[Mesa-users] Trouble w. convective stability criteria

[Warrick Ball]

Hi Peter,

I've just taken a quick look at your run.  Using the inlists you sent, `profile4.data` seems to be the model you sent, based on the age, and I can see the part that matches what you sent.

I've plotted the mixing coefficient for the overall mixing, MLT and overshooting. i.e I uncommented

     log_D_mix
     log_mlt_D_mix
     log_D_ovr

in `profile_columns.list`.  The MLT mixing coefficient is, correctly, greater than zero in the small unstable region but is zero in the final, total diffusion coefficient.

I haven't tested this hypothesis but I think the problem is that the convective region you're seeing is narrower than your `overshoot_f0` value (or perhaps twice this) of 0.008 Hp.  That already seems quite large, so try using something smaller.  Although this parameter is often not reported, I believe values around 0.0001 to 0.001 (i.e. 1e-4 to 1e-3) are typical but I invite others to comment.

Cheers,
Warrick

___________

Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552

On Fri, 9 Apr 2021, mesa-users at lists.mesastar.org wrote:

> Hi all.I am having trouble with an area of a stellar model, where the Schwarzvhild criteria fails (ie. the area should be convective), but the Diffusion coefficient is effectively 0.
> The system I work on is: 
> Debian 3.16.43-2 (as far as I can figure out from what the server login tells me)
> MESA ver. mesa-r12778
> mesasdk-20200325
> 
> The trouble arises in 0.927 < r/R < 0.930
> MixingTrouble2.png
> It should be noted that the f_OV in the plot title is the effective overshoot, which I calculate from f_effective = overshoot_f(:) - overshoot_f0(:). Also, the area where log_D_mix = -3 is an artificial cutoff I set, log_D_mix < -3 gets set to -3.
> There is an attached figure, where I remove this cutoff, and you can see that log_D_mix=-100 in this area. I have also included the inlist and the loaded model, for reproducibility.
> 
> 
> Kind regards
>  - Peter Juelsgaard
> 
> 
> 
> 
> I have attached the inlist files, a png. detailing 
> 
>