Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the Texas Sections of the APS, AAPT, Zone 13 of SPS and the National Society of Hispanic Physicists
Volume 55, Number 11
Thursday–Saturday, October 21–23, 2010; San Antonio, Texas
Session SM2: Astrophysics, Astronomy, Space Science III |
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Chair: Eric Schlegel, University of Texas at San Antonio Room: University Center III Bexar Room, 1st floor |
Saturday, October 23, 2010 10:00AM - 10:12AM |
SM2.00001: Determining geoeffective length from LFM simulation Elijah Murphy, Shree Bhattarai, Ramon Lopez The orientation of Interplanetary Magnetic Field (IMF) plays an important role in Space weather prediction. The process in which Earth's magnetic field interacts with IMF is called magnetic reconnection. The amount of reconnection determines the amount of energy transfer from the solar wind to Earth. For a given orientation of the IMF there exist effective length out in the solar wind, perpendicular to both the IMF and the Sun-Earth line, over which the solar wind flow is able to reach the reconnection region. This controls the rate at which the magnetic flux is merged and therefore the voltage imposed on the magnetosphere-ionosphere system. This length is called the geoeffective length. We present a method for determining geoeffective length from simulations of the solar wind magnetosphere interaction obtained from the Lyon-Fedder-Mobarry (LFM) code. [Preview Abstract] |
Saturday, October 23, 2010 10:12AM - 10:24AM |
SM2.00002: TWINS Stereo Images of the Three-Dimensional Ring Current During Geomagnetic Storms in the Rising Phase of Solar Cycle 24 Jerry Goldstein, David McComas Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is the first stereoscopic magnetospheric imaging mission. In operation since June 2008, the TWINS observatory performs simultaneous Energetic Neutral Atom (ENA) imaging from two widely-separated Molniya orbits on two separate spacecraft. TWINS global, stereo imaging of magnetospheric ENAs provides a dynamic monitor of fundamental processes of energetic particle physics in geospace. The TWINS prime mission (2008--2010) saw extremely quiet conditions associated with the unprecedented, extended minimum of solar cycle 23. The recent emergence into the rising phase of solar cycle 24 has witnessed geospace as it responds to an evolving balance in Sun and solar wind drivers not seen before in the space age. Through stereo imaging, TWINS measures the anisotropy in ENA emissions that can be used to infer the 3D parent ion distribution. For several rising-phase storms, the TWINS-observed spatial dependence of ENA intensity is characterized in terms of the viewing geometry relative to the magnetic field in the ENA source region. This characterization is used to determine the relationship between the ENA emission anisotropy and the global pitch angle distribution of the parent ions (both trapped and precipitating). [Preview Abstract] |
Saturday, October 23, 2010 10:24AM - 10:36AM |
SM2.00003: Applying Empirical Magnetopause Prediction to Results Obtained from MHD Simulations Kevin Pham, Robert Bruntz, Ramon Lopez One unresolved issue with the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamics (MHD) simulation is which ionospheric conductivity best fits with real data. The boundary between the Earth's magnetic field and the surrounding solar wind plasma is known as the magnetopause. The location of the magnetopause as a function of interplanetary magnetic field has previously been empirically determined. Using this empirical magnetopause fit, we superimposed the magnetopause prediction onto various LFM simulations. The LFM simulations are run with a constant ionospheric conductivity of 5mhos and 10mhos. By normalizing the subsolar point of the magnetopause fit to the subsolar point in the LFM simulation, we have found that the magnetopause fit aligns better with the 10mhos than the 5mhos simulations. This provides additional evidence that the real ionospheric conductivity is closer to 10mhos. [Preview Abstract] |
Saturday, October 23, 2010 10:36AM - 10:48AM |
SM2.00004: Sawtooth Oscillations and Helicity of Magnetic Clouds John Petersen When an interplanetary magnetic field (IMF) running north-south encounters the Earth's south-north magnetic field, magnetic reconnection occurs, and solar wind plasma is injected through the resulting gap in the magnetosphere. This process, known as a geomagnetic storm, can have substorms with different characteristics. One such substorm is a sawtooth event or sawtooth oscillation. These quasi-periodic oscillations are caused by a specific type of IMF called a magnetic cloud. It is postulated herein that the helical structure of magnetic clouds as they are incident upon the magnetosphere is the root of the quasi-periodicity. Furthermore, a simple calculation (H = 1/vt) can predict the helicity of the magnetic cloud, within the statistically accepted range, using the periodicity of the sawtooth oscillation and the velocity of the magnetic cloud for t and v, respectively. [Preview Abstract] |
