[mesa-users] Off-center Ne and O burning

[David Arnett]

I am running a 25 Msun with TYCHO, in which I am careful about convective
boundaries. I get semiconvective stairsteps which I interpret as a
numerically under-resolved version of double diffusive instability that
Garaud, Wood, and Mirouh have  discussed.
Convective boundaries have associated turbulent boundary layers which are
thin, and have a entropy deficit to cause braking of the flow. This is
different from MLT. These braking layers are mixed, so the instability
criterion is effectively Schwarzschild. A lot of this fiddling with
parameters can be avoided by a coherent physical model of convection,
including abundance gradients and boundaries. The model seems to like your
choices of fudge parameters,  at least roughly, in the sense that it gives
similar behavior. I am optimistic that it will preserve much of what we
thought we knew, while eliminating much of the arbitrary tuning. We will
find out when we have the algorithm in MESA so it can be extensively tested.

-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona

Facts are stubborn, but statistics are more pliable.  Mark Twain
Facts do not cease to exist because they are ignored.  Aldous Huxley
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