A New Equation of State for Dense Hydrogen-Helium Mixtures
Abstract
We present a new equation of state (EOS) for dense hydrogen/helium mixtures that covers a range of densities from 10-8 to {10}6 {{g}} {cm}}-3, pressures from 10-9 to 1013 GPa, and temperatures from 102 to 108 K. The calculations combine the EOS of Saumon, Chabrier & van Horn in the low-density, low-temperature molecular/atomic domain, the EOS of Chabrier & Potekhin in the high-density, high-temperature fully ionized domain, the limits of which differ for H and He, and ab initio quantum molecular dynamics calculations in the regime of intermediate density and temperature, characteristic of pressure dissociation and ionization. The EOS for the H/He mixture is based on the so-called additive volume law and thus does not take into account the interactions between the two species. A major improvement of the present calculations over existing ones is that we calculate the entropy over the entire density-temperature domain, a necessary quantity for calculations of stellar or planetary evolution. The EOS results are compared with existing experimental data, namely Hugoniot shock experiments for pure H and He, and with first-principles numerical simulations for both the single elements and the mixture. This new EOS covers a wide range of physical and astrophysical conditions, from Jovian planets to solar-type stars, and recovers the existing relativistic EOS at very high densities, in the domains of white dwarfs and neutron stars. All the tables are made publicly available.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2019
- DOI:
- 10.3847/1538-4357/aaf99f
- arXiv:
- arXiv:1902.01852
- Bibcode:
- 2019ApJ...872...51C
- Keywords:
-
- brown dwarfs;
- dense matter;
- equation of state;
- planets and satellites: general;
- plasmas;
- stars: low-mass;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- To appear in Astrophysical Journal. Figures in the published version will be larger