[mesa-users] MESA opacities

[Aaron Dotter]

Hi Manos,

1) Does "X" in the file names (like x00, x10...etc) represent the Hydrogen
> abundance? Is that a mass fraction representative of the shell or the
> overall abundance?


Yes, X is hydrogen mass fraction.  Opacity is a local quantity, called
microphysics in the MESA instrument papers.  In MESA, opacity is evaluated
in every shell using the local values of X and Z.  In a stellar model in
which any degree of nuclear burning has occurred you'll want to interpolate
to the appropriate composition (as much as possible).


> 2) I look at three variants of solar metallicity (z0.02, z2m2) data with X
> = 0.0000 attached (OP_gs98_z2m2_x00.data,
> gs98_z2m2_x00.data and lowT_Freedman11_z0.02). I notice that there is some
> overlap both in terms of logR = logRho - 3*logT + 18
> and in terms of logT itself between the Freedman and the gs98 tables. For
> the overlapped values I see significant differences
> in the opacity. For example, for logR = -6 and logT = 4.25 the
> lowT_Freedman table yields a value of -4.229 and the
> gs98 table a value of -0.870 (-0.863 for the OP_gs98 table). What values
> are correct in the over-lapping regime?
>

You can find references to the relevant papers in the MESA instrument
papers.  Maybe Freedman et al only comes into Paper II.  The "fa05" tables
are from Ferguson et al and are more appropriate for stellar conditions.
The Freedman et al tables are designed for the planetary regime.

I hope that helps!

Aaron
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