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Compact Stars: structure, dynamics, and gravitational waves
Abstracts and presentations (22 Jul 2005)

Here you will find abstracts and presentation files of talks given by the workshop participants. Enjoy!

Modelling dissipative superfluid neutron stars
Michał BEJGER (ppt file: 219kb) (pdf file: 952kb)
Neutron star core-quakes caused by a transition to the mixed-phase EOS
Calculations describing the changes in the neutron star parameters caused by the first-order phase transition, and resulting in the formation of a mixed-phase core are presented. The formulae for the changes in radius, moment of inertia and the amount of energy released during the core-quake are derived by means of the linear response theory, both for realistic and polytropic equations of state.
Tomek BULIK (ppt file: 4.0mb)
Binary population synthesis implications for gravitational wave sources
Binary population synthesis is a tool to investigate the expected properties of compact object (black hole, neutron star) binaries. I will review the implications of population synthesis studies, for the binary coalescence rates, as well as properties of the merging objects to be seen in gravitational waves.
Brandon CARTER
Effect of BCS pairing on superfluid neutron current in starcrust
It will be shown how superfluid pairing stabilises the current against resistive dissipation while making little difference to the effective mass enhancement due to entrainment.
Nicolas CHAMEL
Entrainment in neutron star crust
The two fluid model of neutron star outer core is extended to describe the inner crust which is immersed in a neutron superfluid. Drawing the analogy with conduction electrons in ordinary solids, the entrainment coefficients are found to arise from Bragg scattering of dripped neutrons upon crustal nuclei. Adapting band theory to this nuclear context, the neutron superfluid is found to be strongly coupled to the crust in the middle layers.
Dorota GONDEK-ROSIŃSKA (pdf file: 746kb)
Binary neutron stars as sources of gravitational waves
Coalescing neutron star binaries are expected to be among the strongest sources of gravitational radiation to be seen by laser interferometers. I will present the results of our studies of relativistic quasiequilibrium sequences of close binary systems composed of neutron stars described by realistic equation of states. I will focus on characteristic features in the waveform that will help to distinguish between different models of dense nuclear matter. The calculation are done for different mass ratios of neutron stars taking into account both the properties of the known double neutron star binaries and recent results obtained by using the well tested StarTrack binary population synthesis code.
Eric GOURGOULHON (pdf file: 749kb)
A new formulation for evolving neutron star spacetimes
Suprathermal radial pulsations of non-superfluid neutron stars.
The damping of neutron star radial pulsations due to non-equilibrium Urca processes is studied for a simple model of a star with core composed of neutrons, protons, and electrons. Special attention is paid to suprathermal regime of pulsations for which: |μn - μp - μe| > T, where μn, μp, and μeare the chemical potentials of neutrons, protons, and electrons, respectively; T is the stellar temperature. It is shown that in this case simultaneous account of thermal balance equation and the equation describing damping of the radial modes is required. A set of "self-consistent" solutions of these equationsis numerically obtained in the isothermal approximation for a star with forbidden direct Urca process. The dissipation mechanisms taken into consideration are viscous dampingdue to modified Urca process and shear viscosity in the core. It is demonstrated that radial pulsations can substantially influence the neutron star cooling on a time scale of the order of 1000 years.
Oscillating torii and kHz QPOs
Recent progress in understanding non-linear oscillations in accretion disks will be reviewed. The highest frequency quasi-periodic oscillations observed in Galactic black-holeX-ray sources can be understood as incompressible vertical oscillations of a torus whose X-ray emission is lensed at the source.
Francois LIMOUSIN (pdf file: 321kb)
Initial data for coalescing binary strange stars in general relativity
Inspiraling compact binaries are expected to be among the strongest sources of gravitational waves for VIRGO, LIGO and other laser interferometers. I will present the first relativistic calculations of the final phase of inspiral of binary strange quark stars. We studied the precoalescing stage in the conformal flatness approximation of general relativity using a multidomain spectral method. The hydrodynamical treatment is performed under the assumption that the flow is either rigidly rotating or irrotational. In each of theses cases, I will show the difference in the gravitational waves signal from neutron stars described by polytropic equation of state.
Lap-Ming LIN (pdf file: 300kb)
Numerical Study of Nonlinear R-modes in Neutron Stars
R-modes of rotating neutron stars are unstable growing modes driven by the back reaction of the gravitational radiation the modes themselves emit. The discovery of the r-mode instability has attracted much attention due to its possible implication on the spin rates ofneutron stars; and the possibility of being a promising source of gravitational waves detectable by advanced gravitational wave detectors. However, whether this instability is astrophysically relevant or not depends critically on how large the r-mode amplitude can grow up to. In this talk, we will present our fully nonlinear neutron star simulation and show that a large amplitude r-mode will couple nonlinearly to other fluid modes in a way that leads to a catastrophic decay of the r-mode. We identify the mode-coupling mechanism responsible for this decay. The limit this mechanism imposes on ther-mode amplitude is studied.
Adam SZMAGLIŃSKI (ppt file: 830kb)
Behaviour of proton component in neutron star matter for realistic nuclear models
We study properties of proton component of neutron star matter for ten realistic nuclear models. Vanishing of the nuclear symmetry energy implies proton-neutron separation instability in dense nuclear matter. Negative values of the symmetry energy results in disappearance of protons at high densities. We consider a bulk separation of protons and neutrons. Protons which form admixture tend to be localized in potential wells corresponding to neutron matter inhomogeneities created by the protons in the neutron medium. At low densities this inhomogeneity is a neutron bulge, whereas at high densities a neutron deficiency occurs. To compare the energy of a normal phase of uniform density and a phase with localized protons we apply the Wigner-Seitz approximation and divide the system into cells, each of them enclosing a single localized proton. The neutron background is treated in the Thomas-Fermi approximation and the localized proton is described by the Gaussian wave function. The neutron density profile is obtained by solving the appropriate variational equation. This approach gives lower energies of localized protons than obtained previously with less sophisticated methods. We discuss astrophysical consequences of occurring localized protons inside neutron stars.
Beta equilibrium breaking in the presence of superfluidity and pulsar cooling
After a brief summary of the reasons why beta-equilibrium breaking has to be taken into account in the cooling of pulsars, very preliminary microphysics results will be presented to explain how superfluidity complicates that story.
Leszek ZDUNIK (ppt file: 9.1mb)
EOS and back bending phenomenon in rotating neutron stars
I present the back bending phenomenon (spin up by angular momentum loss) in rotating neutron stars. This effect results from the softening of the matter due to the phase transitions in the interior of neutron stars. The back bending and possible instability of rotating neutron stars are discussed for realistic equations of state and for polytropic models corresponding to the appearance of the mixed phase.

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See also:

» Motivation and topics (Compact Stars: structure, dynamics, and gravitational waves)
» Programme of the 1st Astro-PF Workshop at CAMK (Compact Stars: structure, dynamics, and gravitational waves)
» The list of workshop participants (Compact Stars: structure, dynamics, and gravitational waves)
» Compact Stars: structure, dynamics, and gravitational waves workshop (gallery)

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