Astron. Astrophys. 323, 415-428 (1997)

Internal temperatures and cooling of neutron stars with accreted envelopes

A.Y. , Potekhin ^{1 2 *}, G. , Chabrier ², D.G. and Yakovlev <sup>1

1</sup> Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021 St.-Petersburg, Russia
² Centre de Recherche Astronomique de Lyon (UMR CNRS # 5574), Ecole Normale Supérieure de Lyon, F-69364 Lyon Cedex 07, France

Received 2 October 1996 / Accepted 23 December 1996

Abstract

The relationships between the effective surface () and internal temperatures of neutron stars (NSs) with and without accreted envelopes are calculated for  K using new data on the equation of state and opacities in the outer NS layers. We examine various models of accreted layers (H, He, C, O shells produced by nuclear transformations in accreted matter). We employ new Opacity Library (OPAL) radiative opacities for H, He, and Fe. In the outermost NS layers, we implement the modern OPAL equation of state for Fe, and the Saumon-Chabrier equation of state for H and He. The updated thermal conductivities of degenerate electrons include the Debye-Waller factor for the electron-phonon scattering in solidified matter, while in liquid matter they include the contributions from electron-ion collisions (evaluated with non-Born corrections and with the ion structure factors in responsive electron background) and from the electron-electron collisions. For K, the electron conduction in non-degenerate layers of the envelope becomes important, reducing noticeably the temperature gradient. The accreted matter further decreases this gradient at K. Even a small amount of accreted matter (with mass ) affects appreciably the NS cooling, leading to higher at the neutrino cooling stage and to lower at the subsequent photon stage.

Key words: stars: neutron pulsars: general dense matter

* (palex@astro.ioffe.rssi.ru)

Send offprint requests to: A.Y. Potekhin (Ioffe Institute)

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Contents

• 1. Introduction
• 2. Physical input
  • 2.1. Thermal structure equation
  • 2.2. Equation of state
    • 2.2.1. Plasma parameters
    • 2.2.2. High density regime
    • 2.2.3. Low density regime
    • 2.2.4. Intermediate density regime
    • 2.2.5. Effective charge
  • 2.3. Opacities
    • 2.3.1. Radiative opacities
    • 2.3.2. Conductive opacities
    • 2.3.3. Coulomb logarithm
• 3. Results and discussion
  • 3.1. Thermal structure of non-accreted envelopes
  • 3.2. Thermal structure of accreted envelopes
  • 3.3. Effect of accreted envelope on cooling
• 4. Conclusions
• Acknowledgements
• Appendix A
• Appendix: fitting formulae
• A.1. Electron-electron collisions
• A.2. Coulomb logarithms
• A.3. Relation between internal and effective temperatures
• References

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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