[mesa-users] main sequence problem

[Joseph W. <joe...@gm...>]

Hi there,

I'm curious about what you've seen, and I was wondering if you could
send me your infiles.  Something
that I've found to be useful in looking at convective related issues
is to plot out the convective zones.

One thing that I've noticed in massive stars is how quickly the
convective structure of the star can
change once you hit a nuclear threshold.  Say you have a massive star
with a large convective core
that's burning hydrogen.  The convective core insures that there is a
fresh supply of hydrogen.  Then
the interior of the star hits stars burning helium.  What ends up
happening is that you end up with
carbon ash in the center of the star, and since this ash isn't
radiating this causes the center to suddenly
becomes convectively stable.  Once the center of the star stops
mixing, the nuclear burning shell
quickly burns up the the remaining unburned material, creating more
ash, which causes the radiative
shell to move outward, and you can very quickly have the convective
core disappear.  Now if you
put in overshooting or Ledoux, then the interaction between the
burning and the mixing is different.

Once you hit more nuclear thresholds, things get very complicated, as
you have an interaction between
nuclear burning and convection, and I've seen runs where there are
bursts of convection which move
material around and change the nuclear burning which changes the
convective regions, and there
are situations in which I suspect are chaotic.

I haven't seen how and if this affects the H-R diagram, so I'm quite
interested in running your models
and seeing what happens.  In addition, my quick impression is that the
code is "misbehaving" but
it's misbehaving for reasons that telling us something deep and
significant about how stars work.