Bulletin of the American Physical Society
15th Annual Meeting of the Northwest Section of the APS
Volume 59, Number 6
Thursday–Saturday, May 1–3, 2014; Seattle, Washington
Session G2: Astronomy and Cosmology |
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Chair: Miguel Morales, University of Washington Room: Alder Commons 107 |
Saturday, May 3, 2014 1:30PM - 2:00PM |
G2.00001: Ion and Electron Imaging on Swarm and ePOP: A New View of the Ionosphere Invited Speaker: David Knudsen Late 2013 has seen the successful launch of two new space missions. Canada's Enhanced Polar Outflow Probe (ePOP) was launched in September in order to search for the causes of so-called polar outflow: loss to space of significant amounts of atmospheric material in spite of the fact that Earth's atmosphere is bound strongly to the planet by gravity. The European Space Agency's Swarm satellites, launched in November, are carrying out precision mapping of the Earth's geomagnetic and, simultaneously, electric fields, allowing detailed study of the flow of up to 10$^{12}$ W of solar wind energy into the upper atmosphere. Both of these missions carry a new generation of CCD-based charged particle detector capable of recording 2-D snapshots of particle distribution functions at rates of 100 per second (in the case of ePOP), providing a picture of ionospheric dynamics at unprecedented resolution in time, space, and energy. This talk will provide an overview of the two missions and the first scientific findings resulting from the low-energy particle imagers on both. [Preview Abstract] |
Saturday, May 3, 2014 2:00PM - 2:12PM |
G2.00002: Cross-Scale Correlation in the Galactic Magnetic Field Anna Ordog, Jo-Anne Brown The Galactic Magnetic Field (GMF) is an important constituent of the interstellar medium, contributing, for example, to star formation and providing pressure balance for the Galaxy. Determining the GMF structure will lead to a better understanding of its origin and evolution. Studies of the large-scale GMF structure have revealed spiral shaped field lines with a radially varying pitch angle and a predominantly clockwise orientation. In contrast, the GMF on far smaller scales is not well understood. We present an analysis of Rotation Measure (RM) data from the Canadian Galactic Plane Survey that indicates a potential correlation between the large- and small-scale field components, previously assumed to be independent. We hypothesize a small-scale field component that varies randomly in direction but within a maximum angular deviation from the large-scale field lines. We model both field components using the RM data to constrain the parameters, with the aim of determining whether a statistically significant improvement in data-fitting can be obtained compared to modelling only the large-scale component. Preliminary results suggest a likely cross-scale correlation, taking us one step closer to a comprehensive model of the GMF that includes structure over a wide range of scale sizes. [Preview Abstract] |
Saturday, May 3, 2014 2:12PM - 2:24PM |
G2.00003: Finding the coldest star-forming regions in our Galaxy Will Nettke Surveys of the sky at different wavelengths are the pathfinders for driving astronomical research. In particular, catalogues of sources found in new surveys give us objects that can be followed up with other observations to probe the physical conditions in the distant Universe. The sub-millimetre part of the electromagnetic spectrum is ideal for studying the coldest and dustiest regions, and in particular to trace star-formation. However, the use of these wavelengths requires high-and-dry sites and state-of-the art instruments. Such data come from the Sub-millimetre Common User Bolometer Array 2 (SCUBA-2) on the James Clerk Maxwell Telescope, located at an altitude of 4000m on the summit of Mauna Kea, Hawaii. Using data obtained from the SCUBA-2 `All-Sky' Survey (SASSy), which covers a large part of the Milky Way, I have been extracting and cataloguing compact sources of interstellar dust and gas. Efficient source extraction methods have been developed by utilizing a matched-filtering approach to increase the signal-to-noise ratio in large mosaicked maps of the sub-millimetre sky. I have created a catalogue of sources, testing the efficiency of the extraction procedure through the use of artificial stars inserted into the real images. Some of these objects are previously unknown, and have properties characteristic of the earliest stages of star formation. Further study of these objects may tell us more about the birth of stars from clouds of gas and dust. [Preview Abstract] |
Saturday, May 3, 2014 2:24PM - 2:36PM |
