[Mesa-users] Implementing star-spots in MESA

[James Wild]

Hi All,

I have two questions, one I hope is easy to answer and one perhaps less so.
First, does MESAbinary account for the non-spherical teardop shape of stars
that are filling their Roche lobes when reporting their radii? If so, what
method does it use to calculate this, and is this accounted for when the
internal structure of the star is computed?


You may remember a while ago, I emailed here about artificially inflating a
star. We're looking for a co-author proficient in MESA to check what we've
done.

We have written code to add starspots to the surface of a star, using the
method given in this Sommers and Pinsonneault (2015) paper
<https://arxiv.org/abs/1506.01393>. This consists of three corrections,
based on two parameters: the ratio between the temperature of a spot and
the temperature of the unspotted surface, *x*; and the spot coverage
fraction, *f*. These produce *alpha* = 1-f + (f*x^4)

   - The surface temperature of the star is altered to the surface-weighted
   average temperature of the spotted photosphere when looking up the surface
   conditions.
   - We modify the temperature of each layer to be the flux-weighted
   average temperature between spotted and unspotted regions. The spot region
   is a constant amount (Tdiff) cooler than the unspotted region.
   - The radiative gradient is made steeper at all zones by dividing it by
   *alpha*. This uses a constant Tdiff similar to above.


These modifications result in models that run and seem to behave as we
expect, but we are concerned about breaking MESA internals in some subtle
way, particularly in the second step. I've attached our run_star_extras
file to this email, and we are looking for collaborators familiar with the
MESA to help validate what we've done here. Please let us know if you're
interested!

Cheers,
James Wild, Stuart Littlefair
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