[Mesa-users] Adding a new particle species

[Josiah Schwab]

Hi Jeremy,

If you need to add a species that is subject to advection-diffusion,
then I don't think that's easy.  (As far as I know, MESA can't evolve
passive scalars.)

However, it sounds like your species may be able to be calculated from
the local cell conditions and equilibrium considerations.  (By analogy
with pair production, in that case we don't have to solve a separate
composition equation for positrons.)  If that's the case, then it seems
like you'll need to adjust the eos, as you said in your initial email.

If you need to adjust gravity, you could consider using the other_cgrav
hook to set a different effective G in each cell.  Alternatively, you
could add an extra gravitational force via the other_momentum hook.

Let me also add the general reminder that you should make sure to look
through the equations that MESA is solving and their range of validity
so you can be sure about what corrections you need.

Josiah