G2.00004: Characterizing thermal sweeping: a rapid disc dispersal mechanism Mathias Hudoba de Badyn, James E. Owen, Cathie J. Clarke, Luke Robbins Protoplanetary discs form from the remnants of the accretion discs left over after star formation. Inside these discs, planets and other planetary objects are formed. To constrain timescales of planet formation, an important area of research is in protoplanetary disc dissipation. We study the photoevaporation of discs in their late lifetimes, in particular a dynamically short period of intense dissipation called thermal sweeping, ending in the destruction of the disc. This mechanism is proposed to occur when the inner edge of the disc reaches a sufficiently low surface density, and the disc is dynamically unstable to runaway x-ray penetration. We present numerical simulations that show thermal sweeping has a linear x-ray luminosity dependence, and we discuss the critical surface density for the process to occur. [Preview Abstract] |
Saturday, May 3, 2014 2:36PM - 2:48PM |
G2.00005: Quantum Raychaudhuri equation Saurya Das We compute quantum corrections to the Raychaudhuri equation, by replacing classical geodesics with quantal (Bohmian) trajectories, and show that they prevent focusing of geodesics, and the formation of conjugate points. We discuss implications for the Hawking-Penrose singularity theorems, for curvature singularities, for the Einstein equation of state and for Cosmology. [Preview Abstract] |
Saturday, May 3, 2014 2:48PM - 3:00PM |
G2.00006: Parallel-Plate Test of Gravity At Sub-Millimeter Distances Charles Hagedorn, Matthew Turner, Krishna Venkateswara, Jens Gundlach Gravity has not been experimentally observed at scales smaller than the diameter of human hair, barely smaller than the dark energy length-scale of 85 microns. Our sensitive ($10^{-14}$ N-m/$\sqrt{\mbox{Hz}}$) torsion balance uses a parallel-plate mass configuration to maximize signal and to create a Gauss's Law null-test of short range gravity. The measurement's sensitivity is comparable to the existing best limits at $\sim56$ microns, but with complimentary sources of systematic uncertainty. The talk will highlight our approach to systematic uncertainty and data analysis. [Preview Abstract] |
Saturday, May 3, 2014 3:00PM - 3:12PM |
G2.00007: Dark Matter Halo Models and ADMX Christopher Jantzi The axion is a theoretical particle hypothesized to solve the strong CP problem and also a compelling dark matter candidate. The Axion Dark Matter eXperiment (ADMX) searches for dark matter axions by stimulating the decay of axions to photons using a magnetic field and a tunable resonant cavity. In this talk, I will discuss what could be learned about the velocity distribution and density of dark matter in our galaxy if ADMX successfully detects axion dark matter. [Preview Abstract] |
Saturday, May 3, 2014 3:12PM - 3:24PM |
G2.00008: Resonant modes of a high Q microwave cavity in the detection of Axions Justin Thiele The axion is a hypothetical particle that solves the strong CP problem and is a promising candidate for dark matter in the universe. The Axion Dark Matter eXperiment (ADMX) searches for axions by placing a high Q microwave cavity in a strong magnetic field. The magnet stimulates the conversion of axions into photons with a frequency that corresponds to the axion mass. Although the mass of the axion is unknown, the range in which axions contribute significantly to dark matter is well constrained and the resonant frequency of the cavity can be tuned to cover a range of masses. The resonant frequency is dependent on the size of the cavity as well as the position of tuning rods placed inside. By adjusting the position of these rods the detector can search over a range of frequencies corresponding to mass of the axion. Here I will give an overview of the application of resonant modes of the microwave cavity in the context of ADMX. [Preview Abstract] |
Saturday, May 3, 2014 3:24PM - 4:00PM |
G2.00009: Break
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Saturday, May 3, 2014 4:00PM - 4:30PM |
G2.00010: Overview of the Canadian Hydrogen Intensity-Mapping Experiment, CHIME Invited Speaker: Mark Halpern Baryon Acoustic Oscillations (BAO) which occurred in the early universe have left a distinctive imprint in subsequent large-scale structure, providing a standard, cosmological ruler. Measurements of the apparent diameter of BAO over cosmic time reveal the expansion history of the Universe and thus provide valuable data for constraining models of dark energy. Intensity mapping of the hydrogen 21 cm line over a broad range in frequencies is an exciting new technique for determining the large scale, three-dimensional structure of the Universe. CHIME is a transit radio interferometer in the interior of British Columbia specifically designed to map cosmic structure over a redshift range of $0.8 < z < 2.5. $ An initial $40\times 37~m^2$ instrument with 128 dual- polarization feeds has seen first light, and construction of the full-sized, $100\times 100~m^2$ instrument is funded. CHIME is projected to provide a measurement of the dark energy equation of state that will be competitive with Stage IV Dark Energy Task Force experiments but at a tiny fraction of the cost and starting now. I will give an overview of CHIME, its science goals as well as the challenges, key among which is the task of separating the galactic foregrounds from the cosmic 21 cm signal [Preview Abstract] |
Saturday, May 3, 2014 4:30PM - 4:42PM |
