Mihalas / Wittmann EOS and background opacity package (from Kurucz)

Written by J. de la Cruz Rodriguez (ISP-SU 2017).

This python package includes a very simple equation of state originally proposed by Mihalas (1970) and later improved by Wittmann (1975?). Background opacities can be automatically computed at a given array of wavelengths.

This EOS considers in detail H, H+, H- and H2, no other molecules. The purpose of this package is to provide the user with a simple EOS that can be used to play with toy models or to compute electron densities / pressure in LTE.

All units in CGS.

The same implementation is found in the SIR code (Fortran) and in NICOLE (Fortran).

Dependencies:

• It requires a pf_Kurucz.input containing the partition function data.
• Numpy

Usage:

import witt
eos = witt.witt()

temp = 5000.
Pgas = 10000.

Pe = eos.pe_from_pg(temp,Pgas)
rho= eos.rho_from_pg(temp, Pgas)

But if we know rho instead of pgas:

rho = 3.e-7

Pgas= eos.pg_from_rho(temp, rho)
Pe  = eos.pe_from_rho(temp, rho)

Or if we only know the electron pressure:

Pe = 7.0
Pgas= eos.pg_from_pe(temp, Pe)
rho  = eos.rho_from_pe(temp, Pe)

Remember that Pgas is the total gas pressure and it includes the electron pressure. To compute the particle density and the electron pressure, we can use the ideal gas equation: P = n B T:

Na = (Pgas - Pe) / (eos.BK * temp)
Ne = Pe          / (eos.BK * temp)

Finally, background opacities can be obtained for an array of wavelengths in Angstroms:

wav = np.float64([5000., 6000.])
alpha = eos.contOpacity(temp, Pgas, Pe, wav)