One- and two-argument equation of state parametrizations with continuous sound speed for neutron star simulations
Physical Review D(2023)
摘要
We describe two fitting schemes that aim to represent the high-density part
of realistic equations of state for numerical simulations such as neutron star
oscillations. The low-density part of the equation of state is represented by
an arbitrary polytropic crust, and we propose a generic procedure to stitch any
desired crust to the high-density fit, which is performed on the internal
energy, pressure and sound speed of barotropic equations of state that describe
cold neutron stars in β-equilibrium. An extension of the fitting schemes
to equations of state with an additional compositional argument is proposed. In
particular we develop a formalism that ensures the existence of a
β-equilibrium at low densities. An additional feature of this low-density
model is that it can be, in principle, applied to any parametrization. The
performance of the fits is checked on mass, radius and tidal deformability as
well as on the dynamical radial oscillation frequencies. To that end, we use a
pseudospectral isolated neutron star evolution code based on a non-conservative
form of the hydrodynamical equations. A comparison to existing parametrizations
is proposed, as far as possible, and to published radial frequency values in
the literature. The static and dynamic quantities are well reproduced by the
fitting schemes. Our results suggest that, even though the radius is very
sensitive to the choice of the crust, this choice has little influence on the
oscillation frequencies of a neutron star.
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