Variability of the adiabatic parameter in monoatomic thermal and nonthermal plasmas
Abstract
Context. Numerical models of the evolution of interstellar and integalactic plasmas often assume that the adiabatic parameter γ (the ratio of the specific heats) is constant (5/3 in monoatomic plasmas). However, γ is determined by the total internal energy of the plasma, which depends on the ionic and excitation state of the plasma. Hence, the adiabatic parameter may not be constant across the range of temperatures available in the interstellar medium.
Aims: We aim to carry out detailed simulations of the thermal evolution of plasmas with MaxwellBoltzmann and nonthermal (κ and n) electron distributions in order to determine the temperature variability of the total internal energy and of the adiabatic parameter.
Methods: The plasma, composed of H, He, C, N, O, Ne, Mg, Si, S, and Fe atoms and ions, evolves under collisional ionization equilibrium conditions, from an initial temperature of 10^{9} K. The calculations include electron impact ionization, radiative and dielectronic recombinations and line excitation. The ionization structure was calculated solving a system of 112 linear equations using the Gauss elimination method with scaled partial pivoting. Numerical integrations used in the calculation of ionization and excitation rates are carried out using the doubleexponential over a semifinite interval method. In both methods a precision of 10^{15} is adopted.
Results: The total internal energy of the plasma is mainly dominated by the ionization energy for temperatures lower than 8 × 10^{4} K with the excitation energy having a contribution of less than one percent. In thermal and nonthermal plasmas composed of H, He, and metals, the adiabatic parameter evolution is determined by the H and He ionizations leading to a profile in general having three transitions. However, for κ distributed plasmas these three transitions are not observed for κ < 15 and for κ < 5 there are no transitions. In general, γ varies from 1.01 to 5/3. Lookup tables of the γ parameter are presented as supplementary material.
Tables of the gamma parameter variability with temperature (Fig. 5) + data for n = 25 and κ = 25 are only available at the CDS via anonymous ftp to http://cdsarc.ustrasbg.fr (http://130.79.128.5) or via http://cdsarc.ustrasbg.fr/vizbin/qcat?J/A+A/616/A58
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 2018
 DOI:
 10.1051/00046361/201832948
 arXiv:
 arXiv:1805.00770
 Bibcode:
 2018A&A...616A..58D
 Keywords:

 atomic processes;
 atomic data;
 hydrodynamics;
 methods: numerical;
 ISM: general;
 intergalactic medium;
 Astrophysics  Solar and Stellar Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 Accepted for publication in Astronomy &