[mesa-users] what is the radius of the star in mesa?

Bill Paxton paxton at kitp.ucsb.edu
Thu Aug 11 13:09:54 EDT 2011

On Aug 11, 2011, at 9:45 AM, Jeremy Sakstein wrote:
> I'm just trying to check a few details in my data, what does MESA use as the radius of the star? Is it the radius where T and P are 0 or is the the photospheric radius where T=Teff and the optical depth is 2/3 (I'm assuming this is how Teff is definied)?

Hi Jeremy,

There is a distinction between "photospheric radius" and "surface radius".
The surface of the star is defined to be the outer edge of the outermost cell in the model.
The optical depth of the surface is = tau_base * tau_factor (see star_data.dek for these).
The photosphere radius is defined in terms of the total luminosity and the effective temperature.
The atmosphere module decides what tau corresponds to the photosphere (2/3 typically),
and it also tells us what Teff is.

In the current options in log_columns.list, I'm only giving information for the surface radius.
I'll add options for the photosphere for the next release -- thanks for leading me to discover this shortfall.

In the meantime, if you'd like to add a log column for the photosphere radius to your logs, you can of course 
do it in your run_star_extras.   You'll even find the desired value in s% photosphere_r (Rsun units).


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