Bulletin of the American Physical Society
80th Annual Meeting of the APS Southeastern Section
Volume 58, Number 17
Wednesday–Saturday, November 20–23, 2013; Bowling Green, Kentucky
Session BA: Astrophysics |
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Chair: Rebecca Surman, Union College Room: Ballroom A |
Thursday, November 21, 2013 8:30AM - 8:42AM |
BA.00001: A search for enhanced very-high-energy gamma-ray emission during the March 2013 Crab Nebula flare Greg Richards In March 2013, a flaring episode from the Crab Nebula lasting $\sim$2 weeks was detected by the Fermi-LAT (Large Area Telescope on board the Fermi Gamma-ray Space Telescope). VERITAS provides simultaneous observations throughout this period. During the flare, the Fermi-LAT detected a 20-fold increase in the synchrotron flux above 100 MeV from the Crab Nebula. Simultaneous measurements with VERITAS are consistent with the non-variable long-term average Crab Nebula flux at TeV energies. Assuming a linear correlation between the very-high-energy flux change $>$ 1 TeV and the flux change seen in the Fermi-LAT band $>$ 100 MeV during the period of simultaneous observations, the linear correlation factor can be constrained to be at most 8.6 $\times$ 10$^{-3}$ with 95\% confidence. The VERITAS observations are put in context with models that attempt to explain the nature of the observed flares. [Preview Abstract] |
Thursday, November 21, 2013 8:42AM - 8:54AM |
BA.00002: ``Flickering'' found in Sagittarius B2 Star-forming region Ashley Monsrud, Chris Depree, Jasmyn Heathe Ultracompact HII regions are dense areas of ionized gas within the galaxy in which massive star formation takes place. Based on simulation models, it is thought that these regions vary in brightness, commonly known as ``flickering,'' as they evolve. By using radio interferometry and radio imaging with the Very Large Array, we compared two images taken 23 years apart, the first image was taken in 1989 and the second in 2012, of the star-forming region Sagittarius B2, in order to detect any flux variations in the sources. By using the continuum and recombination line data our team of researchers has the ability to identify these flux variations in the ultracompact and hypercompact sources. In order to have a significant flux variance, we calculated that the integrated flux has to be ten percent or greater than the flux calculated in the 1989 data. After all of the calculations were made, sources F2 and F3 are the two sources in the Sagittarius B2 region that met the qualifications in order to have a significant change in both peak flux density and integrated flux. The total changes in peak flux density are 1.032 and .876 and differences in integrated flux density are .1483 and -0.105 for F2 and F3 respectively. The F2 and F3 sources changed by 77{\%} and 10{\%} in integrated flux difference respectively. This concludes that two out of our twenty-five HC regions are detected to have what we consider to be a significant change. [Preview Abstract] |
Thursday, November 21, 2013 8:54AM - 9:06AM |
BA.00003: ABSTRACT WITHDRAWN |
Thursday, November 21, 2013 9:06AM - 9:18AM |
BA.00004: A Survey of Hidden Molecular Clouds in the Milky Way James Hughes, Steven Gibson It is critical to understand the internal processes of galaxies, such as star formation, which occurs in the coldest, densest interstellar clouds. Unlike stars, these clouds are difficult to detect in visible light, but radio and infrared telescopes allow observations of the gas and dust particles they contain. In regions of the galaxy, ambient neutral atomic hydrogen gas is forming molecules, a sign of condensing clouds. We are interested in these clouds as precursors to stellar evolution where molecular hydrogen is critical. However, it is difficult to observe molecular hydrogen directly. Thus, proxy detectors such as carbon monoxide (CO) are used as indicators of molecular hydrogen. This method is not flawless. Through a comparative study, we propose substantial dark molecular hydrogen is not detected with current methods. We use far-infrared dust emission measurements from the IRAS and the Planck satellites for two independent measures of total column density. We trace visible gas column density using radio 21-cm hydrogen emission from Arecibo and 3-mm CO data from multiple surveys. Without dark gas, the dust and visible gas column densities should be equivalent. As this is not the case, there is evidence for dark molecular hydrogen overlooked in standard observations. [Preview Abstract] |
Thursday, November 21, 2013 9:18AM - 9:30AM |
BA.00005: Break
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Thursday, November 21, 2013 9:30AM - 9:42AM |
BA.00006: A Multi-wavelength Analysis of Cold Evolving Interstellar Clouds Mary Spraggs, Steven Gibson Since galaxies are essential parts of the universe's structure, it is important to understand their inner workings, including star formation and related processes in the interstellar medium (ISM). The ISM is made up of atomic and molecular gas, mostly hydrogen, with a small amount of other elements and solid dust particles.~ Interstellar gas is found with a wide range of temperatures and densities, but only the coldest, densest clouds can undergo gravitational collapse to form new stars. The manner in which such clouds condense out of warmer, more tenuous material is not understood but may follow a phase transition from atomic to molecular hydrogen. We have assembled a large data set of atomic and molecular spectral line image cubes and infrared dust maps to track this phase transition and any corresponding changes in gas temperature, density, and related properties in different parts of our own Galaxy. We will present an overview of our technique and preliminary results from the analysis. [Preview Abstract] |
Thursday, November 21, 2013 9:42AM - 9:54AM |
BA.00007: Entropy of the Black Hole Universe Amelia Allen, Tianxi Zhang This project aimed to determine the entropy of the black hole universe and the entropy of the cosmic microwave background and to compare these calculations to observations of the universe. The black hole universe model was proposed by Dr. Zhang in an earlier paper. Black hole universe entropy was calculated and graphed as a function of mass and compared to the entropy of an object forming a black hole of that mass. The graph showed a direct relationship between mass and black hole universe entropy and that black hole entropy is greater than the entropy of objects forming the black hole. Black hole universe entropy was graphed as a function of density, which showed an inverse relationship between entropy and universe density. Both of these graphs are consistent with observations of the universe and with the Second Law of Thermodynamics. Cosmic microwave background (CMB) entropy was calculated and graphed as a function of temperature, showing an inverse relationship as expected. CMB entropy graphed as a function of radius showed a direct relationship, which agrees with observations of the universe. These results show that the black hole universe theory is consistent with existing laws of physics and observations of the universe. [Preview Abstract] |
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