[mesa-users] Z=0.04 and MESA r9793

[Aaron Dotter]

>
> What I don't understand (and will have to investigate) is why this
> particular case behaves so badly.  There was not supposed to have been a
> significant change in the default behavior.
>

I've done experiments like this in the past.  This situation seems to be in
line with those.  The key difference in the EOS is the treatment of
ionization.  HELM assumes full ionization and so will have a very different
mean molecular weight than the OPAL tables in the outer layers of the
model.  This is a metal-rich model evolving toward the RGB.  The attached
shows two different evolutionary tracks, done with the same inlist and
initial model supplied by Philip.  1000 timesteps in each.  The only
difference is that I've only one EOS or the other in each.
[image: Inline image 1]
The difference is quite striking and becomes more pronounced as Teff
decreases.  I'm not saying there is anything wrong with HELM, it does what
it's designed to do. The only problem occurs when it is used out of context.

I would suggest based on this that we should have a test_suite case that
specifically checks the behavior at the Z=0.04.


Aaron
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