[Mesa-users] other_torque question

[Alexander Heger]

Dear Arend Jan,

whereas I don't know the internals of MESA, it seems your star is 
rapidly expanding from the pattern in the last figure).
Is there convection?
You have a Kippenhahn Diagram?

After you remove j, if there is an instability, it may just be 
replenished; if the outer layers are convective, j would be replenished 
swiftly.
maybe useful to plot integrated total j as a function of time to see 
where j goes or comes from, as in 2000 paper.

If the star expands and keeps the outer layers in co-rotation due to 
convection, and you couple with layers deep enough, you get a 'rotator' 
effect.

-Alexander


On Tue, 9 Mar 2021 at 05:16, AJ Poelarends <aj.poelarends at wheaton.edu 
<mailto:aj.poelarends at wheaton.edu>> wrote:

     Hello everyone,____

     __ __

     My two research students are experimenting with a very simple toy
     model to see whether torques in an accretor can keep the angular
     momentum of that accretor at (or below) critical rotation (such as
     in an accretion disk boundary layer).____

     In this simple model, we use the other_torque routine, and “shave
     off” any angular momentum that is above the critical angular
     momentum, by defining ____

     __ __

     omega_cr = sqrt(gamma_factor*cgrav*mmid/rmid**3)____

     j_cr = s% i_rot(k) * omega_cr____

     j_extra= max(s% j_rot(k)-j_cr,0.0d0)____

     __ __

     if (s% j_rot(k) > j_cr) then ____

          s% extra_jdot(k) = -j_extra/s% dt ____

     end if____

     __ __

     We’re aware that we don’t conserve angular momentum, and that you
     can’t really “shave off” excess angular momentum, but it’s a first
     iteration that we hope to improve in the future by redistributing
     the angular momentum. However, for whatever reason, this simple
     model does not work, and the accretor keeps spinning up above
     critical rotation, and we’re not really sure why that is. Does
     anyone have any insight in what we might be doing wrong?____

     __ __

     A couple of observations that I can’t explain:____

       * surf_avg_omega_div_omega_crit (first figure) rises higher than
         omega_div_omega_crit. I would have expected them to be close, or
         omega_div_omega_crit higher than surf_avg_omega_div_omega_crit
         as the latter one is averaged over several surface cells.____
       * The second figure plots j_rot, j_crit and extra_jdot. extra_jdot
         is calculated as j_rot-j_crit (in run_star_extras), but it does
         not have the same magnitude as the gap between j_rot and j_crit,
         as plotted from the profiles data.____
       * The third graph shows the time evolution of
         omega_div_omega_crit, and it seems that there is no effect
         extra_jdot at all once the outer layers of the star become
         super-critical.____

     __ __

     I’ve attached our inlists and run_star_extras.f files and some plots
     showing the evolution of the star. We use mesa-r12778.____

     Any help would be appreciated.  Thanks!____

     __ __

     __ __

     Vnqx6PzwAAAABJRU5ErkJggg==____

     Evolution of surf_avg_omega_div_omega_crit.____

     __ __

     ____

     Profiles of j_rot, j_crit and extra_jdot for model number 430.____

     __ __

     ____

     Evolution of the omega_div_omega_crit profile for model numbers 300
     – 433.____

     __ __

     __ __

     *Arend J. Poelarends, PhD____*

     *Associate Professor of Physics and Astronomy, Wheaton College____*

     __ __

     (630) 752-5894  | www.wheaton.edu <http://www.wheaton.edu>____

     501 College Ave  |  Wheaton, IL 60187

     _______________________________________________
     mesa-users at lists.mesastar.org <mailto:mesa-users at lists.mesastar.org>
     https://lists.mesastar.org/mailman/listinfo/mesa-users
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