[mesa-users] Gradually turning off diffusion?

[Evan Bauer]

Hi Earl,

Aaron’s suggestion is definitely the right one from an engineering standpoint, but I’m also surprised to hear that diffusion would cause a big jump on the HR just by turning it off. Do you have a sense of what’s causing that in your model?

I can think of one control that might help prevent diffusion from having too large of an impact on the photosphere:

         !### diffusion_v_max

         ! Max velocity (cm/sec).
         ! We can get extremely large velocities in the extreme outer envelope
         ! that cause problems numerically without really effecting the results,
         ! so we allow a max for the velocities that should help the numerics
         ! without changing the results.
         ! Note: change `diffusion_v_max` to at least 1d-2 when using radiative levitation.

      diffusion_v_max = 1d-5

Have you tried using that at all?

Cheers,
Evan

> On Jan 12, 2017, at 11:50 AM, Aaron Dotter <aaron.dotter at gmail.com> wrote:
> 
> Hi Earl,
> 
> How about using run_star_extras?  If you're willing to add some code to extras_finish_step, you can change this array:
> 
>          !### diffusion_class_factor(:)
> 
>          ! Arbitrarily enhance or inhibit diffusion effects by class.
> 
>       diffusion_class_factor(:) = 1d0
> 
> Change it gradually from 1 to 0 over a number of timesteps and then, when it gets to zero, you can set do_element_diffusion = .false.
> 
> 
> Aaron
> 
> 
> On Thu, Jan 12, 2017 at 2:28 PM, Earl Bellinger <bellinger at mps.mpg.de <mailto:bellinger at mps.mpg.de>> wrote:
> Hello mesa-users,
> 
> I want element diffusion on the main sequence but not past that point.
> However, switching between an inlist with diffusion and one without
> causes a big jump in the HR diagram. Does anyone have any advice as to
> how one should go about turning it off more gradually?
> 
> Best regards,
> Earl Bellinger
> 
> ---
> www.earlbellinger.com <http://www.earlbellinger.com/>
> Department of Astronomy, Yale University
> Stellar Ages & Galactic Evolution Group, Max Planck Institute
> 
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