[mesa-users] EoS & partial ionization

[Aaron Dotter]

Hi Ken,

>From eos/public/eos_lib.f:

      ! The MESA EOS is based on the OPAL, SCVH, and HELM EOS's.
      ! The OPAL-SCVH values are used for approximately
      !     Z < 0.04, logRho < 3.3, and logT < 7.7
      ! HELM is used for all other cases.

Since you're in pure "Z" territory, you're accessing the HELM EoS which
assumes full ionization  (Frank, correct me if I am wrong).

Aaron



On Wed, Aug 3, 2011 at 8:20 PM, Ken Shen <kenshen at astro.berkeley.edu> wrote:

> Hi all.  I've got a question about how the MESA EoS handles partial
> ionization.  In particular, are the changes in free electron fraction
> taken into account when the EoS returns, e.g., chiT and chiRho?  As a
> test, here are the results for two calls to the EoS for X_12C = X_16O
> = 0.5 and rho = 2e-8 g/cm^3:
>
> T = 6.5e4 K
> P = 9.022e4 dyne/cm^2
> free_e = 0.3463
> chiT = 2.499
> mu = 1.745
>
> T = 6.4e4 K
> P = 8.577e4 dyne/cm^2
> free_e = 0.3364
> chiT = 2.482
> mu = 1.745
>
> A crude calculation from these two calls gives dlnP/dlnT = 3.26, which
> is significantly different from the returned value of chiT = 2.5.
> Also, the mean molecular weight that is returned seems to assume full
> ionization; it should be 2.39 for the first call and 2.44 for the
> second.
>
>
> Thanks,
> Ken
>
>
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