[mesa-users] Diffusion of Heavy elements (Instability in some evolution tracks)

[Aaron Dotter]

Hi Nsamba,

I have had success in avoiding this sort of behavior by setting

      diffusion_min_dq_at_surface = 1d-3

in your the controls section of your inlist.  It defaults to a much smaller
number (1d-9).

In my case, the issue is that a small cell at the surface may fluctuate
back and forth between Z>0 and Z=0.  Requiring this cell to be larger stops
this from happening.


Aaron






On Mon, Jan 23, 2017 at 10:13 AM, Nsamba Benard <nsambabenard2net at gmail.com>
wrote:

> Greetings to You all,
>
> I am making a grid of models with diffusion included using mesa-r7624. In
> some of my models, the evolution track has some instabilities (fast
> variation in temperature and luminosity) as shown in the attached plot.
>
> However, when I consider diffusion of only Hydrogen and Helium, the model
> track is good (plot attached).
>
> I would like to know what is causing this instability when diffusion of
> heavier elements is included (this happens to some models)? Any suggestions
> on how to fix this problem? I have also attached my inlists.
>
> Thank you.
>
> Cheers,
> Benard
>
>
> ------------------------------------------------------------
> ----------------------------------------------
> Benard Nsamba
> PhD student                                  Centro de Astrofisica
>                                                     Universidade do Porto
>                                                     Rua das Estrelas
> Tel: +351 920 404 108 <+351%20920%20404%20108>                   4150-762
> Porto, Portugal
> E-mail: benard.nsamba at astro.up.pt <Benard.Nsamba at astro.up.pt>
> Skype: benardnsamba
>
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