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    QPO observations related to neutron star equations of state

    Zdeněk Stuchlík · Leden 01, 2008 · Fyzika · 0 comments
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    Publication date: Jan 2008

    Abstract:
    We apply a genetic algorithm method for selection of neutron star models
    relating them to the resonant models of the twin peak quasiperiodic
    oscillations observed in the X-ray neutron star binary systems. It was
    suggested that pairs of kilo-hertz peaks in the X-ray Fourier power
    density spectra of some neutron stars reflect a non-linear resonance
    between two modes of accretion disk oscillations. We investigate this
    concept for a specific neutron star source. Each neutron star model is
    characterized by the equation of state (EOS), rotation frequency Ω and
    central energy density ρc . These determine the spacetime structure
    governing geodesic motion and position dependent radial and vertical
    epicyclic oscillations related to the stable circular geodesics.
    Particular kinds of resonances (KR) between the oscillations with
    epicyclic frequencies, or the frequencies derived from them, can take
    place at special positions assigned ambiguously to the spacetime
    structure. The pairs of resonant eigenfrequencies relevant to those
    positions are therefore fully given by KR,ρc , Ω, EOS and can be
    compared to the observationally determined pairs of eigenfrequencies in
    order to eliminate the unsatisfactory sets (KR,ρc , Ω, EOS). For the
    elimination we use the advanced genetic algorithm. Genetic algorithm
    comes out from the method of natural selection when subjects with the
    best adaptation to assigned conditions have most chances to survive. The
    chosen genetic algorithm with sexual reproduction contains one
    chromosome with restricted lifetime, uniform crossing and genes of type
    3/3/5. For encryption of physical description (KR,ρ, Ω, EOS) into
    chromosome we used Gray code. As a fitness function we use
    correspondence between the observed and calculated pairs of
    eigenfrequencies.

    Authors:
    Stuchlik, Zdenek; Urbanec, Martin; Török, Gabriel; Bakala, Pavel; Cermak, Petr;

    https://ui.adsabs.harvard.edu/abs/2008cosp…37.3067S

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