;\;I_{P}\;is\;always>0$. Thus from a Planck perspective, wavelength increase should not be a factor in defining detector temperature. The corresponding expression for Gall's law is $\left( I_{G}=\sigma \frac{T^{6}}{b^{2}}\lambda e^{-\frac{\lambda T}{b}}-\sigma \frac{T_{d}^{6}}{b^{2}}\lambda e^{-\frac{\lambda T_{d}}{b}}\right) $. Above the crossover wavelength (http://absimage.aps.org/image/MWS\_MAR09-2008-000004.pdf), even though $T>T_{d}\;;\;I_{G}<0$. From a Gall perspective, this sets a limit on the long wavelength range for a given detector temperature. Longer wavelength measurements require lower detector temperatures. For a 6000 K black body radiator, the long wavelength crossover limits for detectors at 300 K, 100 K and 4 K are 9.138, 12.066 and 21.206 microns respectively. [Preview Abstract] |
Friday, May 15, 2009 3:02PM - 3:14PM |
B1.00009: Implementing wavelet technique for reconstructing the equation of state of Dark Energy Alireza Hojjati, Gong-Bo Zhao, Levon Pogosian Acceleration of the universe can be caused by a dark energy component with a negative equation of state, w, which can be redshift dependent. In this work, we investigate the efficiency of using wavelets for reconstructing the dark energy equation of state from supernovae data. We consider several theoretically motivated redshift dependencies of w and study how well these dependencies can be recovered from simulated data. [Preview Abstract] |
Friday, May 15, 2009 3:14PM - 3:26PM |
B1.00010: Numerical modeling of pulse shapes of the millisecond X-ray pulsar SAX J1808-3658 Denis Leahy, Sharon Morsink Numerical methods are developed for modeling X-ray pulse shapes for rapidly rotating neutron stars. The calculations include analytic approximations to the full General-Relativity neutron star metric and for ray-tracing in that metric. They also include time-delays, Doppler effects and oblateness of the rapidly rotating neutron star, which are all important for accurately modeling pulse shapes. The aim is to enable extraction of constraints on the neutron star's mass and radius. The analysis here includes RXTE observations of SAX J1808-3658 from the 1998, 2002 and 2005 outbursts. This is important since the observed pulse shape varies greatly. We can fit a consistent neutron star model to all of the observations by including a small amount of disk scattered light into the model. The resulting pulse shape model will be discussed together with new mass and radius constraints for SAX J1808-3658. [Preview Abstract] |
Friday, May 15, 2009 3:26PM - 3:38PM |
B1.00011: A null experiment shows that superluminal group velocity of tunneling photons is not superluminal energy flow because it is not sensitive to Earth's absolute motion George Soli A method for showing that superluminal group velocity, associated with tunneling photons, is not superluminal energy flow is to measure possible preferred frame effects. In Lorentz invariant theories, causal superluminal energy propagation in one reference frame is acausal in other frames. But Lorentz-violating theories have a preferred frame in which causal evolution is defined and superluminal propagation becomes causal in all reference frames. Null measurements show that preferred frame effects do not exist down to an absolute Earth velocity of 62 $\pm $ 426 km/s relative to a CMB rest frame velocity of 369 km/s. The signal is pulled out of the noise by allowing Earth's daily rotation to align photon tunneling direction with the CMB dipole and comparing to diurnally driven oscillations in Earth's absolute velocity measurement. [Preview Abstract] |
Friday, May 15, 2009 3:38PM - 3:50PM |
B1.00012: Looking toward the Horizon, a revisit of Gaussian Curves Richard Kriske On a curved surface such as the Earth, there is a special line that does not behave like any other, and that is the Horizon. If the Earth where flat a magnification of the horizon with a telescope would reveal a world identical to the one in which the observer is situated. The distant features would enlarge and ignoring atmospheric problems a larger telescope would reveal a further feature that would enlarge in the same manner. Of course a curved surface such as the Earth reveals something different, the Horizon is a mathematical line that is much different, magnifying the line shows features that are tilted away from the observer at a predictable angle easily calculated from the overall curvature of the sphere. Although this observation is obvious to anyone who has spent time with Gaussian theory, or with a pair of binoculars, it has been largely ignored in both Astrophysics and in (looking downward) particle physics, although in both cases a similar experimental phenomena has been observed (small things do not behave like large things) that seem to have similar ratios to curved surface calculations of tilting at the horizon. The author proposes a way to reconcile these special lines with Curvature, at least as an abstraction. [Preview Abstract] |
Friday, May 15, 2009 3:50PM - 4:02PM |
B1.00013: NASA's LCROSS Mission and the Search for Water Ice on the Moon Gwendolyn Bart, Anthony Colaprete The Lunar Prospector neutron spectrometer found evidence for hydrogen on the Moon, possibly as water, in permanently shadowed polar regions. To directly detect this water ice, the LCROSS spacecraft (Lunar CRater Observation and Sensing Satellite), will guide the empty Earth departure upper stage of the rocket into a controlled impact in a permanently shadowed region on the Moon. The LCROSS spacecraft will follow the impactor, using its nine instruments to detect the presence of water ice in the crater's ejecta. This presentation will give an overview of the LCROSS mission, its scientific rationale, and the expected return. Furthermore, this presentation will discuss the ongoing characterization of potential lunar impact sites. The impact site must be permanently shadowed from the sun and show an increased hydrogen signal in the neutron spectrometer data. The impact plume must be ejected up into sunlight and should be visible from Earth. The ideal site would be smooth on meter scales and be relatively flat. Lunar water would be a valuable resource for future human lunar explorers and the establishment of a permanent lunar base. [Preview Abstract] |
Friday, May 15, 2009 4:02PM - 4:14PM |
B1.00014: Vibrational Spectroscopy of Aerosols in Titan's Atmosphere Chia Wang, Ruth Signorell Aerosols play a crucial role in cloud formation, energy balance and chemical processes in terrestrial as well as extraterrestrial body's atmosphere (if there is one). Properties of these aerosols critically depend on their phase, size, shape, composition and architecture, which significantly differ from their bulk, liquid or gas phase counterparts. It is thus important to understand intrinsic properties of these aerosols at molecular level. Aerosols prevalent in Titan's atmosphere are demonstrated in this contribution. Aerosols are generated and suspended in a cooling cell and characterized by Fourier-transform mid-infrared extinction spectroscopy. Temperature, total pressure and mole fractions of targeted substances are carefully adjusted to mimic Titan's condition. The temporal evolution of aerosol formation and phase transition are monitored \textit{in situ}, and thermal equilibrium of aerosols with the surrounding is established during the time of measurement. From the co-crystallization dynamics of acetylene and carbon dioxide, we demonstrate that an intrinsically-mixed C$_{2}$H$_{2}\cdot $CO$_{2}$ crystalline phase is formed, which in turn suggests regional abundance of trace species and intermolecular interactions between them are important factors for the formation of mixed aerosols at corresponding regional composition in Titan's atmosphere. [Preview Abstract] |
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