Last stable orbit around rapidly rotating neutron stars

We compute the binding energy and angular momentum of a test particle at the last stable circular orbit(LSO) on the equatorial plane around a general relativistic, rotating neutron star (NS). We present simple,analytic, but accurate formulas for these quantities that fit the numerical results and which can be used inseveral astrophysical applications. We demonstrate the accuracy of these formulas for three differentequations of state (EOS) based on nuclear relativistic mean-field theory models and argue that they shouldremain still valid for any NS EOS that satisfy current astrophysical constraints. We compare and contrastour numerical results with the corresponding ones for the Kerr metric characterized by the same mass andangular momentum.