[Mesa-users] other_torque question

[AJ Poelarends]

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.

[cid:image002.png at 01D71414.D36D0E00]
Profiles of j_rot, j_crit and extra_jdot for model number 430.

[cid:image003.png at 01D71414.D36D0E00]
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
501 College Ave  |  Wheaton, IL 60187
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