Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session C8: Neutron Stars and Pulsars |
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Sponsoring Units: DAP Chair: Slavko Bogdanov, Columbia University Room: 202 |
Saturday, April 5, 2014 1:30PM - 1:42PM |
C8.00001: Neutron Star Equation of State Constraints from Pulsed X-ray Emission Sharon Morsink, Abigail Stevens, Jason Fiege, Denis Leahy The observation of pulsed X-ray emission originating from the surfaces of accreting rapidly rotating neutron stars combined with relativistic ray-tracing provides an excellent opportunity to study the properties of neutron stars and to constrain the equation of state of supernuclear density matter. I will review the basic principles behind this method, including the degeneracies inherent in the problem. We are applying a modern genetic algorithm to search for the best-fit masses and radii of the accreting ms period X-ray pulsars that produce X-ray bursts. I will discuss the application of this method to observations that could be performed by the proposed LOFT (Large Observatory for X-ray Timing) mission. [Preview Abstract] |
Saturday, April 5, 2014 1:42PM - 1:54PM |
C8.00002: Universal I-Love-Q and Multipole-Love Relations Kent Yagi, Nicolas Yunes One of largest uncertainties in nuclear physics is the equation of state (EoS) in nuclear and supra-nuclear densities. Neutron-star (NS) and quark-star (QS) observables such as the mass and radius depend strongly on the EoS. We find universal relations among the moment-of-inertia, quadrupole moment and various tidal deformabilities of a slowly-rotating NS and QS that are almost EoS-independent. Such unexpected relations have several interesting applications. On an observational astrophysical front, independent measurement of any two quantities automatically determines the others that are not easily accessible. On a gravitational-wave front, such relations allow us to break the degeneracy between the spins and quadrupole moment, or between various tidal deformabilities.On a fundamental physics front, any two independent measurements of the quantities allow for a model-independent and EoS-independent test of general relativity. [Preview Abstract] |
Saturday, April 5, 2014 1:54PM - 2:06PM |
C8.00003: Three-Hair Newtonian Relations for Rotating Stars Leo Stein, Kent Yagi, Nicolas Yunes Astrophysical black holes can be completely described by their mass and spin, as seen in the no-hair theorems. This was not expected to hold for stars because of their internal structure. We analytically find that arbitrarily-rapidly uniformly-rotating stars can still be completely described by only three numbers (mass, spin and quadrupole moment) in the Newtonian limit. Surprisingly, this description is approximately universal (independent of internal structure) for low multipole order, analytically confirming previous numerical results in full general relativity. [Preview Abstract] |
Saturday, April 5, 2014 2:06PM - 2:18PM |
C8.00004: Non-Spherical Stellar Models of Compact Stars Omair Zubairi, Fridolin Weber, Efrain Ferrer, Vivian Incera Conventionally, the structure of compact stellar objects such as neutron or quark stars are modeled with the assumption that they are perfect spheres. However, due to high magnetic fields, certain classes of compact stars (such as magnetars and neutron stars containing cores of color-superconducting quark matter) are expected to be deformed (non-spherical) making them ob-longed spheroids. In this work, we seek to investigate the stellar structure of these such deformed compact objects in the framework of general relativity. Using a metric that describes a non-spherical mass distribution, we derive the stellar structures equations of these non-spherical compact objects. Since we do not have spherical symmetry, we need to take into the account the pressure gradient not only in the radial but in the polar direction as well. We then calculate stellar properties such as mass and radii along with density and pressure profiles for neutron stars with high magnetic fields and investigate any changes from the standard spherical models. [Preview Abstract] |
Saturday, April 5, 2014 2:18PM - 2:30PM |
C8.00005: Nucleosynthesis in Neutron Stars Samina Masood We compute the rate of change in beta decay processes at extremely high densities of cores of neutron star. The rate of change in beta decay affects different type of nuclear processes which change the rate of synthesis of different elements in the core of star and have non-ignorable effects on the composition of stellar core. We estimate the changes in nucleosynthesis of stellar interior and relate it to the structural model of star and observational results. [Preview Abstract] |
Saturday, April 5, 2014 2:30PM - 2:42PM |
C8.00006: Thermal Conductivity of the Neutron Star Crust Abbar Sajad, Joseph Carlson, Huaiyu Duan, Sanjay Reddy Observations of neutron star crust cooling times after extended outbursts are very sensitive to the thermal conductivity of the neutron star crust. We calculate the thermal conductivity of neutron star crust at relatively low temperatures using static structure factor S(q) obtained from Quantum Monte Carlo (QMC) and one-phonon approximation. We investigate the importance of quantum effects on the static structure factor. We also compare QMC and the one-phonon approximation over a range of temperatures and show that the thermal conductivity can be calculated directly from S(q) obtained from QMC for temperatures larger than 0.3T$_{\mathrm{P\thinspace }}$where T$_{\mathrm{P\thinspace }}$is the plasma temperature. [Preview Abstract] |
Saturday, April 5, 2014 2:42PM - 2:54PM |
C8.00007: The Long Term Variability and X-ray Bursts of Cygnus X-2 Alan Smale, Patricia Boyd, Shaina Reisman The bright, persistent low-mass X-ray binary Cygnus X-2 is composed of a neutron star (NS) in a 9.8-day orbit with its late-type companion, V1341 Cyg. It is one of six bright Galactic sources that traces out a Z-curve on its color-color diagram on timescales of about a day, and one of only two of these Z-sources that also displays Type 1 X-ray bursts (explosive nuclear ignition events on the NS surface). On timescales of weeks to months, Cyg X-2 shows large-amplitude but non-periodic X-ray fluctuations that have been attributed to a warped accretion disk. The extensive archival data from NASA's Rossi X-ray Timing Explorer (1995-2012), including both pointed and all-sky monitor data, allow us to study the long-term variability, spectral behavior, and burst behavior of the source in unprecedented detail. We have investigated 575 PCA datasets totaling over 2.2 Msec of data spread over the lifetime of the RXTE mission, and have detected 61 Type I bursts. Here we present early results of a spectral analysis of these bursts to determine whether properties such as the duration, peak flux level, or spectral parameters of the bursts are correlated with source properties such as time-averaged flux or instantaneous intensity and position on the Z-diagram. [Preview Abstract] |
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