Large drops in opacity near edges of table

[pmocz]

This is related to issue: https://github.com/MESAHub/mesa/issues/814

Plotting the opacity as a function of temperature and density using kap/plotter (extending the bounds) reveals big drops in the opacity on the left side of the plot, and nans (white) on the bottom below a critical temperature

This is probably unphysical and causes numerical issues. Generally, MESA simulations try to avoid being in this part of parameter space, but sometimes a cell may inevitably land here.

The issue comes from the calculation of the Compton_Opacity() (see Get_eosDT_Results in kap_eval.f90). Specifically, the features are due to lnfree_e, which comes from the EOS: see Get_eosDT_Results() in eosdt_eval.f90

In fact, the features match up with different EOS regions as @Debraheem points out:

So to fix the issue of huge drops in opacity (which would be nice for better numerical control), we will need the EOS to supply better values of lnfree_e in the edge regions