Bulletin of the American Physical Society
2015 Annual Meeting of the APS Mid-Atlantic Section
Volume 60, Number 14
Friday–Sunday, October 23–25, 2015; Morgantown, West Virginia
Session A7: Astrophysics I |
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Chair: Jeff Peterson, Carnagie Mellon University Room: Waterfront Hotel Salon G |
Saturday, October 24, 2015 10:30AM - 11:06AM |
A7.00001: The CMB and Neutrinos Invited Speaker: Lyman Page The standard model of cosmology has passed many stringent tests and its basic parameters have been tightly constrained. The model is now so well established that we may use it as a foundation to address such questions as "What is the sum of the neutrino masses?" and "How many neutrino-like species are there?" We review the status of observations and recent results. We also present what we might hope to learn in the next half decade of observations. [Preview Abstract] |
Saturday, October 24, 2015 11:06AM - 11:42AM |
A7.00002: High-Precision Pulsar Timing and the Search for Nanohertz Gravitational Waves Invited Speaker: David Nice The NANOGrav collaboration makes high-precision radio telescope observations of an array of millisecond pulsars with the goal of detecting gravitational waves in the nanohertz band, i.e., gravitational waves with periods of several years. Gravitational waves will be detected via small perturbations in measured pulse arrival times correlated across the pulsars in the array. We use the Green Bank Telescope and Arecibo Observatory to observe 49 millisecond pulsars at intervals of three to four weeks. Arrival time measurement accuracy for individual pulsars ranges from 50 ns to 1 $\mu$s (daily post-fit RMS). Observations are made over wide bands with two receivers at each telescope to aid in mitigating interstellar dispersion. In this talk we will present an overview of the pulsar timing array technique for detecting gravitational waves; summarize the NANOGrav observing program; describe our most recent data release, the NANOGrav nine-year data set; discuss upper limits on gravitational wave from our data, along with astrophysical implications; and describe some ancillary astrophysics that is being accomplished with the NANOGrav data. [Preview Abstract] |
Saturday, October 24, 2015 11:42AM - 11:54AM |
A7.00003: DIRECT COSMIC-RAY MEASUREMENTS WITH CREAM AND ISS-CREAM Sai Im Cosmic ray science has evolved since its earliest forays into the stratosphere with particle detectors flown on hydrogen balloons over 100 years ago. There has been significant recent progress in elucidating the mechanisms by which galactic cosmic rays accelerate and propagate. I will discuss one ongoing endeavor to measure the individual fluxes and energies of cosmic ray species with elemental resolution, the cosmic ray energetics and mass (CREAM) program. This is a series of nasa-supported long-duration balloon flights over antarctica since 2004. I will also cover ISS-CREAM, the next generation of cream on the international space station, planned for launch in 2016 by spacex rocket. I will describe the design and status of the instrument, and in particular the new boronated scintillator detector, which permits the identification of cosmic-ray electrons and thus augments the science program of the ISS-CREAM mission. [Preview Abstract] |
Saturday, October 24, 2015 11:54AM - 12:06PM |
A7.00004: A ground parameter for energy reconstruction of gamma rays with the HAWC Observatory Kelly Malone Measuring the energy spectra of sources up to 100 TeV is critical to understanding the nature of cosmic accelerators. The High Altitude Water Cherenkov (HAWC) Observatory, located at an altitude of 4100m near Pico de Orizaba in Mexico, was designed to observe TeV gamma rays from air showers. It consists of a large array of 300 water Cherenkov detectors, each of which is equipped with 4 PMTs. On an event-by-event basis, measuring the energy density at some optimum distance from the air shower axis can be used to determine the energy of the primary gamma ray. I will present this method for reconstructing energy based on the determination of the lateral distribution function. This method greatly improves upon the current energy estimation technique employed by the HAWC Collaboration. The improvement is especially remarkable at energies above 10 TeV. [Preview Abstract] |
Saturday, October 24, 2015 12:06PM - 12:18PM |
A7.00005: USING CALIBRATION INFORMATION TO CHARACTERIZE DETECTOR AGING AT THE PIERRE AUGER OBSERVATORY Alan Coleman The Pierre Auger Observatory is an ultra high energy cosmic ray detector in Mendoza, Argentina which has been taking data since 2004. It is comprised of both fluorescence detectors and ground-based water cherenkov detectors (WCDS). As the WCDS age, the properties of the measured signals change as a function of time, due to effects such as changes in liner reflectivity and water absorption. a number of simulations to anticipate WCD performance with time indicates that the detector calibration information can be used to quantify this effect. A new method of WCD calibration has been devised for the Pierre Auger Observatory in order to characterize the detectors' aging. [Preview Abstract] |
Saturday, October 24, 2015 12:18PM - 12:30PM |
A7.00006: Science with a Complete Catalog of Galactic HII Regions Loren Anderson HII regions are the ionized gas spheres that surround high mass stars larger than about 10 times the mass of the Sun. Such stars are enormously luminous, but are rare compared to lower mass stars. HII regions are found almost exclusively in spiral arms and are short-lived; they reveal the locations of high mass star formation in the present epoch. The high luminosities of massive stars in turn allow us to detect the emission from HII regions across the entire Galactic disk. They are one of the only objects for which we can create a complete Galactic sample. In this talk I will describe the creation of our sample of Galactic HII regions using data from the WISE satellite and our followup radio observations. I will also describe our recent work on Galactic structure and the Galactic star formation rate. [Preview Abstract] |
Saturday, October 24, 2015 12:30PM - 12:42PM |
A7.00007: The C($^{\mathrm{3}}$P) $+$ NH$_{\mathrm{3}}$ reaction in interstellar chemistry. Fabien Goulay, Jeremy Bourgalais, Michael Capron, Ranjith Kailasanathan, David Osborn, Kevin Hickson, Jean-Christophe Loison, Valentine Wakelam, Sebastien Le Picard The kinetics and product formation channels of ground state carbon atoms, C($^{\mathrm{3}}$P), reacting with ammonia, NH$_{\mathrm{3}}$, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C $+$ NH$_{\mathrm{3}}$ reaction. In addition, C($^{\mathrm{3}}$P) decay and H-atom formation are monitored by laser induced fluorescence from room temperature to 50 K in a supersonic gas flow. The combination of experiments supported by theoretical calculations indicates that in the temperature and pressure range investigated, the H $+$ H$_{\mathrm{2}}$CN production channel represents 100{\%} of the product yield for this reaction. The effects of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are discussed. [Preview Abstract] |
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