Diffusive heat blanketing envelopes of neutron stars

TL;DR

This paper develops models of neutron star heat blanketing envelopes with binary ion mixtures, analyzing how ion composition affects surface temperature relations, providing simplified formulas for astrophysical modeling.

Contribution

It introduces generalized models for ion diffusion in non-isothermal neutron star envelopes, extending previous work to include non-equilibrium ion distributions.

Findings

Ts - Tb relations are insensitive to ion distribution details.

Relations depend mainly on the mass of lighter ions, DeltaM.

Analytic expressions for temperature relations are provided for modeling.

Abstract

We construct new models of outer heat blanketing envelopes of neutron stars composed of binary ion mixtures (H - He, He - C, C - Fe) in and out of diffusive equilibrium. To this aim, we generalize our previous work on diffusion of ions in isothermal gaseous or Coulomb liquid plasmas to handle non-isothermal systems. We calculate the relations between the effective surface temperature Ts and the temperature Tb at the bottom of heat blanketing envelopes (at a density rhob= 1e8 -- 1e10 g/cc) for diffusively equilibrated and non-equilibrated distributions of ion species at different masses DeltaM of lighter ions in the envelope. Our principal result is that the Ts - Tb relations are fairly insensitive to detailed distribution of ion fractions over the envelope (diffusively equilibrated or not) and depend almost solely on DeltaM. The obtained relations are approximated by analytic expressions which are convenient for modeling the evolution of neutron stars.