Saturday, October 23, 2010 10:48AM - 11:00AM |
SM2.00005: Time delay between IMF changes and the response of the nightside geosynchronous magnetic field Dustin Brewer, Robert Bruntz, Ramon Lopez The interplanetary magnetic field, or IMF, is the Sun's magnetic field which is carried to the Earth via the solar wind. Some models predict that there will be a difference in how quickly Earth's magnetic field responds to changes in the solar wind, depending on the strength of the IMF. In order to investigate the timing delay, we have found sudden, high-magnitude reversals in the north-south component of the IMF, using the OMNI database. We then observed the delay between the change in the IMF and the change in Earth's magnetic field in the midnight sector using GOES satellites in geosynchronous orbit. We will report the magnitude of the delay between IMF changes and corresponding changes in the nightside magnetic field of the Earth, as well as the correlation between the delay and the magnitude of the IMF. [Preview Abstract] |
Saturday, October 23, 2010 11:00AM - 11:12AM |
SM2.00006: Variations in the Polar Cap Boundary Location Based on Solar Wind Parameters Robert Allen, Sophia Cockrell, Bethany Hiller, Perla Gonzalez, Ramon E. Lopez The Earth's magnetic field is a dipole with field lines coming out from the southern hemisphere and into the northern hemisphere. When the interplanetary magnetic field (IMF) is pointed southward, the Earth's magnetic field becomes interconnected with the IMF. The boundary that separates the region of field lines that are connected to the Earth at both ends and the region of field lines that are connected to both the Earth and the IMF is called the polar cap boundary. We can detect the polar cap boundary using particle precipitation measurements from the Defense Meteorological Satellite Program (DMSP) satellite F13. The DMSP satellite F13 has approximately a 104 minute polar orbit that makes roughly dusk-dawn passes. We will investigate the variation of the polar cap boundary's location based on solar wind parameters. [Preview Abstract] |
Saturday, October 23, 2010 11:12AM - 11:24AM |
SM2.00007: The nuclear symmetry energy dependence of the nuclear ``pasta'' phases in the inner crust of neutron stars Michael Gearheart Neutron stars are the end point of the evolution of a star with between about 8 and 25 solar masses. The star's core collapses to form an object with about 1.5 times the mass of our Sun and a radius of only 10km. The average density of matter in a neutron star is comparable with that of the nuclei of atoms, making them interesting probes of nuclear physics in a regime inaccessible to terrestrial experiments. We present a study of the inner crust of neutron stars, a region of the star between 0.5km and 1km in depth where super-heavy neutron rich nuclei arranged in a lattice co-exist with a gas of neutrons. Near the transition from the inner crust to the core of the star, the nuclei are expected to assume exotic shapes such as cylinders and slabs, referred to collectively as nuclear `pasta'. Using a compressible liquid drop model and a variety of different descriptions of the nucleon-nucleon interaction, we examine the composition and shape of nuclei at different depths in the inner crust up to the point where the nuclei dissolve into a uniform fluid of neutrons, protons and electrons. We examine the dependence of the densities at which nuclear shape transitions through various forms of the surface energy using experimentally measurable properties of nuclear matter such as the nuclear symmetry energy, comparing our results with that of measured nuclei masses. [Preview Abstract] |
Saturday, October 23, 2010 11:24AM - 11:36AM |
SM2.00008: Distribution of Carbon and Sulfur in the Crab Nebula Andrea Katz, Gordon MacAlpine Chemical elements heavier than hydrogen and helium are made in stars, and investigations of the Crab Nebula supernova remnant provide excellent opportunities for understanding how stars make elements through nucleosynthesis processing and distribute them explosively. Carbon and sulfur are particularly important in this regard, because they are tracers of where helium and oxygen nuclear fusion have taken place. During the past year, we obtained and calibrated [CI] $\lambda \lambda $9823, 9850 and [SIII] $\lambda $9069 emission-line images of the Crab Nebula, using appropriate filters at the 1.3-meter telescope of the Michigan-Dartmouth-MIT Observatory located on Kitt Peak in Arizona. Then we combined the emission-line flux distributions with a suite of more than 1000 numerical photoionization computations in order to map the actual carbon and sulfur abundances over the observed nebular structure. The results and implications for nuclear processing and distribution will be discussed. [Preview Abstract] |
