Structure of neutron star envelopes

Abstract

We have investigated the envelopes of nonmagnetic neutron stars using the best available opacities and equation of state. The temperature at the inner boundary of the envelope, T b , is found to be very nearly a universal function of the parameter Tt/g s , where T s is the eifective surface temperature, and g s is the surface gravity of the neutron star. This result is used to derive a number of other scaling relations, to investigate the effects of general relativity on the thermal structure of the envelope, and to compare envelope calculations by different workers. Tests of the sensitivity of the computations to variations of the input physics show that the accuracy of the T b versus T s relation depends largely on having accurate values for the conductive opacity in the region where it is dominated by electron-ion scattering. In our calculations we use the conductive opacities calculated by Yakovlev and Urpin, which are the most accurate ones available. For a given T b we find luminosities that are 2-2.5 times lower than those calculated using Flowers and Itoh's calculations of the conductive opacities.