[Mesa-users] [Fe/H] Calculation with MESA Outputs

Aaron Dotter aaron.dotter at gmail.com
Wed Nov 3 12:11:14 UTC 2021

Hi Mitchell,

A couple of additions to Rob's good suggestion.

- You can add isotopes to a network without adding the nuclear reactions.
For example, if you're interested in tracking the surface evolution of Fe56
in solar type stars, which won't create or destroy Fe56, then you can still
use a simple net like basic for energy generation but also track the mixing
history of other isotopes.

- Whether you do the above or not, beware of a little known feature in
MESA: In the star_job inlist there is a flag called

      ! dump_missing_metals_into_heaviest
      ! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

      ! this controls the treatment metals that are not included in the
current net.
      ! if this flag is true, then the mass fractions of missing metals are
      ! to the mass fraction of the most massive metal included in the net.
      ! if this flag is false, then the mass fractions of the metals in the
      ! are renormalized to make up for the total mass fraction of missing

      ! ::

    dump_missing_metals_into_heaviest = .true.

What this means is that any elements in the solar mixture that are not
explicitly included in the network are going to be added to the heaviest
element in the network.  Depending on the network you choose, this may be a
small fraction.  If you use an approx21 net, or follow my suggestion above,
make sure that the element you want to track is not the heaviest in the net
(or turn the above flag to false but then you have a different problem . .

See attached example.  I use Zn64 as a placeholder for all the extras so
that Fe56 will just be Fe56.

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