Bulletin of the American Physical Society
2015 Annual Meeting of the Far West Section of the APS
Thursday–Saturday, October 29–31, 2015; Long Beach, California
Session S1: Astrophysics |
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Chair: John Price, California State University, Dominguez-Hills Room: CBA-139A |
Saturday, October 31, 2015 2:00PM - 2:24PM |
S1.00001: Lest We Forget: Impact of the Great War on Physics & Astronomy Virginia Trimble For astronomers, World War I began with the capture and imprisonment of a German eclipse expedition that had gone to the Crimea in August 1914 to look for bending of starlight by the sun, at the request of Einstein himself, who had, in 1911, predicted a value of about 0.8 arcsec (at the limb), one half of what definitive GR would say in 1915-16. Over the next few years Schwarzschild wrote his spherically symmetric solution to Einstein's equation, then died of service-related pemphigus. Physicists developed telesite meters to determine distances and directions to artillery fire, submarines, and aircraft. Paul Merrill learned to sensitive photographic emulsions to red and IR photons, later employing such plate to discover Tc on stellar surfaces (the first incontrovertible evidence of nuclear reactions inside). And much else. The end came with the 1919 establishment of the International Astronomical Union and International Union of Pure & Applied Physics and with Eddington's eclipse expedition which really did see relativistic light bending by the sun. A few words will be said about how parallel presentation of scientific advances and world history can help to fix both in our and our students' minds. [Preview Abstract] |
Saturday, October 31, 2015 2:24PM - 2:36PM |
S1.00002: Constraining the Satellite Quenching Timescale at z $<$ 1.5 Maria Wimberly, Michael Cooper Despite remarkable success at modeling the evolution of massive galaxies over cosmic time, modern hydrodynamic and semi-analytic models of galaxy formation generally fail to reproduce the properties of low-mass galaxies. This shortcoming in our theoretical picture is largely driven by an inability to understand the physics of satellite (or "environmental") quenching. Using abundance matching prescriptions to populate large dissipationless N-body simulations, including the Bolshoi Simulation, we study the dependence of satellite properties on cluster-centric distance within massive host halos at z $<$ 1.5, focusing on the potential physical mechanisms that may be a play in suppressing star formation in the satellite population. Our results illustrate the potential power of ongoing cluster surveys, such as the multi-year GOGREEN Survey at the Gemini Observatories, to constrain the quenching timescale over more than half of cosmic time. [Preview Abstract] |
Saturday, October 31, 2015 2:36PM - 2:48PM |
S1.00003: Non-radial Modes of Oscillation in Neutron Stars and Quark Stars: Modes f, p and g. Jessica Asbell, Prashanth Jaikumar Efforts to determine the internal compositions of compact stars focus largely on the observation and interpretation of non-radial oscillations that occur when these bodies are perturbed in pressure, buoyancy and gravity. Future observations of these oscillations can distinguish between stars comprised of nuclear matter and possibly quark matter. This work presents a comparison of the f, p and g-mode spectra for both neutron and strange quark equations of state. In particular, g-modes, which result from fluctuations in buoyancy, are sensitive to convective gradients, as well as chemical and thermal inhomogeneities. The gmodes we study arise from buoyancy effects in the core and have frequencies of tens of Hertz. We find that the p-modes for quark matter are much higher in frequency (tens of kilohertz) than for neutron matter (few kilohertz). By exploring the MIT Bag model for quark matter we find that the average density and the f-mode, tracks linearly with the MIT bag constant. These results pave the way to model and understand the gravitational wave signals emitted by oscillating neutron or strange quark stars. [Preview Abstract] |
Saturday, October 31, 2015 2:48PM - 3:00PM |
