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

[Warrick Ball]

Hi Christopher,

You mention that these models are before the RGB bump, so the convection zone has already reached its greatest depth and started become *smaller* in terms of mass.  So my guess is that you're seeing the region that was mixed by convection that has since "receded".

There's no reason a radiative region can't have uniform composition.  If, however, a convective region has a non-uniform composition, I'd be surprised!

Cheers,
Warrick

___________

Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552

On Wed, 8 Sep 2021, mesa-users at lists.mesastar.org wrote:

> 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. 
> 
> Screen Shot 2021-09-06 at 1.12.29 PM.png
> Thanks!
> Christopher Lindsay. 
> 
>