Publication date: n/a 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;