[mesa-users] Scratchy surface metallicity profile with diffusion in 1.3Msun star

[Warrick Ball]

Okay, I'll get back to this in the morning, but it looks like

(a) T_mix_limit smooths out the behaviour in the expected fashion, and

(b) the jump of about 0.07 dex in [Fe/H] around 2.5 Gyr is a result of the 
convection zone penetrating inwards past one of those peaks I found 
before, caused by the diffusion velocity varying in ionization zones.

Watch this space!

W

On Tue, 25 Nov 2014, Bill Paxton wrote:

> 
> On Nov 25, 2014, at 7:34 AM, Warrick Ball wrote:
>
>        I'm mainly hoping to smooth out the outermost meshpoints so that the fluctuations are suppressed and
>       the surface abundance matches the underlying layers.
> 
> 
> Hi Warrick,
> 
> Your comment suggests that you want to have diffusion on for the effects deeper in the model and don't
> particularly care about the effects of diffusion near the surface.   If so, you might just use some other trick to
> mix things near the surface.  In some cases, you can use "T_mix_limit" for this, but it depends on having a
> near-surface convection zone that can simply be extended to the surface.  That may not work for you.   An
> alternative would be "radiation turbulence" -- here's the description from controls.defaults:
> 
>       !## radiation turbulence
> 
>             !### radiation_turbulence_coeff
> 
>             ! To counter depletion of h and metals in outer envelope of stars with M > 1.4 Msun.
>             ! Morel, P., and Thevenin, F.,  
>             ! Atomic diffusion in stellar models of type earlier than G.,  
>             ! A&A, 390:611-620 (2002)  
> 
>             !     D = radiation_turbulence-coef * 4*crad*T^4/(15*clight*opacity*rho^2)
> 
>             ! 1 is reasonable value for this coefficient
> 
>          radiation_turbulence_coeff = 0
> 
> Give that a try --- if it isn't what you need, then we can go back to tweaking diffusion controls.
> 
> Good luck,
> Bill
> 
> 
> 
> 
> 
>


------------
Warrick Ball
Postdoc, Institut für Astrophysik Göttingen
wball at astro.physik.uni-goettingen.de
+49 (0) 551 39 5069