mesa-users] Regarding the MESA EOS

Bill Paxton paxton at
Mon Feb 22 11:04:35 EST 2010

On Feb 22, 2010, at 7:53 AM, Ricky Olivier wrote:

> Ok, looks like this is going to be harder than I thought. I could  
> subtract off the effect of radiation to the various thermodynamic  
> variables. This should be ok in those parts of the Rho-T plane where  
> the radiation energy density and radiation pressure do not dominate.  
> In other parts of the Rho-T plane it will be dodgy to say the least.

Hi Ricky,

As you know, the MESA/EOS is a blend of SCVH/OPAL/HELM eos's.
HELM is for situations in which it is okay to assume complete  
and HELM does provide separate results with/without radiation.
So one possible approach is to by-pass the standard routine and
call the mesa/public/eos_lib routine 'eos_get_helm_results'.
In mesa/public/eos_def you'll find a long list of integer parameter
definitions for the results from HELM.   There are separate items
for pressure ('p'), energy ('e'), and entropy ('s').   The partials are
wrt temperature ('d_t'), density ('d_d' ), zbar ('d_z'), and abar  
And there are 2nd partials, 'd_dt', etc.    The 'total' value is the
sum of the contributions from gas and radiation -- that what mesa/eos
reports of course.  But you will also find the separate terms for
gas and radiation -- e.g., ptot, pgas, prad, etc.

For derived quantities such as specific heats and gammas, you
will find both values based on totals and on for the gas alone:
e.g., h_cp for the total and h_cp_gas for the gas alone.

So for the regions where you are willing to assume complete ionization,
you can go straight to the HELM results and get what you want.

Perhaps that will help?

Let me know.


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