[Mesa-users] Implementing star-spots in MESA

[Francis Timmes]

hi james,

on your questions, perhaps appendix B of mesa V will answer them:
https://ui.adsabs.harvard.edu/abs/2019ApJS..243...10P/abstract

fxt




> On Apr 9, 2021, at 3:02 AM, James Wild via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> 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. 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
> <run_star_extras.f90>_______________________________________________
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>