mesa-users] Massive stars not reaching TPAGB

[Bill Paxton]

I'm CC'ing this to the mesa-users list because it is an interesting case, and
it has a message for everyone -- sometimes when the code doesn't
do what you want it to do, there might be an interesting physical reason.
it isn't always a bug in the code (usually it is, but not always!)


Hi Eric,


Turning on velocities and supersonic winds has given some interesting results!

I restarted the run at step 12000 which was a bit before the surface velocities went crazy before.

Here's a plot of v_surf/csound_surf covering the period where the previous run died.
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when the outward velocity is supersonic, the supersonic wind routine kicks in.
the effect is dramatic!  look at the mass loss -- about 0.5 Msun ejected in
a supersonic wind! 
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however the timesteps have gotten small, so now the progress is slow.
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I'll see if I can find a way around that.   however this profile shows
that we are getting into difficult territory -- we have supersonic infall
happening in the lower envelope at the same time we have nearly
supersonic outward velocities near the surface.   a lot of the envelope
that we tried to eject is now falling back and running into the lower
part of the envelope.  a train wreck in progress.   if left to itself
the code will try to follow the gory details and that will take lots
and lots of tiny timesteps.   if we don't care about the details,
we need to find a way to make the code ignore them.
but that needs to be done in a way that doesn't mess up
the results for the stuff we are actually interested in.
tricky business this stellar evolution!  ; - )

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-Bill