[mesa-users] optical_depth -- and a message for MESA BLACK BELT USERS

[Aaron Dotter]

Hi Jing,

I took a look at the model you sent and the numbers that you're getting for
tau are reasonable; there's nothing wrong with the calculation.  The
physical explanation for why tau grows so quickly is that you're looking at
a white dwarf with log(g)~8.

The reason your "tau_phot" is different from what MESA reports in s% tau(:)
is that you're not taking into account that some variables are "face"
variables and some are "cell" mass-average, but MESA is.  Also, if you look
at the way s% photosphere_r is defined, you'll see that it's s% r(1)/Rsun
unless you intentionally modify tau_factor in the star_job inlist.  That is
to say that cell #1 is the "photosphere."  In your model, if you output s%
tau(1) you should get 2/3 (or whatever is appropriate for your atmosphere
BC).

Aaron
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