G2.00011: Discovering the Epoch of Reionization Nichole Barry, Bryna Hazelton, Ian Sullivan, Adam Beardsley, Jonathan Pober, Patricia Carroll, Miguel Morales The Murchison Widefield Array seeks to directly detect the Epoch of Reionization, the era of early structure formation, via the 21 cm hyperfine transition of hydrogen. With a possible detection of 14$\sigma$ on the anisotropies of ionized hydrogen bubbles during the early universe, significant advancements in astrophysics will be made, including topics on the physics of galaxy formation, quasars, and mean free path of photons in the early universe. Recent breakthroughs in foreground subtraction of the hydrogen signal have prepared the state-of-the-art radio interferometry analysis for the incoming slew of over two petabytes of data in the coming months. [Preview Abstract] |
Saturday, May 3, 2014 4:42PM - 4:54PM |
G2.00012: The Axion Dark Matter Experiment Receiver Chain Lloyd Pasion The ADMX experiment is a search for axionic dark matter consisting primarily of a microwave cavity immersed in a strong magnetic field. Dark matter axions in the presence of the experiment's magnetic field should resonantly convert into detectable photons in the cavity. The expected power due to the conversion of dark matter axions is very small; to detect the signals above the background thermal noise, ADMX requires a specialized receiver. I will describe the ADMX receiver, tracing the signal path from the microwave cavity to data analysis. [Preview Abstract] |
Saturday, May 3, 2014 4:54PM - 5:06PM |
G2.00013: In-Situ Noise Temperature Characterization of a SQUID MSA in Axion Dark Matter Experiment (AMDX) Cliff Plesha Axions are hypothetical particles proposed to solve the strong CP problem and are also good candidates for cold dark matter. ADMX is an experiment directly searching for axion dark matter converting to photons in a microwave cavity. Superconducting Quantum Interference Device (SQUID) Micro-Strip Amplifiers (MSA) are a key component in the AMDX receiver chain because they introduce only quantum limited noise, maximizing sensitivity to axion signal. I will discuss how ADMX tunes a SQUID MSA to achieve optimum noise performance while in a high magnetic field. [Preview Abstract] |
Saturday, May 3, 2014 5:06PM - 5:18PM |
G2.00014: Josephson Junction Quantum Electronics and ADMX Katleiah Ramos Josephson junctions have numerous applications in quantum electronic devices. One specific application of Josephson junctions is used in the Axion Dark Matter eXperiment in the form of a highly sensitive SQUID microwave amplifier. I will review the basic physics of Josephson junctions as well as their characterization at both cryogenic and room temperatures. Preliminary data from Josephson foundry process developed at the Washington Nano-fabrication facility will be presented. [Preview Abstract] |
Saturday, May 3, 2014 5:18PM - 5:30PM |
G2.00015: Instrumentation and Thermal Design of the Axion Dark Matter Experiment (ADMX) Scott McCulloch The axion, a hypothetical elementary particle, may prove to be a component of cold dark matter in the universe. ADMX has been searching for this elementary particle through the conversion of axions into microwave photons in a resonant cavity within a high magnetic field. To maximize sensitivity to the axion signal, the cavity and associated electronics must be cooled to millikelvin temperatures. This talk will discuss the design and performance of the cryogenic system that meets ADMX's unique needs. [Preview Abstract] |
Saturday, May 3, 2014 5:30PM - 5:42PM |
G2.00016: Helium Recovery at the Axion Dark Matter Experiment Kelly Olsen ADMX (Axion Dark Matter eXperiment) is a search for the axion, an elementary particle first postulated to solve the strong CP problem and later realized to be a promising dark matter candidate. ADMX stimulates the resonant conversion of axions into detectable photons. However, because the expected power resulting from the conversion is so weak, sophisticated cryogenic electronics are necessary to amplify the signal and minimize thermal noise. The low temperature refrigeration and superconducting magnets require prodigious amounts of liquid helium. I will discuss the closed loop recovery and reliquefaction system that allows ADMX to continue operating at low temperatures with minimal helium loss. [Preview Abstract] |
Saturday, May 3, 2014 5:42PM - 5:54PM |
G2.00017: Searching for Higher Mass Dark Matter Axions Robert Percival Axions are a promising dark matter candidate with masses constrained to be roughly between a $\mu$eV and a meV. Experiments searching for axions with masses of 1-10 $\mu$eV using microwave cavities are already in operation. However, some models favor masses 40 $\mu$eV and above, where microwave cavity experiments face significant challenges. This mass range may be accessible with a series of wire planes placed inside an open resonator or Fabry-Perot etalon. I will describe a prototype of this technique searching for axions of approximately 70 $\mu$eV corresponding to cavity and receiver operating in the 17GHz range. [Preview Abstract] |
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