fixed incorrect metal mass fraction array for Freedman lowT opacity t…

[Debraheem]

(#993) @esandford

Co-authored-by: Emily Sandford emily@Emilys-MacBook-Air.local

Louis Siebenaler (cc'd) and I noticed a problem with the preprocessing & evaluation of the Freedman11 low-temperature opacity tables. Specifically, the "Z" values associated with each table, as e.g. enumerated in $MESA_DIR/kap/public/kap_def.f90, num_kap_lowT_Zs(i) = 7
kap_lowT_Zs(1:num_kap_lowT_Zs(i), i) = [ 0.01d0, 0.02d0, 0.04d0, 0.100d0, 0.200d0, 0.63d0, 1.00d0 ]

are not metal mass fractions. Rather, they are related to number fractions; for example, a Freedman [M/H] value of -0.3 corresponds to a metal number fraction of 10**(-0.3)solar = 0.5solar; [M/H]=0 corresponds to a solar number fraction, etc. It appears that there was a decision made to equate the solar metal number fraction with a metal mass fraction of 0.02 and scale the other values in the array accordingly.

The metal mass fraction array should instead look something like this (with small variations possible depending on which protosolar abundance table you work with; the below values are based on Lodders 2003 table 2): [M/H] = [-0.3, 0.0, 0.3, 0.7, 1.0, 1.5, 1.7]
Z = [0.0075, 0.0148, 0.029, 0.0698, 0.1303, 0.3215, 0.4288]

[Debraheem]

commit incoming, once git lfs let's me upload these files.

[Debraheem]

I think this pr is the simplest way of changing the opacities from [M/H] to Z but it only does 6 sig figs in Z, using the file names. Is this enough, should the file be named such that they include near full precision names?