[mesa-users] brunt frequency error

[David Arnett]

It is not so much an error, but rather a result of MESA (or any other
stellar evolution code) dealing poorly with the turbulent boundary layer
that must necessarily be there, and is seen in highly-resolved 3D
simulations of such boundaries. MESA uses the standard algorithm, invented
by Peter Eggleton, which models turbulent convection as heuristic
diffusion. Eggleton warned that the model was only for mathematical
convenience and should be replaced by a physically realistic model of
convection when one became available. The boundary layers are very thin, so
in some respects may be ignored. That is not true for the run of the brunt
frequency or for entrainment, unfortunately, and composition gradients pose
further complications. We may be able to use 3D (not 2D, which distorts the
flow) simulations to improve the algorithm for convective boundaries in
MESA, but that is work  in progress.

Cheer up, there are new discoveries to be made;-)

-- 
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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