Saturday, October 23, 2010 11:36AM - 11:48AM |
SM2.00009: Investigate the magnitude of gravitational wave due to quark-hyperon-transition during inside the neutron star Weikang Lin, Bao-An Li In the next decade, it is hopeful to be able to detect gravitational waves. The detection of gravitational wave provides us a new way to investigate our universe or even the microscopic world, the nuclear matter for example. There is strong relation between the gravitational waves and the state of matter inside the neutron stars. Extreme environment might appear inside the neutron stars. Hyperons or even a transition from hadrons to quark matter might be presented. A hyperons-Quark transition might by a low mass neutron star acreting mass from its companion in an X-ray binary, or by spinning down and increasing the density at its central. We investigated the maximum energy available for stochastic gravitational waves generated by neutron stars through oscillations coupling with rotations during a phase transition from hadron matter to deconfined quark-gluon matter in the core of them. The energy difference, between the configurations with and without a quark-gluon matter core, is used to estimate the maximum available energy. The properties of neutron stars were computed using isospin- and momentum-dependent MDI interaction and MIT model. Our results indicate the available energy is not large enough to reach the present detectable interest. However, the results show that the available energy depends on the different bag constants and symmetry energies. [Preview Abstract] |
Saturday, October 23, 2010 11:48AM - 12:00PM |
SM2.00010: The Segmented Universe: Identifying Cosmic Voids with a Multi-scale Geometric Flow Andrew Miller, Ali Snedden, Lara Arielle Phillips The complex, filamentary nature of large-scale dark matter and density structure in the universe has been detected by redshift surveys and modeled by large N-body simulations of cosmic evolution. We present a multi-scale geometric flow algorithm as a quantitative method for the analysis of such structure. The algorithm, adapted from medical imaging identification of brain vasculature, segments a volumetric density field according measures of local structure derived from local curvature, identifying vessel-like, sheet-like, and clump-like formations. We apply this structure segmentation to a cold dark matter (CDM) density field prepared from the Virgo Consortium's 2005 Millennium Simulation (MS) output, focusing on identification of regions of cosmic void to determine the robustness of this segmentation method through a systematic comparison of its results with those of previously published void-finding algorithms. The initial results of our application of this segmentation algorithm and the data pipeline used will be presented. [Preview Abstract] |
Saturday, October 23, 2010 12:00PM - 12:12PM |
SM2.00011: Mapping Class I Methanol Masers in the DR21 Region Talitha Muehlbrad, V. Fish, P. Pratap, L.O. Sjouwerman, V. Strelnitski, Y.M. Pihlstrom, T.L. Bourke Class I methanol masers are believed to be produced in the shock-excited environment around star-forming regions and are believed to be indicative of stages of star formation or excitation conditions. We report on the first EVLA observations of the 36-GHz methanol masers as well as on Submillimeter Array observations of the 229-GHz methanol masers in DR21OH, DR21N, and DR21W. The data are compared to existing Class I methanol data in other transitions in each region. In the outflow of DR21OH, the distribution of the 36-GHz masers is similar to that of the other transitions. At the main continuum source in this region, the 36- and 229-GHz masers virtually overlap with the Class II 6.7-GHz masers. To the south of the region, 36-GHz masers are scattered with 44-GHz masers, but the two transitions do not appear coincident. A magnetic field of 58.1$\pm $6.2 mG is detected in DR21W. If this magnetic field is related to the density with usual scaling, the resultant high density may be indicative of an alternative pumping scheme than that commonly assumed for Class I masers. [Preview Abstract] |
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