[Mesa-users] MESA convective boundary not matching up with element abundance profile

[Christopher Lindsay]

Hi All,

I've been looking at elemental abundance and temperature gradient profiles
for red giant stellar models before the red giant luminosity bump and I've
noticed that for a period before the luminosity bump, the point where the
element abundance profile goes from being steady (in the convection zone)
to being variant (outside the convection zone) doesn't match up with the
position of the convection zone according to the temperature gradient
(nabla - nabla_adiabatic) profile.

Here is a figure showing what I'm talking about with the Hydrogen abundance
plotted in the dot-dashed line and the temperature gradient profile (nabla
- nabla_ad) plotted in a dotted line. The cz_bot_radius line in the
history.data output seems to line up with the temperature gradient profile
so I wanted to know if anyone could point me to the code which shifts the
elemental abundance profile turning point with respect to the convection
zone position.

I would expect that the fully mixed portion of the elemental abundance
profile would only extend as deep as the convection zone bottom. I made
sure that all overshoot options and element diffusion were off. This plot
was made with MESA version r12778 but the same thing happens in r15140.

[image: Screen Shot 2021-09-06 at 1.12.29 PM.png]
Thanks!
Christopher Lindsay.
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