Skye: A Differentiable Equation of State

Adam S. Jermyn, Josiah Schwab, Evan Bauer, F. X. Timmes, Alexander Y. Potekhin

Research output: Contribution to journalArticlepeer-review

Abstract

Stellar evolution and numerical hydrodynamics simulations depend critically on access to fast, accurate, thermodynamically consistent equations of state. We present Skye, a new equation of state for fully ionized matter. Skye includes the effects of positrons, relativity, electron degeneracy, Coulomb interactions, nonlinear mixing effects, and quantum corrections. Skye determines the point of Coulomb crystallization in a self-consistent manner, accounting for mixing and composition effects automatically. A defining feature of this equation of state is that it uses analytic free energy terms and provides thermodynamic quantities using automatic differentiation machinery. Because of this, Skye is easily extended to include new effects by simply writing new terms in the free energy. We also introduce a novel thermodynamic extrapolation scheme for extending analytic fits to the free energy beyond the range of the fitting data while preserving desirable properties like positive entropy and sound speed. We demonstrate Skye in action in the MESA stellar evolution software instrument by computing white dwarf cooling curves.

Original languageEnglish (US)
Article number72
JournalAstrophysical Journal
Volume913
Issue number1
DOIs
StatePublished - May 20 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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