NS EOS: fitting subroutines

	Analytical EOSs of Neutron Star Matter Fitting programs
Neutron Star Group

Description

The equations of state (EOSs) for neutron-star matter are fitted from mass density rho about 10⁵ g cm^-3 to a few times 10¹⁵ g cm^-3 (baryon number density n about 10^-10 fm^-3 - a few fm^-3). At the low end of this density range, the EOS starts to depend on temperature T. The fits are extended below this density by matching to the dependence P=3.5x10¹⁴rho, where pressure P and rho are in CGS units; this is an approximation for the EOS of iron at T = 10⁷ K and rho = (0.1 - 1000) g cm^-3.

Arguments of the program:

MODE - an integer (1, 2, or 3) that identifies which of the arguments is the input (XN, RHO, or H1)
KEOS - an integer (1 or 2) that identifies which EOS has to be used (SLy or FPS)
XN - number density n in fm^-3
RHO - mass density rho in g cm^-3;
RLG=log₁₀(RHO)
H1 - h/h₀-1, where h is the enthalpy per baryon, and h₀=m₀c² is its value near the surface
P - pressure P in dyn cm^-2;
PLG=log₁₀(P)
Gamma - adiabatic index, (d log P) / (d log n)

(for more explanations and definitions see the references).

The subroutine NSEOSFIT(MODE,KEOS,XN,RHO,H1,P,Gamma) returns 4 fitted arguments for 1 input (XN, RHO, or H1). It uses subroutines that realize separate fits: P(rho), n(rho), rho(n), rho(H1). Typical accuracy of the fits is a few percent or better. To achieve the perfect thermodynamic consistency, however, it is advised not to use all the fitted outputs, but to calculate either XN(RHO,P) or RHO(XN,P) using the thermodynamic identities given, e.g., by Eqs.(2),(3) of the basic reference paper (Haensel and Potekhin 2004).

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Tabular EOSs:

SLy
FPS

Code to download:

Fortran
C/C++

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Page created on April 8, 2004, last updated on June 15, 2007 by Alexander Potekhin.