[mesa-users] Semiconvection in Intermediate Mass Stars

[Spencer C Wallace]

Hi all,

We've been working on implementing a turbulent entrainment law in MESA in
hopes of more accurately modeling the mixing that occurs at convective
boundaries during main sequence evolution. Originally, we were working with
~20 M_sun models, but it turned out that semiconvective mixing played too
large of a role to be able to see if we were getting the entrainment
physics right.

We are now looking at less massive models (~3 M_sun) in hopes of not having
to deal with semiconvection. I was curious if anyone could comment on what
they know about the role of semiconvection during main sequence evolution
in stars of this mass.

My inital hunch was that semiconvection should be minimal or nonexistent in
these models. However, when I run a 3 M_sun model in MESA with Ledoux
criterion enabled and no mixing, I see that the receding convective core
leaves behind a semiconvective layer, rather than a stable layer. The
semiconvective layer dissapears as soon as I turn on any kind of mixing, or
run the simulation with Schwarzchild criterion, however. Am I simply
getting bogus results because my models are not physically realistic, or is
it reasonable to have semiconvection in stars this small? A literature
search didn't turn up any solid answers to my question, so I was hoping
someone on here might know better.

Spencer Wallace
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