[mesa-users] Post-processing of mixing regions

[Kevin Moore]

Hi all,

I’m trying to understand the post-processing that’s done by MESA to tidy up different mixing regions (eg. gap removal) that happens after the MLT module is called. This code (I think) is all in star/private/mix_info.f.

I’m working with models where the only non-default mixing is semiconvection and I see examples of both semiconvective regions turning radiative (eg. MLT_mixing_type = 3 and mixing_type = 0) as well as radiative regions turning semiconvective (eg. MLT_mixing_type = 0 and mixing_type = 3). As I understand it, MLT_mixing_type is the mixing type of the cell that the MLT module returns, while mixing_type is the actual mixing type after some post-processsing.

It appears that by default, the only mixing ‘glitches’ that MESA deals with are remove_small_D_limit, which is checked when the MLT module is called, so shouldn’t cause differences between MLT_mixing_type and mixing_type, and remove_mixing_singletons(), which can turn isolated radiative zones into mixing zones and vice-versa. There’s also a check to remove entire convective regions that are smaller than 10% of the mixing length (along with any mixing in cells that border that region), called from locate_convection_boundaries().

I can’t, however, find anywhere in the code where an isolated radiative zone (surrounded by convective zones) can be converted into a semiconvective zone. I also observe isolated radiative zones that persist from MLT_mixing_type into mixing_type without being absorbed into their surrounding convective zones. Are there additional places in the code (other than star/private/mix_info.f) where mixing types can be changed?

-Kevin