Neutron star envelopes

We point out that the separate study of neutron star envelopes is a valuable technique for gaining insights into neutron star cooling calculations. We show that, to an excellent approximation, the temperature at the inner boundary of the envelope, T/sub b/, is a function only of T4/sub s//g/sub s/, where T/sub s/ is the effective temperature and g/sub s/ is the surface gravity. This result enables us to investigate very simply the effects of general relativity and of opacity changes on the T/sub b/-T/sub s/ relation, and also to compare calculations by different workers, even though they use different neutron star models. We also show that the most important opacity source for obtaining a reliable T/sub b/-T/sub s/ relation is the conductive opacity of matter when the ions are liquid. We present calculations in which we pay particular attention to this region and use the best available opacities