S1.00004: Timing Measurements of Scintillator Bars with Silicon Phtotomultiplier Light Detectors Mark Shelor, Leonardo Elizondo, Stefan Riit To construct a cosmic ray tracker for precise measurements of particle airshower axes directions, we developed a prototype apparatus consisting of two 1 meter long scintillator bars. Each bar is embedded with green wavelength shifting fibers. At the two ends of the fibers are coupled silicon photomultipler (SiPM) light detectors to record the scintillation light produced from energetic cosmic rays. We did extensive evaluation for two makes of SiPM devices using this apparatus. Our detectors include devices from AdvanSiD and from Hamamatsu. We performed timing measurements for the scintillator bars using several trigger conditions. The trigger conditions included: coincidence trigger with 2 photomultiplier detectors and SiPM detectors in self triggered mode. The SiPM detector waveforms were digitized using a 4 channel fast waveform sampler, the DRS4 digitizer. The signals were analyzed with the CERN PAW package. From our results, we deduced the speed of light in the scintillator to be about 66{\%} of the speed light in vacuum. This is in accordance with the specifications of the index of refraction for the fibers given by the manufacturer's specifications. The results of our timing measurements would be presented. [Preview Abstract] |
Saturday, October 31, 2015 3:00PM - 3:12PM |
S1.00005: Constraints on Axions and Axion-like Particles from Fermi Large Area Telescope Observations of Neutron Stars Bijan Berenji, Jennifer Gaskins, Manuel Meyer We present constraints on the nature of axions and axion--like particles (ALPs) by analyzing gamma--ray data from neutron stars using the Fermi Large Area Telescope. In addition to axions solving the strong CP problem of particle physics, axions and ALPs are also possible dark matter candidates. We investigate axions and ALPs produced by nucleon--nucleon bremsstrahlung within neutron stars. We derive a phenomenological model for the gamma--ray spectrum arising from axion decays. By analyzing 5 years of gamma-ray data (between 60 MeV and 200 MeV) for a sample of 4 nearby neutron stars, we do not find evidence for an axion or ALP signal, thus we obtain a combined 95\% confidence level upper limit on the axion mass of 5.6$\times 10^{-2}$ eV, which corresponds to a lower limit for the Peccei-Quinn scale $f_a$ of 1.07$\times 10^8$ GeV. Our constraints are more stringent than previous results probing the same physical process, and are competitive with results probing axions and ALPs by different mechanisms. [Preview Abstract] |
Saturday, October 31, 2015 3:12PM - 3:24PM |
S1.00006: A Compact Cosmic Rey Telescope for use in High Schools and Colleges Luis Castro, Daniel Moquia, Stefan Ritt Trough 2 very successful outreach projects, the QuarkNet and the LBL Cosmic Ray Project, thousands of high school students and teachers learned about cosmic ray physics. To get students in the Salinas area interested and excited about cosmic ray physics, we constructed compact and cost effective cosmic ray telescope using silicon photomultipliers (SiPM) light detectors. Our apparatus consists of a cosmic ray scintillation detector module, fast preampefiers, 50 Ohm matching signal splitters and a coincidence logic circuit board. We designed costume circuit boards that form AND logic signals for triggering data acquisition devices. These devices could be, an oscilloscope, a wave form digitizer or an Arduino. To ensure proper routing of the signal traces, the circuit boards were laid out on Eagle and fabricated using an in-house circuit board maker from LPKF LASER. We carried out measurements to digitize the SiPM signal waveforms using a fast analog sampler, the DRS4 and controlled by a Raspberry Pi computer. Using the PAW data analysis software from CERN, we analyze the SiPM signal amplitudes and the time at the maximum amplitude. The results from out coincidence experiment, circuit fabrication procedure, and the data analysis work flow would be presented. [Preview Abstract] |
Saturday, October 31, 2015 3:24PM - 3:36PM |
S1.00007: Investigation of Very Fast Light Detectors: Silicon Photomultiplier and Micro PMT for a Cosmic Ray Array Omar Cervantes, Liliana Reyes, Tyler Hooks, Luis Perez, Stefan Ritt To construct a cosmic detector array using 4 scintillation detectors, we investigated 2 recent light sensor technologies from Hamamatsu, as possible readout detectors. First, we investigated several home-made versions of the multipixel photon counter (MPPC) light sensors. These detectors were either biased with internal or external high voltage power supplies. We made extensive measurements to confirm for the coincidence of the MPPC devices. Each sensor is coupled to a wavelength shifting fiber (WSF) that is embedded along a plastic scintillator sheet (30cmx60cmx1/4''). Using energetic cosmic rays, we evaluated several of these home-made detector modules placed above one another in a light proof enclosure. Next, we assembled 2 miniaturized micro photomultiplier (micro PMT), a device recently marketed by Hamamatsu. This sensors showed very fast response times. With 3 WSF embedded in scintillator sheets, we performed coincidence experiments. The detector waveforms were captured using the 5GS/sec domino ring sampler, the DRS4 and our work flow using the CERN PAW package and data analysis results would be presented. [Preview Abstract] |
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