[mesa-users] main sequence problem

[David A. <wda...@gm...>]

I wish to add a comment to the point made by Arlette.

Actually, the convection region is not static, but fluctuates
vigorously (high Reynolds number).  Thus the boundary is determined by
the accumulated effect of these fluctuations (in velocity, pressure,
etc.). I think that, in addition to the suggestion of Arlette, there
will probably be important modifications due to this. We certainly see
such behavior in simulations.

Note that many astro simulations are single fluid, so that the effect
of abundance is ignored (eg., the Stagger code and ASH, to name two
illustrious examples). Properly doing multi-fluid flow, to describe
composition differences, is still a challenge, but we seem to be
making progress.

I think Schwarzschild was used historically because it gave more
mixing than Ledoux, and agreed with the larger cores needed for
fitting observational data on massive stars. Ledoux with entrainment
would also give larger cores than without entrainment. The
observations do not yet tell us which (if either) is what nature does.

Experiment suggests Ledoux plus entrainment (basically a Richardson
criterion). Because Schwarzschild has no composition dependence, it
cannot be correct in general. Composition can affect stability, as
Arlette emphasizes.