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

[Bill Paxton]

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




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