[mesa-users] rotation: problem with smooth parameters

[Radek Smolec]

Hi again,

I studied the effects of rotation on the computed tracks. I focus on the
evolution of 7M_S star with Z=0.004 from the ZAMS till the depletion of
helium in the core. The surface rotation at ZAMS was set to 200 km/s. To
check the sensitivity of the results on the rotation parameters I played
with the smoothing parameters and got significantly different results,
which was a surprise for me. I played both with mesa 4631 with dq_smooth_*
parameters and with the current version of MESA (4740) where averaging of
the diffusion coefficients is done over adjacent zones  (smooth_D*
parameters) rather than over a mass range (dq_smooth_* parameters). In both
cases I got the same problems and here describe the calculations with MESA
4740. As you can see in the attached figure (evol.rotALL.eps) the tracks
are very different even for small change of the smooth* parameters (also
there are small problems with smoothness of the tracks at the beginning
which you may see in the zoom-in). As I understand these smooth_D_*
parameters have both 'numerical'  and 'physical' meaning, i.e. proper
values help the convergence and allow to produce smooth tracks
('numerical') but also change the diffusion law, which is uncertain
('physical'). Am I right? But I expected a rather small effect on the
computed tracks, which is not the case. To investigate the effect further I
turned off all the diffusion coefficients, except the one for
Eddington-Sweet circulation and played with smooth_D_ES - the result is
presented in evol.rotES.eps. Again the difference is very large even
between smooth_D_ES=0 (no averaging) and smooth_D_ES=1.

I attach the inlist I used in the computations. For particular tracks I
changed the D_*_factor parameters (either all to 1 or only D_ES_factor=1
and all other 0) and smooth_D_* parameters as indicated in the Figures.
Note that overshooting is turned off  in these models (but I also allowed
for small overshoot from the h-burning core and got qualitatively the same
results). I run MESA 4740 installed with SDK on Ubuntu.

Can someone check whether the settings I use for rotation are OK and
comment on these results (in particular on the meaning of smooth_D
parameters and how to set them reliably)?
Thanks in advance,
Radek
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