Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-10-18
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
46 pages, 23 figures, Submitted to Physical Review C
Scientific paper
Within the liquid drop model, and using a phenomenological Skyrme-like parameterization of the uniform nuclear matter equation of state (EoS), we first construct a set of `baseline' crustal equations of state that span the experimentally constrained values of the symmetry energy at nuclear saturation density, as well as the theoretically constrained region of the pure neutron matter (PNM) EoS at low density. The resulting range of crustal compositional parameters relevant for macroscopic models of the crust is explored, as well as the crust-core transition densities and pressures and the density range of the `pasta' phases of nuclei at the bottom of the crust. We explore the deviation of these parameters from the baseline models as a result of the remaining experimental uncertainties in the symmetric nuclear matter (SNM) EoS and the parameterization of the surface energy in the liquid drop model. The transition densities and pressures are found to be quite sensitive to the behavior of the surface tension \emph{at very low proton fractions}; recent calculations of the energies of neutron drops suggest that this might be higher than previously thought, which our study suggests may result in a much reduced volume of pasta in the crust. Most crustal compositional parameters are shown to be insensitive to the SNM EoS and the surface energy relative to the uncertainties in the symmetry energy, with the notable exception of the size of the nuclei which show a similar dependence on all the model parameters. We establish a set of crustal equations of state which can be matched with any core EoS based upon the symmetry energy and its derivative, allowing a consistent exploration of the dependence on the symmetry energy of global crustal models and potentially observable phenomena such as pulsar glitches and oscillation modes that incorporate a coupling between crust and core.
Gearheart Michael
Li Bao-An
Newton William G.
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