[Mesa-users] EOS/opacity (?) issues in proto-WDs

[Josiah Schwab]

Hi Patrick,

After some more experimentation, here are my current thoughts.

We're having some struggles with the high-Z (Z > 0.02) blend of OPAL & SCVH
in the DT2 eos.  Probably best to fall back to the older DT version.  (The
difference is the way the interpolation is done; they're the same OPAL /
SCVH data underneath.)  So set

    use_eosDT2 = .false

in controls.  It is possible that you may no longer be able to satisfy the
tight "gold" tolerances.  If not, you may have to set use_gold_tolerances =
.false. .

When we reach Z near 0.04, we change between OPAL/SCVH (or DT2) and PTEH
(controlled by Z_for_all_PTEH = 0.040d0 and Z_for_any_PTEH = 0.039d0 in
star_job).  These EOSes have different limits in logQ (= logRho - 2 *
logT + 12).  By default we have

      logQ_max_for_low_Z_PTEH_or_DT2 = 4d0
      logQ_max_for_high_Z_PTEH_or_DT2 = -0.4d0

so the coolest outer layers at Z ~= 0.04 don't go to PTEH, but flip to
ELM/HELM.  That abrupt EOS switch seems to be why models want to stop when
the surface metalicity nears 0.04.

If you're willing to push PTEH a beyond its limits, you can make these
cutoffs the same, i.e., set

      logQ_max_for_high_Z_PTEH_or_DT2 = 4d0

and prevent this transition.  We just don't have a good high Z EOS down at
this Rho,T so it seems like picking whatever makes things smooth is
reasonable.  Doing that, I got your model down to about M = 0.1 Msun.  Then
it seemed to get into trouble again, which I don't have time to investigate
at the moment.  Presumably also the EOS.

Josiah
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