Bulletin of the American Physical Society
18th Annual Meeting of the APS Northwest Section,
Volume 62, Number 7
Thursday–Saturday, June 1–3, 2017; Forest Grove, Oregon
Session C2: Astrophysics & Gravity |
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Room: Prince Hall 202 |
Friday, June 2, 2017 1:30PM - 2:05PM |
C2.00001: Gravitational coupling in protostellar star-disk models including computationally resolved stars Invited Speaker: Kathryn Hadley We find that gravitational coupling between modes inherent in a computationally resolved protostar and its surrounding disk can significantly alter evolution of the disk. Typical hydrodynamic calculations of star-disk systems treat the star as a point mass. Our linear, quasi-linear and nonlinear hydrodynamic calculations were performed on fully self-gravitating systems including a star with spatial extent, enabling multipole gravitational coupling between the star and disk. Model sequences were calculated for stars with \textit{increasing flatness} for uniformly rotating (UR) and differentially rotating (DR) stars. Slowly rotating UR stars did not exhibit large effects due to multipole coupling. Our flattest DR stars, however, fell well above the dynamic barlike mode instability threshold for Maclaurin spheroids. Coupling between the star and disk produced qualitative changes, with disks supporting smoothly winding arms uncharacteristic of models with more spherical stars. Monopole coupling drives one-armed modes in both the point star and resolved star models. In the nonlinear simulation, flattening in the star caused redistribution of angular momentum, leading to significant mass-shedding from the star onto the disk, an effect not seen in the point star case.\\ \\In collaboration with: James Imamura, Willis Rogers and Attila Varga, Oregon State University [Preview Abstract] |
Friday, June 2, 2017 2:05PM - 2:17PM |
C2.00002: Non-Axisymmetric Instabilities in Circumbinary Disks: Giant Planet Formation Rebecka Tumblin, James Imamura, William Dumas, Kathryn Hadley, Erik Keever Gravitational instabilities (GIs) in protoplanetary disks are a proposed mechanism of forming gas giants on timescales associated with the orbital period in the disk. Protoplanetary disks in the pre-T-Tauri phase of disk evolution are expected to be weakly ionized, massive, and relatively cool; conditions under which disk self-gravity is expected to play a large role in stellar and planetary evolution. Recent discoveries of binary and multiple star systems harboring planets could provide constraints on planet formation mechanisms because the tidal potential produced by orbiting binaries is expected to enhance GIs in protoplanetary disks by setting up a periodic forcing potential. We perform 3D grid-based hydrodynamic simulations of circumbinary disks using the radiative hydrodynamics code CHYMERA to test the viability of the disk instability model of Jovian planet formation. We model two systems previously studied without a binary companion, one subject to an m=1 mode and one subject to a j-mode to understand the effects of binarity on which unstable eigenmode dominates the evolution of the system. We find that for the m=1 mode, binarity suppresses instability, and for the j-mode, prompt fragmentation occurs on the orbital period of the disk. [Preview Abstract] |
Friday, June 2, 2017 2:17PM - 2:29PM |
C2.00003: Using Higher Order Statistics to Find Instances of Nonlinear Couplings in LIGO Data Bernard Hall Previously, we have worked on developing a robust tool to analyze digital signals using higher order statistics, specifically, bicoherence. This method differs from other more commonly employed linear methods of signal analysis, such as coherence or autocoherence, in that it is able to see characteristics of data that the former methods are unable to detect conclusively. In particular, quadratic phase coupling--in which two signals may combine nonlinearly to create sidebands and some additional frequencies--can be detected with the bicoherence statistic. In contrast, such a relationship cannot be confirmed with, for example, coherence, or by looking at a power spectrum.Once our tool was able to successfully function on test data, we then incorporated it into the analysis of real data from the LIGO interferometers. We have been able to scan large stretches of data, revealing a number of transient nonlinear features. Such a study has provided an additional dimension of understanding of LIGO data, as we emerge into the era of gravitational wave astronomy. [Preview Abstract] |
Friday, June 2, 2017 2:29PM - 2:41PM |
C2.00004: A fast sky scanner for compact binary sources of gravitational waves William Dupree, Sukanta Bose We develop a geometric optimization method to speed up the coherent search in the sky for compact binary sources of gravitational waves (GWs) in multi-detector data. Currently, a metric-based sky grid is used over the region of interest in the sky to perform this search. This method, however, does not use the fact that the coherent statistic is a convex function in the sky, which allows reduction in the number of compute operations by more than a factor ~3. We demonstrate this computational efficiency in simulated data for the three-detector network comprising LIGO-Hanford, LIGO-Livingston and Virgo. Our method may help speed up electromagnetic follow-ups of GW candidates. [Preview Abstract] |
Friday, June 2, 2017 2:41PM - 2:53PM |
C2.00005: Physical Constants and Computational limits duality (Estakhr's Principle of Physical Constants) Ahmad Reza Estakhr Physical Constants-Computational limits duality. A physical constant, sometimes fundamental physical constant, is a physical quantity that is generally believed to be both universal in nature and having constant value in time. Computational limits are physical and practical limits to the amount of computation or data storage that can be performed with a given amount of mass, volume, or energy Estakhr's Principle of Physical Constants states that Physical Constants (such as G,h,c, ...etc) are Computational limitsŲ and it is impossible for a physical computer to compute out of the range of these limits (the range of physical constants), because they are 'unbreakable limits'. Physical Constants are limits to computation of Universe after the Big Bang (If the Big Bang gave birth to the universe). Physical constants are limits to the amount of computation or data storage that can be performed. Estakhr's principle also explains the values of all fundamental physical constants: 'Fundamental Physical Constants takes their values from Computational limits of universe'. [Preview Abstract] |
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